From a72ed9a8934864c1f7d4d5d6636ec24f77341695 Mon Sep 17 00:00:00 2001 From: Peter Saint-Andre Date: Thu, 25 Jul 2013 07:18:30 -0600 Subject: [PATCH] 0.3 --- xep-0322.xml | 2891 +++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 2410 insertions(+), 481 deletions(-) diff --git a/xep-0322.xml b/xep-0322.xml index e9017670..399964e8 100644 --- a/xep-0322.xml +++ b/xep-0322.xml @@ -1,7 +1,8 @@ + + %ents; ]> @@ -28,44 +29,83 @@ Waher peter.waher@clayster.com peter.waher@jabber.org - http://se.linkedin.com/pub/peter-waher/1a/71b/a29/ + http://www.linkedin.com/in/peterwaher - - 0.1 - 2013-04-16 - psa -

Initial published version approved by the XMPP Council.

 - - - 0.0.4 - 2013-03-19 - pwa - -

Added support for uploading EXI-compressed schema files.

- - - - 0.0.3 - 2013-03-15 - pwa - -

Added definition: EXI body.

-

Added note regarding preserverance of namespace prefixes.

-

Corrected the language.

- - - - 0.0.2 - 2013-03-13 - pwa - -

Added support for session-wide buffers and string tables.

- - + + Yusuke + DOI + yusuke.doi@toshiba.co.jp + yusuke.doi@gmail.com + http://www.linkedin.com/in/yusukedoi + + + 0.3 + 2013-07-19 + pw, yd + +
    +
  • Added examples of communication in alternate bindings.
    • +
  • Default parameter, canonical namespace, and reserved schemaId of EXI encoding are revised.
    • +
  • Added clarifications on use of streamStart, streamEnd elements with namespace prefix mappings.
    • +
  • EXI options are now described in the context of use in XMPP communication.
    • +
  • A bug in setupResponse element type definition is fixed.
    • +
  • Changed domanname schemavault.se used in schema download examples to schemavault.example.org to clarify this is an example.
    • +
+ + + + 0.2 + 2013-06-27 + pw, yd + +
    +
  • Added support for a binary binding.
    • +
  • Changed namespace urn:xmpp:sn to urn:xmpp:iot
    • +
  • Added streamStart and streamEnd elements.
    • +
  • Added central XMPP schemas used for XMPP communication.
    • +
  • Added references to core XMPP schemas in examples.
    • +
  • Added quick setup attributes: configurationId, configurationLocation.
    • +
+ + + + 0.1 + 2013-04-16 + psa + +

Initial published version approved by the XMPP Council.

+ + + + 0.0.4 + 2013-03-19 + pw + +

Added support for uploading EXI-compressed schema files.

+ + + + 0.0.3 + 2013-03-15 + pw + +

Added definition: EXI body.

+

Added note regarding preserverance of namespace prefixes.

+

Corrected the language.

+ + + + 0.0.2 + 2013-03-13 + pw + +

Added support for session-wide buffers and string tables.

+ + 0.0.1 2013-03-12 - pwa + pw

First draft.

 @@ -73,7 +113,9 @@

- The Efficient XML Interchange (EXI) Format Efficient XML Interchange (EXI) Format <http://www.w3.org/TR/exi/>. is an + The Efficient XML Interchange (EXI) Format + Efficient XML Interchange (EXI) Format <http://www.w3.org/TR/exi/>. + is an efficient way to compress XML documents and XML fragments. This document provides information on how EXI can be used in XMPP streams to efficiently compress data transmitted between the server and the client. For certain applications (like applications in sensor networks) EXI is a vital component, decreasing packet size enabling sensors with limited memory to communicate efficiently. The strong support in EXI for generating efficient stubcodes is also vital to build efficient code in constrained devices. @@ -103,11 +145,33 @@ describing the format of the expected XML. Since the server is not supposed to know all possible XML schemas, a mechanism is provided in this document whereby schemas can be interchanged, so that the server can adapt its compression to the needs of the client.

+

+ EXI can be used through two bindings: +

+
    +
  • Normal XMPP Port
    • +
  • Dedicated Binary EXI Port
    • +
+

+ Both will be described in turn, in the following sections. +

- + +

- This XEP is based on &xep0138;. When the client connects to the XMPP Server, it will receive a list of features supported by the server: + There are two ways to use EXI to make efficient XMPP communication. The first method describes how to activate EXI-compression using &xep0138; (XEP-0138). + The second method describes an alternative binding. This method does not use Stream compression as defined in + XEP-0138, rather it allows clients to connect + to the server and start using EXI directly from the beginning. +

+ + +

+ The following sections assume the client connects through the normal XMPP port, and starts communicating with the server using uncompressed XML fragments. + When the client connects to the XMPP Server, it will receive a list of features supported by the server:

zlib lzw exi + exi:54321 ]]>

- Support for EXI compression is detected by the existence of the exi compression method in the features stanza. + Support for EXI compression through the normal XMPP port is detected by the existence of the exi compression method in the features stanza. + If a port (static or dynamic) is available for a dedicated binary EXI/XMPP binding, this can be detected by the existence of the exi:PORT compression method, + where PORT is replaced by the port number used. More information about this alternative method is available in the Alternative Bindings section.

- -

- If the client attempts to activate an EXI stream at this point, before the negotiation of EXI properties has been performed, the server must respond with a - setup-failed response. + Note: If the client already knows the port number of the dedicated binary EXI/XMPP binding, it can connect there directly, without the need to check the + server features using the normal XMPP port.

- - + Following is a list of use cases displaying how the client can configure and activate EXI compression on the current binding. +

+ +

+ If the client attempts to activate an EXI stream at this point, before the negotiation of EXI properties has been performed, the server must respond with a + setup-failed response. +

+ + exi @@ -138,56 +211,91 @@ ]]> - - - -

- When the client decides to activate EXI compression, it sends a setup stanza containing parameter proposals to the server as follows: -

- - - - + + + +

+ When the client decides to activate EXI compression, it sends a setup stanza containing parameter proposals to the server as follows: +

+ + + + + + + + + + + + + + + + ]]> - -

- The server in turn responds with a setupResponse stanza containing the parameters it can accept, based on the initial values provided by the client. - Any buffer sizes, etc., may have been changed, but only lowered, never raised. -

- - +

+ Note: Schema files are identified using three properties: Its target namespace, its byte size and its + MD5 hash. The MD5 hash provides a way to detect small changes in the file, even if the byte size and namespace are the same. +

+

+ It is important that the client specify not only application specific namespaces in this request, but also the versions of the schemas for the + core XMPP protocol namespaces and the schema for the XML namespace, containing XML attributes. +

+

+ Note: Hash values and byte sizes of known schemas at the time of writing, can be found here. + However, these values are informational only. It is recommended that the developer makes sure exactly what version of the schema to use, and + calculate the hash for it correspondingly. Also, some changes to some schemas might be necessary, which will affect the hash values. For more + information about this, see the inforamtion about known problems. +

+

+ After receiving the request, the server responds with a setupResponse stanza containing the parameters it can accept, based + on the initial values provided by the client. Any buffer sizes, etc., may have been changed, but only lowered, never raised. +

+ + - - + + + + + + + + + + + + + + ]]> - -

- Note: Schema files are identified using three properties: Its target namespace, its byte size and its - MD5 hash. The MD5 hash provides a way to detect small changes in the file, even if the byte size and namespace are the same. -

-

- Schema files that the server does not have (based on namespace, byte size and MD5 hash) are marked with the missingSchema element instead of the - normal schema element. -

-

- At this point the client can choose to abort the EXI enablement sequence, if it cannot accommodate itself with the proposed parameter settings provided by the server. - The XMPP session will continue to work in its current state. Aborting does not require taking further action from the client. -

- - -

- If the server lacks information about a schema file, it is specified in the response through the missingSchema elements. At this point, the client can - either choose to accept that these schema files are not available, making compression less efficient, or choose to upload the missing schema files to the server. Of course, - uploading schema files would require the device to have sufficient buffers and memory to store and upload the schema files in the first place. (If it is not possible to upload the - schema files, consideration should be given to installing the schema files manually at the server.) -

-

- To upload a schema file, the client simply sends the schema file using an uploadSchema element, as follows: -

- - +

+ Schema files that the server does not have (based on namespace, byte size and MD5 hash) are marked with the missingSchema element instead of the + normal schema element. +

+

+ At this point the client can choose to abort the EXI enablement sequence if it cannot accommodate itself with the proposed parameter settings provided by the server. + The XMPP session will continue to work in its current state. Aborting does not require taking further action from the client. +

+ + +

+ If the server lacks information about a schema file, it is specified in the response through the missingSchema elements. At this point, the client can + either choose to accept that these schema files are not available, making compression less efficient, or choose to upload the missing schema files to the server. Of course, + uploading schema files would require the device to have sufficient buffers and memory to store and upload the schema files in the first place. (If it is not possible to upload the + schema files, consideration should be given to installing the schema files manually at the server.) +

+

+ To upload a schema file, the client simply sends the schema file using an uploadSchema element, as follows: +

+ + PD94bWwgdmVyc2lvbj0nMS4wJyBlbmNvZGluZz0nVVRGLTgnPz4NCjx4czpzY2hlbWENCiAgICB4 bWxuczp4cz0naHR0cDovL3d3dy53My5vcmcvMjAwMS9YTUxTY2hlbWEnDQogICAgdGFyZ2V0TmFt @@ -198,320 +306,933 @@ dmlsZWdlJz4NCgkJPHhzOmF0dHJpYnV0ZSBuYW1lPSdpZCcgdHlwZT0nUHJpdmlsZWdlSWQnIHVz ZT0ncmVxdWlyZWQnLz4NCgk8L3hzOmNvbXBsZXhUeXBlPg0KIA0KPC94czpzY2hlbWE+DQo= ]]> - -

- The schema itself is sent using base64 encoding to the server. This is to make sure a binary exact copy is transferred, maintaining encoding, processing instructions, etc. The - server then computes the target namespace, byte size and MD5 Hash from the sent schema file. -

-

- If the client desires, it can test the EXI setup again. This is optional, but can be used to test that uploading the schema files, and any new property values - are accepted by the server. -

- - - - + +

+ The schema itself is sent using base64 encoding to the server. This is to make sure a binary exact copy is transferred, maintaining encoding, processing instructions, etc. The + server then computes the target namespace, byte size and MD5 Hash from the sent schema file. +

+

+ If the client desires, it can test the EXI setup again. This is optional, but can be used to test that uploading the schema files, and any new property values + are accepted by the server. +

+ + + + + + + + + + + + + + + + ]]> - -

- And the server should then respond: -

- - +

+ And the server should then respond: +

+ + - - + blockSize='1024' valueMaxLength='32' valuePartitionCapacity='100' agreement='true' + configurationId='c76ab4ec-4993-4285-8c7a-098060581bb8'> + + + + + + + + + + + + + + ]]> - -

- Note the agreement attribute in the response this time. The server must set this attribute to true if it agrees with the proposal from the client. - The client in turn can check this attribute as a quick way to check if agreement exists. -

- - -

- The uploadSchema command has an optional attribute called contentType that can be used to send different types of documents - to the server. This is not a MIME content type, but an enumeration with the following options: -

- - - - - - - - - - - - - - - - - -
ValueDescription
TextThe schema is sent as plain text. If no encoding is provided in the XML header of the schema file, UTF-8 encoding is assumed. This is the default value.
ExiBodyThe schema file is sent as an EXI compressed file, but only the body is sent. *
ExiDocumentThe schema file is sent as an EXI compressed file. The entire file, including Exi header is provided. *
-

- (*) These options assume the following set of default EXI options are used. It is assumed the XMPP server has more capabilities than the client, so the following - set of options must be supported by the XMPP server. The schema files can be precompressed and stored as binary files on the client for easier transmission. -

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
OptionDefault value
Version1
alignmentbit-packed
compressionfalse
strictfalse
fragmentfalse
preserveall false
selfContainedfalse
schemaIdNo schema
datatypeRepresentationMapNo map
blockSize1000000 (one million)
valueMaxLengthunbounded
valuePartitionCapacityunbounded
-

- Since EXI compression does not perserve the extact binary representation of the schema file (for instance it doesn't preserve white space), the server - cannot correctly compute byte size and an MD5 hash for the file. Therefore, the client needs to provide this information in the uploadSchema - command using the bytes and md5Hash attributes. They are mandatory in case EXI compressed schema files are uploaded to the - server. Also note that the byte length and MD5 Hash should be computed on the original XML Schema file, not the compressed or decompressed version. -

- - -

- As an alternative to uploading a schema file to the server, the client can ask the server to download a schema file by itself. This is done using the downloadSchema - command, as follows: -

- - ]]> - -

- The server tries to download the schema by itself, and then computes the target namespace, byte size and MD5 Hash - from the downloaded schema. -

-

- When the schema has been downloaded, the following successful download response is returned: -

- - ]]> - -

- If an HTTP error occurred while trying to download the schema, a response as follows is returned: -

- - + +

+ Note the agreement attribute in the response this time. The server must set this attribute to true if it agrees with the proposal from the client. + The client in turn can check this attribute as a quick way to check if agreement exists. When the server is in agreement it must also return a Configuration ID + in the configurationId attribute. This Configuration ID can be used later to quicker enter into EXI compressed mode. +

+ + +

+ The uploadSchema command has an optional attribute called contentType that can be used to send different types of documents + to the server. This is not a MIME content type, but an enumeration with the following options: +

+ + + + + + + + + + + + + + + + + +
ValueDescription
Text + The schema is sent as plain text, albeit base-64 encoded. If no encoding is provided in the XML header of the schema file, + UTF-8 encoding is assumed. This is the default value. +
ExiBodyThe schema file is sent as an EXI compressed file, but only the body is sent. *
ExiDocumentThe schema file is sent as an EXI compressed file. The entire file, including Exi header is provided. *
+

+ (*) These options assume the following set of default EXI options are used. It is assumed the XMPP server has more capabilities than the client, so the following + set of options must be supported by the XMPP server. The schema files can be precompressed and stored as binary files on the client for easier transmission. +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
OptionDefault value
Version1
alignmentbit-packed
compressionfalse
strictfalse
fragmentfalse
preserveall false, except preserve prefixes that must be true or schema negotation may fail.
selfContainedfalse
schemaId + The Schema of schemas: http://www.w3.org/2001/XMLSchema.xsd. +
datatypeRepresentationMapNo map
blockSizeN/A
valueMaxLengthunbounded
valuePartitionCapacityunbounded
+

+ Since EXI compression does not perserve the extact binary representation of the schema file (for instance it doesn't preserve white space), the server + cannot correctly compute byte size and an MD5 hash for the file. Therefore, the client needs to provide this information in the uploadSchema + command using the bytes and md5Hash attributes. They are mandatory in case EXI compressed schema files are uploaded to the + server. Also note that the byte length and MD5 Hash should be computed on the original XML Schema file, not the compressed or decompressed version. +

+ + +

+ As an alternative to uploading a schema file to the server, the client can ask the server to download a schema file by itself. This is done using the downloadSchema + command, as follows: +

+ + ]]> + +

+ The server tries to download the schema by itself, and then computes the target namespace, byte size and MD5 Hash + from the downloaded schema. +

+

+ When the schema has been downloaded, the following successful download response is returned: +

+ + ]]> + +

+ If an HTTP error occurred while trying to download the schema, a response as follows is returned: +

+ + ]]> - -

- If the URL could not be resolved, the following response is returned: -

- - +

+ If the URL could not be resolved, the following response is returned: +

+ + ]]> - -

- If a timeout occurred during the download attempt, the following response is returned: -

- - + +

+ If a timeout occurred during the download attempt, the following response is returned: +

+ + ]]> - -

- If the url points to something that is not a schema, the following response is returned: -

- - + +

+ If the url points to something that is not a schema, the following response is returned: +

+ + ]]> - -

- If an error occurs that is unforeseen by this specification, the server can simply respond with a generic error message, as follows: -

- - + +

+ If an error occurs that is unforeseen by this specification, the server can simply respond with a generic error message, as follows: +

+ + ]]> - -

- Note: Downloading a schema, might download a version which does not correspond to the desired version - of the schema. It's more important in this case so the client checks that the server actually has the version of the schema required by the client. -

- - -

- When EXI option negotiation has been completed, the client can tell the server that it is ready to start compression. It does this using the normal compress - stanza, as follows: -

- - +

+ Note: Downloading a schema, might download a version which does not correspond to the desired version + of the schema. It might for instance have been updated. This means the bytes and md5Hash values + corresponding to the downloaded file will not match the values expected by the client. Therefore, it's in this case important the client + checks that the server actually downloaded the version of the schema required by the client so it doesn't assume the server uses + the same version of the schema when in actuality it doesn't. +

+ + +

+ Once an EXI setup has been accepted by the server, and agreement is reched, the server will provide the client with a quick Configuration ID + through the configurationId attribute. This Configuration ID can be used by the client during successive connections to the server, + to skip the larger part of the handshake, as is shown in the following example: +

+ + ]]> + +

+ Note: the quick configuration includes all accepted schemas and all EXI options agreed upon during the + session when the configuration ID was returned. The configurationId attribute MUST NOT be used together + with other option attributes or schema definitions in the setup request. +

+

+ If the configuration is still available on the server, the server responds: +

+ + ]]> + +

+ Note that schemas or options are not mentioned explicitly when using this quick setup approach. +

+ + +

+ If the server for some reason does not remember the specific configuration requested by the client (the client might have been disconnected for + a long time), it responds in the following manner: +

+ + ]]> + +

+ The agreement attribute is optional, with a default value of false. So, if the attribute is omitted, the client must consider the + agreement to be nonexistent. When no agreement is reached using the quick configuration approach, the client must restart the handshake + and propose new compression parameters. +

+ + +

+ When EXI option negotiation has been completed, the client can tell the server that it is ready to start compression. It does this using the normal compress + stanza, as follows: +

+ + exi ]]> - -

- The server now has the necessary knowledge on how the EXI engine should be configured for the current session and it responds as follows: -

- - +

+ The server now has the necessary knowledge on how the EXI engine should be configured for the current session and it responds as follows: +

+ + ]]> - + +

+ When the client receives acknowledgement that the compression method has been accepted, it restarts the stream, as explained in + XEP 0138, except that it must not resend the <stream> + start element sequence. Similarly, the client must not send a </stream> element when closing the session. + Instead, special streamStart and streamEnd elements are sent. More information + about that later. +

+ + +

- When the client receives acknowledgement that the compression method has been accepted, it restarts the stream, as explained in - XEP 0138, except that it must not resend the <stream> - start element sequence. Similarly, the client must not send a </stream> element when closing the session. Closing the connection is sufficient. + Becuase EXI engines need to close all open XML elements before decompressing, it cannot start the stream by sending only an open <stream> element, + and close the stream by sending a closing </stream> element. Instead separate streamStart and streamEnd elements + have to be sent, allowing for similar semantics on the EXI-compressed channel, as described in the following subsections.

+

+ For clarity, examples in this section are displayed in XML for readability. But it is understood that the elements are sent using EXI compression and + using the options defined during setup. +

+ +

+ The first thing the client needs to do, once it opens the new EXI-compressed connection, whether it be through the normal XMPP connection or through + the alternative EXI-only binding, is to send a streamStart element. This element replaces the start stream tag normally sent. +

+ + + + + + ]]> + +

+ There's a semantic difference between only writing an open XML element, and sending a closed XML element separately, and that is in the definition + of XML namespaces. XML namespaces and their corresponding prefixes defined in the normal <streams:stream> element will be available to all + child elements following in a normal XMPP stream. However, to be able to do the same in an EXP-compressed XMPP stream, you need to define the + namespaces and prefixes separately. Furthermore, the EXI/XMPP layer needs to make these namespace and prefix-definitions available to all following + elements sent on the stream. The empty prefix is synonymous with the default namespace to use. +

+ + +

+ Before closing the connection, the client needs to send a streamEnd element. This element replaces the closing stream tag send normally. +

+ + ]]> + + + + + + +

+ Alternative binding for EXI/XMPP is suitable for use cases such as factory automation, smart grid appliances, and other + embedded use of communications. It works best if clients are constrained and does not update its specification frequently. + In addition, the network should allow clients and servers to use not well-known port because this commeunication involves + alternative TCP port. +

+

+ Typical steps of communication is as follows (based on &rfc6120;). +

+ + + +
    +
  1. +

    + (Optional) + A client (foo@example.net) try to resolve a server with alternative binding for EXI/XMPP with DNS SRV lookup (ex. _xmpp-bclient._tcp.example.net. IN SRV) +

    +
    2. +
  2. +

    + (Optional) + A DNS server tells a set of DNS RR to notify a server accepts EXI/XMPP binding (ex. SRV 10 10 15222 srv.example.net.) (Optional: the DNS server may tell the version of the default schema supported by the server. Currently there is only one version and has no effect. For further discussion, see draft-doi-exi-messaging-requirement. +

    +
    3. +
  3. +

    The client connects to srv.example.net. 15222 with TCP and the server accepts the connection.

    +
    4. +
  4. +

    + The client sends out 'EXI Cookie' (e.g. '$EXI') and starts EXI stream with an EXI Header without any option document (implies default encoding parameters). It sends out EXI events corresponds to start tag of <stream:stream>. Following shows XML Equivalent and EXI events +

    + + + + + + + + +]]> + + + + + +
    5. +
  5. +

    The server responds with EXI stream, with EXI cookie, without EXI option, and with appropriate events for stream tag.

    + + + + + + + + +]]> + + + + + + +
    6. +
  6. +

    + If client needs TLS or SASL negotiation, it should be done at this step. As specified in Section 4.3.3 of RFC6120, both parties MUST not send events corresponds to </stream:stream> tag. (e.g. exi:streamEnd element) +

    +
    7. +
  7. +

    + If client needs to use different encoding option or schema than the default encoding options or the default schema, then the client shall start schema negotiation. The streams with alternate options/schemas SHOULD NOT have an EXI Options document to indicate the parameter is negotiated via previous XMPP stream. +

    +

    + For example, the client want to use MUC option (XEP-0045)), the following communication will occur. First, client try to renegotiate XML schema used in the communication. +

    + + + + + + + +]]> + + + + + +
    8. +
  8. +

    + In the response the server accepts schema change. +

    + + + + + + + +]]> + + + + + +

    + Note that the server may deny the negotiation with agreement="false" setupResponse (example omitted). +

    +
    9. +
  9. + +

    Just after receiving the setupResponse, client re-opens the stream. The new stream should have EXI header and may have EXI option header with updated options.

    + + + + + + + + + +]]> + + + + + +
    10. +
  10. +

    In response, server re-opens the stream with exi:streamStart tag.

    + + + + + + + + + +]]> + + + + + +
    11. +
  11. +

    After an exi:streamStart from the server to the client, they can communicate with EXI stream. The first level element in conventional XMPP is encoded as root element of EXI message. For example, a client may send MUC query with EXI.

    + + + + + + + + +]]> + + + + + +

    + This message has a query element under muc#owner namespace. This is performed efficiently because + this series of messages from the last streamStart element has been encoded with the set of schemas and the set inclues schemas for MUC. + Otherwise, the encoding will become 'built-in grammar' even if the encoder and the decoder uses non-strict schema-informed grammar. + This is not possible if either encoder or decoder does not support built-in grammar or the stream uses strict schema-informed grammar. + In such cases, the whole message that contains undefined element or attribute SHOULD be dropped. +

    +
    12. +
  12. +

    The client and the server may end the stream with exi:streamEnd tag anytime.

    + + + + +]]> + + + + + +

    + Exactly same message should be sent from the server to the client to close the opposite way of the stream (example omitted). +

    +
    13. +
  13. +

    + The client now can start a preconfigured EXI/XMPP stream with explicit EXI option with the encoding option and canoinc schema used in the previous negotiated session (shortcut setup) +

    + + + +
    + + c:761aabc0-a255-4b9b-89a1-4cb859559691 + +
    + ]]> +     + + + + + + + + + ]]> + + +
    14. +
  14. +

    + The server may respond with the given configuration ID. This can skip the configuration setup and the communication can continue with preconfigured schemas. +

    + + + + +
    + + c:761aabc0-a255-4b9b-89a1-4cb859559691 + +
    + ]]> +     + + + + + + + + +]]> + + +

    + Or server may deny to start the new communication by just sending streamEnd tag with default encoding. +

    + + + + ]]> + + +
    15. +
+ +

+ Just same with section 3.2.1 of RFC6120. The service name MUST be + 'xmpp-bclient' (for binary client-to-server connections) or + 'xmpp-bserver' (for binary server-to-server connections). +

+ + +

+ Fallback to well-known XMPP ports (5222, 5269) without doing SRV + lookup is allowed. In this case, an initiating entity SHOULD give up + connection if it receives non-EXI data (e.g. no EXI cookie and no + distinguishing bit is set) and SHOULD NOT do automatic retry. +

+

+ When an initiating entity tries to communicate with an XMPP server + with EXI, it SHOULD start the stream with an EXI cookie + ('$EXI') to avoid ambiguity. +

+

+ Note: this expects an XMPP server shall return some error in plain + XML if the server receives EXI. +

+ + + +

+ When no EXI encoding option is given, or not specified by given EXI encoding option while negotiation, followings are the default + encoding options for EXI/XMPP messages. +

+
    +
  • alignment: bit-packed
    • +
  • compression: false
    • +
  • strict: true
    • +
  • fragment: false
    • +
  • preserve: all false
    • +
  • selfContained: false
    • +
  • schemaId: "urn:xmpp:exi:default"
    • + +
  • datatypeReresentationMap: not exist
    • +
  • blockSize: N/A
    • +
  • valueMaxLength: 64
    • +
  • valuePartitionCapacity: 64
    • +
+ +

+ In addition, local value learning mechanism is disabled by + default as described in section 4 of EXI Profile. + +

+
    +
  • localValuePartitions: 0
    • +
  • maximumNumberOfBuiltInElementGrammars: 0 (means no grammar learning)
    • +
  • maximumNumberOfBuiltInProductions: 0 (means no production learning)
    • +
+

+ Corresponding parameter for EXI Profile is as follows: +

+ + <p xmlns="http://www.w3.org/2009/exi" + xmlns:xsd="http://www.w3.org/2001/XMLSchema" + xsi:type="xsd:decimal">1.1</p> + + + + +

+ This section describes a common view on programming model between EXI/XMPP servers and clients. This is just an example and an implementation may do it in different ways. However, messages exchanged as a result should be identical. +

+

+ As shown in this document, XMPP documents represented by EXI is slightly different from documents represented in XML. + For example, each stanzas and first level elements under <stream:stream> tags must be encoded as a standalone EXI + body (document). If namespace prefixes are declared in the root element of XML process (<stream:stream> tag), + the prefix should be recovered on decoded XML on the receiver side (EXI may or may not preserve prefix). + Therefore, some preprocessing and postprocessing is required to make current XMPP implementations work properly over + EXI/XMPP channel. An example of the configuration is described in the following figure. +

+ + | | | +| |XMPP| | | |XMPP| | +| | | <-[Proc]-[EXI]<------- EXI Channel ------>[EXI]-[Proc]-> | | | +| +----+ | | +----+ | ++-------------------------+ +-----------------------+ + ]]> + + +

+ In the example, the box XMPP is conventional XMPP process. [EXI] represents EXI processor (encoder and decoder). [Proc] means preprocessor and postprocessor. + Following pre-process must be applied to XML streams from XMPP process before giving the stream to EXI processors. +

+
    +
  1. <stream:stream> start tag must be converted to standalone <exi:streamStart> element. All attributes defined in the input XML except namespace declarations should be copied as is. Namespace declarations and prefixes must be converted to exi:xmlns element under exi:streamStart element.
    2. +
  2. All first level elements under the root <stream:stream> element must be converted to standalone (root) element of corresponding stanza elements. If there are missing namespace declarations in the element, appropriate prefix declarations should be added to the element before giving the element to the EXI encoder as a document. Contents of the elements should not be modified.
    3. +
  3. </stream:stream> end tag must be converted to standalone <exi:streamEnd> element.
    4. +
+ +

+ Following post-process must be applied to XML streams from EXI processors before giving the stream to XMPP process. +

+
    +
  1. Received <exi:streamStart> element must be converted to <stream:stream> start tag with appropriate attributes and namespace declarations. Prefixies defined in the <exi:streamStart> content must be saved under the current connection context of postprocessor.
    2. +
  2. Received EXI messages must be reproduced as elements under <stream:stream> root element. In addition, the namespace declarations in the element must be replaced to prefixes given in the streamStart tag content if there is a corresponding namespace declaration.
    3. +
  3. <exi:streamEnd> element must be converted to </stream:stream> end tag. The context created under the connection may be released.
    4. +
+ + + +

- The following segment is taken from the EXI specification. It describes the different EXI options that need to be negotiated before enabling EXI. + There are many EXI options in EXI Format. Followings are brief description for use in XMPP.

- The alignment option is used to control the alignment of event codes and content items. The value is one of bit-packed, byte-alignment or pre-compression, of which bit-packed is the default value assumed when the "alignment" element is absent in the EXI Options document. The option values byte-alignment and pre-compression are effected when "byte" and "pre-compress" elements are present in the EXI Options document, respectively. When the value of compression option is set to true, alignment of the EXI Body is governed by the rules specified in 9. EXI Compression instead of the alignment option value. The "alignment" element MUST NOT appear in an EXI options document when the "compression" element is present. + The alignment option is to control how the values are encoded. The default option 'bit-packed' fits most of communication use cases. If TLS compression is used at the same time, pre-compression will make the best result.

- The alignment option value bit-packed indicates that the event codes and associated content are packed in bits without any padding in-between. + The compression option is a Boolean to specify additional entropy-based compression is performed over EXI encoding. This option works best for larger documents. Usual use cases expected in XMPP/EXI may not give much additional compactness to messages.

- The alignment option value byte-alignment indicates that the event codes and associated content are aligned on byte boundaries. While byte-alignment generally results in EXI streams of larger sizes compared with their bit-packed equivalents, byte-alignment may provide a help in some use cases that involve frequent copying of large arrays of scalar data directly out of the stream. It can also make it possible to work with data in-place and can make it easier to debug encoded data by allowing items on aligned boundaries to be easily located in the stream. + The strict option is a Boolean to let EXI grammars (schema-informed grammars) work more strictly. With a strict schema-informed grammar, only valid data with the schema is allowed in streams. This makes best compactness of a grammar and messages without additional entropy-based compression. With nonstrict schema-informed grammar, derived elements and attributes could be encoded in the built-in grammar. The built-in grammar is a dynamic, self-learning grammar model that gives full flexibility, with larger message size.

- The alignment option value pre-compression indicates that all steps involved in compression (see section 9. EXI Compression) are to be done with the exception of the final step of applying the DEFLATE algorithm. The primary use case of pre-compression is to avoid a duplicate compression step when compression capability is built into the transport protocol. In this case, pre-compression just prepares the stream for later compression. + The preserve option is a set of Booleans to alter some production of events. Usually, all false (no preservation of comments, processing instructions, DTDs, namespace declarations and its prefixes, and lexical values) makes no problem on XMPP communication. However, uploading a binary schema may require the schema encoded with preserved namespace prefixes. The prefixes are used in type definitions, and without prefix preservation binding between type definition references and actual definitions will be lost.

- The compression option is a Boolean used to increase compactness using additional computational resources. The default value "false" is assumed when the "compression" element is absent in the EXI Options document whereas its presence denotes the value "true". When set to true, the event codes and associated content are compressed according to 9. EXI Compression regardless of the alignment option value. As mentioned above, the "compression" element MUST NOT appear in an EXI options document when the "alignment" element is present. + The selfContained option is a Boolean to enable self contained encoding of elements. Self contained element has no dependency to context (string table state in EXI processors) and can be copied to other context with the same grammar. However, self contained elements cannot use external string tables in EXI processors and may result larger size.

- The strict option is a Boolean used to increase compactness by using a strict interpretation of the schemas and omitting preservation of certain items, such as comments, processing instructions and namespace prefixes. The default value "false" is assumed when the "strict" element is absent in the EXI Options document whereas its presence denotes the value "true". When set to true, those productions that have NS, CM, PI, ER, and SC terminal symbols are omitted from the EXI grammars, and schema-informed element and type grammars are restricted to only permit items declared in the schemas. A note in section 8.5.4.4.2 Adding Productions when Strict is True describes some additional restrictions consequential of the use of this option. The "strict" element MUST NOT appear in an EXI options document when one of "dtd", "prefixes", "comments", "pis" or "selfContained" element is present in the same options document. + The datatypeRepresentationMap option can be used to modify how types encoded in EXI. If encoders and decoders have special encoding, it can be specified here. In most use cases in XMPP/EXI, this option will not be used.

- The preserve option is a set of Booleans that can be set independently to each enable or disable a share of the format's capacity determining whether or how certain information items can be preserved in the EXI stream. Section 6.3 Fidelity Options describes the set of information items affected by the preserve option. The presence of "dtd", "prefixes", "lexicalValues", "comments" and "pis" in the EXI Options document each turns on fidelity options Preserve.comments, Preserve.pis, Preserve.dtd, Preserve.prefixes and Preserve.lexicalValues whereas the absence denotes turning each off. The elements "dtd", "prefixes", "comments" and "pis" MUST NOT appear in an EXI options document when the "strict" element is present in the same options document. The element "lexicalValues", on the other hand, is permitted to occur in the presence of "strict" element. + The blockSize option specifies the block size used for EXI compression. It has no effect if compression is not used.

- The selfContained option is a Boolean used to enable the use of self-contained elements in the EXI stream. Self-contained elements may be read independently from the rest of the EXI body, allowing them to be indexed for random access. The "selfContained" element MUST NOT appear in an EXI options document when one of "compression", "pre-compression" or "strict" elements are present in the same options document. The default value "false" is assumed when the "selfContained" element is absent from the EXI Options document whereas its presence denotes the value "true". + The valueMaxLength option specifies the maximum length of re-used string in a stream. Larger value makes more strings captured in string tables in EXI processors. This means more memory needs to be allocated to process a stream. Because some use cases, such as Internet of Things, expects constrained nodes in the network, default value specified in ths XEP is very small (64 characters).

- The datatypeRepresentationMap option specifies an alternate set of datatype representations for typed values in the EXI body as described in 7.4 Datatype Representation Map. When there are no "datatypeRepresentationMap" elements in the EXI Options document, no Datatype Representation Map is used for processing the EXI body. This option does not take effect when the value of the Preserve.lexicalValues fidelity option is true (see 6.3 Fidelity Options), or when the EXI stream is a schema-less EXI stream. + The valuePartitionCapacity option specifies how many strings should be kept in a string table in a time. Default value of this is also small in this XEP (64 strings).

+

- The blockSize option specifies the block size used for EXI compression. When the "blockSize" element is absent in the EXI Options document, the default blocksize of 1,000,000 is used. The default blockSize is intentionally large but can be reduced for processing large documents on devices with limited memory. -

-

- The valueMaxLength option specifies the maximum length of value content items to be considered for addition to the string table. The default value "unbounded" is assumed when the "valueMaxLength" element is absent in the EXI Options document. -

-

- The valuePartitionCapacity option specifies the maximum number of value content items in the string table at any given time. The default value "unbounded" is assumed when the "valuePartitionCapacity" element is absent in the EXI Options document. Section 7.3.3 Partitions Optimized for Frequent use of String Literals specifies the behavior of the string table when this capacity is reached. -

-

- The sessionWideBuffers controls buffer and string table life time. If set to true, all buffers, string tables, etc. will be maintained during the entire session. - This may improve performance during time since strings can be omitted in the compressed binary stream, but it might also in some cases degrade performance since more options are + To control buffer and string table life time, this XEP adds a new option: sessionWideBuffers. + If set to true, all buffers, string tables, etc. will be maintained during the entire session. + This may improve performance during time since strings can be omitted in the compressed binary stream, but it might also in some cases degrade performance since more options are available in the tables, requiring more bits to encode strings. The default value is false, meaning that buffers, string tables, etc., are cleared between each stanza. (This option is EXI/XMPP specific.)

+ +

+ This section describes effects in message size for some options. +

+

+ The option sessionWideBuffers must have large effect in XMPP communication, because many XIDs are re-used many time within a XMPP stream. + If sessionWideBuffers option is enabled, most of XIDs can be encoded in short identifiers as it appears in some previous messages. Followings are + preliminary evaluation of message size of XML (plain old XML), EXI with sessionWideBuffers=false, and EXI with sessionWideBuffers=true. +

+
    +
  • + + Plain Old XML (without XML declaration, whitespaces): 5011 bytes in 22 messages +
    • +
  • + + EXI without sessionWideBuffers: 1614 bytes in 22 messages +
    • +
  • + + EXI with sessionWideBuffers: 1458 bytes in 22 messages +
    • +
+ -

- The transmission of EXI-compressed stanzas takes the form of a sequence of EXI bodies. In order for the recipient to be able to correctly interpret these incoming - EXI bodies, the sender is required to flush any pending bits at the end of the last End Document (ED) event for each stanza and then send any pending bytes available - in the output buffer. Since this makes sure each EXI body starts at an even byte boundary, it permits the recipient to decompress the body into an XML stanza. -

-

- Therefore, each stanza sent on the stream, must be compressed separately, reusing the same options as used by the stream. - (Options are not sent on the stream, only the generated EXI bodies). -

-

- Compression of the stanza must be done in document mode, not fragment mode, including the Start Document (SD) and End Document (ED) events. - If there are unwritten bits pending after the last End Document (ED) event (after the end of the stanza), Zero-bits are written until a byte boundary is created. - The receptor must ignore bits in the last byte after the last End Document event has been received. -

+

+ The transmission of EXI-compressed stanzas takes the form of a sequence of EXI bodies. In order for the recipient to be able to correctly interpret these incoming + EXI bodies, the sender is required to flush any pending bits at the end of the last End Document (ED) event for each stanza and then send any pending bytes available + in the output buffer. Since this makes sure each EXI body starts at an even byte boundary, it permits the recipient to decompress the body into an XML stanza. +

+

+ Therefore, each stanza sent on the stream, must be compressed separately, reusing the same options as used by the stream. + (Options are not sent on the stream, only the generated EXI bodies). +

+

+ Compression of the stanza must be done in document mode, not fragment mode, including the Start Document (SD) and End Document (ED) events. + If there are unwritten bits pending after the last End Document (ED) event (after the end of the stanza), Zero-bits are written until a byte boundary is created. + The receptor must ignore bits in the last byte after the last End Document event has been received. +

During setup of the EXI compression engine, the client can choose if buffers are to be reused between stanzas, or cleared between each stanza. This is done using the EXI over XMPP specific option sessionWideBuffers, which is false by default, meaning buffers and string tables are cleared between each stanza.

- There may be cases where maintaining buffers and string tables throughout the session is preferrable. Since strings are already available in the buffers, - they don't need to be output in the stream the first time they appear in a stanza. However, the number of strings in tables increase, and so does the number of bits required to + There may be cases where maintaining buffers and string tables throughout the session is preferrable. Since strings are already available in the buffers, + they don't need to be output in the stream the first time they appear in a stanza. However, the number of strings in tables increase, and so does the number of bits required to encode them. Depending on what type of communication is performed, this option might give better results one way or another. If the same type of message is always - sent, maintaining string buffers may be more efficient. But if the client sends many many different types of messages, clearing buffers may be more efficient. + sent, maintaining string buffers may be more efficient. But if the client sends many many different types of messages, clearing buffers may be more efficient. +

+

+ Note that the stream of EXI bodies is indefinite. It only stops when the session is closed, i.e. when the socket connection is dropped. Therefore, the buffers can grow + indefinitely unless control is maintained on what types of messages are sent, their contents (specifically string values), and to whom they are sent (JIDs being strings). + All string tables and buffers must be cleared when a connection is lost.

-

- Note that the stream of EXI bodies is indefinite. It only stops when the session is closed, i.e. when the socket connection is dropped. Therefore, the buffers can grow - indefinitely unless control is maintained on what types of messages are sent, their contents (specifically string values), and to whom they are sent (JIDs being strings). - All string tables and buffers must be cleared when a connection is lost. -

Note also that if you want the option to enter a session in the middle of the flow to listen to the communication, you need to clear tables and buffers between each stanza, or you will not be able to decode the binary stream appropriately.

- -

- Normally, prefixes are not preserved during EXI compression and decompression. If the communicating parties (sending client, XMPP server(s) and receiving clients) - interpret incoming stanzas and content according to namespace, this should be sufficient. However, some implementations do not check namespaces, but prefix names used. - In such cases, all communicating parties are required to enable the preserve prefixes option during negotionating. -

-

- Note: It is not sufficient that one party enable this option. Both sender and received are required to enable this option, or prefix names will be - lost in the transmission. -

-

- Note also, that preserving prefix names result in less efficient compression. Therefore, all clients implementing EXI compression should strive to parse incoming - XML based on namespace, not prefix name. -

- + +

+ Normally, prefixes are not preserved during EXI compression and decompression. If the communicating parties (sending client, XMPP server(s) and receiving clients) + interpret incoming stanzas and content according to namespace, this should be sufficient. However, some implementations do not check namespaces, but prefix names used. + In such cases, all communicating parties are required to enable the preserve prefixes option during negotionating. +

+

+ Note: It is not sufficient that one party enable this option. Both sender and received are required to enable this option, or prefix names will be + lost in the transmission. +

+

+ Note also, that preserving prefix names result in less efficient compression. Therefore, all clients implementing EXI compression should strive to parse incoming + XML based on namespace, not prefix name. +

+

To successfully implement a network with clients having limited memory, such as sensor networks, care should be taken to make sure necessary schema files are @@ -557,9 +1278,1183 @@

Since the server always needs to decompress incoming EXI compressed packets to decode headers, omitting the compression part might save the server - some processing power, but not all. Note that, in some networks it might be common using similar compression settings, while in others different compression + some processing power, but not all. Note that, in some networks it might be common using similar compression settings, while in others different compression settings are most common.

+

+ Also note that binary forwarding is only possible if session-wide buffers are not used. +

+ + + + +

+ Errata and other updates may happen to well-known schemas. Slightest + modification to XML schemas may break interoperability of EXI + nodes. However, negotiating everything is not efficient. Well-known + and aged schemas that referred from the schema for EXI/XMPP shall be + snapshoted for use in EXI processors. + + +

+

+ Actual snapshot is located in (TBD-URL). +

+ + +

+ The interface between the XMPP engine, whether in the client or the server, and the EXI compression engine is required to provide the engine + with ONE XML Schema to use during the compression. The Efficient XML Interchange (EXI) Format + also specifies the use of Schema IDs identifying the schema to use. +

+

+ However, in the XMPP case, the schema to provide to the EXI compression engine must be created dynamically based on the handshake provided during + setup of the connection. Since this generation must be done both on the server side as well as the client side, it is important that the schemas be + created semantically equivalent. This section describes how to create such schemas, henceforth called Canonical Schemas is described + in this section. +

+

+ A canonical schema is simply a wrapper importing each of the schemas negotiated for the connection. The schemas MUST be imported in ascending namespace + order. +

+

+ After generating the canonical schema, it's a good idea to create a corresponding Configuration ID. The Configuration ID however, includes not only + the schemas imported into the canonical schema, but also the EXI options to use during compression/decompression. The canonical schema should be + persisted for simple reuse when quick setup is used. +

+

+ The target namespace of the canonical schema MUST be urn:xmpp:exi:cs. +

+

+ The Schema ID to use is irrelevant in the XMPP layer of communiction. Therefore, the server and client can create their own Schema IDs, according to some + algorithm. It is not important if the Schema IDs match, since they are not used in data transmitted between the client and server. +

+ + +

+ The configurationId attribute has a similar attribute called configurationLocation. This attribute provides + a mechanism to setup an EXI connection rapidly using option documents installed as files on the server or available on the network accessible + through an URL. +

+

+ A client may specify a configurationId or configurationLocation on exi:setup element. If the server has corresponding setup configuration, the server may respond with an exi:setupResponse with agreement="true". If the server does not know the configurationId or does not be able to use the given configurationLocation, the server shall respond with an exi:setupResponse with agreement="false". +

+

+ This specification does not define the format of this Configuration Location attribute, and so it is server specific, or if it is supported. + If used on a server not supporting this attribute, or if the contents of the attribute is invalid, the server returns an agreement=false + response. Otherwise the semantics of the configurationLocation attribute is the same as for the configurationId + attribute, except it provide a mechism for static configurations, while the configurationId provides a mechanism for + dynamic configurations. +

+

+ The format for these opton documents or locations is beyond the scope of this specification. +

+

+ The format for these opton documents or locations is beyond the scope of this specification. +

+ + With alternative transport bind, following rule for shortcut may be used, assuming a server and a client have common shared configuration with configurationId="01234" as an example. +
    +
  • + Client can start configured stream with a exi:streamStart element encoded in the configuration given in configurationId="01234". To indicate configurationId, a schemaId corresponds to the configurationId prefixed by "c:" SHALL be used. In this example, schemaId is "c:01234". EXI option in EXI option header other than the schemaId SHOULD NOT be specified. +
    • +
  • + If the server accepts the configuration, the server SHOULD respond with a exi:streamStart element encoded in the configuration given in the configurationId. The server SHALL put the schemaId in the EXI header of the response. No EXI options other than the schemaId SHOULD NOT be specified in the response EXI header. The EXI header is the indication of configuration agreement and SHALL NOT be omitted. +
    • +
  • + If the server does not accept the configuration, the server SHALL respond with a exi:streamEnd element encoded in the default schema and the EXI header option SHOULD be empty. +
    • +
  • + The client can continue pre-configured stream if and only if it receives exi:streamStart element encoded in the configurationId with EXI option header that contains the identical schemaId. Otherwise, the client SHOULD start a new exi:streamStart with a new TCP connection an empty EXI option header (e.g. default schema). Current TCP connection SHOULD NOT be used for re-negotiation (configuration setup). +
    • +
+ + + +

+ The following table lists XMPP schemas at the time of writing, and their corresponding bytes sizes and MD5 Hash values. +

+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
NamespaceSchemaBytesMD5 hash
http://etherx.jabber.org/streams + streams.xsd + 345068719b98725477c46a70958d1ea7c781
http://jabber.org/features/amp + amp-feature.xsd + 635cb4f48c999c1cce15df4f3129e55f381
http://jabber.org/features/compress + compress-feature.xsd + 6708ff631b7aaf9a196470ec57897251f7c
http://jabber.org/protocol/activity + activity.xsd + 5043b6168aac76260aed41071fbe5c930279
http://jabber.org/protocol/address + address.xsd + 19158770419083d7f4044ee4b55e39e3c6e3
http://jabber.org/protocol/amp + amp.xsd + 1858b929b5024af92ccb2f21af944e1caa6b
http://jabber.org/protocol/amp#errors + amp-errors.xsd + 9637a366c21bbf2060f2658e9118bfc32e9
http://jabber.org/protocol/bytestreams + bytestreams.xsd + 234383211fe7c25510d9254a9aa6cf31b1e0
http://jabber.org/protocol/caps + caps.xsd + 1072ed68bc908f301556d1cf9ad111c34184
http://jabber.org/protocol/chatstates + chatstates.xsd + 827c00838d97b9c2a37ac098130a27b1b4c
http://jabber.org/protocol/commands + commands.xsd + 355198b0e90b35e00b04b2253af26faaab6f
http://jabber.org/protocol/compress + compress.xsd + 15057ac2a9dc7472af2796be239dbc7097ac
http://jabber.org/protocol/compress/exi + exi.xsd + 150948b8f91b95d9101f0781e0ba9b4e106be
http://jabber.org/protocol/disco#info + disco-info.xsd + 1783d5e696ad7aa800cba7f54740b0e2a6c8
http://jabber.org/protocol/disco#items + disco-items.xsd + 14826010e2e5dafd587fc1609987805c7295
http://jabber.org/protocol/feature-neg + feature-neg.xsd + 766a154eeb514f8acbe0291c48d4e7335a5
http://jabber.org/protocol/geoloc + geoloc.xsd + 232290b0df99a0e6ee77929955b63b384656
http://jabber.org/protocol/http-auth + http-auth.xsd + 1020fdd34da7014b044fd659091843d802cd
http://jabber.org/protocol/httpbind + httpbind.xsd + 402859559ed6a5025c2e4ecf1a9ad675c707
http://jabber.org/protocol/ibb + ibb.xsd + 155745bac4486abb974f0d92ee98d8e356de
http://jabber.org/protocol/mood + mood.xsd + 399493bb8be5dab135b7189c475f3d80a03a
http://jabber.org/protocol/muc + muc.xsd + 1322853ad555f102bb2b71da9a2f2787f4f9
http://jabber.org/protocol/muc#admin + muc-admin.xsd + 2260627d39d09e18208f0b068ff3ee1e4dc2
http://jabber.org/protocol/muc#owner + muc-owner.xsd + 12846e4e2257c1a4ba937fbdf71664a7e793
http://jabber.org/protocol/muc#unique + muc-unique.xsd + 51243f77e28d5574453f1208c653a4eb710
http://jabber.org/protocol/muc#user + muc-user.xsd + 38814c2643e702a591ed09dd4e1af15f46f5
http://jabber.org/protocol/nick + nick.xsd + 498280d55dac18c98559ea514e822d692d1
http://jabber.org/protocol/offline + offline.xsd + 1157e0c329c185c3339480a78b8662be92a0
http://jabber.org/protocol/pubsub + pubsub.xsd + 729618b754fd463509c7c95bde5a6bf54a07
http://jabber.org/protocol/pubsub#errors + pubsub-errors.xsd + 463720479f150ffe1fa932da529528d89aa0
http://jabber.org/protocol/pubsub#event + pubsub-event.xsd + 4866003ba8f4780822511a84cc8f83ca6c95
http://jabber.org/protocol/pubsub#owner + pubsub-owner.xsd + 4387f0d2a4733fe7991135172ff6cfec66d9
http://jabber.org/protocol/rosterx + rosterx.xsd + 133897bfd4958edef7fb962eba8fe38ce810
http://jabber.org/protocol/rsm + rsm.xsd + 1379340cfcdf0827a12f8ba0fbca6b28aa37
http://jabber.org/protocol/shim + shim.xsd + 911989fc4e6a95c1e763ec17245ac622c1a
http://jabber.org/protocol/si + si.xsd + 1530d00cd67eec0a6923ad01865c507d4808
http://jabber.org/protocol/si/profile/file-transfer + file-transfer.xsd + 14798fbc4d2d7972696b30132a4092336122
http://jabber.org/protocol/sipub + sipub.xsd + 16553eafe26f5ade2fbbf0cc9d354051ead7
http://jabber.org/protocol/soap#fault + soap-fault.xsd + 856df3517931ab9dcc747f89e7c84851d8e
http://jabber.org/protocol/tune + tune.xsd + 1237d5ba7c1a0e061e7c2c1ec325f583edfb
http://jabber.org/protocol/waitinglist + waitinglist.xsd + 243145637c6ae8a3db8048edeb241d54ff3e
http://jabber.org/protocol/xdata-color + color-parameter.xsd + 558fdd94654b15532501f30541e52253a7f
http://jabber.org/protocol/xdata-layout + xdata-layout.xsd + 2021c74f116543466f6a39352a2f95bc5e2d
http://jabber.org/protocol/xdata-validate + xdata-validate.xsd + 18740ace852dda1d5e9a72427515e934b342
http://jabber.org/protocol/xhtml-im + xhtml-im-wrapper.xsd + 1402a3733bf495c05653e86ef20a825c62cb
jabber:client + jabber-client.xsd + 69685e2d5cbf0506e3f16336d295093d66c4
jabber:component:accept + component-accept.xsd + 6635eb052d6aadc60e4a704728e68e9b71b4
jabber:component:connect + component-connect.xsd + 663774497cf7c9a306fdbd3c336d471dba87
jabber:iq:auth + iq-auth.xsd + 1075524d617af8f30feae26b92cd83a21d7f
jabber:iq:gateway + iq-gateway.xsd + 766736df8b8976add34b6065512dad8352f
jabber:iq:last + iq-last.xsd + 70093a08299e6a987209704502256b21721
jabber:iq:oob + iq-oob.xsd + 739556fa1cd4d36ae1780ed2e0c1053c296
jabber:iq:pass + iq-pass.xsd + 12744cf2bab840ce9d592f573db2d1dde1ef
jabber:iq:privacy + iq-privacy.xsd + 31161dfec6d0dbd1f625f46fb3f68c188338
jabber:iq:private + iq-private.xsd + 605b8d0aebb2370a2f8658304ba57677623
jabber:iq:register + iq-register.xsd + 2598b79db0064b527f0da817e90333896eac
jabber:iq:roster + roster.xsd + 1898936bbba0ef836bc173735c3b416ff553
jabber:iq:rpc + jabber-rpc.xsd + 4853351909f64a5a6b66c35972a53d498e88
jabber:iq:search + iq-search.xsd + 15741f202602ae9b46d43a6e5791d8c54d93
jabber:iq:time + iq-time.xsd + 933dde555d546b4f460ba3abb9848acc2aa
jabber:iq:version + iq-version.xsd + 76322a89a8dcf2fb54710b534b85333f5a7
jabber:server + jabber-server.xsd + 6948dd95bd3055dfdd69984ed427cd6356e0
jabber:server:dialback + dialback.xsd + 1606ddb71d38501ceea6dbf04b96aeabd6fc
jabber:x:conference + x-conference.xsd + 1339d06113e71790a8b4f92fe38d0e76dda6
jabber:x:data + x-data.xsd + 3562ed9ac8c241c7f6503887c86b3d9ef2f1
jabber:x:delay + x-delay.xsd + 94060cbc644095747e5f5e987845ce3a233
jabber:x:encrypted + x-encrypted.xsd + 46995816171d561dad6d412112bb698aed4
jabber:x:event + x-event.xsd + 1013305f4bef3c118b9d3d11d96aea753026
jabber:x:expire + x-expire.xsd + 9162c4f88b96a5ba140532788ca47c6216e
jabber:x:oob + x-oob.xsd + 668d85e431c630889f65e3139d947be1cca
jabber:x:roster + x-roster.xsd + 107700cb233dee83919067559c5dcee04f3d
jabber:x:signed + x-signed.xsd + 463979b382c4f4b0d9278f184f078e291c3
roster:delimiter + delimiter.xsd + 435aa7d17ef59561634d78a5c3acf0cc23c
storage:bookmarks + bookmarks.xsd + 1588a500b821a46a4dece20671abe259c4fd
storage:rosternotes + rosternotes.xsd + 10452d5a4c3e97af7650a941b74473b18903
urn:ietf:params:xml:ns:xmpp-bind + bind.xsd + 852ef4bc7405e969b05e1df4c0f8fbb5e71
urn:ietf:params:xml:ns:xmpp-e2e + e2e.xsd + 598da2132f0a69fc389685a7c8fe7f66e92
urn:ietf:params:xml:ns:xmpp-sasl + sasl.xsd + 2769fd9a83f5c75628486ce18c0eb3a35995
urn:ietf:params:xml:ns:xmpp-session + session.xsd + 444cc1dad32ba05d18407579b7a1c98c64b
urn:ietf:params:xml:ns:xmpp-stanzas + stanzaerror.xsd + 31331a8d21588424f9134dc497de64b10c3f
urn:ietf:params:xml:ns:xmpp-streams + streamerror.xsd + 331575cd95aecb9f1fd66110c3ddcf00c9b8
urn:ietf:params:xml:ns:xmpp-tls + tls.xsd + 688dc18bc4da35bc1be7a6c52aa43330825
urn:xmpp:archive + archive.xsd + 10355379f31dbd639e577cc3671989f89eac7
urn:xmpp:attention:0 + attention.xsd + 62142f9232182d298aa92f29d300d4087c5
urn:xmpp:avatar:data + avatar-data.xsd + 482d705ada4740d78c5d404f470e61ea06c
urn:xmpp:avatar:metadata + avatar-metadata.xsd + 1782d8cb3ff5805145161c81f73dc4f1d5dc
urn:xmpp:blocking + blocking.xsd + 1437f9540f863f741e300e4706c8f773d02d
urn:xmpp:blocking:errors + blocking-errors.xsd + 62728eb443b113cbe7147cfed90834a68fd
urn:xmpp:bob + bob.xsd + 846990e71ba1e657f3a587cd6f0e758c69b
urn:xmpp:captcha + captcha.xsd + 7522128162d221b39d19530769ccdedd01b
urn:xmpp:delay + delay.xsd + 76234283385814c8db0dc3ad874ae57e9ab
urn:xmpp:features:rosterver + versioning-feature.xsd + 619089d67a345ba701d21c1d3316a03c7e6
urn:xmpp:http + http-over-xmpp.xsd + 513551c68b927a5cc0ab4a6e8d081e100cb0
urn:xmpp:iot:concentrators + sensor-network-concentrators.xsd + 372359923874ce246c24e6fe488cb58f48c9d
urn:xmpp:iot:control + sensor-network-control.xsd + 629374dcea52300e8c8df8c4de2c9e90495b
urn:xmpp:iot:interoperability + xep-0000-IoT-Interoperability.xsd + 12755d39845a0082715ff8807691698353bb
urn:xmpp:iot:provisioning + sensor-network-provisioning.xsd + 88563ed5360bc17eadb2a8949498c9af3f0c
urn:xmpp:iot:sensordata + sensor-data.xsd + 875249b101e7deea39ccc31340a3c7871c43
urn:xmpp:jingle:1 + jingle.xsd + 492629d29c6f994ce1b1cc3d5da8c1b54d80
urn:xmpp:jingle:apps:rtp:1 + jingle-apps-rtp.xsd + 34813f1d6e7fc12ebddd3c196fb44dc0912b
urn:xmpp:jingle:apps:rtp:errors:1 + jingle-apps-rtp-errors.xsd + 705bb476ac38da026742ddb94862f8d3e1f
urn:xmpp:jingle:apps:rtp:info:1 + jingle-apps-rtp-info.xsd + 1467c8fc00ddcff8c69cf4a923c3797a9d04
urn:xmpp:jingle:apps:rtp:zrtp:1 + jingle-apps-rtp-zrtp.xsd + 7329144b780fc33098ad0c5725394d53e8e
urn:xmpp:jingle:errors:1 + jingle-errors.xsd + 783fa8cefea805ce412615a0e19fcc90f29
urn:xmpp:jingle:transports:ibb:1 + jingle-transports-ibb.xsd + 1424284b6271054657577a380c654f90453f
urn:xmpp:jingle:transports:ice-udp:1 + jingle-transports-ice-udp.xsd + 310303a3be93d48a393e5756717d74b27efc
urn:xmpp:jingle:transports:raw-udp:1 + jingle-transports-raw-udp.xsd + 182654ab91e95e7d070a26b1b6afbd5559ca
urn:xmpp:jingle:transports:s5b:1 + jingle-transports-s5b.xsd + 3336fe5cb4f3077307279a7c0e5da7c5c6e7
urn:xmpp:langtrans + langtrans.xsd + 193442fd5d84bfdab64d405146500833ff95
urn:xmpp:langtrans:items + langtrans-items.xsd + 1500c28ef67fe38aeaed5ba44e239c1c1886
urn:xmpp:media-element + media-element.xsd + 10510d4c292aa81f6eb1ad3f8b06421e1cee
urn:xmpp:pie:0 + pie.xsd + 1590a1a80b05609760cc0bf73c81c48a8ab6
urn:xmpp:ping + ping.xsd + 602a2a720f5ee6da310e3a05ba89b89eb20
urn:xmpp:receipts + receipts.xsd + 879e11be9d296fa183a1c06ea021fd69559
urn:xmpp:sec-label:0 + sec-label.xsd + 38659e98b80af0f6376c24a678d14a9a642f
urn:xmpp:sec-label:catalog:2 + sec-label-catalog.xsd + 3378f63f39aaacb09726ceabf6638008b13a
urn:xmpp:sec-label:ess:0 + sec-label-ess.xsd + 80499311ef62e7f29be25eb78d68baaff2a
urn:xmpp:sm:3 + sm.xsd + 3583392326992f88327d9958fb6afbbb4382
urn:xmpp:time + time.xsd + 658001c5347c00da7aad231504ec706fbb3
urn:xmpp:xbosh + xbosh.xsd + 7600920ea082f0ba162c8b96611368941a8
vcard-temp:x:update + vcard-avatar.xsd + 625edaf52356eb306390849641bdc33fdc9
+ + +

+ The following sections list some known problems that might affect already defined schemas. For these schemas to be used + together with EXI compression, the recommended procedures should be considered. If changes to the schema is required, + new byte sizes and hash values must be computed for the changed schema correspondingly. +

+

+ Patched version of XML schemas may be placed in the snapshot repository for well-known schemas to avoid wild patches (and too many derived schema for the same model). +

+ + +

+ TBD: group discussion needed +

+

+ streams.xsd defined in RFC6120 has 'unique particle attribution (UPA)' problem. + UPA is undeterministic attribution of an element between a wildcard and an explicit definition. + Details could be found in Appendix H of XML schema specification. +

+

+ A simple + way to solve UPA is to insert delimiters around wildcards to eliminate + ambiguity. A deterministic delimiter can resolve ambiguity. + The other way to solve UPA is to use 'weak wildcard model' + introduced in XML schema 1.1. The cause of ambiguity is lack of + precedence between explicit definitions and wildcard definitions. As + weak wildcards have weaker precedence against explicit definitions, + there are no ambiguity with UPA. +

+

+ To keep the same semantics with current XML implementations, by + default this proposal recommends weak wildcard model on + implementations. However, if an implementation does not support weak + wildcards, it may use streams.xsd with following patch applied. +

+ + + --- streams.xsd 2013-03-25 17:37:52.733451313 +0900 + +++ streams-UPA-patched.xsd 2013-03-25 17:57:44.889469868 +0900 + @@ -32,10 +32,12 @@ + <xs:any namespace='urn:ietf:params:xml:ns:xmpp-sasl' + minOccurs='0' + maxOccurs='1'/> + + <xs:element name="delim" type="xs:boolean" minOccurs="1" maxOccurs="1" /> + <xs:any namespace='##other' + minOccurs='0' + maxOccurs='unbounded' + processContents='lax'/> + + <xs:element name="delim" type="xs:boolean" minOccurs="1" maxOccurs="1" /> + <xs:choice minOccurs='0' maxOccurs='1'> + <xs:choice minOccurs='0' maxOccurs='unbounded'> + <xs:element ref='client:message'/> + @@ -77,6 +79,7 @@ + <xs:element ref='err:text' + minOccurs='0' + maxOccurs='1'/> + + <xs:element name="delim" type="xs:boolean" minOccurs="1" maxOccurs="1" /> + <xs:any namespace='##other' + minOccurs='0' + maxOccurs='1' + + + + + + + +

+ Default EXI grammar used in EXI/XMPP SHALL be equivalent to the EXI grammar defined by the following schema. The default EXI grammar + is used in initiating connection of EXI/XMPP alternate binding. The default schema is defined by following definition, and all + the imported schemas SHOULD be same schemas described in the snapshot and SHOULD have the identical + MD5 hash value described in this section. +

+ + + + + + +]]> + +

+ The ${snapshot-url} corresponds to yet-to-be-specified schema snapshot repository described in snapshot repository for well-known schemas section. + The schemaId of this schema will is 'urn:xmpp:exi:default'. SchemaId is ID for this instance and not a namespace identifier and intentionally different from the target namespace of the schema. +

+ + + + Following schema Ids are reserved. +
    +
  • + Schema IDs starts with "c:". This is used as shortcut setup for alternative transport binding. +
    • +
  • Schema IDs starts with "urn:xmpp". This may be used to describe XEP-based schemas.
    • +
@@ -567,92 +2462,115 @@ Note that EXI compressed information, even though it is hard to decode by humans, is by no means encrypted. If sensitive data is to be sent over an EXI compressed channel, encryption should be considered as well.

+

+ The reason for using MD5 as a hashing mechanism to identify schema versions, is because MD5 has a small memory footprint and is easy to implement. + However, it has a weakness: Given a hash value, it's relatively easy to create another file returning the same hash value. However, it's very + difficult to create another file of the same size as the original, resulting in the same hash value. For this reason, file sizes are also included + when identifying a schema. Since the security threat, and any possible consequences of somebody trying to inject invalid schemas to a server is + relatively small, this is considered a sufficient protection against such threats. +

+

+ The feature of uploading and downloading new schemas to the server is a feature that the server can disable for exceptional high security reasons, for instance, + in high-security installations where total control of the domain is necessary. Clients should be aware + if this fact and check setup after uploading or asking the server to download new schemas. If the setup fails a second time, i.e. schemas are still missing, + the client MUST NOT try to upload or download the missing schemas again, since this would provoke an indefinite loop. +

-

This document requires no interaction with &IANA;.

+

+ + This XEP requires new service names (proposed 'xmpp-bclient' and 'xmpp-bserver') for SRV records registered in IANA. + A static port number for a dedicated binary EXI/XMPP binding may also be requested. +

-

REQUIRED.

- +

+ Some of schemas should be kept 'as-is' format in XSF registry. EXI interoperability + requires schema stability, so a snapshot repository of version-controlled well-known schemas is requested to XMPP Registrar. + Related discussion is in here. Also, patched versions such as described in Known problems + should be placed in the same snapshot repository. +

+

+ Furthermore, it is suggested that the table at http://xmpp.org/resources/schemas/ is updated + with two columns containing updated byte size and MD5 hash information for the current files. Tools can be provided by the authors to automate + the extraction of byte size and MD5 Hash information from the collection of schema files and transform them to appropriate formats. +

+

+ The protocol schema needs to be added to the list of XMPP protocol schemas. +

+

+ The target namespace for canonical schemas urn:xmpp:exi:cs, for default schemas urn:xmpp:exi:default, as well as the EXI compress schema namespace + http://jabber.org/protocol/compress/exi need to be registered on the list of known XSF schemas. +

+ + + + - + + + - + - - - - - - - - + + + + + + + + + - + - + - + - The alignment option is used to control the alignment of event codes and content items. - The value is one of bit-packed, byte-alignment or pre-compression, of which bit-packed is the default value - assumed when the "alignment" element is absent in the EXI Options document. The option values byte-alignment - and pre-compression are effected when "byte" and "pre-compress" elements are present in the EXI Options - document, respectively. When the value of compression option is set to true, alignment of the EXI Body is - governed by the rules specified in 9. EXI Compression instead of the alignment option value. The "alignment" - element MUST NOT appear in an EXI options document when the "compression" element is present. + The alignment option is used to control the alignment of event codes and content items. The value is one of bit-packed, byte-alignment or pre-compression, of which bit-packed is the default value assumed when the "alignment" element is absent in the EXI Options document. The option values byte-alignment and pre-compression are effected when "byte" and "pre-compress" elements are present in the EXI Options document, respectively. When the value of compression option is set to true, alignment of the EXI Body is governed by the rules specified in 9. EXI Compression instead of the alignment option value. The "alignment" element MUST NOT appear in an EXI options document when the "compression" element is present. - The compression option is a Boolean used to increase compactness using additional - computational resources. The default value "false" is assumed when the "compression" element is absent in - the EXI Options document whereas its presence denotes the value "true". When set to true, the event codes - and associated content are compressed according to 9. EXI Compression regardless of the alignment option - value. As mentioned above, the "compression" element MUST NOT appear in an EXI options document when the - "alignment" element is present. + The compression option is a Boolean used to increase compactness using additional computational resources. The default value "false" is assumed when the "compression" element is absent in the EXI Options document whereas its presence denotes the value "true". When set to true, the event codes and associated content are compressed according to 9. EXI Compression regardless of the alignment option value. As mentioned above, the "compression" element MUST NOT appear in an EXI options document when the "alignment" element is present. - The strict option is a Boolean used to increase compactness by using a strict - interpretation of the schemas and omitting preservation of certain items, such as comments, processing - instructions and namespace prefixes. The default value "false" is assumed when the "strict" element is - absent in the EXI Options document whereas its presence denotes the value "true". When set to true, those - productions that have NS, CM, PI, ER, and SC terminal symbols are omitted from the EXI grammars, and - schema-informed element and type grammars are restricted to only permit items declared in the schemas. - A note in section 8.5.4.4.2 Adding Productions when Strict is True describes some additional restrictions - consequential of the use of this option. The "strict" element MUST NOT appear in an EXI options document - when one of "dtd", "prefixes", "comments", "pis" or "selfContained" element is present in the same - options document. + The strict option is a Boolean used to increase compactness by using a strict interpretation of the schemas and omitting preservation of certain items, such as comments, processing instructions and namespace prefixes. The default value "false" is assumed when the "strict" element is absent in the EXI Options document whereas its presence denotes the value "true". When set to true, those productions that have NS, CM, PI, ER, and SC terminal symbols are omitted from the EXI grammars, and schema-informed element and type grammars are restricted to only permit items declared in the schemas. A note in section 8.5.4.4.2 Adding Productions when Strict is True describes some additional restrictions consequential of the use of this option. The "strict" element MUST NOT appear in an EXI options document when one of "dtd", "prefixes", "comments", "pis" or "selfContained" element is present in the same options document. @@ -662,8 +2580,7 @@ - Processing instructions are preserved. Must not be used together with the strict - option. + Processing instructions are preserved. Must not be used together with the strict option. @@ -678,159 +2595,171 @@ - Lexical form of element and attribute values can be preserved in value content items. - Can be used together with the strict option. + Lexical form of element and attribute values can be preserved in value content items. Can be used together with the strict option. - The selfContained option is a Boolean used to enable the use of self-contained elements - in the EXI stream. Self-contained elements may be read independently from the rest of the EXI body, - allowing them to be indexed for random access. The "selfContained" element MUST NOT appear in an EXI - options document when one of "compression", "pre-compression" or "strict" elements are present in the - same options document. The default value "false" is assumed when the "selfContained" element is absent - from the EXI Options document whereas its presence denotes the value "true". + The selfContained option is a Boolean used to enable the use of self-contained elements in the EXI stream. Self-contained elements may be read independently from the rest of the EXI body, allowing them to be indexed for random access. The "selfContained" element MUST NOT appear in an EXI options document when one of "compression", "pre-compression" or "strict" elements are present in the same options document. The default value "false" is assumed when the "selfContained" element is absent from the EXI Options document whereas its presence denotes the value "true". - The blockSize option specifies the block size used for EXI compression. When the - "blockSize" element is absent in the EXI Options document, the default blocksize of 1,000,000 is used. - The default blockSize is intentionally large but can be reduced for processing large documents on - devices with limited memory. + The blockSize option specifies the block size used for EXI compression. When the "blockSize" element is absent in the EXI Options document, the default blocksize of 1,000,000 is used. The default blockSize is intentionally large but can be reduced for processing large documents on devices with limited memory. - The valueMaxLength option specifies the maximum length of value content items to be - considered for addition to the string table. The default value "unbounded" is assumed when the - "valueMaxLength" element is absent in the EXI Options document. + The valueMaxLength option specifies the maximum length of value content items to be considered for addition to the string table. The default value "unbounded" is assumed when the "valueMaxLength" element is absent in the EXI Options document. - The valuePartitionCapacity option specifies the maximum number of value content - items in the string table at any given time. The default value "unbounded" is assumed when the - "valuePartitionCapacity" element is absent in the EXI Options document. Section 7.3.3 Partitions - Optimized for Frequent use of String Literals specifies the behavior of the string table when this - capacity is reached. - - - - - If set to true, all buffers, string tables, etc. will be maintained during the - entire session. This may improve performance during time since strings can be omitted in the - compressed binary stream, but it might also in some cases degrade performance since more options - are available in the tables, requiring more bits to encode strings. The default value is false, - meaning that buffers, string tables, etc., are cleared between each stanza. + The valuePartitionCapacity option specifies the maximum number of value content items in the string table at any given time. The default value "unbounded" is assumed when the "valuePartitionCapacity" element is absent in the EXI Options document. Section 7.3.3 Partitions Optimized for Frequent use of String Literals specifies the behavior of the string table when this capacity is reached. + + + If set to true, all buffers, string tables, etc. will be maintained during the entire session. This may improve performance during time since strings + can be omitted in the compressed binary stream, but it might also in some cases degrade performance since more options are available in the tables, requiring more bits + to encode strings. The default value is false, meaning that buffers, string tables, etc., are cleared between each stanza. + + - + - + - + - The alignment option value bit-packed indicates that the event codes and associated - content are packed in bits without any padding in-between. + The alignment option value bit-packed indicates that the event codes and associated content are packed in bits without any padding in-between. - The alignment option value byte-alignment indicates that the event codes and - associated content are aligned on byte boundaries. While byte-alignment generally results in EXI - streams of larger sizes compared with their bit-packed equivalents, byte-alignment may provide a - help in some use cases that involve frequent copying of large arrays of scalar data directly out - of the stream. It can also make it possible to work with data in-place and can make it easier to - debug encoded data by allowing items on aligned boundaries to be easily located in the stream. + The alignment option value byte-alignment indicates that the event codes and associated content are aligned on byte boundaries. While byte-alignment generally results in EXI streams of larger sizes compared with their bit-packed equivalents, byte-alignment may provide a help in some use cases that involve frequent copying of large arrays of scalar data directly out of the stream. It can also make it possible to work with data in-place and can make it easier to debug encoded data by allowing items on aligned boundaries to be easily located in the stream. - The alignment option value pre-compression indicates that all steps involved - in compression (see section 9. EXI Compression) are to be done with the exception of the final - step of applying the DEFLATE algorithm. The primary use case of pre-compression is to avoid a - duplicate compression step when compression capability is built into the transport protocol. In - this case, pre-compression just prepares the stream for later compression. + The alignment option value pre-compression indicates that all steps involved in compression (see section 9. EXI Compression) are to be done with the exception of the final step of applying the DEFLATE algorithm. The primary use case of pre-compression is to avoid a duplicate compression step when compression capability is built into the transport protocol. In this case, pre-compression just prepares the stream for later compression. - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + - + - - - - - - - - - - - - - - - - - - - - - - - - - - - - + + + + + + + + + + + + + + + + + + + + + + + + + + + + - + + + + + + + + + + + + + + + + + + + + + + + + + + + + ]]> -

Thanks to Joachim Lindborg, Yusuke Doi, Takuki Kamiya, Tina Beckman, Karin Forsell, Jeff Freund and Rumen Kyusakov for all valuable feedback.

+

Thanks to Joachim Lindborg, Takuki Kamiya, Tina Beckman, Karin Forsell, Jeff Freund and Rumen Kyusakov for all valuable feedback.

 +