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As more people begin to make use of streams in Jabber, there becomes a need
for more descriptive negotiation of which stream to use. This document provides
a method to negotiate a stream and provide some meta-information about the
streams usage.
Sender wishes to interact with another user, using a method that requires
streams.
Primary Flow:
Error Conditions:
Before a Stream Initiation is attempted the Sender should be sure that the
Receiver supports both Stream Initiation and the specific profile that they
wish to use. This is discovered by using &xep0030;:
The Receiver will advertise the "http://jabber.org/protocol/si" namespace as
a feature to represent they implement this document. The specific profiles can
be found by looking for
"http://jabber.org/protocol/si/profile/profile-name". Shown in the result
is a potential file transfer profile:
Now that the Sender is sure that the Receiver support Stream Initiation they
send the offer:
At this point the Receiver can view the headers and other information to
decide if they wish to accept the Stream Initiation. If they accept they
MUST select one of the presented stream types to use. If none of the stream
types are acceptable the Receiver MUST reply with an error:
If the Receiver has accepted the Stream Initiation the Sender may then used
the semantics defined by the selected stream and start the usage.
While Stream Initiation itself is helpful, it makes much more sense when
what is being transported over the stream is known. Knowing this
allows the Receiver to make a more educated choice about whether or not to
accept the stream. This information is transported in Stream Initiation
through a profile. A profile is a series of required and
optional headers that describe the stream data or how the stream is to be
used. Each Stream Initiation MUST have only one profile, so the stream
usage is kept clear.
Creating a profile is fairly simple. First, a name is chosen, the
complete name is formatted like:
This document does not define any profiles, nor does it place any restrictions
on what type of information a profile should detail. This document also does
not place restrictions on what may be placed in a <header>. Other
XEPs will define profiles to be used with Stream Initiation.
While Stream Initiation is not directly required for stream usage, it does
provide many benefits. In order to fully appreciate these benefits,
streams must link the Stream Initiation to the stream. The id
attribute of the <si> node is intended to provide this link. It is
out of scope of this document to define how streams will make use of this
facility, but it does suggest some methods:
http://jabber.org/protocol/si/profile/profile-name
The complete name is what is presented in information discovery requests
in order to show that the profile is supported. It is also used for the
<si> profile attribute. Next, the information for the headers is
decided upon. Each piece of information will be transported in a
<header> tag. The name attribute is a descriptive key that can be
looked up at the XMPP Registrar or XEP describing the profile. The
actual data in the <header> is the fact related to the name
attribute. It must also be stated whether the header is required or
optional.
The attributes and data of <si> are fairly simple:
When the Sender is offering a Stream Initiation all of the attributes must be present. The data MUST contain the required profile headers and the feature negotiation for the stream MUST be present with at least one option. The optional profile headers MAY also be in the node data.
When the Receiver accepts a Stream Initiation the id attribute MUST be present, all other attributes MUST NOT be present. The selected stream MUST be in the feature negotiation for the stream. There MUST only be one selected stream.
There are two error codes that are used. Following are the conditions, meanings and data:
Data security concerns are left to the profiles to define. Wire security concerns are left to the stream definitions.
This document uses the MIME types as recorded by IANA, but no other direct interaction is necessary.
The "http://jabber.org/protocol/si" namespace will be registered. The registrar will track header profiles for different stream initiation uses.
To follow.
To follow.