Introducing a number of options to the multi interface that
allows for multiple pipelines to the same host, in order to
optimize the balance between the penalty for opening new
connections and the potential pipelining latency.
Two new options for limiting the number of connections:
CURLMOPT_MAX_HOST_CONNECTIONS - Limits the number of running connections
to the same host. When adding a handle that exceeds this limit,
that handle will be put in a pending state until another handle is
finished, so we can reuse the connection.
CURLMOPT_MAX_TOTAL_CONNECTIONS - Limits the number of connections in total.
When adding a handle that exceeds this limit,
that handle will be put in a pending state until another handle is
finished. The free connection will then be reused, if possible, or
closed if the pending handle can't reuse it.
Several new options for pipelining:
CURLMOPT_MAX_PIPELINE_LENGTH - Limits the pipeling length. If a
pipeline is "full" when a connection is to be reused, a new connection
will be opened if the CURLMOPT_MAX_xxx_CONNECTIONS limits allow it.
If not, the handle will be put in a pending state until a connection is
ready (either free or a pipe got shorter).
CURLMOPT_CONTENT_LENGTH_PENALTY_SIZE - A pipelined connection will not
be reused if it is currently processing a transfer with a content
length that is larger than this.
CURLMOPT_CHUNK_LENGTH_PENALTY_SIZE - A pipelined connection will not
be reused if it is currently processing a chunk larger than this.
CURLMOPT_PIPELINING_SITE_BL - A blacklist of hosts that don't allow
pipelining.
CURLMOPT_PIPELINING_SERVER_BL - A blacklist of server types that don't allow
pipelining.
See the curl_multi_setopt() man page for details.
No more use exit(3) but instead tell libcurl that no byte has been
written to let it return a `CURLE_WRITE_ERROR`. In addition, check
curl easy handle return code.
Updated the POP3 sub-section to refer to message ID rather than mailbox.
Added an IMAP sub-section with example URLs depicting the specification
of mailbox, uid and section.
* Elaborates on default values of some curl_easy_setopt() options.
* Reminds the user to cast variadic arguments to curl_easy_setopt() to
'void *' where curl internally interprets them as such.
* Clarifies the working of the CURLOPT_SEEKFUNCTION option for
curl_easy_setopt().
* Fixes typo 'forth' → 'fourth'.
* Elaborates on CURL_SOCKET_TIMEOUT.
* Adds some missing periods.
* Notes that the return value of curl_version() must not be passed to
free().
* Adds several links to documentation of library functions which were
missing.
* Marks documentation of deprecated library functions "(deprecated)".
* Removes spurious .html suffixes.
Schannel and darwinssl use the certificates built into the
OS to do vert verification instead of bundles. darwinssl
is thread-safe. Corrected typos in the NSS docs.
VC6 is _very_ old and we provide working makefiles even for that
compiler. Users who build with the IDE never use that method and project
file anyway and it was just lingering in the root dir.
Added IDN and HTTP data compression as they were left out of the
document until now.
Added notes for qssl, schannel and Secure Transport supporting SSLv2,
Secure Transport supports NTLM, and axTLS does not support SSLv3.
There was also a typo; "AUTH TSL" should be "AUTH TLS".
- document the double-quote and backslash need be escaped if quoting.
- libcurl formdata escape double-quote in filename by backslash.
- curl formparse can parse filename both contains '"' and ',' or ';'.
- curl now can uploading file with ',' or ';' in filename.
Bug: http://curl.haxx.se/bug/view.cgi?id=1171
Remove internal separated behavior of the easy vs multi intercace.
curl_easy_perform() is now using the multi interface itself.
Several minor multi interface quirks and bugs have been fixed in the
process.
Much help with debugging this has been provided by: Yang Tse
This commit renames lib/setup.h to lib/curl_setup.h and
renames lib/setup_once.h to lib/curl_setup_once.h.
Removes the need and usage of a header inclusion guard foreign
to libcurl. [1]
Removes the need and presence of an alarming notice we carried
in old setup_once.h [2]
----------------------------------------
1 - lib/setup_once.h used __SETUP_ONCE_H macro as header inclusion guard
up to commit ec691ca3 which changed this to HEADER_CURL_SETUP_ONCE_H,
this single inclusion guard is enough to ensure that inclusion of
lib/setup_once.h done from lib/setup.h is only done once.
Additionally lib/setup.h has always used __SETUP_ONCE_H macro to
protect inclusion of setup_once.h even after commit ec691ca3, this
was to avoid a circular header inclusion triggered when building a
c-ares enabled version with c-ares sources available which also has
a setup_once.h header. Commit ec691ca3 exposes the real nature of
__SETUP_ONCE_H usage in lib/setup.h, it is a header inclusion guard
foreign to libcurl belonging to c-ares's setup_once.h
The renaming this commit does, fixes the circular header inclusion,
and as such removes the need and usage of a header inclusion guard
foreign to libcurl. Macro __SETUP_ONCE_H no longer used in libcurl.
2 - Due to the circular interdependency of old lib/setup_once.h and the
c-ares setup_once.h header, old file lib/setup_once.h has carried
back from 2006 up to now days an alarming and prominent notice about
the need of keeping libcurl's and c-ares's setup_once.h in sync.
Given that this commit fixes the circular interdependency, the need
and presence of mentioned notice is removed.
All mentioned interdependencies come back from now old days when
the c-ares project lived inside a curl subdirectory. This commit
removes last traces of such fact.
I ran the 2.59 version of autoupdate that updates obsoleted configure.ac
constructs to the 2.59 standard. With a little hands-on fiddling I
prevented it from ruining the quoting in AS_HELP_STRING() uses.
I subsequently also bumped the required autoconf version to 2.59
(released in December 2003) as I don't have an older autoconf version
around to test with and I can't be bothered to install one either...
Inspired by: Björn Stenberg
Related blog post: http://cazfi.livejournal.com/195108.html
This reverts renaming and usage of lib/*.h header files done
28-12-2012, reverting 2 commits:
f871de0... build: make use of 76 lib/*.h renamed files
ffd8e12... build: rename 76 lib/*.h files
This also reverts removal of redundant include guard (redundant thanks
to changes in above commits) done 2-12-2013, reverting 1 commit:
c087374... curl_setup.h: remove redundant include guard
This also reverts renaming and usage of lib/*.c source files done
3-12-2013, reverting 3 commits:
13606bb... build: make use of 93 lib/*.c renamed files
5b6e792... build: rename 93 lib/*.c files
7d83dff... build: commit 13606bbfde follow-up 1
Start of related discussion thread:
http://curl.haxx.se/mail/lib-2013-01/0012.html
Asking for confirmation on pushing this revertion commit:
http://curl.haxx.se/mail/lib-2013-01/0048.html
Confirmation summary:
http://curl.haxx.se/mail/lib-2013-01/0079.html
NOTICE: The list of 2 files that have been modified by other
intermixed commits, while renamed, and also by at least one
of the 6 commits this one reverts follows below. These 2 files
will exhibit a hole in history unless git's '--follow' option
is used when viewing logs.
lib/curl_imap.h
lib/curl_smtp.h
BLANK_AT_MAKETIME may be used in our Makefile.am files to blank
LIBS variable used in generated makefile at makefile processing
time. Doing this functionally prevents LIBS from being used for
all link targets in given makefile.
Blocking connect on the socket has been removed from opensocket
callback. opensocket just opens a new socket and gives it back to
libcurl and libcurl will take care of the connect. sockopt_callback has
also been removed, as it is no longer required.
After a research team wrote a document[1] that found several live source
codes out there in the wild that misused the CURLOPT_SSL_VERIFYHOST
option thinking it was a boolean, this change now bans 1 as a value and
will make libcurl return error for it.
1 was never a sensible value to use in production but was introduced
back in the days to help debugging. It was always documented clearly
this way.
1 was never supported by all SSL backends in libcurl, so this cleanup
makes the treatment of it unified.
The report's list of mistakes for this option were all PHP code and
while there's a binding layer between libcurl and PHP, the PHP team has
decided that they have an as thin layer as possible on top of libcurl so
they will not alter or specifically filter a 'TRUE' value for this
particular option. I sympathize with that position.
[1] = http://daniel.haxx.se/blog/2012/10/25/libcurl-claimed-to-be-dangerous/
Since automake 1.12.4, the warnings are issued on running automake:
warning: 'INCLUDES' is the old name for 'AM_CPPFLAGS' (or '*_CPPFLAGS')
Avoid INCLUDES and roll these flags into AM_CPPFLAGS.
Compile tested on:
Ubuntu 10.04 (automake 1:1.11.1-1)
Ubuntu 12.04 (automake 1:1.11.3-1ubuntu2)
Arch Linux (automake 1.12.4)
The URL we used before is the one that goes directly to 'add' a bug
report, but since you can only do that after first having logged in to
sourceforge, the link often doesn't work for visitors.
Bug: http://curl.haxx.se/bug/view.cgi?id=3582408
Reported by: Oscar Norlander
This is a minor change in behavior after having been pointed out by Mark
Tully and discussed on the list. Initially this case would internally
call poll() with no sockets and a timeout which would equal a sleep for
that specified time.
Bug: http://curl.haxx.se/mail/lib-2012-10/0076.html
Reported by: Mark Tully
The test would hang and get aborted with a "ABORTING TEST, since it
seems that it would have run forever." until I prevented that from
happening.
I also fixed the data file which got broken CRLF line endings when I
sucked down the path from Joe's repo == my fault.
Removed #37 from KNOWN_BUGS as this fix and test case verifies exactly
this.
"Currently you can only share DNS and/or COOKIE data" is incorrect since
also SSL sessions can be shared.
Bug: http://curl.haxx.se/bug/view.cgi?id=3562261
Reported by: Joe Mason
It's conceivable that after the first time curl_multi_perform returns,
the outvalue still_running will be 0, but work will have been done. This
is shown by a workload of small, purely file:// based URLs. Ensure that
we always read pending messages off the multi handle by forcing the
while loop to run at least once.
Removed APOP and SASL authentication from the POP3 section and metalink
support from the client section as these features were implemented in
this release.
Moved adding gssapi to SASL into it's own section rather than repeat it
for each protocol.
Documented that --include will be ignored if both --metalink
and --include are specified.
Also documented that a Metalink file in the local file system
cannot be used if FILE protocol is disabled.
Version number is removed in order to make this info consistent with
how we do it with other MS and Linux system libraries for which we don't
provide this info.
Identifier changed from 'WinSSPI' to 'schannel' given that this is the
actual provider of the SSL/TLS support. libcurl can still be built with
SSPI and without SCHANNEL support.
- For all *FUNCTION options, they now all show the complete prototype in
the description. Previously some of them would just refer to a
typedef'ed function pointer in the curl.h header.
- I made the phrasing of that "Pass a pointer to a function that matches
the following prototype" the same for all *FUNCTION option descriptions.
- I removed some uses of 'should'. I think I sometimes over-use this
word as in many places I actually mean MUST or otherwise more specific
and not-so-optional synonyms.
Added new sections 11. IMAP and 12. LDAP to document adding SASL based
authentication.
Renumbered current sections 11 to 17 as 13 to 19.
Additionally added 19.10 Add CURLOPT_MAIL_CLIENT option.
Setting bit 2 for this value was documented as having a constant value
defined as CURL_REDIR_POST_303 yet referenced a 302 request.
Additionally corrected the meaning of CURL_REDIR_POST_ALL for all three
bits and fixed problems with the bolding of keywords in this section.
Standardised how RFCs are referenced so that the website may autolink to
the correct documentation on ietf.org. Additionally removed the one link
to RFC3986 on curl.haxx.se.
The curl-config command must be used twice in the single command line to
work properly in some environments.
Bug: http://curl.haxx.se/bug/view.cgi?id=3528241
Reported by: Julian Taylor
BUILDING_LIBCURL and CURL_STATICLIB are no longer defined in curl_config.h,
configure will generate appropriate conditionals so that mentioned symbols
get defined and used in Makefiles at compilation time
Configuration files such as curl_config.h and all config-*.h no longer exist
nor are generated/copied into 'src' directory, now these only exist in 'lib'
directory from where curl tool sources uses them.
Additionally old src/setup.h has been refactored into src/tool_setup.h which
now pulls lib/setup.h
The possibility of a makefile needing an include path adjustment exists.
By modifying the parameter list for ourWriteOut() and passing the
OutStruct that collects data in tool_operate, we get access to the
remote name that we're writing to. Shell scripters should find this
useful when used in conjuntion with the --remote-header-name option.
If an empty string is passed to CURLOPT_SSH_PUBLIC_KEYFILE, libcurl will
pass no public key to libssh2 which then tries to compute it from the
private key. This is known to work when libssh2 1.4.0+ is linked against
OpenSSL.
Original wording could lead users in thinking it tries to
somehow parse the filename for a date expression (like
news_2012_03_05.html). It never mentions that it actually
reads the mtime of the file in filesystem.
Set the conn->data->info.httpcode variable in smtp_statemach_act() to
allow Curl_getinfo() to return the SMTP response code via the
CURLINFO_RESPONSE_CODE action.
Added information relating to the new CURLOPT_MAIL_AUTH parameter and
reworked CURLOPT_MAIL_FROM and CURLOPT_MAIL_RCPT to be a clearer.
Fixed inconsistencies of "vocalisation of the abbreviation" versus
"vocalisation of the first word" for all abbreviations.
Corrected a typo in CURLOPT_NOPROXY.
Modify configure.ac to test for new CyaSSL Init function and remove
default install path to system. Change to CyaSSL OpenSSL header and
proper Init in code as well.
Note that this no longer detects or works with CyaSSL before v2
This new option tells curl to not work around a security flaw in the
SSL3 and TLS1.0 protocols. It uses the new libcurl option
CURLOPT_SSL_OPTIONS with the CURLSSLOPT_ALLOW_BEAST bit set.
Allow an appliction to set libcurl specific SSL options. The first and
only options supported right now is CURLSSLOPT_ALLOW_BEAST.
It will make libcurl to disable any work-arounds the underlying SSL
library may have to address a known security flaw in the SSL3 and TLS1.0
protocol versions.
This is a reaction to us unconditionally removing that behavior after
this security advisory:
http://curl.haxx.se/docs/adv_20120124B.html
... it did however cause a lot of programs to fail because of old
servers not liking this work-around. Now programs can opt to decrease
the security in order to interoperate with old servers better.
Use the new library CURLOPT_TCP_KEEPALIVE rather than disabling this via
the sockopt callback. If --keepalive-time is used, apply the value to
CURLOPT_TCP_KEEPIDLE and CURLOPT_TCP_KEEPINTVL.
This adds three new options to control the behavior of TCP keepalives:
- CURLOPT_TCP_KEEPALIVE: enable/disable probes
- CURLOPT_TCP_KEEPIDLE: idle time before sending first probe
- CURLOPT_TCP_KEEPINTVL: delay between successive probes
While not all operating systems support the TCP_KEEPIDLE and
TCP_KEEPINTVL knobs, the library will still allow these options to be
set by clients, silently ignoring the values.
As is pointed out in this bug report, there can indeed be situation
where --stderr has a point even when the "real" stderr can be
redirected. Remove the superfluous and wrong comment.
bug: http://curl.haxx.se/bug/view.cgi?id=3476020
These examples show how to fetch a single message (RETR command) and how to
list all the messages in a given mailbox (LIST command), with authentication
via SSL.
They were both based on the https.c example.
The INTERNALS document suggested that compatibility should be
maintained with perl version 4, but this was untrue - scripts such as
chksource.pl and runtests.pl use perl5-isms.
1- Two new error codes are introduced.
CURLE_FTP_ACCEPT_FAILED to be set whenever ACCEPTing fails because of
FTP server connected.
CURLE_FTP_ACCEPT_TIMEOUT to be set whenever ACCEPTing timeouts.
Neither of these errors are considered fatal and control connection
remains OK because it could just be a firewall blocking server to
connect to the client.
2- One new setopt option was introduced.
CURLOPT_ACCEPTTIMEOUT_MS
It sets the maximum amount of time FTP client is going to wait for a
server to connect. Internal default accept timeout is 60 seconds.
Parameters were underquoted, resulting in
warning: AC_LANG_CONFTEST: no AC_LANG_SOURCE call detected in body
Signed-off-by: Bernhard Reutner-Fischer <rep.dot.nop@gmail.com>
Document the possibility of providing multiple values using the ":"
separator, and the fact that the default value will be ignored if the
option is used.
Do not try to resolve interfaces names via DNS by recognizing interface
names in a few ways. If the interface option argument has a prefix of
"if!" then treat the argument as only an interface. Similarly, if the
interface argument is the name of an interface (even if it does not have
an IP address assigned), treat it as an interface name. Finally, if the
interface argument is prefixed by "host!" treat it as a hostname that
must be resolved by /etc/hosts or DNS.
These changes allow a client using the multi interfaces to avoid
blocking on name resolution if the interface loses its IP address or
disappears.
If the option is set to 0, the default timeout will be used - which in
modern libcurl versions equals 300 seconds (== 5 minutes).
Bug: http://curl.haxx.se/mail/lib-2011-12/0051.html
Reported by: Vladimir Grishchenko
Adds a timer based off of CURLINFO_TOTAL_TIME that is used to perform
certain actions after a minimum amount of time has passed using the
progress function. As a consequence the curl handle is now also passed
into the progress function. Progress example now also includes an
example of how to retreive the TOTAL_TIME and print it out.
When the new socket is created for an active connection, it is now done
using the open socket callback.
Test case 596 was modified to run fine, although it hides the fact that
the close callback is still called too many times, as it also gets
called for closing sockets that were created with accept().
Experience has shown that the symbols-in-versions file is very useful to
applications that want to build with a wide range of libcurl versions.
It is however easy to get it wrong and the source gets a bit messy with
all the fixed numerical comparisions.
The point of this script is to provide an easy-to-use macro for libcurl-
using applications to do preprocessor checks for specific libcurl
defines, and yet make the code clearly show what the macro is used for.
Added pop3 username and password example as well as an explanation of
how path part of the URL is used under pop3.
Additionally have corrected a couple of typos.
Don't even declare the struct members for disabled features
Introducing the CURLSHE_NOT_BUILT_IN return code for the share interface
when trying to set a sharing option that has been disabled (or not
enabled) in the library.
Slight rewording of the CURLOPT_URL SMTP sub-section.
Corrected the incorrect use of hyphens on the three uses of
"zero-terminated" with "zero terminated" to match the rest of the
document.
Corrected the use of an out of place hyphen in CURLOPT_NOPROXY section.
Allow (*curl_write_callback) write callbacks to return
CURL_WRITEFUNC_OUT_OF_MEMORY to properly indicate libcurl of OOM conditions
inside the callback itself.
If a socket is larger than FD_SETSIZE, avoid using FD_SET() on the
platforms where this is possible.
Bug: http://curl.haxx.se/bug/view.cgi?id=3413274
Reported by: Tim Starling
Zero-copy and "Avoid having to remove/readd handles" are not really
features we think are worthwhile to add. Removed.
SRP features have been added already, removed.
11.9 IPv6 addresses with globbing added
Trimmed the newlines to be LF-only. Converted the source to plain C, to
use curl style indents, to compile warning-free with picky options and
fixed the minor fprintf() bug on line 245. Added to makefile.
Drop the pre-release part from this text as we don't use that in
practise since many years.
Update the phrasing to reflect our more strict interpretation:
http://curl.haxx.se/mail/lib-2011-08/0064.html
Using 'socks5h' as proxy protocol will make it a
CURLPROXY_SOCKS5_HOSTNAME proxy which is SOCKS5 and asking the proxy to
resolve host names. I found no "standard" protocol name for this.
Follow style of GNU layout (cp, mv ...) where options are separated with
comma: -o, --option
Order item alphabetically (by length also): -o, -O, --option
Follow style of GNU layout by moving help related options to the end:
--help, -M, --version
Clarify that the '-', '.', '_' or '~' letters are also not escaped since
they shouldn't according to RFC3986 section 2.3.
This is how this function has behaved since sep 2010, commit
5df13c3173.
As it is already included by curlbuild.h if it exists on the platform it
was included here superfluously anyway.
Reported by: Dagobert Michelsen
Bug: http://curl.haxx.se/bug/view.cgi?id=3294509
Improved library search by check_function_exists_concat() macro:
it does not revert the list of libraries any more.
Improved OpenSSL library search: first find zlib, then search for
openssl libraries that may depend on zlib.
For Unix: openssl libraries can now be detected in nonstandard
locations. Supply CMAKE_LIBRARY_PATH to CMake on command line.
Added installation capability (very basic one yet).
Added CURLOPT_TRANSFER_ENCODING as the option to set to request Transfer
Encoding in HTTP requests (if built zlib enabled). I also renamed
CURLOPT_ENCODING to CURLOPT_ACCEPT_ENCODING (while keeping the old name
around) to reduce the confusion when we have to encoding options for
HTTP.
--tr-encoding is now the new command line option for curl to request
this, and thus I updated the test cases accordingly.
Stop the abuse of CURLE_FAILED_INIT as return code for things not being
init related by introducing two new return codes:
CURLE_NOT_BUILT_IN and CURLE_UNKNOWN_OPTION
CURLE_NOT_BUILT_IN replaces return code 4 that has been obsoleted for
several years. It is used for returning error when something is
attempted to be used but the feature/option was not enabled or
explictitly disabled at build-time. Getting this error mostly means that
libcurl needs to be rebuilt.
CURLE_FAILED_INIT is now saved and used strictly for init
failures. Getting this problem means something went seriously wrong,
like a resource shortage or similar.
CURLE_UNKNOWN_OPTION is the option formerly known as
CURLE_UNKNOWN_TELNET_OPTION (and the old name is still present,
separately defined to be removed in a very distant future). This error
code is meant to be used to return when an option is given to libcurl
that isn't known. This problem would mostly indicate a problem in the
program that uses libcurl.
The read callback must return the exact requested amount of data when it
is used for doing TFTP uploads. This is due to how it deals with data
internally. This could/should be fixed but for now we document the
existing behavior.
Reported by: Colin Blair
Bug: http://curl.haxx.se/mail/lib-2011-03/0319.html
This is a new documentation for the source tree. This information has
been present since a long time at
http://curl.haxx.se/mail/etiquette.html but now it is put into a plain
text version too for wider distribution. The web version will be
automatically generated from this source document.
When NSS-powered libcurl connected to a SSL server with
CURLOPT_SSL_VERIFYPEER equal to zero, NSS remembered that the peer
certificate was accepted by libcurl and did not ask the second time when
connecting to the same server with CURLOPT_SSL_VERIFYPEER equal to one.
This patch turns off the SSL session cache for the particular SSL socket
if peer verification is disabled. In order to avoid any performance
impact, the peer verification is completely skipped in that case, which
makes it even faster than before.
Bug: https://bugzilla.redhat.com/678580
All C and H files now (should) feature the proper project curl source
code header, which includes basic info, a copyright statement and some
basic disclaimers.
Stress that it is for client certificates and then mention that it also
works for all other SSL-based protocols apart from HTTPS and
FTPS. Namely POP3S, IMAPS and SMTPS for now.
This enables people to specify a path to the netrc file to use.
The new option override --netrc if both are present. However it
does follow --netrc-optional if specified.
On second thought, I think CURLE_TLSAUTH_FAILED should be eliminated. It
was only being raised when an internal error occurred while allocating
or setting the GnuTLS SRP client credentials struct. For TLS
authentication failures, the general CURLE_SSL_CONNECT_ERROR seems
appropriate; its error string already includes "passwords" as a possible
cause. Having a separate TLS auth error code might also cause people to
think that a TLS auth failure means the wrong username or password was
entered, when it could also be a sign of a man-in-the-middle attack.
"6.7 What are my obligations when using libcurl in my commercial apps?"
got the piece about what exactly "in all copies" mean to a user of the
code.
This interpretation is based on what other MIT-like licenses have made
more explicit.
Extended the intial HTTP protcol part and added a mention of --trace and
--trace-ascii.
Replaced most URLs in the text to use example.com instead of all the
made up strange names.
Shortened a bunch of lines.
... and update the curl.1 and curl_easy_setopt.3 man pages such that
they do not suggest to use an OpenSSL utility if curl is not built
against OpenSSL.
Bug: https://bugzilla.redhat.com/669702
Add a simple SMTP example program, patterned after some of the existing
examples, and the curl application.
This version addresses issues raised by David Woodhouse on comments in
the simplesmtp.c example.
This script is the start of a helper tool that scans a source code and
outputs the most recent libcurl version it finds symbols for. Meaning
that if there's no conditions in the code, that's the earliest libcurl
version the scanned code requires.
It is not added to the Makefile.am yet as it is still a bit crude, but
I'm committing it to keep it and allow us to work on it.
This is a meta symbol. OR this value together with a single specific
auth value to force libcurl to probe for un-restricted auth and if not,
only that single auth algorithm is acceptable.
For example you can use CURLAUTH_DIGEST|CURLAUTH_ONLY to make libcurl
first probe for what method to use, but yet only consider Digest to be
acceptable.
Using _only_ CURLAUTH_DIGEST without the CURLAUTH_ONLY field, will make
libcurl explicitly use Digest right away and not do any probing.
