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.\" You can view this file with:
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.\" $Id: libcurl.3,v 1.1 2002/03/04 10:09:49 bagder Exp $
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.TH libcurl 5 "14 August 2001" "libcurl 7.8.1" "libcurl overview"
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libcurl \- client-side URL transfers
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This is an overview on how to use libcurl in your C programs. There are
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specific man pages for each function mentioned in here. There's also the
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libcurl-the-guide document for a complete tutorial to programming with
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libcurl can also be used directly from within your Java, PHP, Perl, Ruby or
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Tcl programs as well, look elsewhere for documentation on this!
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All applications that use libcurl should call \fIcurl_global_init()\fP exactly
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once before any libcurl function can be used. After all usage of libcurl is
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complete, it \fBmust\fP call \fIcurl_global_cleanup()\fP. In between those two
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calls, you can use libcurl as described below.
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When using libcurl you init your session and get a handle, which you use as
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input to the following interface functions you use. Use \fIcurl_easy_init()\fP
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You continue by setting all the options you want in the upcoming transfer,
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most important among them is the URL itself (you can't transfer anything
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without a specified URL as you may have figured out yourself). You might want
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to set some callbacks as well that will be called from the library when data
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is available etc. \fIcurl_easy_setopt()\fP is there for this.
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When all is setup, you tell libcurl to perform the transfer using
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\fIcurl_easy_perform()\fP. It will then do the entire operation and won't
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return until it is done (successfully or not).
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After the transfer has been made, you can set new options and make another
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transfer, or if you're done, cleanup the session by calling
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\fIcurl_easy_cleanup()\fP. If you want persistant connections, you don't
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cleanup immediately, but instead run ahead and perform other transfers using
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the same handle. See the chapter below for Persistant Connections.
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There is also a series of other helpful functions to use. They are:
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displays the libcurl version
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converts a date string to time_t
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portable environment variable reader
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.B curl_easy_getinfo()
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get information about a performed transfer
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helps building a HTTP form POST
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free a list built with curl_formparse()/curl_formadd()
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.B curl_slist_append()
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.B curl_slist_free_all()
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frees a whole curl_slist
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portable printf() functions
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portable case insensitive string comparisons
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.SH "LINKING WITH LIBCURL"
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Starting with 7.7.2 (on unix-like machines), there's a tool named curl-config
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that gets installed with the rest of the curl stuff when 'make install' is
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curl-config is added to make it easier for applications to link with libcurl
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and developers to learn about libcurl and how to use it.
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Run 'curl-config --libs' to get the (additional) linker options you need to
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link with the particular version of libcurl you've installed.
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For details, see the curl-config.1 man page.
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.SH "LIBCURL SYMBOL NAMES"
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All public functions in the libcurl interface are prefixed with 'curl_' (with
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a lowercase c). You can find other functions in the library source code, but
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other prefixes indicate the functions are private and may change without
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further notice in the next release.
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Only use documented functions and functionality!
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the same, on any of the platforms it compiles and builds on.
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There's only one caution, and that is the win32 platform that may(*) require
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you to init the winsock stuff before you use the libcurl functions. Details on
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this are noted on the curl_easy_init() man page.
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(*) = it appears as if users of the cygwin environment get this done
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automatically, also libcurl 7.8.1 and later can handle this for you.
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Never ever call curl-functions simultaneously using the same handle from
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several threads. libcurl is thread-safe and can be used in any number of
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threads, but you must use separate curl handles if you want to use libcurl in
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more than one thread simultaneously.
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.SH "PERSISTANT CONNECTIONS"
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With libcurl 7.7, persistant connections were added. Persistant connections
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means that libcurl can re-use the same connection for several transfers, if
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the conditions are right.
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libcurl will *always* attempt to use persistant connections. Whenever you use
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curl_easy_perform(), libcurl will attempt to use an existing connection to do
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the transfer, and if none exists it'll open a new one that will be subject
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for re-use on a possible following call to curl_easy_perform().
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To allow libcurl to take full advantage of persistant connections, you should
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do as many of your file transfers as possible using the same curl
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handle. When you call curl_easy_cleanup(), all the possibly open connections
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held by libcurl will be closed and forgotten.
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Note that the options set with curl_easy_setopt() will be used in on every
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repeat curl_easy_perform() call
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.SH "COMPATIBILITY WITH OLDER LIBCURLS"
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Repeated curl_easy_perform() calls on the same handle were not supported in
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pre-7.7 versions, and caused confusion and undefined behaviour.
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