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122 lines
4.7 KiB
Groff
122 lines
4.7 KiB
Groff
.\" You can view this file with:
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.\" nroff -man [file]
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.\" $Id$
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.\"
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.TH libcurl 3 "19 March 2002" "libcurl 7.9.6" "libcurl overview"
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.SH NAME
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libcurl \- client-side URL transfers
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.SH DESCRIPTION
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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 are also the
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\fIlibcurl-easy\fP man page, the \fIlibcurl-multi\fP man page, the
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\fIlibcurl-share\fP man page and the \fIlibcurl-the-guide\fP document for
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further reading on how to do programming with libcurl.
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There exist more than a dozen custom bindings that bring libcurl access to
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your favourite language. Look elsewhere for documentation on those.
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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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To transfer files, you always set up an "easy handle" using
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\fIcurl_easy_init()\fP, but when you want the file(s) transfered you have the
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option of using the "easy" interface, or the "multi" interface.
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The easy interface is a synchronous interface with which you call
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\fIcurl_easy_perform\fP and let it perform the transfer. When it is completed,
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the function return and you can continue. More details are found in the
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.BR "libcurl-easy (3)"
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man page.
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The multi interface on the other hand is an asynchronous interface, that you
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call and that performs only a little piece of the tranfer on each invoke. It
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is perfect if you want to do things while the transfer is in progress, or
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similar. The multi interface allows you to select() on libcurl action, and
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even to easily download multiple files simultaneously using a single thread.
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You can have multiple easy handles share certain data, even if they are used
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in different threads. This magic is setup using the share interface, as
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described in the \fIlibcurl-share\fP man page.
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There is also a series of other helpful functions to use. They are:
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.RS
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.TP 10
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.B curl_version()
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displays the libcurl version
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.TP
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.B curl_getdate()
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converts a date string to time_t
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.TP
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.B curl_getenv()
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portable environment variable reader
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.TP
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.B curl_easy_getinfo()
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get information about a performed transfer
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.TP
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.B curl_formadd()
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helps building a HTTP form POST
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.TP
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.B curl_formfree()
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free a list built with curl_formparse()/curl_formadd()
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.TP
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.B curl_slist_append()
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builds a linked list
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.TP
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.B curl_slist_free_all()
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frees a whole curl_slist
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.TP
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.B curl_mprintf()
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portable printf() functions
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.TP
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.B curl_strequal()
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portable case insensitive string comparisons
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.RE
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.SH "LINKING WITH LIBCURL"
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On unix-like machines, there's a tool named curl-config that gets installed
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with the rest of the curl stuff when 'make install' is performed.
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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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.SH "PORTABILITY"
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libcurl works
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.B exactly
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the same, on any of the platforms it compiles and builds on.
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.SH "THREADS"
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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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Persistent connections means that libcurl can re-use the same connection for
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several transfers, if the conditions are right.
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libcurl will *always* attempt to use persistent connections. Whenever you use
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\fIcurl_easy_perform()\fP or \fIcurl_multi_perform()\fP, libcurl will attempt
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to use an existing connection to do the transfer, and if none exists it'll
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open a new one that will be subject for re-use on a possible following call to
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\fIcurl_easy_perform()\fP or \fIcurl_multi_perform()\fP.
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To allow libcurl to take full advantage of persistent connections, you should
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do as many of your file transfers as possible using the same curl handle. When
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you call \fIcurl_easy_cleanup()\fP, all the possibly open connections held by
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libcurl will be closed and forgotten.
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Note that the options set with \fIcurl_easy_setopt()\fP will be used in on
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every repeated \fIcurl_easy_perform()\fP call.
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