mirror of
https://github.com/moparisthebest/curl
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162 lines
6.2 KiB
Plaintext
162 lines
6.2 KiB
Plaintext
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INTERNALS
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The project is kind of split in two. The library and the client. The client
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part uses the library, but the library is meant to be designed to allow other
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applications to use it.
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Thus, the largest amount of code and complexity is in the library part.
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Windows vs Unix
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===============
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There are a few differences in how to program curl the unix way compared to
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the Windows way. The four most notable details are:
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1. Different function names for close(), read(), write()
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2. Windows requires a couple of init calls for the socket stuff
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3. The file descriptors for network communication and file operations are
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not easily interchangable as in unix
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4. When writing data to stdout, Windows makes end-of-lines the DOS way, thus
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destroying binary data, although you do want that conversion if it is
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text coming through... (sigh)
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In curl, (1) is made with defines and macros, so that the source looks the
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same at all places except for the header file that defines them.
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(2) must be made by the application that uses libcurl, in curl that means
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src/main.c has some code #ifdef'ed to do just that.
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(3) is simply avoided by not trying any funny tricks on file descriptors.
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(4) we set stdout to binary under windows
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Inside the source code, I do make an effort to avoid '#ifdef WIN32'. All
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conditionals that deal with features *should* instead be in the format
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'#ifdef HAVE_THAT_WEIRD_FUNCTION'. Since Windows can't run configure scripts,
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I maintain two config-win32.h files (one in / and one in src/) that are
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supposed to look exactly as a config.h file would have looked like on a
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Windows machine!
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Library
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=======
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As described elsewhere, libcurl is meant to get two different "layers" of
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interface. At the present point only the high-level, the "easy", interface
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has been fully implemented and thus documented. We assume the easy-interface
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in this description, the low-level interface will be documented when fully
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implemented.
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There are plenty of entry points to the library, namely each publicly defined
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function that libcurl offers to applications. All of those functions are
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rather small and easy-to-follow. All the ones prefixed with 'curl_easy' are
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put in the lib/easy.c file.
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curl_easy_setopt() takes a three arguments, where the option stuff must be
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passed in pairs, the parameter-ID and the parameter-value. The list of
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options is documented in the man page.
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curl_easy_perform() does a whole lot of things.
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The function analyzes the URL, get the different components and connects to
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the remote host. This may involve using a proxy and/or using SSL. The
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GetHost() function in lib/hostip.c is used for looking up host names.
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When connected, the proper function is called. The functions are named after
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the protocols they handle. ftp(), http(), dict(), etc. They all reside in
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their respective files (ftp.c, http.c and dict.c).
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The protocol-specific functions deal with protocol-specific negotiations and
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setup. They have access to the sendf() (from lib/sendf.c) function to send
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printf-style formatted data to the remote host and when they're ready to make
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the actual file transfer they call the Transfer() function (in
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lib/download.c) to do the transfer. All printf()-style functions use the
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supplied clones in lib/mprintf.c.
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While transfering, the progress functions in lib/progress.c are called at a
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frequent interval (or at the user's choice, a specified callback might get
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called). The speedcheck functions in lib/speedcheck.c are also used to verify
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that the transfer is as fast as required.
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When completed curl_easy_cleanup() should be called to free up used
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resources.
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HTTP(S)
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HTTP offers a lot and is the protocol in curl that uses the most lines of
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code. There is a special file (lib/formdata.c) that offers all the multipart
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post functions.
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base64-functions for user+password stuff is in (lib/base64.c) and all
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functions for parsing and sending cookies are found in
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(lib/cookie.c).
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HTTPS uses in almost every means the same procedure as HTTP, with only two
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exceptions: the connect procedure is different and the function used to read
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or write from the socket is different, although the latter fact is hidden in
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the source by the use of curl_read() for reading and curl_write() for writing
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data to the remote server.
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FTP
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The if2ip() function can be used for getting the IP number of a specified
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network interface, and it resides in lib/if2ip.c. It is only used for the FTP
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PORT command.
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TELNET
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Telnet is implemented in lib/telnet.c.
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FILE
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The file:// protocol is dealt with in lib/file.c.
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LDAP
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Everything LDAP is in lib/ldap.c.
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GENERAL
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URL encoding and decoding, called escaping and unescaping in the source code,
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is found in lib/escape.c.
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While transfering data in Transfer() a few functions might get
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used. curl_getdate() in lib/getdate.c is for HTTP date comparisons (and
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more).
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lib/getenv.c offers curl_getenv() which is for reading environment variables
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in a neat platform independent way. That's used in the client, but also in
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lib/url.c when checking the PROXY variables.
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lib/netrc.c keeps the .netrc parser
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lib/timeval.c features replacement functions for systems that don't have
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A function named curl_version() that returns the full curl version string is
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found in lib/version.c.
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Client
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======
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main() resides in src/main.c together with most of the client
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code. src/hugehelp.c is automatically generated by the mkhelp.pl perl script
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to display the complete "manual" and the src/urlglob.c file holds the
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functions used for the multiple-URL support.
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The client mostly mess around to setup its config struct properly, then it
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calls the curl_easy_*() functions of the library and when it gets back
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control after the curl_easy_perform() it cleans up the library, checks status
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and exits.
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When the operation is done, the ourWriteOut() function in src/writeout.c may
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be called to report about the operation. That function is using the
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curl_easy_getinfo() function to extract useful information from the curl
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session.
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