internals

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 base64-functions for user+password stuff (and more) is in (lib/base64.c) and
 all functions for parsing and sending cookies are found in (lib/cookie.c).

 HTTPS uses in almost every means the same procedure as HTTP, with only two
 exceptions: the connect procedure is different and the function used to read
 or write from the socket is different, although the latter fact is hidden in
 the source by the use of curl_read() for reading and curl_write() for writing
 data to the remote server.

 http_chunks.c contains functions that understands HTTP 1.1 chunked transfer
 encoding.

 An interesting detail with the HTTP(S) request, is the add_buffer() series of
 functions we use. They append data to one single buffer, and when the
 building is done the entire request is sent off in one single write. This is
 done this way to overcome problems with flawed firewalls and lame servers.

 FTP

 The Curl_if2ip() function can be used for getting the IP number of a
 specified network interface, and it resides in lib/if2ip.c.

 Curl_ftpsendf() is used for sending FTP commands to the remote server. It was
 made a separate function to prevent us programmers from forgetting that they
 must be CRLF terminated. They must also be sent in one single write() to make
 firewalls and similar happy.

 Kerberos

 The kerberos support is mainly in lib/krb4.c and lib/security.c.

 TELNET

 Telnet is implemented in lib/telnet.c.

 FILE

 The file:// protocol is dealt with in lib/file.c.

 LDAP

 Everything LDAP is in lib/ldap.c.

 GENERAL

 URL encoding and decoding, called escaping and unescaping in the source code,
 is found in lib/escape.c.

 While transfering data in Transfer() a few functions might get
 used. curl_getdate() in lib/getdate.c is for HTTP date comparisons (and
 more).

 lib/getenv.c offers curl_getenv() which is for reading environment variables
 in a neat platform independent way. That's used in the client, but also in
 lib/url.c when checking the proxy environment variables. Note that contrary
 to the normal unix getenv(), this returns an allocated buffer that must be
 free()ed after use.

 lib/netrc.c holds the .netrc parser

 lib/timeval.c features replacement functions for systems that don't have
 gettimeofday() and a few support functions for timeval convertions.
 
 A function named curl_version() that returns the full curl version string is
 found in lib/version.c.

 If authentication is requested but no password is given, a getpass_r() clone
 exists in lib/getpass.c. libcurl offers a custom callback that can be used
 instead of this, but it doesn't change much to us.

Persistent Connections
======================

 The persistent connection support in libcurl requires some considerations on
 how to do things inside of the library.

 o The 'SessionHandle' struct returned in the curl_easy_init() call must never
   hold connection-oriented data. It is meant to hold the root data as well as
   all the options etc that the library-user may choose.
 o The 'SessionHandle' struct holds the "connection cache" (an array of
   pointers to 'connectdata' structs). There's one connectdata struct
   allocated for each connection that libcurl knows about.
 o This also enables the 'curl handle' to be reused on subsequent transfers,
   something that was illegal before libcurl 7.7.
 o When we are about to perform a transfer with curl_easy_perform(), we first
   check for an already existing connection in the cache that we can use,
   otherwise we create a new one and add to the cache. If the cache is full
   already when we add a new connection, we close one of the present ones. We
   select which one to close dependent on the close policy that may have been
   previously set.
 o When the transfer operation is complete, we try to leave the connection
   open. Particular options may tell us not to, and protocols may signal
   closure on connections and then we don't keep it open of course.
 o When curl_easy_cleanup() is called, we close all still opened connections.

 You do realize that the curl handle must be re-used in order for the
 persistent connections to work.

Library Symbols
===============
 
 All symbols used internally in libcurl must use a 'Curl_' prefix if they're
 used in more than a single file. Single-file symbols must be made static.
 Public ("exported") symbols must use a 'curl_' prefix. (There are exceptions,
 but they are to be changed to follow this pattern in future versions.)

Return Codes and Informationals
===============================

 I've made things simple. Almost every function in libcurl returns a CURLcode,
 that must be CURLE_OK if everything is OK or otherwise a suitable error code
 as the curl/curl.h include file defines. The very spot that detects an error
 must use the Curl_failf() function to set the human-readable error
 description.

 In aiding the user to understand what's happening and to debug curl usage, we
 must supply a fair amount of informational messages by using the Curl_infof()
 function. Those messages are only displayed when the user explicitly asks for
 them. They are best used when revealing information that isn't otherwise
 obvious.

Client
======

 main() resides in src/main.c together with most of the client code.

 src/hugehelp.c is automatically generated by the mkhelp.pl perl script to
 display the complete "manual" and the src/urlglob.c file holds the functions
 used for the URL-"globbing" support. Globbing in the sense that the {} and []
 expansion stuff is there.

 The client mostly messes around to setup its 'config' struct properly, then
 it calls the curl_easy_*() functions of the library and when it gets back
 control after the curl_easy_perform() it cleans up the library, checks status
 and exits.

 When the operation is done, the ourWriteOut() function in src/writeout.c may
 be called to report about the operation. That function is using the
 curl_easy_getinfo() function to extract useful information from the curl
 session.

 Recent versions may loop and do all this several times if many URLs were
 specified on the command line or config file.

Memory Debugging
================

 The file lib/memdebug.c contains debug-versions of a few functions. Functions
 such as malloc, free, fopen, fclose, etc that somehow deal with resources
 that might give us problems if we "leak" them. The functions in the memdebug
 system do nothing fancy, they do their normal function and then log
 information about what they just did. The logged data can then be analyzed
 after a complete session,

 memanalyze.pl is the perl script present only present in CVS (not part of the
 release archives) that analyzes a log file generated by the memdebug
 system. It detects if resources are allocated but never freed and other kinds
 of errors related to resource management.

 Use -DMALLOCDEBUG when compiling to enable memory debugging, this is also
 switched on by running configure with --enable-debug.

Test Suite
==========

 Since November 2000, a test suite has evolved. It is placed in its own
 subdirectory directly off the root in the curl archive tree, and it contains
 a bunch of scripts and a lot of test case data.

 The main test script is runtests.pl that will invoke the two servers
 httpserver.pl and ftpserver.pl before all the test cases are performed. The
 test suite currently only runs on unix-like platforms.

 You'll find a complete description of the test case data files in the
 tests/README file.

 The test suite automatically detects if curl was built with the memory
 debugging enabled, and if it was it will detect memory leaks too.

Building Releases
=================

 There's no magic to this. When you consider everything stable enough to be
 released, run the 'maketgz' script (using 'make distcheck' will give you a
 pretty good view on the status of the current sources). maketgz prompts for
 version number of the client and the library before it creates a release
 archive. maketgz uses 'make dist' for the actual archive building, why you
 need to fill in the Makefile.am files properly for which files that should
 be included in the release archives.