Skip to content
This repository


Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
tag: curl-7_9_3
Fetching contributors…

Cannot retrieve contributors at this time

file 380 lines (282 sloc) 16.538 kb
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380
                                    Updated for curl 7.9.1 on November 2, 2001
                                  _ _ ____ _
                              ___| | | | _ \| |
                             / __| | | | |_) | |
                            | (__| |_| | _ <| |___
                             \___|\___/|_| \_\_____|


 The project is split in two. The library and the client. The client part uses
 the library, but the library is designed to allow other applications to use

 The largest amount of code and complexity is in the library part.

 All changes to the sources are committed to the CVS repository as soon as
 they're somewhat verified to work. Changes shall be commited as independently
 as possible so that individual changes can be easier spotted and tracked

 Tagging shall be used extensively, and by the time we release new archives we
 should tag the sources with a name similar to the released version number.

Windows vs Unix

 There are a few differences in how to program curl the unix way compared to
 the Windows way. The four perhaps most notable details are:

 1. Different function names for socket operations.

   In curl, this is solved with defines and macros, so that the source looks
   the same at all places except for the header file that defines them. The
   macros in use are sclose(), sread() and swrite().

 2. Windows requires a couple of init calls for the socket stuff.

   Those must be made by the application that uses libcurl, in curl that means
   src/main.c has some code #ifdef'ed to do just that.

 3. The file descriptors for network communication and file operations are
    not easily interchangable as in unix.

   We avoid this by not trying any funny tricks on file descriptors.

 4. When writing data to stdout, Windows makes end-of-lines the DOS way, thus
    destroying binary data, although you do want that conversion if it is
    text coming through... (sigh)

   We set stdout to binary under windows

 Inside the source code, We make an effort to avoid '#ifdef [Your OS]'. All
 conditionals that deal with features *should* instead be in the format
 '#ifdef HAVE_THAT_WEIRD_FUNCTION'. Since Windows can't run configure scripts,
 we maintain two config-win32.h files (one in / and one in src/) that are
 supposed to look exactly as a config.h file would have looked like on a
 Windows machine!

 Generally speaking: always remember that this will be compiled on dozens of
 operating systems. Don't walk on the edge.


 There are plenty of entry points to the library, namely each publicly defined
 function that libcurl offers to applications. All of those functions are
 rather small and easy-to-follow. All the ones prefixed with 'curl_easy' are
 put in the lib/easy.c file.

 Starting with libcurl 7.8, curl_global_init_() and curl_global_cleanup() were
 introduced. They should be called by the application to initialize and clean
 up global stuff in the library. As of today, they just do the global SSL
 initing if SSL is enabled. libcurl itself has no "global" scope.

 All printf()-style functions use the supplied clones in lib/mprintf.c. This
 makes sure we stay absolutely platform independent.

 curl_easy_init() allocates an internal struct and makes some initializations.
 The returned handle does not reveal internals. This is the 'SessionHandle'
 struct which works as an "anchor" struct for all curl_easy functions. All
 connections performed will get connect-specific data allocated that should be
 used for things related to particular connections/requests.

 curl_easy_setopt() takes three arguments, where the option stuff must be
 passed in pairs: the parameter-ID and the parameter-value. The list of
 options is documented in the man page. This function mainly sets things in
 the 'SessionHandle' struct.

 curl_easy_perform() does a whole lot of things:

 It starts off in the lib/easy.c file by calling Curl_perform() and the main
 work then continues in lib/url.c. The flow continues with a call to
 Curl_connect() to connect to the remote site.

 o Curl_connect()

   ... analyzes the URL, it separates the different components and connects to
   the remote host. This may involve using a proxy and/or using SSL. The
   Curl_gethost() function in lib/hostip.c is used for looking up host names.

   When Curl_connect is done, we are connected to the remote site. Then it is
   time to tell the server to get a document/file. Curl_do() arranges this.

   This function makes sure there's an allocated and initiated 'connectdata'
   struct that is used for this particular connection only (although there may
   be several requests performed on the same connect). A bunch of things are
   inited/inherited from the SessionHandle struct.

 o Curl_do()

   Curl_do() makes sure the proper protocol-specific function is called. The
   functions are named after the protocols they handle. Curl_ftp(),
   Curl_http(), Curl_dict(), etc. They all reside in their respective files
   (ftp.c, http.c and dict.c). HTTPS is handled by Curl_http() and FTPS by

   The protocol-specific functions of course deal with protocol-specific
   negotiations and setup. They have access to the Curl_sendf() (from
   lib/sendf.c) function to send printf-style formatted data to the remote
   host and when they're ready to make the actual file transfer they call the
   Curl_Transfer() function (in lib/transfer.c) to setup the transfer and

   Starting in 7.9.1, if this DO function fails and the connection is being
   re-used, libcurl will then close this connection, setup a new connection
   and re-issue the DO request on that. This is because there is no way to be
   perfectly sure that we have discovered a dead connection before the DO
   function and thus we might wrongly be re-using a connection that was closed
   by the remote peer.

 o Transfer()

   Curl_perform() then calls Transfer() in lib/transfer.c that performs
   the entire file transfer.

   During transfer, the progress functions in lib/progress.c are called at a
   frequent interval (or at the user's choice, a specified callback might get
   called). The speedcheck functions in lib/speedcheck.c are also used to
   verify that the transfer is as fast as required.

 o Curl_done()

   Called after a transfer is done. This function takes care of everything
   that has to be done after a transfer. This function attempts to leave
   matters in a state so that Curl_do() should be possible to call again on
   the same connection (in a persistent connection case). It might also soon
   be closed with Curl_disconnect().

 o Curl_disconnect()

   When doing normal connections and transfers, no one ever tries to close any
   connections so this is not normally called when curl_easy_perform() is
   used. This function is only used when we are certain that no more transfers
   is going to be made on the connection. It can be also closed by force, or
   it can be called to make sure that libcurl doesn't keep too many
   connections alive at the same time (there's a default amount of 5 but that
   can be changed with the CURLOPT_MAXCONNECTS option).

   This function cleans up all resources that are associated with a single

 Curl_perform() is the function that does the main "connect - do - transfer -
 done" loop. It loops if there's a Location: to follow.

 When completed, the curl_easy_cleanup() should be called to free up used
 resources. It runs Curl_disconnect() on all open connectons.

 A quick roundup on internal function sequences (many of these call
 protocol-specific function-pointers):

  curl_connect - connects to a remote site and does initial connect fluff
   This also checks for an existing connection to the requested site and uses
   that one if it is possible.

   curl_do - starts a transfer
    curl_transfer() - transfers data
   curl_done - ends a transfer

  curl_disconnect - disconnects from a remote site. This is called when the
   disconnect is really requested, which doesn't necessarily have to be
   exactly after curl_done in case we want to keep the connection open for
   a while.


 HTTP offers a lot and is the protocol in curl that uses the most lines of
 code. There is a special file (lib/formdata.c) that offers all the multipart
 post functions.

 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

 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.


 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.


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


 Telnet is implemented in lib/telnet.c.


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


 Everything LDAP is in lib/ldap.c.


 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

 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

 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


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

 src/hugehelp.c is automatically generated by the 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

 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, 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 that will invoke the two servers and 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 files properly for which files that should
 be included in the release archives.
Something went wrong with that request. Please try again.