1Updated: March 8, 2011 (http://curl.haxx.se/docs/faq.html) 2 _ _ ____ _ 3 ___| | | | _ \| | 4 / __| | | | |_) | | 5 | (__| |_| | _ <| |___ 6 \___|\___/|_| \_\_____| 7 8FAQ 9 10 1. Philosophy 11 1.1 What is cURL? 12 1.2 What is libcurl? 13 1.3 What is curl not? 14 1.4 When will you make curl do XXXX ? 15 1.5 Who makes curl? 16 1.6 What do you get for making curl? 17 1.7 What about CURL from curl.com? 18 1.8 I have a problem who do I mail? 19 1.9 Where do I buy commercial support for curl? 20 1.10 How many are using curl? 21 1.11 Why don't you update ca-bundle.crt 22 1.12 I have a problem who can I chat with? 23 1.13 curl's ECCN number? 24 1.14 How do I submit my patch? 25 26 2. Install Related Problems 27 2.1 configure doesn't find OpenSSL even when it is installed 28 2.1.1 native linker doesn't find OpenSSL 29 2.1.2 only the libssl lib is missing 30 2.2 Does curl work/build with other SSL libraries? 31 2.3 Where can I find a copy of LIBEAY32.DLL? 32 2.4 Does curl support SOCKS (RFC 1928) ? 33 34 3. Usage Problems 35 3.1 curl: (1) SSL is disabled, https: not supported 36 3.2 How do I tell curl to resume a transfer? 37 3.3 Why doesn't my posting using -F work? 38 3.4 How do I tell curl to run custom FTP commands? 39 3.5 How can I disable the Accept: */* header? 40 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 41 3.7 Can I use curl to delete/rename a file through FTP? 42 3.8 How do I tell curl to follow HTTP redirects? 43 3.9 How do I use curl in my favorite programming language? 44 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 45 3.11 How do I POST with a different Content-Type? 46 3.12 Why do FTP specific features over HTTP proxy fail? 47 3.13 Why does my single/double quotes fail? 48 3.14 Does curl support Javascript or PAC (automated proxy config)? 49 3.15 Can I do recursive fetches with curl? 50 3.16 What certificates do I need when I use SSL? 51 3.17 How do I list the root dir of an FTP server? 52 3.18 Can I use curl to send a POST/PUT and not wait for a response? 53 3.19 How do I get HTTP from a host using a specific IP address? 54 3.20 How to SFTP from my user's home directory? 55 3.21 Protocol xxx not supported or disabled in libcurl 56 57 4. Running Problems 58 4.1 Problems connecting to SSL servers. 59 4.2 Why do I get problems when I use & or % in the URL? 60 4.3 How can I use {, }, [ or ] to specify multiple URLs? 61 4.4 Why do I get downloaded data even though the web page doesn't exist? 62 4.5 Why do I get return code XXX from a HTTP server? 63 4.5.1 "400 Bad Request" 64 4.5.2 "401 Unauthorized" 65 4.5.3 "403 Forbidden" 66 4.5.4 "404 Not Found" 67 4.5.5 "405 Method Not Allowed" 68 4.5.6 "301 Moved Permanently" 69 4.6 Can you tell me what error code 142 means? 70 4.7 How do I keep user names and passwords secret in Curl command lines? 71 4.8 I found a bug! 72 4.9 Curl can't authenticate to the server that requires NTLM? 73 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work! 74 4.11 Why does my HTTP range requests return the full document? 75 4.12 Why do I get "certificate verify failed" ? 76 4.13 Why is curl -R on Windows one hour off? 77 4.14 Redirects work in browser but not with curl! 78 4.15 FTPS doesn't work 79 4.16 My HTTP POST or PUT requests are slow! 80 4.17 Non-functional connect timeouts on Windows 81 4.18 file:// URLs containing drive letters (Windows, NetWare) 82 4.19 Why doesn't cURL return an error when the network cable is unplugged? 83 84 5. libcurl Issues 85 5.1 Is libcurl thread-safe? 86 5.2 How can I receive all data into a large memory chunk? 87 5.3 How do I fetch multiple files with libcurl? 88 5.4 Does libcurl do Winsock initing on win32 systems? 89 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ? 90 5.6 What about Keep-Alive or persistent connections? 91 5.7 Link errors when building libcurl on Windows! 92 5.8 libcurl.so.X: open failed: No such file or directory 93 5.9 How does libcurl resolve host names? 94 5.10 How do I prevent libcurl from writing the response to stdout? 95 5.11 How do I make libcurl not receive the whole HTTP response? 96 5.12 Can I make libcurl fake or hide my real IP address? 97 5.13 How do I stop an ongoing transfer? 98 5.14 Using C++ non-static functions for callbacks? 99 5.15 How do I get an FTP directory listing? 100 101 6. License Issues 102 6.1 I have a GPL program, can I use the libcurl library? 103 6.2 I have a closed-source program, can I use the libcurl library? 104 6.3 I have a BSD licensed program, can I use the libcurl library? 105 6.4 I have a program that uses LGPL libraries, can I use libcurl? 106 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 107 6.6 Can you please change the curl/libcurl license to XXXX? 108 6.7 What are my obligations when using libcurl in my commercial apps? 109 110 7. PHP/CURL Issues 111 7.1 What is PHP/CURL? 112 7.2 Who wrote PHP/CURL? 113 7.3 Can I perform multiple requests using the same handle? 114 115============================================================================== 116 1171. Philosophy 118 119 1.1 What is cURL? 120 121 cURL is the name of the project. The name is a play on 'Client for URLs', 122 originally with URL spelled in uppercase to make it obvious it deals with 123 URLs. The fact it can also be pronounced 'see URL' also helped, it works as 124 an abbreviation for "Client URL Request Library" or why not the recursive 125 version: "Curl URL Request Library". 126 127 The cURL project produces two products: 128 129 libcurl 130 131 A free and easy-to-use client-side URL transfer library, supporting DICT, 132 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, 133 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP. 134 135 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, 136 kerberos, HTTP form based upload, proxies, cookies, user+password 137 authentication, file transfer resume, http proxy tunneling and more! 138 139 libcurl is highly portable, it builds and works identically on numerous 140 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX, 141 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOs, Mac 142 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF, 143 Android, Minix, IBM TPF and more... 144 145 libcurl is free, thread-safe, IPv6 compatible, feature rich, well 146 supported and fast. 147 148 curl 149 150 A command line tool for getting or sending files using URL syntax. 151 152 Since curl uses libcurl, curl supports the same wide range of common 153 Internet protocols that libcurl does. 154 155 We pronounce curl and cURL with an initial k sound: [kurl]. 156 157 There are numerous sub-projects and related projects that also use the word 158 curl in the project names in various combinations, but you should take 159 notice that this FAQ is directed at the command-line tool named curl (and 160 libcurl the library), and may therefore not be valid for other curl-related 161 projects. (There is however a small section for the PHP/CURL in this FAQ.) 162 163 1.2 What is libcurl? 164 165 libcurl is a reliable and portable library which provides you with an easy 166 interface to a range of common Internet protocols. 167 168 You can use libcurl for free in your application, be it open source, 169 commercial or closed-source. 170 171 libcurl is most probably the most portable, most powerful and most often 172 used C-based multi-platform file transfer library on this planet - be it 173 open source or commercial. 174 175 1.3 What is curl not? 176 177 Curl is not a wget clone. That is a common misconception. Never, during 178 curl's development, have we intended curl to replace wget or compete on its 179 market. Curl is targeted at single-shot file transfers. 180 181 Curl is not a web site mirroring program. If you want to use curl to mirror 182 something: fine, go ahead and write a script that wraps around curl to make 183 it reality (like curlmirror.pl does). 184 185 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl 186 but if you want systematic and sequential behavior you should write a 187 script (or write a new program that interfaces libcurl) and do it. 188 189 Curl is not a PHP tool, even though it works perfectly well when used from 190 or with PHP (when using the PHP/CURL module). 191 192 Curl is not a program for a single operating system. Curl exists, compiles, 193 builds and runs under a wide range of operating systems, including all 194 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2, 195 OS X, QNX etc. 196 197 1.4 When will you make curl do XXXX ? 198 199 We love suggestions of what to change in order to make curl and libcurl 200 better. We do however believe in a few rules when it comes to the future of 201 curl: 202 203 * Curl -- the command line tool -- is to remain a non-graphical command line 204 tool. If you want GUIs or fancy scripting capabilities, you should look 205 for another tool that uses libcurl. 206 207 * We do not add things to curl that other small and available tools already 208 do very fine at the side. Curl's output is fine to pipe into another 209 program or redirect to another file for the next program to interpret. 210 211 * We focus on protocol related issues and improvements. If you wanna do more 212 magic with the supported protocols than curl currently does, chances are 213 big we will agree. If you wanna add more protocols, we may very well 214 agree. 215 216 * If you want someone else to make all the work while you wait for us to 217 implement it for you, that is not a very friendly attitude. We spend a 218 considerable time already on maintaining and developing curl. In order to 219 get more out of us, you should consider trading in some of your time and 220 efforts in return. 221 222 * If you write the code, chances are bigger that it will get into curl 223 faster. 224 225 1.5 Who makes curl? 226 227 curl and libcurl are not made by any single individual. Daniel Stenberg is 228 project leader and main developer, but other persons' submissions are 229 important and crucial. Anyone can contribute and post their changes and 230 improvements and have them inserted in the main sources (of course on the 231 condition that developers agree on that the fixes are good). 232 233 The full list of all contributors is found in the docs/THANKS file. 234 235 curl is developed by a community, with Daniel at the wheel. 236 237 1.6 What do you get for making curl? 238 239 Project cURL is entirely free and open. No person gets paid for developing 240 (lib)curl on full or even part time. We do this voluntarily on our spare 241 time. Occasionally companies pay individual developers to work on curl, but 242 that's up to each company and developer. It is not controlled by nor 243 supervised in any way by the project. 244 245 We still get help from companies. Haxx provides web site, bandwidth, mailing 246 lists etc and sourceforge.net hosts project services we take advantage from, 247 like the bug tracker. Also again, some companies have sponsored certain 248 parts of the development in the past and I hope some will continue to do so 249 in the future. 250 251 If you want to support our project, consider a donation or a banner-program 252 or even better: by helping us coding, documenting, testing etc. 253 254 1.7 What about CURL from curl.com? 255 256 During the summer 2001, curl.com was busy advertising their client-side 257 programming language for the web, named CURL. 258 259 We are in no way associated with curl.com or their CURL programming 260 language. 261 262 Our project name curl has been in effective use since 1998. We were not the 263 first computer related project to use the name "curl" and do not claim any 264 first-hand rights to the name. 265 266 We recognize that we will be living in parallel with curl.com and wish them 267 every success. 268 269 1.8 I have a problem who do I mail? 270 271 Please do not mail any single individual unless you really need to. Keep 272 curl-related questions on a suitable mailing list. All available mailing 273 lists are listed in the MANUAL document and online at 274 http://curl.haxx.se/mail/ 275 276 Keeping curl-related questions and discussions on mailing lists allows 277 others to join in and help, to share their ideas, contribute their 278 suggestions and spread their wisdom. Keeping discussions on public mailing 279 lists also allows for others to learn from this (both current and future 280 users thanks to the web based archives of the mailing lists), thus saving us 281 from having to repeat ourselves even more. Thanks for respecting this. 282 283 If you have found or simply suspect a security problem in curl or libcurl, 284 mail curl-security at haxx.se (closed list of receivers, mails are not 285 disclosed) and tell. Then we can produce a fix in a timely manner before the 286 flaw is announced to the world, thus lessen the impact the problem will have 287 on existing users. 288 289 1.9 Where do I buy commercial support for curl? 290 291 curl is fully open source. It means you can hire any skilled engineer to fix 292 your curl-related problems. 293 294 We list available alternatives on the curl web site: 295 http://curl.haxx.se/support.html 296 297 1.10 How many are using curl? 298 299 It is impossible to tell. 300 301 We don't know how many users that knowingly have installed and use curl. 302 303 We don't know how many users that use curl without knowing that they are in 304 fact using it. 305 306 We don't know how many users that downloaded or installed curl and then 307 never use it. 308 309 Some facts to use as input to the math: 310 311 curl packages are downloaded from the curl.haxx.se and mirrors over a 312 million times per year. curl is installed by default with most Linux 313 distributions. curl is installed by default with Mac OS X. curl and libcurl 314 as used by numerous applications that include libcurl binaries in their 315 distribution packages (like Adobe Acrobat Reader and Google Earth). 316 317 More than a hundred known named companies use curl in commercial 318 environments and products and more than a hundred known named open source 319 projects depend on (lib)curl. 320 321 In a poll on the curl web site mid-2005, more than 50% of the 300+ answers 322 estimated a user base of one million users or more. 323 324 In March 2005, the "Linux Counter project" estimated a total Linux user base 325 of some 29 millions, while Netcraft detected some 4 million "active" Linux 326 based web servers. A guess is that a fair amount of these Linux 327 installations have curl installed. 328 329 The Debian project maintains statistics on packages installed by people 330 who have voluntarily run their package counting application. In mid-2010, 331 libcurl3 was installed on over 55000 such systems (62% of reporting systems) 332 and was one of the 320 most popular installed packages (out of about 107000 333 possible packages). 334 335 All this taken together, there is no doubt that there are millions of 336 (lib)curl users. 337 338 http://curl.haxx.se/docs/companies.html 339 http://curl.haxx.se/docs/programs.html 340 http://curl.haxx.se/libcurl/using/apps.html 341 http://counter.li.org/estimates.php 342 http://news.netcraft.com/archives/2005/03/14/fedora_makes_rapid_progress.html 343 http://qa.debian.org/popcon.php?package=curl 344 345 1.11 Why don't you update ca-bundle.crt 346 347 The ca-bundle.crt file that used to be bundled with curl was very outdated 348 (it being last modified year 2000 should tell) and must be replaced with a 349 much more modern and up-to-date version by anyone who wants to verify peers 350 anyway. It is no longer provided, the last curl release that shipped it was 351 curl 7.18.0. 352 353 In the cURL project we've decided not to attempt to keep this file updated 354 (or even present anymore) since deciding what to add to a ca cert bundle is 355 an undertaking we've not been ready to accept, and the one we can get from 356 Mozilla is perfectly fine so there's no need to duplicate that work. 357 358 Today, with many services performed over HTTPS, every operating system 359 should come with a default ca cert bundle that can be deemed somewhat 360 trustworthy and that collection (if reasonably updated) should be deemed to 361 be a lot better than a private curl version. 362 363 If you want the most recent collection of ca certs that Mozilla Firefox 364 uses, we recommend that you extract the collection yourself from Mozilla 365 Firefox (by running 'make ca-bundle), or by using our online service setup 366 for this purpose: http://curl.haxx.se/docs/caextract.html 367 368 1.12 I have a problem who can I chat with? 369 370 There's a bunch of friendly people hanging out in the #curl channel on the 371 IRC network irc.freenode.net. If you're polite and nice, chances are big 372 that you can get -- or provide -- help instantly. 373 374 1.13 curl's ECCN number? 375 376 The US government restricts exports of software that contains or uses 377 cryptography. When doing so, the Export Control Classification Number (ECCN) 378 is used to identify the level of export control etc. 379 380 ASF gives a good explanation at http://www.apache.org/dev/crypto.html 381 382 We believe curl's number might be ECCN 5D002, another possibility is 383 5D992. It seems necessary to write them, asking to confirm. 384 385 Comprehensible explanations of the meaning of such numbers and how to 386 obtain them (resp.) are here 387 388 http://www.bis.doc.gov/licensing/exportingbasics.htm 389 http://www.bis.doc.gov/licensing/do_i_needaneccn.html 390 391 An incomprehensible description of the two numbers above is here 392 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf 393 394 1.14 How do I submit my patch? 395 396 When you have made a patch or a change of whatever sort, and want to submit 397 that to the project, there are a few different ways we prefer: 398 399 o send a patch to the curl-library mailing list. We're many subscribers 400 there and there are lots of people who can review patches, comment on them 401 and "receive" them properly. 402 403 o if your patch changes or fixes a bug, you can also opt to submit a bug 404 report in the bug tracker and attach your patch there. There are less 405 people involved there. 406 407 Lots of more details are found in the CONTRIBUTE and INTERNALS docs. 408 409 4102. Install Related Problems 411 412 2.1 configure doesn't find OpenSSL even when it is installed 413 414 This may be because of several reasons. 415 416 2.1.1 native linker doesn't find openssl 417 418 Affected platforms: 419 Solaris (native cc compiler) 420 HPUX (native cc compiler) 421 SGI IRIX (native cc compiler) 422 SCO UNIX (native cc compiler) 423 424 When configuring curl, I specify --with-ssl. OpenSSL is installed in 425 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find 426 CRYPTO_lock in -lcrypto 427 428 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER 429 -lcrypto, so ld can't find the library. This is due to a bug in the GNU 430 autoconf tool. 431 432 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of 433 ./configure places the -L/usr/local/ssl/lib early enough in the command 434 line to make things work 435 436 2.1.2 only the libssl lib is missing 437 438 If all include files and the libcrypto lib is present, with only the 439 libssl being missing according to configure, this is mostly likely because 440 a few functions are left out from the libssl. 441 442 If the function names missing include RSA or RSAREF you can be certain 443 that this is because libssl requires the RSA and RSAREF libs to build. 444 445 See the INSTALL file section that explains how to add those libs to 446 configure. Make sure that you remove the config.cache file before you 447 rerun configure with the new flags. 448 449 2.2 Does curl work/build with other SSL libraries? 450 451 Curl has been written to use OpenSSL, GnuTLS, yassl, NSS, PolarSSL, axTLS or 452 qssl, although there should not be many problems using a different 453 library. If anyone does "port" curl to use a different SSL library, we are 454 of course very interested in getting the patch! 455 456 2.3 Where can I find a copy of LIBEAY32.DLL? 457 458 That is an OpenSSL binary built for Windows. 459 460 Curl uses OpenSSL to do the SSL stuff. The LIBEAY32.DLL is what curl needs 461 on a windows machine to do https://. Check out the curl web site to find 462 accurate and up-to-date pointers to recent OpenSSL DLLs and other binary 463 packages. 464 465 2.4 Does curl support SOCKS (RFC 1928) ? 466 467 Yes, SOCKS 4 and 5 are supported. 468 469 4703. Usage problems 471 472 3.1 curl: (1) SSL is disabled, https: not supported 473 474 If you get this output when trying to get anything from a https:// server, 475 it means that the instance of curl/libcurl that you're using was built 476 without support for this protocol. 477 478 This could've happened if the configure script that was run at build time 479 couldn't find all libs and include files curl requires for SSL to work. If 480 the configure script fails to find them, curl is simply built without SSL 481 support. 482 483 To get the https:// support into a curl that was previously built but that 484 reports that https:// is not supported, you should dig through the document 485 and logs and check out why the configure script doesn't find the SSL libs 486 and/or include files. 487 488 Also, check out the other paragraph in this FAQ labelled "configure doesn't 489 find OpenSSL even when it is installed". 490 491 3.2 How do I tell curl to resume a transfer? 492 493 Curl supports resumed transfers both ways on both FTP and HTTP. 494 Try the -C option. 495 496 3.3 Why doesn't my posting using -F work? 497 498 You can't simply use -F or -d at your choice. The web server that will 499 receive your post assumes one of the formats. If the form you're trying to 500 "fake" sets the type to 'multipart/form-data', then and only then you must 501 use the -F type. In all the most common cases, you should use -d which then 502 causes a posting with the type 'application/x-www-form-urlencoded'. 503 504 This is described in some detail in the MANUAL and TheArtOfHttpScripting 505 documents, and if you don't understand it the first time, read it again 506 before you post questions about this to the mailing list. Also, try reading 507 through the mailing list archives for old postings and questions regarding 508 this. 509 510 3.4 How do I tell curl to run custom FTP commands? 511 512 You can tell curl to perform optional commands both before and/or after a 513 file transfer. Study the -Q/--quote option. 514 515 Since curl is used for file transfers, you don't use curl to just perform 516 FTP commands without transferring anything. Therefore you must always specify 517 a URL to transfer to/from even when doing custom FTP commands. 518 519 3.5 How can I disable the Accept: */* header? 520 521 You can change all internally generated headers by adding a replacement with 522 the -H/--header option. By adding a header with empty contents you safely 523 disable that one. Use -H "Accept:" to disable that specific header. 524 525 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 526 527 To curl, all contents are alike. It doesn't matter how the page was 528 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain 529 HTML-files. There's no difference to curl and it doesn't even know what kind 530 of language that generated the page. 531 532 See also item 3.14 regarding javascript. 533 534 3.7 Can I use curl to delete/rename a file through FTP? 535 536 Yes. You specify custom FTP commands with -Q/--quote. 537 538 One example would be to delete a file after you have downloaded it: 539 540 curl -O ftp://download.com/coolfile -Q '-DELE coolfile' 541 542 or rename a file after upload: 543 544 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname" 545 546 3.8 How do I tell curl to follow HTTP redirects? 547 548 Curl does not follow so-called redirects by default. The Location: header 549 that informs the client about this is only interpreted if you're using the 550 -L/--location option. As in: 551 552 curl -L http://redirector.com 553 554 Not all redirects are HTTP ones, see 4.14 555 556 3.9 How do I use curl in my favorite programming language? 557 558 There exist many language interfaces/bindings for curl that integrates it 559 better with various languages. If you are fluid in a script language, you 560 may very well opt to use such an interface instead of using the command line 561 tool. 562 563 Find out more about which languages that support curl directly, and how to 564 install and use them, in the libcurl section of the curl web site: 565 http://curl.haxx.se/libcurl/ 566 567 All the various bindings to libcurl are made by other projects and people, 568 outside of the cURL project. The cURL project itself only produces libcurl 569 with its plain C API. If you don't find anywhere else to ask you can ask 570 about bindings on the curl-library list too, but be prepared that people on 571 that list may not know anything about bindings. 572 573 In October 2009, there were interfaces available for the following 574 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria, 575 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET, 576 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby, 577 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro, 578 Q, wxwidgets and XBLite. By the time you read this, additional ones may have 579 appeared! 580 581 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 582 583 Curl adheres to the HTTP spec, which basically means you can play with *any* 584 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and 585 XML-RPC are all such ones. You can use -X to set custom requests and -H to 586 set custom headers (or replace internally generated ones). 587 588 Using libcurl is of course just as fine and you'd just use the proper 589 library options to do the same. 590 591 3.11 How do I POST with a different Content-Type? 592 593 You can always replace the internally generated headers with -H/--header. 594 To make a simple HTTP POST with text/xml as content-type, do something like: 595 596 curl -d "datatopost" -H "Content-Type: text/xml" [URL] 597 598 3.12 Why do FTP specific features over HTTP proxy fail? 599 600 Because when you use a HTTP proxy, the protocol spoken on the network will 601 be HTTP, even if you specify a FTP URL. This effectively means that you 602 normally can't use FTP specific features such as FTP upload and FTP quote 603 etc. 604 605 There is one exception to this rule, and that is if you can "tunnel through" 606 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p) 607 and is generally not available as proxy admins usually disable tunneling to 608 other ports than 443 (which is used for HTTPS access through proxies). 609 610 3.13 Why does my single/double quotes fail? 611 612 To specify a command line option that includes spaces, you might need to 613 put the entire option within quotes. Like in: 614 615 curl -d " with spaces " url.com 616 617 or perhaps 618 619 curl -d ' with spaces ' url.com 620 621 Exactly what kind of quotes and how to do this is entirely up to the shell 622 or command line interpreter that you are using. For most unix shells, you 623 can more or less pick either single (') or double (") quotes. For 624 Windows/DOS prompts I believe you're forced to use double (") quotes. 625 626 Please study the documentation for your particular environment. Examples in 627 the curl docs will use a mix of both these ones as shown above. You must 628 adjust them to work in your environment. 629 630 Remember that curl works and runs on more operating systems than most single 631 individuals have ever tried. 632 633 3.14 Does curl support Javascript or PAC (automated proxy config)? 634 635 Many web pages do magic stuff using embedded Javascript. Curl and libcurl 636 have no built-in support for that, so it will be treated just like any other 637 contents. 638 639 .pac files are a netscape invention and are sometimes used by organizations 640 to allow them to differentiate which proxies to use. The .pac contents is 641 just a Javascript program that gets invoked by the browser and that returns 642 the name of the proxy to connect to. Since curl doesn't support Javascript, 643 it can't support .pac proxy configuration either. 644 645 Some workarounds usually suggested to overcome this Javascript dependency: 646 647 - Depending on the Javascript complexity, write up a script that 648 translates it to another language and execute that. 649 650 - Read the Javascript code and rewrite the same logic in another language. 651 652 - Implement a Javascript interpreter, people have successfully used the 653 Mozilla Javascript engine in the past. 654 655 - Ask your admins to stop this, for a static proxy setup or similar. 656 657 3.15 Can I do recursive fetches with curl? 658 659 No. curl itself has no code that performs recursive operations, such as 660 those performed by wget and similar tools. 661 662 There exist wrapper scripts with that functionality (for example the 663 curlmirror perl script), and you can write programs based on libcurl to do 664 it, but the command line tool curl itself cannot. 665 666 3.16 What certificates do I need when I use SSL? 667 668 There are three different kinds of "certificates" to keep track of when we 669 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl. 670 671 - Client certificate. The server you communicate may require that you can 672 provide this in order to prove that you actually are who you claim to be. 673 If the server doesn't require this, you don't need a client certificate. 674 675 A client certificate is always used together with a private key, and the 676 private key has a pass phrase that protects it. 677 678 - Server certificate. The server you communicate with has a server 679 certificate. You can and should verify this certificate to make sure that 680 you are truly talking to the real server and not a server impersonating 681 it. 682 683 - Certificate Authority certificate ("CA cert"). You often have several CA 684 certs in a CA cert bundle that can be used to verify a server certificate 685 that was signed by one of the authorities in the bundle. curl does not 686 come with a CA cert bundle but most curl installs provide one. You can 687 also override the default. 688 689 The server certificate verification process is made by using a Certificate 690 Authority certificate ("CA cert") that was used to sign the server 691 certificate. Server certificate verification is enabled by default in curl 692 and libcurl and is often the reason for problems as explained in FAQ entry 693 4.12 and the SSLCERTS document 694 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are 695 "self-signed" or otherwise signed by a CA that you do not have a CA cert 696 for, cannot be verified. If the verification during a connect fails, you 697 are refused access. You then need to explicitly disable the verification 698 to connect to the server. 699 700 3.17 How do I list the root dir of an FTP server? 701 702 There are two ways. The way defined in the RFC is to use an encoded slash 703 in the first path part. List the "/tmp" dir like this: 704 705 curl ftp://ftp.sunet.se/%2ftmp/ 706 707 or the not-quite-kosher-but-more-readable way, by simply starting the path 708 section of the URL with a slash: 709 710 curl ftp://ftp.sunet.se//tmp/ 711 712 3.18 Can I use curl to send a POST/PUT and not wait for a response? 713 714 No. 715 716 But you could easily write your own program using libcurl to do such stunts. 717 718 3.19 How do I get HTTP from a host using a specific IP address? 719 720 For example, you may be trying out a web site installation that isn't yet in 721 the DNS. Or you have a site using multiple IP addresses for a given host 722 name and you want to address a specific one out of the set. 723 724 Set a custom Host: header that identifies the server name you want to reach 725 but use the target IP address in the URL: 726 727 curl --header "Host: www.example.com" http://127.0.0.1/ 728 729 3.20 How to SFTP from my user's home directory? 730 731 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to 732 work with. It means that if you don't specify that you want the user's home 733 directory, you get the actual root directory. 734 735 To specify a file in your user's home directory, you need to use the correct 736 URL syntax which for sftp might look similar to: 737 738 curl -O -u user:password sftp://example.com/~/file.txt 739 740 and for SCP it is just a different protocol prefix: 741 742 curl -O -u user:password scp://example.com/~/file.txt 743 744 3.21 Protocol xxx not supported or disabled in libcurl 745 746 When passing on a URL to curl to use, it may respond that the particular 747 protocol is not supported or disabled. The particular way this error message 748 is phrased is because curl doesn't make a distinction internally of whether 749 a particular protocol is not supported (ie never got any code added that 750 knows how to speak that protocol) or if it was explicitly disabled. curl can 751 be built to only support a given set of protocols, and the rest would then 752 be disabled or not supported. 753 754 Note that this error will also occur if you pass a wrongly spelled protocol 755 part as in "htpt://example.com" or as in the less evident case if you prefix 756 the protocol part with a space as in " http://example.com/". 757 758 7594. Running Problems 760 761 4.1 Problems connecting to SSL servers. 762 763 It took a very long time before we could sort out why curl had problems to 764 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The 765 error sometimes showed up similar to: 766 767 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233: 768 769 It turned out to be because many older SSL servers don't deal with SSLv3 770 requests properly. To correct this problem, tell curl to select SSLv2 from 771 the command line (-2/--sslv2). 772 773 There have also been examples where the remote server didn't like the SSLv2 774 request and instead you had to force curl to use SSLv3 with -3/--sslv3. 775 776 4.2 Why do I get problems when I use & or % in the URL? 777 778 In general unix shells, the & symbol is treated specially and when used, it 779 runs the specified command in the background. To safely send the & as a part 780 of a URL, you should quote the entire URL by using single (') or double (") 781 quotes around it. Similar problems can also occur on some shells with other 782 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL. 783 784 An example that would invoke a remote CGI that uses &-symbols could be: 785 786 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl' 787 788 In Windows, the standard DOS shell treats the %-symbol specially and you 789 need to use TWO %-symbols for each single one you want to use in the URL. 790 791 Also note that if you want the literal %-symbol to be part of the data you 792 pass in a POST using -d/--data you must encode it as '%25' (which then also 793 needs the %-symbol doubled on Windows machines). 794 795 4.3 How can I use {, }, [ or ] to specify multiple URLs? 796 797 Because those letters have a special meaning to the shell, and to be used in 798 a URL specified to curl you must quote them. 799 800 An example that downloads two URLs (sequentially) would do: 801 802 curl '{curl,www}.haxx.se' 803 804 To be able to use those letters as actual parts of the URL (without using 805 them for the curl URL "globbing" system), use the -g/--globoff option: 806 807 curl -g 'www.site.com/weirdname[].html' 808 809 4.4 Why do I get downloaded data even though the web page doesn't exist? 810 811 Curl asks remote servers for the page you specify. If the page doesn't exist 812 at the server, the HTTP protocol defines how the server should respond and 813 that means that headers and a "page" will be returned. That's simply how 814 HTTP works. 815 816 By using the --fail option you can tell curl explicitly to not get any data 817 if the HTTP return code doesn't say success. 818 819 4.5 Why do I get return code XXX from a HTTP server? 820 821 RFC2616 clearly explains the return codes. This is a short transcript. Go 822 read the RFC for exact details: 823 824 4.5.1 "400 Bad Request" 825 826 The request could not be understood by the server due to malformed 827 syntax. The client SHOULD NOT repeat the request without modifications. 828 829 4.5.2 "401 Unauthorized" 830 831 The request requires user authentication. 832 833 4.5.3 "403 Forbidden" 834 835 The server understood the request, but is refusing to fulfill it. 836 Authorization will not help and the request SHOULD NOT be repeated. 837 838 4.5.4 "404 Not Found" 839 840 The server has not found anything matching the Request-URI. No indication 841 is given of whether the condition is temporary or permanent. 842 843 4.5.5 "405 Method Not Allowed" 844 845 The method specified in the Request-Line is not allowed for the resource 846 identified by the Request-URI. The response MUST include an Allow header 847 containing a list of valid methods for the requested resource. 848 849 4.5.6 "301 Moved Permanently" 850 851 If you get this return code and an HTML output similar to this: 852 853 <H1>Moved Permanently</H1> The document has moved <A 854 HREF="http://same_url_now_with_a_trailing_slash/">here</A>. 855 856 it might be because you request a directory URL but without the trailing 857 slash. Try the same operation again _with_ the trailing URL, or use the 858 -L/--location option to follow the redirection. 859 860 4.6 Can you tell me what error code 142 means? 861 862 All curl error codes are described at the end of the man page, in the 863 section called "EXIT CODES". 864 865 Error codes that are larger than the highest documented error code means 866 that curl has exited due to a crash. This is a serious error, and we 867 appreciate a detailed bug report from you that describes how we could go 868 ahead and repeat this! 869 870 4.7 How do I keep user names and passwords secret in Curl command lines? 871 872 This problem has two sides: 873 874 The first part is to avoid having clear-text passwords in the command line 875 so that they don't appear in 'ps' outputs and similar. That is easily 876 avoided by using the "-K" option to tell curl to read parameters from a file 877 or stdin to which you can pass the secret info. curl itself will also 878 attempt to "hide" the given password by blanking out the option - this 879 doesn't work on all platforms. 880 881 To keep the passwords in your account secret from the rest of the world is 882 not a task that curl addresses. You could of course encrypt them somehow to 883 at least hide them from being read by human eyes, but that is not what 884 anyone would call security. 885 886 Also note that regular HTTP (using Basic authentication) and FTP passwords 887 are sent in clear across the network. All it takes for anyone to fetch them 888 is to listen on the network. Eavesdropping is very easy. Use more secure 889 authentication methods (like Digest, Negotiate or even NTLM) or consider the 890 SSL-based alternatives HTTPS and FTPS. 891 892 4.8 I found a bug! 893 894 It is not a bug if the behavior is documented. Read the docs first. 895 Especially check out the KNOWN_BUGS file, it may be a documented bug! 896 897 If it is a problem with a binary you've downloaded or a package for your 898 particular platform, try contacting the person who built the package/archive 899 you have. 900 901 If there is a bug, read the BUGS document first. Then report it as described 902 in there. 903 904 4.9 Curl can't authenticate to the server that requires NTLM? 905 906 NTLM support requires OpenSSL, GnuTLS, NSS or Microsoft Windows libraries at 907 build-time to provide this functionality. 908 909 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You 910 should not use such ones. 911 912 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work! 913 914 Many web servers allow or demand that the administrator configures the 915 server properly for these requests to work on the web server. 916 917 Some servers seem to support HEAD only on certain kinds of URLs. 918 919 To fully grasp this, try the documentation for the particular server 920 software you're trying to interact with. This is not anything curl can do 921 anything about. 922 923 4.11 Why does my HTTP range requests return the full document? 924 925 Because the range may not be supported by the server, or the server may 926 choose to ignore it and return the full document anyway. 927 928 4.12 Why do I get "certificate verify failed" ? 929 930 You invoke curl 7.10 or later to communicate on a https:// URL and get an 931 error back looking something similar to this: 932 933 curl: (35) SSL: error:14090086:SSL routines: 934 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed 935 936 Then it means that curl couldn't verify that the server's certificate was 937 good. Curl verifies the certificate using the CA cert bundle that comes with 938 the curl installation. 939 940 To disable the verification (which makes it act like curl did before 7.10), 941 use -k. This does however enable man-in-the-middle attacks. 942 943 If you get this failure but are having a CA cert bundle installed and used, 944 the server's certificate is not signed by one of the CA's in the bundle. It 945 might for example be self-signed. You then correct this problem by obtaining 946 a valid CA cert for the server. Or again, decrease the security by disabling 947 this check. 948 949 Details are also in the SSLCERTS file in the release archives, found online 950 here: http://curl.haxx.se/docs/sslcerts.html 951 952 4.13 Why is curl -R on Windows one hour off? 953 954 During daylight savings time, when -R is used, curl will set a time that 955 appears one hour off. This happens due to a flaw in how Windows stores and 956 uses file modification times and it is not easily worked around. For details 957 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp 958 959 4.14 Redirects work in browser but not with curl! 960 961 curl supports HTTP redirects fine (see item 3.8). Browsers generally support 962 at least two other ways to perform directs that curl does not: 963 964 - Meta tags. You can write a HTML tag that will cause the browser to 965 redirect to another given URL after a certain time. 966 967 - Javascript. You can write a Javascript program embedded in a HTML page 968 that redirects the browser to another given URL. 969 970 There is no way to make curl follow these redirects. You must either 971 manually figure out what the page is set to do, or you write a script that 972 parses the results and fetches the new URL. 973 974 4.15 FTPS doesn't work 975 976 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit 977 mode. 978 979 When a URL is used that starts with FTPS://, curl assumes implicit SSL on 980 the control connection and will therefore immediately connect and try to 981 speak SSL. FTPS:// connections default to port 990. 982 983 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one 984 of its related flavours). This is the most common method, and the one 985 mandated by RFC4217. This kind of connection then of course uses the 986 standard FTP port 21 by default. 987 988 4.16 My HTTP POST or PUT requests are slow! 989 990 libcurl makes all POST and PUT requests (except for POST requests with a 991 very tiny request body) use the "Expect: 100-continue" header. This header 992 allows the server to deny the operation early so that libcurl can bail out 993 already before having to send any data. This is useful in authentication 994 cases and others. 995 996 However, many servers don't implement the Expect: stuff properly and if the 997 server doesn't respond (positively) within 1 second libcurl will continue 998 and send off the data anyway. 999 1000 You can disable libcurl's use of the Expect: header the same way you disable 1001 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0. 1002 1003 4.17 Non-functional connect timeouts 1004 1005 In most Windows setups having a timeout longer than 21 seconds make no 1006 difference, as it will only send 3 TCP SYN packets and no more. The second 1007 packet sent three seconds after the first and the third six seconds after 1008 the second. No more than three packets are sent, no matter how long the 1009 timeout is set. 1010 1011 See option TcpMaxConnectRetransmissions on this page: 1012 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7 1013 1014 Also, even on non-Windows systems there may run a firewall or anti-virus 1015 software or similar that accepts the connection but does not actually do 1016 anything else. This will make (lib)curl to consider the connection connected 1017 and thus the connect timeout won't trigger. 1018 1019 4.18 file:// URLs containing drive letters (Windows, NetWare) 1020 1021 When using cURL to try to download a local file, one might use a URL 1022 in this format: 1023 1024 file://D:/blah.txt 1025 1026 You'll find that even if D:\blah.txt does exist, cURL returns a 'file 1027 not found' error. 1028 1029 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html), 1030 file:// URLs must contain a host component, but it is ignored by 1031 most implementations. In the above example, 'D:' is treated as the 1032 host component, and is taken away. Thus, cURL tries to open '/blah.txt'. 1033 If your system is installed to drive C:, that will resolve to 'C:\blah.txt', 1034 and if that doesn't exist you will get the not found error. 1035 1036 To fix this problem, use file:// URLs with *three* leading slashes: 1037 1038 file:///D:/blah.txt 1039 1040 Alternatively, if it makes more sense, specify 'localhost' as the host 1041 component: 1042 1043 file://localhost/D:/blah.txt 1044 1045 In either case, cURL should now be looking for the correct file. 1046 1047 4.19 Why doesn't cURL return an error when the network cable is unplugged? 1048 1049 Unplugging the cable is not an error situation. The TCP/IP protocol stack 1050 was designed to be fault tolerant, so even though there may be a physical 1051 break somewhere the connection shouldn't be affected, just possibly 1052 delayed. Eventually, the physical break will be fixed or the data will be 1053 re-routed around the physical problem. 1054 1055 In such cases, the TCP/IP stack is responsible for detecting when the 1056 network connection is irrevocably lost. Since with some protocols it is 1057 perfectly legal for the client wait indefinitely for data, the stack may 1058 never report a problem, and even when it does, it can take up to 20 minutes 1059 for it to detect an issue. The curl option --keepalive-time enables 1060 keep-alive support in the TCP/IP stack which makes it periodically probe the 1061 connection to make sure it is still available to send data. That should 1062 reliably detect any TCP/IP network failure. 1063 1064 But even that won't detect the network going down before the TCP/IP 1065 connection is established (e.g. during a DNS lookup) or using protocols that 1066 don't use TCP. To handle those situations, curl offers a number of timeouts 1067 on its own. --speed-limit/--speed-time will abort if the data transfer rate 1068 falls too low, and --connect-timeout and --max-time can be used to put an 1069 overall timeout on the connection phase or the entire transfer. 1070 1071 10725. libcurl Issues 1073 1074 5.1 Is libcurl thread-safe? 1075 1076 Yes. 1077 1078 We have written the libcurl code specifically adjusted for multi-threaded 1079 programs. libcurl will use thread-safe functions instead of non-safe ones if 1080 your system has such. 1081 1082 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you 1083 need to provide one or two locking functions: 1084 1085 http://www.openssl.org/docs/crypto/threads.html 1086 1087 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you 1088 need to provide locking function(s) for libgcrypt (which is used by GnuTLS 1089 for the crypto functions). 1090 1091 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html 1092 1093 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe. 1094 1095 5.2 How can I receive all data into a large memory chunk? 1096 1097 [ See also the examples/getinmemory.c source ] 1098 1099 You are in full control of the callback function that gets called every time 1100 there is data received from the remote server. You can make that callback do 1101 whatever you want. You do not have to write the received data to a file. 1102 1103 One solution to this problem could be to have a pointer to a struct that you 1104 pass to the callback function. You set the pointer using the 1105 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback 1106 instead of a FILE * to a file: 1107 1108 /* imaginary struct */ 1109 struct MemoryStruct { 1110 char *memory; 1111 size_t size; 1112 }; 1113 1114 /* imaginary callback function */ 1115 size_t 1116 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data) 1117 { 1118 size_t realsize = size * nmemb; 1119 struct MemoryStruct *mem = (struct MemoryStruct *)data; 1120 1121 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1); 1122 if (mem->memory) { 1123 memcpy(&(mem->memory[mem->size]), ptr, realsize); 1124 mem->size += realsize; 1125 mem->memory[mem->size] = 0; 1126 } 1127 return realsize; 1128 } 1129 1130 5.3 How do I fetch multiple files with libcurl? 1131 1132 libcurl has excellent support for transferring multiple files. You should 1133 just repeatedly set new URLs with curl_easy_setopt() and then transfer it 1134 with curl_easy_perform(). The handle you get from curl_easy_init() is not 1135 only reusable, but you're even encouraged to reuse it if you can, as that 1136 will enable libcurl to use persistent connections. 1137 1138 5.4 Does libcurl do Winsock initialization on win32 systems? 1139 1140 Yes, if told to in the curl_global_init() call. 1141 1142 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ? 1143 1144 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have 1145 that DLL use the FILE * (as the DLL and the client application cannot access 1146 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must 1147 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the 1148 file, even if that simply writes the data to the specified FILE *. 1149 Similarly, if you use CURLOPT_READDATA you must also specify 1150 CURLOPT_READFUNCTION. 1151 1152 5.6 What about Keep-Alive or persistent connections? 1153 1154 curl and libcurl have excellent support for persistent connections when 1155 transferring several files from the same server. Curl will attempt to reuse 1156 connections for all URLs specified on the same command line/config file, and 1157 libcurl will reuse connections for all transfers that are made using the 1158 same libcurl handle. 1159 1160 When you use the easy interface, the connection cache is kept within the 1161 easy handle. If you instead use the multi interface, the connection cache 1162 will be kept within the multi handle and will be shared among all the easy 1163 handles that are used within the same multi handle. 1164 1165 5.7 Link errors when building libcurl on Windows! 1166 1167 You need to make sure that your project, and all the libraries (both static 1168 and dynamic) that it links against, are compiled/linked against the same run 1169 time library. 1170 1171 This is determined by the /MD, /ML, /MT (and their corresponding /M?d) 1172 options to the command line compiler. /MD (linking against MSVCRT dll) seems 1173 to be the most commonly used option. 1174 1175 When building an application that uses the static libcurl library, you must 1176 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for 1177 dynamic import symbols. If you're using Visual Studio, you need to instead 1178 add CURL_STATICLIB in the "Preprocessor Definitions" section. 1179 1180 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you 1181 have linked against the wrong (static) library. If you want to use the 1182 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of 1183 the import libraries below. These are the libraries produced by the various 1184 lib/Makefile.* files: 1185 1186 Target: static lib. import lib for libcurl*.dll. 1187 ----------------------------------------------------------- 1188 MingW: libcurl.a libcurldll.a 1189 MSVC (release): libcurl.lib libcurl_imp.lib 1190 MSVC (debug): libcurld.lib libcurld_imp.lib 1191 Borland: libcurl.lib libcurl_imp.lib 1192 1193 5.8 libcurl.so.X: open failed: No such file or directory 1194 1195 This is an error message you might get when you try to run a program linked 1196 with a shared version of libcurl and your run-time linker (ld.so) couldn't 1197 find the shared library named libcurl.so.X. (Where X is the number of the 1198 current libcurl ABI, typically 3 or 4). 1199 1200 You need to make sure that ld.so finds libcurl.so.X. You can do that 1201 multiple ways, and it differs somewhat between different operating systems, 1202 but they are usually: 1203 1204 * Add an option to the linker command line that specify the hard-coded path 1205 the run-time linker should check for the lib (usually -R) 1206 1207 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so 1208 should check for libs 1209 1210 * Adjust the system's config to check for libs in the directory where you've 1211 put the dir (like Linux's /etc/ld.so.conf) 1212 1213 'man ld.so' and 'man ld' will tell you more details 1214 1215 5.9 How does libcurl resolve host names? 1216 1217 libcurl supports a large a number of different name resolve functions. One 1218 of them is picked at build-time and will be used unconditionally. Thus, if 1219 you want to change name resolver function you must rebuild libcurl and tell 1220 it to use a different function. 1221 1222 - The non-ipv6 resolver that can use one out of four host name resolve calls 1223 (depending on what your system supports): 1224 1225 A - gethostbyname() 1226 B - gethostbyname_r() with 3 arguments 1227 C - gethostbyname_r() with 5 arguments 1228 D - gethostbyname_r() with 6 arguments 1229 1230 - The ipv6-resolver that uses getaddrinfo() 1231 1232 - The c-ares based name resolver that uses the c-ares library for resolves. 1233 Using this offers asynchronous name resolves. 1234 1235 - The threaded resolver (default option on Windows). It uses: 1236 1237 A - gethostbyname() on plain ipv4 hosts 1238 B - getaddrinfo() on ipv6-enabled hosts 1239 1240 Also note that libcurl never resolves or reverse-lookups addresses given as 1241 pure numbers, such as 127.0.0.1 or ::1. 1242 1243 5.10 How do I prevent libcurl from writing the response to stdout? 1244 1245 libcurl provides a default built-in write function that writes received data 1246 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly 1247 set CURLOPT_WRITEDATA to a different FILE * handle. 1248 1249 5.11 How do I make libcurl not receive the whole HTTP response? 1250 1251 You make the write callback (or progress callback) return an error and 1252 libcurl will then abort the transfer. 1253 1254 5.12 Can I make libcurl fake or hide my real IP address? 1255 1256 No. libcurl operates on a higher level than so. Besides, faking IP address 1257 would imply sending IP packages with a made-up source address, and then you 1258 normally get a problem with intercepting the packages sent back as they 1259 would then not be routed to you! 1260 1261 If you use a proxy to access remote sites, the sites will not see your local 1262 IP address but instead the address of the proxy. 1263 1264 Also note that on many networks NATs or other IP-munging techniques are used 1265 that makes you see and use a different IP address locally than what the 1266 remote server will see you coming from. 1267 1268 5.13 How do I stop an ongoing transfer? 1269 1270 With the easy interface you make sure to return the correct error code from 1271 one of the callbacks, but none of them are instant. There is no function you 1272 can call from another thread or similar that will stop it immediately. 1273 Instead, you need to make sure that one of the callbacks you use returns an 1274 appropriate value that will stop the transfer. Suitable callbacks that you 1275 can do this with include the progress callback, the read callback and the 1276 write callback. 1277 1278 If you're using the multi interface, you can also stop a transfer by 1279 removing the particular easy handle from the multi stack at any moment you 1280 think the transfer is done. 1281 1282 5.14 Using C++ non-static functions for callbacks? 1283 1284 libcurl is a C library, it doesn't know anything about C++ member functions. 1285 1286 You can overcome this "limitation" with a relative ease using a static 1287 member function that is passed a pointer to the class: 1288 1289 // f is the pointer to your object. 1290 static YourClass::func(void *buffer, size_t sz, size_t n, void *f) 1291 { 1292 // Call non-static member function. 1293 static_cast<YourClass*>(f)->nonStaticFunction(); 1294 } 1295 1296 // This is how you pass pointer to the static function: 1297 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func); 1298 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this); 1299 1300 5.15 How do I get an FTP directory listing? 1301 1302 If you end the FTP URL you request with a slash, libcurl will provide you 1303 with a directory listing of that given directory. You can also set 1304 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use 1305 to list the files. 1306 1307 The follow-up question that tend to follow the previous one, is how a 1308 program is supposed to parse the directory listing. How does it know what's 1309 a file and what's a dir and what's a symlink etc. The harsh reality is that 1310 FTP provides no such fine and easy-to-parse output. The output format FTP 1311 servers respond to LIST commands are entirely at the server's own liking and 1312 the NLST output doesn't reveal any types and in many cases don't even 1313 include all the directory entries. Also, both LIST and NLST tend to hide 1314 unix-style hidden files (those that start with a dot) by default so you need 1315 to do "LIST -a" or similar to see them. 1316 1317 The application thus needs to parse the LIST output. One such existing 1318 list parser is available at http://cr.yp.to/ftpparse.html Versions of 1319 libcurl since 7.21.0 also provide the ability to specify a wildcard to 1320 download multiple files from one FTP directory. 1321 1322 13236. License Issues 1324 1325 Curl and libcurl are released under a MIT/X derivate license. The license is 1326 very liberal and should not impose a problem for your project. This section 1327 is just a brief summary for the cases we get the most questions. (Parts of 1328 this section was much enhanced by Bjorn Reese.) 1329 1330 We are not lawyers and this is not legal advice. You should probably consult 1331 one if you want true and accurate legal insights without our prejudice. Note 1332 especially that this section concerns the libcurl license only; compiling in 1333 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect 1334 the licensing obligations of your application. 1335 1336 6.1 I have a GPL program, can I use the libcurl library? 1337 1338 Yes! 1339 1340 Since libcurl may be distributed under the MIT/X derivate license, it can be 1341 used together with GPL in any software. 1342 1343 6.2 I have a closed-source program, can I use the libcurl library? 1344 1345 Yes! 1346 1347 libcurl does not put any restrictions on the program that uses the library. 1348 1349 6.3 I have a BSD licensed program, can I use the libcurl library? 1350 1351 Yes! 1352 1353 libcurl does not put any restrictions on the program that uses the library. 1354 1355 6.4 I have a program that uses LGPL libraries, can I use libcurl? 1356 1357 Yes! 1358 1359 The LGPL license doesn't clash with other licenses. 1360 1361 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 1362 1363 Yes! 1364 1365 The MIT/X derivate license practically allows you to do almost anything with 1366 the sources, on the condition that the copyright texts in the sources are 1367 left intact. 1368 1369 6.6 Can you please change the curl/libcurl license to XXXX? 1370 1371 No. 1372 1373 We have carefully picked this license after years of development and 1374 discussions and a large amount of people have contributed with source code 1375 knowing that this is the license we use. This license puts the restrictions 1376 we want on curl/libcurl and it does not spread to other programs or 1377 libraries that use it. It should be possible for everyone to use libcurl or 1378 curl in their projects, no matter what license they already have in use. 1379 1380 6.7 What are my obligations when using libcurl in my commercial apps? 1381 1382 Next to none. All you need to adhere to is the MIT-style license (stated in 1383 the COPYING file) which basically says you have to include the copyright 1384 notice in "all copies" and that you may not use the copyright holder's name 1385 when promoting your software. 1386 1387 You do not have to release any of your source code. 1388 1389 You do not have to reveal or make public any changes to the libcurl source 1390 code. 1391 1392 You do not have to broadcast to the world that you are using libcurl within 1393 your app. 1394 1395 All we ask is that you disclose "the copyright notice and this permission 1396 notice" somewhere. Most probably like in the documentation or in the section 1397 where other third party dependencies already are mentioned and acknowledged. 1398 1399 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere, 1400 more and more companies are discovering the power of libcurl and take 1401 advantage of it even in commercial environments. 1402 1403 14047. PHP/CURL Issues 1405 1406 7.1 What is PHP/CURL? 1407 1408 The module for PHP that makes it possible for PHP programs to access curl- 1409 functions from within PHP. 1410 1411 In the cURL project we call this module PHP/CURL to differentiate it from 1412 curl the command line tool and libcurl the library. The PHP team however 1413 does not refer to it like this (for unknown reasons). They call it plain 1414 CURL (often using all caps) or sometimes ext/curl, but both cause much 1415 confusion to users which in turn gives us a higher question load. 1416 1417 7.2 Who wrote PHP/CURL? 1418 1419 PHP/CURL is a module that comes with the regular PHP package. It depends and 1420 uses libcurl, so you need to have libcurl installed properly first before 1421 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes. 1422 1423 7.3 Can I perform multiple requests using the same handle? 1424 1425 Yes - at least in PHP version 4.3.8 and later (this has been known to not 1426 work in earlier versions, but the exact version when it started to work is 1427 unknown to me). 1428 1429 After a transfer, you just set new options in the handle and make another 1430 transfer. This will make libcurl to re-use the same connection if it can. 1431