1 _ _ ____ _ 2 ___| | | | _ \| | 3 / __| | | | |_) | | 4 | (__| |_| | _ <| |___ 5 \___|\___/|_| \_\_____| 6 7FAQ 8 9 1. Philosophy 10 1.1 What is cURL? 11 1.2 What is libcurl? 12 1.3 What is curl not? 13 1.4 When will you make curl do XXXX ? 14 1.5 Who makes curl? 15 1.6 What do you get for making curl? 16 1.7 What about CURL from curl.com? 17 1.8 I have a problem who do I mail? 18 1.9 Where do I buy commercial support for curl? 19 1.10 How many are using curl? 20 1.11 Why don't you update ca-bundle.crt 21 1.12 I have a problem who can I chat with? 22 1.13 curl's ECCN number? 23 1.14 How do I submit my patch? 24 25 2. Install Related Problems 26 2.1 configure doesn't find OpenSSL even when it is installed 27 2.1.1 native linker doesn't find OpenSSL 28 2.1.2 only the libssl lib is missing 29 2.2 Does curl work/build with other SSL libraries? 30 2.3 Where can I find a copy of LIBEAY32.DLL? 31 2.4 Does curl support SOCKS (RFC 1928) ? 32 33 3. Usage Problems 34 3.1 curl: (1) SSL is disabled, https: not supported 35 3.2 How do I tell curl to resume a transfer? 36 3.3 Why doesn't my posting using -F work? 37 3.4 How do I tell curl to run custom FTP commands? 38 3.5 How can I disable the Accept: */* header? 39 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 40 3.7 Can I use curl to delete/rename a file through FTP? 41 3.8 How do I tell curl to follow HTTP redirects? 42 3.9 How do I use curl in my favorite programming language? 43 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 44 3.11 How do I POST with a different Content-Type? 45 3.12 Why do FTP specific features over HTTP proxy fail? 46 3.13 Why does my single/double quotes fail? 47 3.14 Does curl support Javascript or PAC (automated proxy config)? 48 3.15 Can I do recursive fetches with curl? 49 3.16 What certificates do I need when I use SSL? 50 3.17 How do I list the root dir of an FTP server? 51 3.18 Can I use curl to send a POST/PUT and not wait for a response? 52 3.19 How do I get HTTP from a host using a specific IP address? 53 3.20 How to SFTP from my user's home directory? 54 3.21 Protocol xxx not supported or disabled in libcurl 55 3.22 curl -X gives me HTTP problems 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 5.16 I want a different time-out! 101 5.17 Can I write a server with libcurl? 102 5.18 Does libcurl use threads? 103 104 6. License Issues 105 6.1 I have a GPL program, can I use the libcurl library? 106 6.2 I have a closed-source program, can I use the libcurl library? 107 6.3 I have a BSD licensed program, can I use the libcurl library? 108 6.4 I have a program that uses LGPL libraries, can I use libcurl? 109 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 110 6.6 Can you please change the curl/libcurl license to XXXX? 111 6.7 What are my obligations when using libcurl in my commercial apps? 112 113 7. PHP/CURL Issues 114 7.1 What is PHP/CURL? 115 7.2 Who wrote PHP/CURL? 116 7.3 Can I perform multiple requests using the same handle? 117 118============================================================================== 119 1201. Philosophy 121 122 1.1 What is cURL? 123 124 cURL is the name of the project. The name is a play on 'Client for URLs', 125 originally with URL spelled in uppercase to make it obvious it deals with 126 URLs. The fact it can also be pronounced 'see URL' also helped, it works as 127 an abbreviation for "Client URL Request Library" or why not the recursive 128 version: "Curl URL Request Library". 129 130 The cURL project produces two products: 131 132 libcurl 133 134 A free and easy-to-use client-side URL transfer library, supporting DICT, 135 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, 136 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP. 137 138 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, 139 kerberos, HTTP form based upload, proxies, cookies, user+password 140 authentication, file transfer resume, http proxy tunneling and more! 141 142 libcurl is highly portable, it builds and works identically on numerous 143 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX, 144 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOS, Mac 145 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF, 146 Android, Minix, IBM TPF and more... 147 148 libcurl is free, thread-safe, IPv6 compatible, feature rich, well 149 supported and fast. 150 151 curl 152 153 A command line tool for getting or sending files using URL syntax. 154 155 Since curl uses libcurl, curl supports the same wide range of common 156 Internet protocols that libcurl does. 157 158 We pronounce curl and cURL with an initial k sound: [kurl]. 159 160 There are numerous sub-projects and related projects that also use the word 161 curl in the project names in various combinations, but you should take 162 notice that this FAQ is directed at the command-line tool named curl (and 163 libcurl the library), and may therefore not be valid for other curl-related 164 projects. (There is however a small section for the PHP/CURL in this FAQ.) 165 166 1.2 What is libcurl? 167 168 libcurl is a reliable and portable library which provides you with an easy 169 interface to a range of common Internet protocols. 170 171 You can use libcurl for free in your application, be it open source, 172 commercial or closed-source. 173 174 libcurl is most probably the most portable, most powerful and most often 175 used C-based multi-platform file transfer library on this planet - be it 176 open source or commercial. 177 178 1.3 What is curl not? 179 180 Curl is not a wget clone. That is a common misconception. Never, during 181 curl's development, have we intended curl to replace wget or compete on its 182 market. Curl is targeted at single-shot file transfers. 183 184 Curl is not a web site mirroring program. If you want to use curl to mirror 185 something: fine, go ahead and write a script that wraps around curl to make 186 it reality (like curlmirror.pl does). 187 188 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl 189 but if you want systematic and sequential behavior you should write a 190 script (or write a new program that interfaces libcurl) and do it. 191 192 Curl is not a PHP tool, even though it works perfectly well when used from 193 or with PHP (when using the PHP/CURL module). 194 195 Curl is not a program for a single operating system. Curl exists, compiles, 196 builds and runs under a wide range of operating systems, including all 197 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2, 198 OS X, QNX etc. 199 200 1.4 When will you make curl do XXXX ? 201 202 We love suggestions of what to change in order to make curl and libcurl 203 better. We do however believe in a few rules when it comes to the future of 204 curl: 205 206 Curl -- the command line tool -- is to remain a non-graphical command line 207 tool. If you want GUIs or fancy scripting capabilities, you should look for 208 another tool that uses libcurl. 209 210 We do not add things to curl that other small and available tools already do 211 very fine at the side. Curl's output is fine to pipe into another program or 212 redirect to another file for the next program to interpret. 213 214 We focus on protocol related issues and improvements. If you wanna do more 215 magic with the supported protocols than curl currently does, chances are big 216 we will agree. If you wanna add more protocols, we may very well agree. 217 218 If you want someone else to make all the work while you wait for us to 219 implement it for you, that is not a very friendly attitude. We spend a 220 considerable time already on maintaining and developing curl. In order to 221 get more out of us, you should consider trading in some of your time and 222 efforts in return. 223 224 If you write the code, chances are bigger that it will get into curl faster. 225 226 1.5 Who makes curl? 227 228 curl and libcurl are not made by any single individual. Daniel Stenberg is 229 project leader and main developer, but other persons' submissions are 230 important and crucial. Anyone can contribute and post their changes and 231 improvements and have them inserted in the main sources (of course on the 232 condition that developers agree on that the fixes are good). 233 234 The full list of all contributors is found in the docs/THANKS file. 235 236 curl is developed by a community, with Daniel at the wheel. 237 238 1.6 What do you get for making curl? 239 240 Project cURL is entirely free and open. No person gets paid for developing 241 (lib)curl on full or even part time. We do this voluntarily on our spare 242 time. Occasionally companies pay individual developers to work on curl, but 243 that's up to each company and developer. It is not controlled by nor 244 supervised in any way by the project. 245 246 We still get help from companies. Haxx provides web site, bandwidth, mailing 247 lists etc, sourceforge.net hosts project services we take advantage from, 248 like the bug tracker and github hosts the primary git repository. Also 249 again, some companies have sponsored certain parts of the development in the 250 past and I hope some will continue to do so in the future. 251 252 If you want to support our project, consider a donation or a banner-program 253 or even better: by helping us coding, documenting, testing etc. 254 255 1.7 What about CURL from curl.com? 256 257 During the summer 2001, curl.com was busy advertising their client-side 258 programming language for the web, named CURL. 259 260 We are in no way associated with curl.com or their CURL programming 261 language. 262 263 Our project name curl has been in effective use since 1998. We were not the 264 first computer related project to use the name "curl" and do not claim any 265 rights to the name. 266 267 We recognize that we will be living in parallel with curl.com and wish them 268 every success. 269 270 1.8 I have a problem who do I mail? 271 272 Please do not mail any single individual unless you really need to. Keep 273 curl-related questions on a suitable mailing list. All available mailing 274 lists are listed in the MANUAL document and online at 275 http://curl.haxx.se/mail/ 276 277 Keeping curl-related questions and discussions on mailing lists allows 278 others to join in and help, to share their ideas, contribute their 279 suggestions and spread their wisdom. Keeping discussions on public mailing 280 lists also allows for others to learn from this (both current and future 281 users thanks to the web based archives of the mailing lists), thus saving us 282 from having to repeat ourselves even more. Thanks for respecting this. 283 284 If you have found or simply suspect a security problem in curl or libcurl, 285 mail curl-security at haxx.se (closed list of receivers, mails are not 286 disclosed) and tell. Then we can produce a fix in a timely manner before the 287 flaw is announced to the world, thus lessen the impact the problem will have 288 on existing users. 289 290 1.9 Where do I buy commercial support for curl? 291 292 curl is fully open source. It means you can hire any skilled engineer to fix 293 your curl-related problems. 294 295 We list available alternatives on the curl web site: 296 http://curl.haxx.se/support.html 297 298 1.10 How many are using curl? 299 300 It is impossible to tell. 301 302 We don't know how many users that knowingly have installed and use curl. 303 304 We don't know how many users that use curl without knowing that they are in 305 fact using it. 306 307 We don't know how many users that downloaded or installed curl and then 308 never use it. 309 310 In May 2012 Daniel did a counting game and came up with a number that may 311 be completely wrong or somewhat accurate. Over 500 million! 312 313 See http://daniel.haxx.se/blog/2012/05/16/300m-users/ 314 315 1.11 Why don't you update ca-bundle.crt 316 317 The ca cert bundle that used to shipped with curl was very outdated and must 318 be replaced with an up-to-date version by anyone who wants to verify 319 peers. It is no longer provided by curl. The last curl release ever that 320 shipped a ca cert bundle was curl 7.18.0. 321 322 In the cURL project we've decided not to attempt to keep this file updated 323 (or even present anymore) since deciding what to add to a ca cert bundle is 324 an undertaking we've not been ready to accept, and the one we can get from 325 Mozilla is perfectly fine so there's no need to duplicate that work. 326 327 Today, with many services performed over HTTPS, every operating system 328 should come with a default ca cert bundle that can be deemed somewhat 329 trustworthy and that collection (if reasonably updated) should be deemed to 330 be a lot better than a private curl version. 331 332 If you want the most recent collection of ca certs that Mozilla Firefox 333 uses, we recommend that you extract the collection yourself from Mozilla 334 Firefox (by running 'make ca-bundle), or by using our online service setup 335 for this purpose: http://curl.haxx.se/docs/caextract.html 336 337 1.12 I have a problem who can I chat with? 338 339 There's a bunch of friendly people hanging out in the #curl channel on the 340 IRC network irc.freenode.net. If you're polite and nice, chances are big 341 that you can get -- or provide -- help instantly. 342 343 1.13 curl's ECCN number? 344 345 The US government restricts exports of software that contains or uses 346 cryptography. When doing so, the Export Control Classification Number (ECCN) 347 is used to identify the level of export control etc. 348 349 ASF gives a good explanation at http://www.apache.org/dev/crypto.html 350 351 We believe curl's number might be ECCN 5D002, another possibility is 352 5D992. It seems necessary to write them, asking to confirm. 353 354 Comprehensible explanations of the meaning of such numbers and how to 355 obtain them (resp.) are here 356 357 http://www.bis.doc.gov/licensing/exportingbasics.htm 358 http://www.bis.doc.gov/licensing/do_i_needaneccn.html 359 360 An incomprehensible description of the two numbers above is here 361 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf 362 363 1.14 How do I submit my patch? 364 365 When you have made a patch or a change of whatever sort, and want to submit 366 that to the project, there are a few different ways we prefer: 367 368 o send a patch to the curl-library mailing list. We're many subscribers 369 there and there are lots of people who can review patches, comment on them 370 and "receive" them properly. 371 372 o if your patch changes or fixes a bug, you can also opt to submit a bug 373 report in the bug tracker and attach your patch there. There are less 374 people involved there. 375 376 Lots of more details are found in the CONTRIBUTE and INTERNALS docs. 377 378 3792. Install Related Problems 380 381 2.1 configure doesn't find OpenSSL even when it is installed 382 383 This may be because of several reasons. 384 385 2.1.1 native linker doesn't find openssl 386 387 Affected platforms: 388 Solaris (native cc compiler) 389 HPUX (native cc compiler) 390 SGI IRIX (native cc compiler) 391 SCO UNIX (native cc compiler) 392 393 When configuring curl, I specify --with-ssl. OpenSSL is installed in 394 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find 395 CRYPTO_lock in -lcrypto 396 397 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER 398 -lcrypto, so ld can't find the library. This is due to a bug in the GNU 399 autoconf tool. 400 401 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of 402 ./configure places the -L/usr/local/ssl/lib early enough in the command 403 line to make things work 404 405 2.1.2 only the libssl lib is missing 406 407 If all include files and the libcrypto lib is present, with only the 408 libssl being missing according to configure, this is mostly likely because 409 a few functions are left out from the libssl. 410 411 If the function names missing include RSA or RSAREF you can be certain 412 that this is because libssl requires the RSA and RSAREF libs to build. 413 414 See the INSTALL file section that explains how to add those libs to 415 configure. Make sure that you remove the config.cache file before you 416 rerun configure with the new flags. 417 418 2.2 Does curl work/build with other SSL libraries? 419 420 Curl has been written to use a generic SSL function layer internally, and 421 that SSL functionality can then be provided by one out of many different SSL 422 backends. 423 424 curl can be built to use one of the following SSL alternatives: OpenSSL, 425 GnuTLS, yassl, NSS, PolarSSL, axTLS, Secure Transport (native iOS/OS X), 426 WinSSL (native Windows) or qssl (native IBM i). They all have their pros 427 and cons, and we try to maintain a comparison of them here: 428 http://curl.haxx.se/docs/ssl-compared.html 429 430 2.3 Where can I find a copy of LIBEAY32.DLL? 431 432 That is an OpenSSL binary built for Windows. 433 434 Curl can be built with OpenSSL to do the SSL stuff. The LIBEAY32.DLL is then 435 what curl needs on a windows machine to do https:// etc. Check out the curl 436 web site to find accurate and up-to-date pointers to recent OpenSSL DLLs and 437 other binary packages. 438 439 2.4 Does curl support SOCKS (RFC 1928) ? 440 441 Yes, SOCKS 4 and 5 are supported. 442 443 4443. Usage problems 445 446 3.1 curl: (1) SSL is disabled, https: not supported 447 448 If you get this output when trying to get anything from a https:// server, 449 it means that the instance of curl/libcurl that you're using was built 450 without support for this protocol. 451 452 This could've happened if the configure script that was run at build time 453 couldn't find all libs and include files curl requires for SSL to work. If 454 the configure script fails to find them, curl is simply built without SSL 455 support. 456 457 To get the https:// support into a curl that was previously built but that 458 reports that https:// is not supported, you should dig through the document 459 and logs and check out why the configure script doesn't find the SSL libs 460 and/or include files. 461 462 Also, check out the other paragraph in this FAQ labelled "configure doesn't 463 find OpenSSL even when it is installed". 464 465 3.2 How do I tell curl to resume a transfer? 466 467 Curl supports resumed transfers both ways on both FTP and HTTP. 468 Try the -C option. 469 470 3.3 Why doesn't my posting using -F work? 471 472 You can't simply use -F or -d at your choice. The web server that will 473 receive your post expects one of the formats. If the form you're trying to 474 submit uses the type 'multipart/form-data', then and only then you must use 475 the -F type. In all the most common cases, you should use -d which then 476 causes a posting with the type 'application/x-www-form-urlencoded'. 477 478 This is described in some detail in the MANUAL and TheArtOfHttpScripting 479 documents, and if you don't understand it the first time, read it again 480 before you post questions about this to the mailing list. Also, try reading 481 through the mailing list archives for old postings and questions regarding 482 this. 483 484 3.4 How do I tell curl to run custom FTP commands? 485 486 You can tell curl to perform optional commands both before and/or after a 487 file transfer. Study the -Q/--quote option. 488 489 Since curl is used for file transfers, you don't normally use curl to 490 perform FTP commands without transferring anything. Therefore you must 491 always specify a URL to transfer to/from even when doing custom FTP 492 commands, or use -I which implies the "no body" option sent to libcurl. 493 494 3.5 How can I disable the Accept: */* header? 495 496 You can change all internally generated headers by adding a replacement with 497 the -H/--header option. By adding a header with empty contents you safely 498 disable that one. Use -H "Accept:" to disable that specific header. 499 500 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 501 502 To curl, all contents are alike. It doesn't matter how the page was 503 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain HTML 504 files. There's no difference to curl and it doesn't even know what kind of 505 language that generated the page. 506 507 See also item 3.14 regarding javascript. 508 509 3.7 Can I use curl to delete/rename a file through FTP? 510 511 Yes. You specify custom FTP commands with -Q/--quote. 512 513 One example would be to delete a file after you have downloaded it: 514 515 curl -O ftp://download.com/coolfile -Q '-DELE coolfile' 516 517 or rename a file after upload: 518 519 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname" 520 521 3.8 How do I tell curl to follow HTTP redirects? 522 523 Curl does not follow so-called redirects by default. The Location: header 524 that informs the client about this is only interpreted if you're using the 525 -L/--location option. As in: 526 527 curl -L http://redirector.com 528 529 Not all redirects are HTTP ones, see 4.14 530 531 3.9 How do I use curl in my favorite programming language? 532 533 There exist many language interfaces/bindings for curl that integrates it 534 better with various languages. If you are fluid in a script language, you 535 may very well opt to use such an interface instead of using the command line 536 tool. 537 538 Find out more about which languages that support curl directly, and how to 539 install and use them, in the libcurl section of the curl web site: 540 http://curl.haxx.se/libcurl/ 541 542 All the various bindings to libcurl are made by other projects and people, 543 outside of the cURL project. The cURL project itself only produces libcurl 544 with its plain C API. If you don't find anywhere else to ask you can ask 545 about bindings on the curl-library list too, but be prepared that people on 546 that list may not know anything about bindings. 547 548 In October 2009, there were interfaces available for the following 549 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria, 550 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET, 551 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby, 552 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro, 553 Q, wxwidgets and XBLite. By the time you read this, additional ones may have 554 appeared! 555 556 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 557 558 Curl adheres to the HTTP spec, which basically means you can play with *any* 559 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and 560 XML-RPC are all such ones. You can use -X to set custom requests and -H to 561 set custom headers (or replace internally generated ones). 562 563 Using libcurl is of course just as fine and you'd just use the proper 564 library options to do the same. 565 566 3.11 How do I POST with a different Content-Type? 567 568 You can always replace the internally generated headers with -H/--header. 569 To make a simple HTTP POST with text/xml as content-type, do something like: 570 571 curl -d "datatopost" -H "Content-Type: text/xml" [URL] 572 573 3.12 Why do FTP specific features over HTTP proxy fail? 574 575 Because when you use a HTTP proxy, the protocol spoken on the network will 576 be HTTP, even if you specify a FTP URL. This effectively means that you 577 normally can't use FTP specific features such as FTP upload and FTP quote 578 etc. 579 580 There is one exception to this rule, and that is if you can "tunnel through" 581 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p) 582 and is generally not available as proxy admins usually disable tunneling to 583 other ports than 443 (which is used for HTTPS access through proxies). 584 585 3.13 Why does my single/double quotes fail? 586 587 To specify a command line option that includes spaces, you might need to 588 put the entire option within quotes. Like in: 589 590 curl -d " with spaces " url.com 591 592 or perhaps 593 594 curl -d ' with spaces ' url.com 595 596 Exactly what kind of quotes and how to do this is entirely up to the shell 597 or command line interpreter that you are using. For most unix shells, you 598 can more or less pick either single (') or double (") quotes. For 599 Windows/DOS prompts I believe you're forced to use double (") quotes. 600 601 Please study the documentation for your particular environment. Examples in 602 the curl docs will use a mix of both these ones as shown above. You must 603 adjust them to work in your environment. 604 605 Remember that curl works and runs on more operating systems than most single 606 individuals have ever tried. 607 608 3.14 Does curl support Javascript or PAC (automated proxy config)? 609 610 Many web pages do magic stuff using embedded Javascript. Curl and libcurl 611 have no built-in support for that, so it will be treated just like any other 612 contents. 613 614 .pac files are a netscape invention and are sometimes used by organizations 615 to allow them to differentiate which proxies to use. The .pac contents is 616 just a Javascript program that gets invoked by the browser and that returns 617 the name of the proxy to connect to. Since curl doesn't support Javascript, 618 it can't support .pac proxy configuration either. 619 620 Some workarounds usually suggested to overcome this Javascript dependency: 621 622 Depending on the Javascript complexity, write up a script that translates it 623 to another language and execute that. 624 625 Read the Javascript code and rewrite the same logic in another language. 626 627 Implement a Javascript interpreter, people have successfully used the 628 Mozilla Javascript engine in the past. 629 630 Ask your admins to stop this, for a static proxy setup or similar. 631 632 3.15 Can I do recursive fetches with curl? 633 634 No. curl itself has no code that performs recursive operations, such as 635 those performed by wget and similar tools. 636 637 There exist wrapper scripts with that functionality (for example the 638 curlmirror perl script), and you can write programs based on libcurl to do 639 it, but the command line tool curl itself cannot. 640 641 3.16 What certificates do I need when I use SSL? 642 643 There are three different kinds of "certificates" to keep track of when we 644 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl. 645 646 CLIENT CERTIFICATE 647 648 The server you communicate may require that you can provide this in order to 649 prove that you actually are who you claim to be. If the server doesn't 650 require this, you don't need a client certificate. 651 652 A client certificate is always used together with a private key, and the 653 private key has a pass phrase that protects it. 654 655 SERVER CERTIFICATE 656 657 The server you communicate with has a server certificate. You can and should 658 verify this certificate to make sure that you are truly talking to the real 659 server and not a server impersonating it. 660 661 CERTIFICATE AUTHORITY CERTIFICATE ("CA cert") 662 663 You often have several CA certs in a CA cert bundle that can be used to 664 verify a server certificate that was signed by one of the authorities in the 665 bundle. curl does not come with a CA cert bundle but most curl installs 666 provide one. You can also override the default. 667 668 The server certificate verification process is made by using a Certificate 669 Authority certificate ("CA cert") that was used to sign the server 670 certificate. Server certificate verification is enabled by default in curl 671 and libcurl and is often the reason for problems as explained in FAQ entry 672 4.12 and the SSLCERTS document 673 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are 674 "self-signed" or otherwise signed by a CA that you do not have a CA cert 675 for, cannot be verified. If the verification during a connect fails, you are 676 refused access. You then need to explicitly disable the verification to 677 connect to the server. 678 679 3.17 How do I list the root dir of an FTP server? 680 681 There are two ways. The way defined in the RFC is to use an encoded slash 682 in the first path part. List the "/tmp" dir like this: 683 684 curl ftp://ftp.sunet.se/%2ftmp/ 685 686 or the not-quite-kosher-but-more-readable way, by simply starting the path 687 section of the URL with a slash: 688 689 curl ftp://ftp.sunet.se//tmp/ 690 691 3.18 Can I use curl to send a POST/PUT and not wait for a response? 692 693 No. 694 695 But you could easily write your own program using libcurl to do such stunts. 696 697 3.19 How do I get HTTP from a host using a specific IP address? 698 699 For example, you may be trying out a web site installation that isn't yet in 700 the DNS. Or you have a site using multiple IP addresses for a given host 701 name and you want to address a specific one out of the set. 702 703 Set a custom Host: header that identifies the server name you want to reach 704 but use the target IP address in the URL: 705 706 curl --header "Host: www.example.com" http://127.0.0.1/ 707 708 You can also opt to add faked host name entries to curl with the --resolve 709 option. That has the added benefit that things like redirects will also work 710 properly. The above operation would instead be done as: 711 712 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/ 713 714 3.20 How to SFTP from my user's home directory? 715 716 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to 717 work with. It means that if you don't specify that you want the user's home 718 directory, you get the actual root directory. 719 720 To specify a file in your user's home directory, you need to use the correct 721 URL syntax which for sftp might look similar to: 722 723 curl -O -u user:password sftp://example.com/~/file.txt 724 725 and for SCP it is just a different protocol prefix: 726 727 curl -O -u user:password scp://example.com/~/file.txt 728 729 3.21 Protocol xxx not supported or disabled in libcurl 730 731 When passing on a URL to curl to use, it may respond that the particular 732 protocol is not supported or disabled. The particular way this error message 733 is phrased is because curl doesn't make a distinction internally of whether 734 a particular protocol is not supported (i.e. never got any code added that 735 knows how to speak that protocol) or if it was explicitly disabled. curl can 736 be built to only support a given set of protocols, and the rest would then 737 be disabled or not supported. 738 739 Note that this error will also occur if you pass a wrongly spelled protocol 740 part as in "htpt://example.com" or as in the less evident case if you prefix 741 the protocol part with a space as in " http://example.com/". 742 743 3.22 curl -X gives me HTTP problems 744 745 In normal circumstances, -X should hardly ever be used. 746 747 By default you use curl without explicitly saying which request method to 748 use when the URL identifies a HTTP transfer. If you just pass in a URL like 749 "curl http://example.com" it will use GET. If you use -d or -F curl will use 750 POST, -I will cause a HEAD and -T will make it a PUT. 751 752 If for whatever reason you're not happy with these default choices that curl 753 does for you, you can override those request methods by specifying -X 754 [WHATEVER]. This way you can for example send a DELETE by doing "curl -X 755 DELETE [URL]". 756 757 It is thus pointless to do "curl -XGET [URL]" as GET would be used 758 anyway. In the same vein it is pointless to do "curl -X POST -d data 759 [URL]"... But you can make a fun and somewhat rare request that sends a 760 request-body in a GET request with something like "curl -X GET -d data 761 [URL]" 762 763 Note that -X doesn't change curl's behavior. It only modifies the actual 764 string sent in the request. 765 766 Accordingly, by using -XPOST on a command line that for example would follow 767 a 303 redirect, you will effectively prevent curl from behaving 768 correctly. Be aware. 769 770 7714. Running Problems 772 773 4.1 Problems connecting to SSL servers. 774 775 It took a very long time before we could sort out why curl had problems to 776 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The 777 error sometimes showed up similar to: 778 779 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233: 780 781 It turned out to be because many older SSL servers don't deal with SSLv3 782 requests properly. To correct this problem, tell curl to select SSLv2 from 783 the command line (-2/--sslv2). 784 785 There have also been examples where the remote server didn't like the SSLv2 786 request and instead you had to force curl to use SSLv3 with -3/--sslv3. 787 788 4.2 Why do I get problems when I use & or % in the URL? 789 790 In general unix shells, the & symbol is treated specially and when used, it 791 runs the specified command in the background. To safely send the & as a part 792 of a URL, you should quote the entire URL by using single (') or double (") 793 quotes around it. Similar problems can also occur on some shells with other 794 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL. 795 796 An example that would invoke a remote CGI that uses &-symbols could be: 797 798 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl' 799 800 In Windows, the standard DOS shell treats the percent sign specially and you 801 need to use TWO percent signs for each single one you want to use in the 802 URL. 803 804 If you want a literal percent sign to be part of the data you pass in a POST 805 using -d/--data you must encode it as '%25' (which then also needs the 806 percent sign doubled on Windows machines). 807 808 4.3 How can I use {, }, [ or ] to specify multiple URLs? 809 810 Because those letters have a special meaning to the shell, and to be used in 811 a URL specified to curl you must quote them. 812 813 An example that downloads two URLs (sequentially) would do: 814 815 curl '{curl,www}.haxx.se' 816 817 To be able to use those letters as actual parts of the URL (without using 818 them for the curl URL "globbing" system), use the -g/--globoff option: 819 820 curl -g 'www.site.com/weirdname[].html' 821 822 4.4 Why do I get downloaded data even though the web page doesn't exist? 823 824 Curl asks remote servers for the page you specify. If the page doesn't exist 825 at the server, the HTTP protocol defines how the server should respond and 826 that means that headers and a "page" will be returned. That's simply how 827 HTTP works. 828 829 By using the --fail option you can tell curl explicitly to not get any data 830 if the HTTP return code doesn't say success. 831 832 4.5 Why do I get return code XXX from a HTTP server? 833 834 RFC2616 clearly explains the return codes. This is a short transcript. Go 835 read the RFC for exact details: 836 837 4.5.1 "400 Bad Request" 838 839 The request could not be understood by the server due to malformed 840 syntax. The client SHOULD NOT repeat the request without modifications. 841 842 4.5.2 "401 Unauthorized" 843 844 The request requires user authentication. 845 846 4.5.3 "403 Forbidden" 847 848 The server understood the request, but is refusing to fulfil it. 849 Authorization will not help and the request SHOULD NOT be repeated. 850 851 4.5.4 "404 Not Found" 852 853 The server has not found anything matching the Request-URI. No indication 854 is given of whether the condition is temporary or permanent. 855 856 4.5.5 "405 Method Not Allowed" 857 858 The method specified in the Request-Line is not allowed for the resource 859 identified by the Request-URI. The response MUST include an Allow header 860 containing a list of valid methods for the requested resource. 861 862 4.5.6 "301 Moved Permanently" 863 864 If you get this return code and an HTML output similar to this: 865 866 <H1>Moved Permanently</H1> The document has moved <A 867 HREF="http://same_url_now_with_a_trailing_slash/">here</A>. 868 869 it might be because you request a directory URL but without the trailing 870 slash. Try the same operation again _with_ the trailing URL, or use the 871 -L/--location option to follow the redirection. 872 873 4.6 Can you tell me what error code 142 means? 874 875 All curl error codes are described at the end of the man page, in the 876 section called "EXIT CODES". 877 878 Error codes that are larger than the highest documented error code means 879 that curl has exited due to a crash. This is a serious error, and we 880 appreciate a detailed bug report from you that describes how we could go 881 ahead and repeat this! 882 883 4.7 How do I keep user names and passwords secret in Curl command lines? 884 885 This problem has two sides: 886 887 The first part is to avoid having clear-text passwords in the command line 888 so that they don't appear in 'ps' outputs and similar. That is easily 889 avoided by using the "-K" option to tell curl to read parameters from a file 890 or stdin to which you can pass the secret info. curl itself will also 891 attempt to "hide" the given password by blanking out the option - this 892 doesn't work on all platforms. 893 894 To keep the passwords in your account secret from the rest of the world is 895 not a task that curl addresses. You could of course encrypt them somehow to 896 at least hide them from being read by human eyes, but that is not what 897 anyone would call security. 898 899 Also note that regular HTTP (using Basic authentication) and FTP passwords 900 are sent in clear across the network. All it takes for anyone to fetch them 901 is to listen on the network. Eavesdropping is very easy. Use more secure 902 authentication methods (like Digest, Negotiate or even NTLM) or consider the 903 SSL-based alternatives HTTPS and FTPS. 904 905 4.8 I found a bug! 906 907 It is not a bug if the behavior is documented. Read the docs first. 908 Especially check out the KNOWN_BUGS file, it may be a documented bug! 909 910 If it is a problem with a binary you've downloaded or a package for your 911 particular platform, try contacting the person who built the package/archive 912 you have. 913 914 If there is a bug, read the BUGS document first. Then report it as described 915 in there. 916 917 4.9 Curl can't authenticate to the server that requires NTLM? 918 919 NTLM support requires OpenSSL, GnuTLS, NSS, Secure Transport, or Microsoft 920 Windows libraries at build-time to provide this functionality. 921 922 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You 923 should not use such ones. 924 925 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work! 926 927 Many web servers allow or demand that the administrator configures the 928 server properly for these requests to work on the web server. 929 930 Some servers seem to support HEAD only on certain kinds of URLs. 931 932 To fully grasp this, try the documentation for the particular server 933 software you're trying to interact with. This is not anything curl can do 934 anything about. 935 936 4.11 Why does my HTTP range requests return the full document? 937 938 Because the range may not be supported by the server, or the server may 939 choose to ignore it and return the full document anyway. 940 941 4.12 Why do I get "certificate verify failed" ? 942 943 You invoke curl 7.10 or later to communicate on a https:// URL and get an 944 error back looking something similar to this: 945 946 curl: (35) SSL: error:14090086:SSL routines: 947 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed 948 949 Then it means that curl couldn't verify that the server's certificate was 950 good. Curl verifies the certificate using the CA cert bundle that comes with 951 the curl installation. 952 953 To disable the verification (which makes it act like curl did before 7.10), 954 use -k. This does however enable man-in-the-middle attacks. 955 956 If you get this failure but are having a CA cert bundle installed and used, 957 the server's certificate is not signed by one of the CA's in the bundle. It 958 might for example be self-signed. You then correct this problem by obtaining 959 a valid CA cert for the server. Or again, decrease the security by disabling 960 this check. 961 962 Details are also in the SSLCERTS file in the release archives, found online 963 here: http://curl.haxx.se/docs/sslcerts.html 964 965 4.13 Why is curl -R on Windows one hour off? 966 967 During daylight savings time, when -R is used, curl will set a time that 968 appears one hour off. This happens due to a flaw in how Windows stores and 969 uses file modification times and it is not easily worked around. For details 970 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp 971 972 4.14 Redirects work in browser but not with curl! 973 974 curl supports HTTP redirects fine (see item 3.8). Browsers generally support 975 at least two other ways to perform redirects that curl does not: 976 977 Meta tags. You can write a HTML tag that will cause the browser to redirect 978 to another given URL after a certain time. 979 980 Javascript. You can write a Javascript program embedded in a HTML page that 981 redirects the browser to another given URL. 982 983 There is no way to make curl follow these redirects. You must either 984 manually figure out what the page is set to do, or you write a script that 985 parses the results and fetches the new URL. 986 987 4.15 FTPS doesn't work 988 989 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit 990 mode. 991 992 When a URL is used that starts with FTPS://, curl assumes implicit SSL on 993 the control connection and will therefore immediately connect and try to 994 speak SSL. FTPS:// connections default to port 990. 995 996 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one 997 of its related flavours). This is the most common method, and the one 998 mandated by RFC4217. This kind of connection then of course uses the 999 standard FTP port 21 by default. 1000 1001 4.16 My HTTP POST or PUT requests are slow! 1002 1003 libcurl makes all POST and PUT requests (except for POST requests with a 1004 very tiny request body) use the "Expect: 100-continue" header. This header 1005 allows the server to deny the operation early so that libcurl can bail out 1006 already before having to send any data. This is useful in authentication 1007 cases and others. 1008 1009 However, many servers don't implement the Expect: stuff properly and if the 1010 server doesn't respond (positively) within 1 second libcurl will continue 1011 and send off the data anyway. 1012 1013 You can disable libcurl's use of the Expect: header the same way you disable 1014 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0. 1015 1016 4.17 Non-functional connect timeouts 1017 1018 In most Windows setups having a timeout longer than 21 seconds make no 1019 difference, as it will only send 3 TCP SYN packets and no more. The second 1020 packet sent three seconds after the first and the third six seconds after 1021 the second. No more than three packets are sent, no matter how long the 1022 timeout is set. 1023 1024 See option TcpMaxConnectRetransmissions on this page: 1025 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7 1026 1027 Also, even on non-Windows systems there may run a firewall or anti-virus 1028 software or similar that accepts the connection but does not actually do 1029 anything else. This will make (lib)curl to consider the connection connected 1030 and thus the connect timeout won't trigger. 1031 1032 4.18 file:// URLs containing drive letters (Windows, NetWare) 1033 1034 When using cURL to try to download a local file, one might use a URL 1035 in this format: 1036 1037 file://D:/blah.txt 1038 1039 You'll find that even if D:\blah.txt does exist, cURL returns a 'file 1040 not found' error. 1041 1042 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html), 1043 file:// URLs must contain a host component, but it is ignored by 1044 most implementations. In the above example, 'D:' is treated as the 1045 host component, and is taken away. Thus, cURL tries to open '/blah.txt'. 1046 If your system is installed to drive C:, that will resolve to 'C:\blah.txt', 1047 and if that doesn't exist you will get the not found error. 1048 1049 To fix this problem, use file:// URLs with *three* leading slashes: 1050 1051 file:///D:/blah.txt 1052 1053 Alternatively, if it makes more sense, specify 'localhost' as the host 1054 component: 1055 1056 file://localhost/D:/blah.txt 1057 1058 In either case, cURL should now be looking for the correct file. 1059 1060 4.19 Why doesn't cURL return an error when the network cable is unplugged? 1061 1062 Unplugging a cable is not an error situation. The TCP/IP protocol stack 1063 was designed to be fault tolerant, so even though there may be a physical 1064 break somewhere the connection shouldn't be affected, just possibly 1065 delayed. Eventually, the physical break will be fixed or the data will be 1066 re-routed around the physical problem through another path. 1067 1068 In such cases, the TCP/IP stack is responsible for detecting when the 1069 network connection is irrevocably lost. Since with some protocols it is 1070 perfectly legal for the client wait indefinitely for data, the stack may 1071 never report a problem, and even when it does, it can take up to 20 minutes 1072 for it to detect an issue. The curl option --keepalive-time enables 1073 keep-alive support in the TCP/IP stack which makes it periodically probe the 1074 connection to make sure it is still available to send data. That should 1075 reliably detect any TCP/IP network failure. 1076 1077 But even that won't detect the network going down before the TCP/IP 1078 connection is established (e.g. during a DNS lookup) or using protocols that 1079 don't use TCP. To handle those situations, curl offers a number of timeouts 1080 on its own. --speed-limit/--speed-time will abort if the data transfer rate 1081 falls too low, and --connect-timeout and --max-time can be used to put an 1082 overall timeout on the connection phase or the entire transfer. 1083 1084 A libcurl-using application running in a known physical environment (e.g. 1085 an embedded device with only a single network connection) may want to act 1086 immediately if its lone network connection goes down. That can be achieved 1087 by having the application monitor the network connection on its own using an 1088 OS-specific mechanism, then signalling libcurl to abort (see also item 5.13). 1089 1090 10915. libcurl Issues 1092 1093 5.1 Is libcurl thread-safe? 1094 1095 Yes. 1096 1097 We have written the libcurl code specifically adjusted for multi-threaded 1098 programs. libcurl will use thread-safe functions instead of non-safe ones if 1099 your system has such. Note that you must never share the same handle in 1100 multiple threads. 1101 1102 libcurl's implementation of timeouts might use signals (depending on what it 1103 was built to use for name resolving), and signal handling is generally not 1104 thread-safe. Multi-threaded Applicationss that call libcurl from different 1105 threads (on different handles) might want to use CURLOPT_NOSIGNAL, e.g.: 1106 1107 curl_easy_setopt(handle, CURLOPT_NOSIGNAL, true); 1108 1109 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you 1110 need to provide one or two locking functions: 1111 1112 http://www.openssl.org/docs/crypto/threads.html 1113 1114 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you 1115 need to provide locking function(s) for libgcrypt (which is used by GnuTLS 1116 for the crypto functions). 1117 1118 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html 1119 1120 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe. 1121 1122 5.2 How can I receive all data into a large memory chunk? 1123 1124 [ See also the examples/getinmemory.c source ] 1125 1126 You are in full control of the callback function that gets called every time 1127 there is data received from the remote server. You can make that callback do 1128 whatever you want. You do not have to write the received data to a file. 1129 1130 One solution to this problem could be to have a pointer to a struct that you 1131 pass to the callback function. You set the pointer using the 1132 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback 1133 instead of a FILE * to a file: 1134 1135 /* imaginary struct */ 1136 struct MemoryStruct { 1137 char *memory; 1138 size_t size; 1139 }; 1140 1141 /* imaginary callback function */ 1142 size_t 1143 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data) 1144 { 1145 size_t realsize = size * nmemb; 1146 struct MemoryStruct *mem = (struct MemoryStruct *)data; 1147 1148 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1); 1149 if (mem->memory) { 1150 memcpy(&(mem->memory[mem->size]), ptr, realsize); 1151 mem->size += realsize; 1152 mem->memory[mem->size] = 0; 1153 } 1154 return realsize; 1155 } 1156 1157 5.3 How do I fetch multiple files with libcurl? 1158 1159 libcurl has excellent support for transferring multiple files. You should 1160 just repeatedly set new URLs with curl_easy_setopt() and then transfer it 1161 with curl_easy_perform(). The handle you get from curl_easy_init() is not 1162 only reusable, but you're even encouraged to reuse it if you can, as that 1163 will enable libcurl to use persistent connections. 1164 1165 5.4 Does libcurl do Winsock initialization on win32 systems? 1166 1167 Yes, if told to in the curl_global_init() call. 1168 1169 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ? 1170 1171 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have 1172 that DLL use the FILE * (as the DLL and the client application cannot access 1173 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must 1174 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the 1175 file, even if that simply writes the data to the specified FILE *. 1176 Similarly, if you use CURLOPT_READDATA you must also specify 1177 CURLOPT_READFUNCTION. 1178 1179 5.6 What about Keep-Alive or persistent connections? 1180 1181 curl and libcurl have excellent support for persistent connections when 1182 transferring several files from the same server. Curl will attempt to reuse 1183 connections for all URLs specified on the same command line/config file, and 1184 libcurl will reuse connections for all transfers that are made using the 1185 same libcurl handle. 1186 1187 When you use the easy interface, the connection cache is kept within the 1188 easy handle. If you instead use the multi interface, the connection cache 1189 will be kept within the multi handle and will be shared among all the easy 1190 handles that are used within the same multi handle. 1191 1192 5.7 Link errors when building libcurl on Windows! 1193 1194 You need to make sure that your project, and all the libraries (both static 1195 and dynamic) that it links against, are compiled/linked against the same run 1196 time library. 1197 1198 This is determined by the /MD, /ML, /MT (and their corresponding /M?d) 1199 options to the command line compiler. /MD (linking against MSVCRT dll) seems 1200 to be the most commonly used option. 1201 1202 When building an application that uses the static libcurl library, you must 1203 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for 1204 dynamic import symbols. If you're using Visual Studio, you need to instead 1205 add CURL_STATICLIB in the "Preprocessor Definitions" section. 1206 1207 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you 1208 have linked against the wrong (static) library. If you want to use the 1209 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of 1210 the import libraries below. These are the libraries produced by the various 1211 lib/Makefile.* files: 1212 1213 Target: static lib. import lib for libcurl*.dll. 1214 ----------------------------------------------------------- 1215 MingW: libcurl.a libcurldll.a 1216 MSVC (release): libcurl.lib libcurl_imp.lib 1217 MSVC (debug): libcurld.lib libcurld_imp.lib 1218 Borland: libcurl.lib libcurl_imp.lib 1219 1220 5.8 libcurl.so.X: open failed: No such file or directory 1221 1222 This is an error message you might get when you try to run a program linked 1223 with a shared version of libcurl and your run-time linker (ld.so) couldn't 1224 find the shared library named libcurl.so.X. (Where X is the number of the 1225 current libcurl ABI, typically 3 or 4). 1226 1227 You need to make sure that ld.so finds libcurl.so.X. You can do that 1228 multiple ways, and it differs somewhat between different operating systems, 1229 but they are usually: 1230 1231 * Add an option to the linker command line that specify the hard-coded path 1232 the run-time linker should check for the lib (usually -R) 1233 1234 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so 1235 should check for libs 1236 1237 * Adjust the system's config to check for libs in the directory where you've 1238 put the dir (like Linux's /etc/ld.so.conf) 1239 1240 'man ld.so' and 'man ld' will tell you more details 1241 1242 5.9 How does libcurl resolve host names? 1243 1244 libcurl supports a large a number of different name resolve functions. One 1245 of them is picked at build-time and will be used unconditionally. Thus, if 1246 you want to change name resolver function you must rebuild libcurl and tell 1247 it to use a different function. 1248 1249 - The non-ipv6 resolver that can use one out of four host name resolve calls 1250 (depending on what your system supports): 1251 1252 A - gethostbyname() 1253 B - gethostbyname_r() with 3 arguments 1254 C - gethostbyname_r() with 5 arguments 1255 D - gethostbyname_r() with 6 arguments 1256 1257 - The ipv6-resolver that uses getaddrinfo() 1258 1259 - The c-ares based name resolver that uses the c-ares library for resolves. 1260 Using this offers asynchronous name resolves. 1261 1262 - The threaded resolver (default option on Windows). It uses: 1263 1264 A - gethostbyname() on plain ipv4 hosts 1265 B - getaddrinfo() on ipv6-enabled hosts 1266 1267 Also note that libcurl never resolves or reverse-lookups addresses given as 1268 pure numbers, such as 127.0.0.1 or ::1. 1269 1270 5.10 How do I prevent libcurl from writing the response to stdout? 1271 1272 libcurl provides a default built-in write function that writes received data 1273 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly 1274 set CURLOPT_WRITEDATA to a different FILE * handle. 1275 1276 5.11 How do I make libcurl not receive the whole HTTP response? 1277 1278 You make the write callback (or progress callback) return an error and 1279 libcurl will then abort the transfer. 1280 1281 5.12 Can I make libcurl fake or hide my real IP address? 1282 1283 No. libcurl operates on a higher level. Besides, faking IP address would 1284 imply sending IP packet with a made-up source address, and then you normally 1285 get a problem with receiving the packet sent back as they would then not be 1286 routed to you! 1287 1288 If you use a proxy to access remote sites, the sites will not see your local 1289 IP address but instead the address of the proxy. 1290 1291 Also note that on many networks NATs or other IP-munging techniques are used 1292 that makes you see and use a different IP address locally than what the 1293 remote server will see you coming from. You may also consider using 1294 http://www.torproject.org . 1295 1296 5.13 How do I stop an ongoing transfer? 1297 1298 With the easy interface you make sure to return the correct error code from 1299 one of the callbacks, but none of them are instant. There is no function you 1300 can call from another thread or similar that will stop it immediately. 1301 Instead, you need to make sure that one of the callbacks you use returns an 1302 appropriate value that will stop the transfer. Suitable callbacks that you 1303 can do this with include the progress callback, the read callback and the 1304 write callback. 1305 1306 If you're using the multi interface, you can also stop a transfer by 1307 removing the particular easy handle from the multi stack at any moment you 1308 think the transfer is done or when you wish to abort the transfer. 1309 1310 5.14 Using C++ non-static functions for callbacks? 1311 1312 libcurl is a C library, it doesn't know anything about C++ member functions. 1313 1314 You can overcome this "limitation" with a relative ease using a static 1315 member function that is passed a pointer to the class: 1316 1317 // f is the pointer to your object. 1318 static YourClass::func(void *buffer, size_t sz, size_t n, void *f) 1319 { 1320 // Call non-static member function. 1321 static_cast<YourClass*>(f)->nonStaticFunction(); 1322 } 1323 1324 // This is how you pass pointer to the static function: 1325 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func); 1326 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this); 1327 1328 5.15 How do I get an FTP directory listing? 1329 1330 If you end the FTP URL you request with a slash, libcurl will provide you 1331 with a directory listing of that given directory. You can also set 1332 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use 1333 to list the files. 1334 1335 The follow-up question that tend to follow the previous one, is how a 1336 program is supposed to parse the directory listing. How does it know what's 1337 a file and what's a dir and what's a symlink etc. The harsh reality is that 1338 FTP provides no such fine and easy-to-parse output. The output format FTP 1339 servers respond to LIST commands are entirely at the server's own liking and 1340 the NLST output doesn't reveal any types and in many cases don't even 1341 include all the directory entries. Also, both LIST and NLST tend to hide 1342 unix-style hidden files (those that start with a dot) by default so you need 1343 to do "LIST -a" or similar to see them. 1344 1345 The application thus needs to parse the LIST output. One such existing 1346 list parser is available at http://cr.yp.to/ftpparse.html Versions of 1347 libcurl since 7.21.0 also provide the ability to specify a wildcard to 1348 download multiple files from one FTP directory. 1349 1350 5.16 I want a different time-out! 1351 1352 Time and time again users realize that CURLOPT_TIMEOUT and 1353 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all 1354 the various use cases and scenarios applications end up with. 1355 1356 libcurl offers many more ways to time-out operations. A common alternative 1357 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to 1358 specify the lowest possible speed to accept before to consider the transfer 1359 timed out. 1360 1361 The most flexible way is by writing your own time-out logic and using 1362 CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and 1363 use that to figure out exactly when the right condition is met when the 1364 transfer should get stopped. 1365 1366 5.17 Can I write a server with libcurl? 1367 1368 No. libcurl offers no functions or building blocks to build any kind of 1369 internet protocol server. libcurl is only a client-side library. For server 1370 libraries, you need to continue your search elsewhere but there exist many 1371 good open source ones out there for most protocols you could possibly want a 1372 server for. And there are really good stand-alone ones that have been tested 1373 and proven for many years. There's no need for you to reinvent them! 1374 1375 5.18 Does libcurl use threads? 1376 1377 Put simply: no, libcurl will execute in the same thread you call it in. All 1378 callbacks will be called in the same thread as the one you call libcurl in. 1379 1380 If you want to avoid your thread to be blocked by the libcurl call, you make 1381 sure you use the non-blocking API which will do transfers asynchronously - 1382 but still in the same single thread. 1383 1384 libcurl will potentially internally use threads for name resolving, if it 1385 was built to work like that, but in those cases it'll create the child 1386 threads by itself and they will only be used and then killed internally by 1387 libcurl and never exposed to the outside. 1388 13896. License Issues 1390 1391 Curl and libcurl are released under a MIT/X derivate license. The license is 1392 very liberal and should not impose a problem for your project. This section 1393 is just a brief summary for the cases we get the most questions. (Parts of 1394 this section was much enhanced by Bjorn Reese.) 1395 1396 We are not lawyers and this is not legal advice. You should probably consult 1397 one if you want true and accurate legal insights without our prejudice. Note 1398 especially that this section concerns the libcurl license only; compiling in 1399 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect 1400 the licensing obligations of your application. 1401 1402 6.1 I have a GPL program, can I use the libcurl library? 1403 1404 Yes! 1405 1406 Since libcurl may be distributed under the MIT/X derivate license, it can be 1407 used together with GPL in any software. 1408 1409 6.2 I have a closed-source program, can I use the libcurl library? 1410 1411 Yes! 1412 1413 libcurl does not put any restrictions on the program that uses the library. 1414 1415 6.3 I have a BSD licensed program, can I use the libcurl library? 1416 1417 Yes! 1418 1419 libcurl does not put any restrictions on the program that uses the library. 1420 1421 6.4 I have a program that uses LGPL libraries, can I use libcurl? 1422 1423 Yes! 1424 1425 The LGPL license doesn't clash with other licenses. 1426 1427 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 1428 1429 Yes! 1430 1431 The MIT/X derivate license practically allows you to do almost anything with 1432 the sources, on the condition that the copyright texts in the sources are 1433 left intact. 1434 1435 6.6 Can you please change the curl/libcurl license to XXXX? 1436 1437 No. 1438 1439 We have carefully picked this license after years of development and 1440 discussions and a large amount of people have contributed with source code 1441 knowing that this is the license we use. This license puts the restrictions 1442 we want on curl/libcurl and it does not spread to other programs or 1443 libraries that use it. It should be possible for everyone to use libcurl or 1444 curl in their projects, no matter what license they already have in use. 1445 1446 6.7 What are my obligations when using libcurl in my commercial apps? 1447 1448 Next to none. All you need to adhere to is the MIT-style license (stated in 1449 the COPYING file) which basically says you have to include the copyright 1450 notice in "all copies" and that you may not use the copyright holder's name 1451 when promoting your software. 1452 1453 You do not have to release any of your source code. 1454 1455 You do not have to reveal or make public any changes to the libcurl source 1456 code. 1457 1458 You do not have to broadcast to the world that you are using libcurl within 1459 your app. 1460 1461 All we ask is that you disclose "the copyright notice and this permission 1462 notice" somewhere. Most probably like in the documentation or in the section 1463 where other third party dependencies already are mentioned and acknowledged. 1464 1465 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere, 1466 more and more companies are discovering the power of libcurl and take 1467 advantage of it even in commercial environments. 1468 1469 14707. PHP/CURL Issues 1471 1472 7.1 What is PHP/CURL? 1473 1474 The module for PHP that makes it possible for PHP programs to access curl- 1475 functions from within PHP. 1476 1477 In the cURL project we call this module PHP/CURL to differentiate it from 1478 curl the command line tool and libcurl the library. The PHP team however 1479 does not refer to it like this (for unknown reasons). They call it plain 1480 CURL (often using all caps) or sometimes ext/curl, but both cause much 1481 confusion to users which in turn gives us a higher question load. 1482 1483 7.2 Who wrote PHP/CURL? 1484 1485 PHP/CURL is a module that comes with the regular PHP package. It depends and 1486 uses libcurl, so you need to have libcurl installed properly first before 1487 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes. 1488 1489 7.3 Can I perform multiple requests using the same handle? 1490 1491 Yes - at least in PHP version 4.3.8 and later (this has been known to not 1492 work in earlier versions, but the exact version when it started to work is 1493 unknown to me). 1494 1495 After a transfer, you just set new options in the handle and make another 1496 transfer. This will make libcurl to re-use the same connection if it can. 1497