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? 102 103 6. License Issues 104 6.1 I have a GPL program, can I use the libcurl library? 105 6.2 I have a closed-source program, can I use the libcurl library? 106 6.3 I have a BSD licensed program, can I use the libcurl library? 107 6.4 I have a program that uses LGPL libraries, can I use libcurl? 108 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 109 6.6 Can you please change the curl/libcurl license to XXXX? 110 6.7 What are my obligations when using libcurl in my commercial apps? 111 112 7. PHP/CURL Issues 113 7.1 What is PHP/CURL? 114 7.2 Who wrote PHP/CURL? 115 7.3 Can I perform multiple requests using the same handle? 116 117============================================================================== 118 1191. Philosophy 120 121 1.1 What is cURL? 122 123 cURL is the name of the project. The name is a play on 'Client for URLs', 124 originally with URL spelled in uppercase to make it obvious it deals with 125 URLs. The fact it can also be pronounced 'see URL' also helped, it works as 126 an abbreviation for "Client URL Request Library" or why not the recursive 127 version: "Curl URL Request Library". 128 129 The cURL project produces two products: 130 131 libcurl 132 133 A free and easy-to-use client-side URL transfer library, supporting DICT, 134 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, 135 POP3S, RTMP, RTSP, SCP, SFTP, SMTP, SMTPS, TELNET and TFTP. 136 137 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, 138 kerberos, HTTP form based upload, proxies, cookies, user+password 139 authentication, file transfer resume, http proxy tunneling and more! 140 141 libcurl is highly portable, it builds and works identically on numerous 142 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HPUX, 143 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOS, Mac 144 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF, 145 Android, Minix, IBM TPF and more... 146 147 libcurl is free, thread-safe, IPv6 compatible, feature rich, well 148 supported and fast. 149 150 curl 151 152 A command line tool for getting or sending files using URL syntax. 153 154 Since curl uses libcurl, curl supports the same wide range of common 155 Internet protocols that libcurl does. 156 157 We pronounce curl and cURL with an initial k sound: [kurl]. 158 159 There are numerous sub-projects and related projects that also use the word 160 curl in the project names in various combinations, but you should take 161 notice that this FAQ is directed at the command-line tool named curl (and 162 libcurl the library), and may therefore not be valid for other curl-related 163 projects. (There is however a small section for the PHP/CURL in this FAQ.) 164 165 1.2 What is libcurl? 166 167 libcurl is a reliable and portable library which provides you with an easy 168 interface to a range of common Internet protocols. 169 170 You can use libcurl for free in your application, be it open source, 171 commercial or closed-source. 172 173 libcurl is most probably the most portable, most powerful and most often 174 used C-based multi-platform file transfer library on this planet - be it 175 open source or commercial. 176 177 1.3 What is curl not? 178 179 Curl is not a wget clone. That is a common misconception. Never, during 180 curl's development, have we intended curl to replace wget or compete on its 181 market. Curl is targeted at single-shot file transfers. 182 183 Curl is not a web site mirroring program. If you want to use curl to mirror 184 something: fine, go ahead and write a script that wraps around curl to make 185 it reality (like curlmirror.pl does). 186 187 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl 188 but if you want systematic and sequential behavior you should write a 189 script (or write a new program that interfaces libcurl) and do it. 190 191 Curl is not a PHP tool, even though it works perfectly well when used from 192 or with PHP (when using the PHP/CURL module). 193 194 Curl is not a program for a single operating system. Curl exists, compiles, 195 builds and runs under a wide range of operating systems, including all 196 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2, 197 OS X, QNX etc. 198 199 1.4 When will you make curl do XXXX ? 200 201 We love suggestions of what to change in order to make curl and libcurl 202 better. We do however believe in a few rules when it comes to the future of 203 curl: 204 205 Curl -- the command line tool -- is to remain a non-graphical command line 206 tool. If you want GUIs or fancy scripting capabilities, you should look for 207 another tool that uses libcurl. 208 209 We do not add things to curl that other small and available tools already do 210 very fine at the side. Curl's output is fine to pipe into another program or 211 redirect to another file for the next program to interpret. 212 213 We focus on protocol related issues and improvements. If you wanna do more 214 magic with the supported protocols than curl currently does, chances are big 215 we will agree. If you wanna add more protocols, we may very well agree. 216 217 If you want someone else to make all the work while you wait for us to 218 implement it for you, that is not a very friendly attitude. We spend a 219 considerable time already on maintaining and developing curl. In order to 220 get more out of us, you should consider trading in some of your time and 221 efforts in return. 222 223 If you write the code, chances are bigger that it will get into curl 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, sourceforge.net hosts project services we take advantage from, 247 like the bug tracker and github hosts the primary git repository. Also 248 again, some companies have sponsored certain parts of the development in the 249 past and I hope some will continue to do so 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 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 In May 2012 Daniel did a counting game and came up with a number that may 310 be completely wrong or somewhat accurate. Over 500 million! 311 312 See http://daniel.haxx.se/blog/2012/05/16/300m-users/ 313 314 1.11 Why don't you update ca-bundle.crt 315 316 The ca cert bundle that used to shipped with curl was very outdated and must 317 be replaced with an up-to-date version by anyone who wants to verify 318 peers. It is no longer provided by curl. The last curl release ever that 319 shipped a ca cert bundle was curl 7.18.0. 320 321 In the cURL project we've decided not to attempt to keep this file updated 322 (or even present anymore) since deciding what to add to a ca cert bundle is 323 an undertaking we've not been ready to accept, and the one we can get from 324 Mozilla is perfectly fine so there's no need to duplicate that work. 325 326 Today, with many services performed over HTTPS, every operating system 327 should come with a default ca cert bundle that can be deemed somewhat 328 trustworthy and that collection (if reasonably updated) should be deemed to 329 be a lot better than a private curl version. 330 331 If you want the most recent collection of ca certs that Mozilla Firefox 332 uses, we recommend that you extract the collection yourself from Mozilla 333 Firefox (by running 'make ca-bundle), or by using our online service setup 334 for this purpose: http://curl.haxx.se/docs/caextract.html 335 336 1.12 I have a problem who can I chat with? 337 338 There's a bunch of friendly people hanging out in the #curl channel on the 339 IRC network irc.freenode.net. If you're polite and nice, chances are big 340 that you can get -- or provide -- help instantly. 341 342 1.13 curl's ECCN number? 343 344 The US government restricts exports of software that contains or uses 345 cryptography. When doing so, the Export Control Classification Number (ECCN) 346 is used to identify the level of export control etc. 347 348 ASF gives a good explanation at http://www.apache.org/dev/crypto.html 349 350 We believe curl's number might be ECCN 5D002, another possibility is 351 5D992. It seems necessary to write them, asking to confirm. 352 353 Comprehensible explanations of the meaning of such numbers and how to 354 obtain them (resp.) are here 355 356 http://www.bis.doc.gov/licensing/exportingbasics.htm 357 http://www.bis.doc.gov/licensing/do_i_needaneccn.html 358 359 An incomprehensible description of the two numbers above is here 360 http://www.access.gpo.gov/bis/ear/pdf/ccl5-pt2.pdf 361 362 1.14 How do I submit my patch? 363 364 When you have made a patch or a change of whatever sort, and want to submit 365 that to the project, there are a few different ways we prefer: 366 367 o send a patch to the curl-library mailing list. We're many subscribers 368 there and there are lots of people who can review patches, comment on them 369 and "receive" them properly. 370 371 o if your patch changes or fixes a bug, you can also opt to submit a bug 372 report in the bug tracker and attach your patch there. There are less 373 people involved there. 374 375 Lots of more details are found in the CONTRIBUTE and INTERNALS docs. 376 377 3782. Install Related Problems 379 380 2.1 configure doesn't find OpenSSL even when it is installed 381 382 This may be because of several reasons. 383 384 2.1.1 native linker doesn't find openssl 385 386 Affected platforms: 387 Solaris (native cc compiler) 388 HPUX (native cc compiler) 389 SGI IRIX (native cc compiler) 390 SCO UNIX (native cc compiler) 391 392 When configuring curl, I specify --with-ssl. OpenSSL is installed in 393 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find 394 CRYPTO_lock in -lcrypto 395 396 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER 397 -lcrypto, so ld can't find the library. This is due to a bug in the GNU 398 autoconf tool. 399 400 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of 401 ./configure places the -L/usr/local/ssl/lib early enough in the command 402 line to make things work 403 404 2.1.2 only the libssl lib is missing 405 406 If all include files and the libcrypto lib is present, with only the 407 libssl being missing according to configure, this is mostly likely because 408 a few functions are left out from the libssl. 409 410 If the function names missing include RSA or RSAREF you can be certain 411 that this is because libssl requires the RSA and RSAREF libs to build. 412 413 See the INSTALL file section that explains how to add those libs to 414 configure. Make sure that you remove the config.cache file before you 415 rerun configure with the new flags. 416 417 2.2 Does curl work/build with other SSL libraries? 418 419 Curl has been written to use a generic SSL function layer internally, and 420 that SSL functionality can then be provided by one out of many different SSL 421 backends. 422 423 curl can be built to use one of the following SSL alternatives: OpenSSL, 424 GnuTLS, yassl, NSS, PolarSSL, axTLS, Secure Transport (native iOS/OS X), 425 WinSSL (native Windows) or qssl (native IBM i). They all have their pros 426 and cons, and we try to maintain a comparison of them here: 427 http://curl.haxx.se/docs/ssl-compared.html 428 429 2.3 Where can I find a copy of LIBEAY32.DLL? 430 431 That is an OpenSSL binary built for Windows. 432 433 Curl can be built with OpenSSL to do the SSL stuff. The LIBEAY32.DLL is then 434 what curl needs on a windows machine to do https:// etc. Check out the curl 435 web site to find accurate and up-to-date pointers to recent OpenSSL DLLs and 436 other binary packages. 437 438 2.4 Does curl support SOCKS (RFC 1928) ? 439 440 Yes, SOCKS 4 and 5 are supported. 441 442 4433. Usage problems 444 445 3.1 curl: (1) SSL is disabled, https: not supported 446 447 If you get this output when trying to get anything from a https:// server, 448 it means that the instance of curl/libcurl that you're using was built 449 without support for this protocol. 450 451 This could've happened if the configure script that was run at build time 452 couldn't find all libs and include files curl requires for SSL to work. If 453 the configure script fails to find them, curl is simply built without SSL 454 support. 455 456 To get the https:// support into a curl that was previously built but that 457 reports that https:// is not supported, you should dig through the document 458 and logs and check out why the configure script doesn't find the SSL libs 459 and/or include files. 460 461 Also, check out the other paragraph in this FAQ labelled "configure doesn't 462 find OpenSSL even when it is installed". 463 464 3.2 How do I tell curl to resume a transfer? 465 466 Curl supports resumed transfers both ways on both FTP and HTTP. 467 Try the -C option. 468 469 3.3 Why doesn't my posting using -F work? 470 471 You can't simply use -F or -d at your choice. The web server that will 472 receive your post expects one of the formats. If the form you're trying to 473 submit uses the type 'multipart/form-data', then and only then you must use 474 the -F type. In all the most common cases, you should use -d which then 475 causes a posting with the type 'application/x-www-form-urlencoded'. 476 477 This is described in some detail in the MANUAL and TheArtOfHttpScripting 478 documents, and if you don't understand it the first time, read it again 479 before you post questions about this to the mailing list. Also, try reading 480 through the mailing list archives for old postings and questions regarding 481 this. 482 483 3.4 How do I tell curl to run custom FTP commands? 484 485 You can tell curl to perform optional commands both before and/or after a 486 file transfer. Study the -Q/--quote option. 487 488 Since curl is used for file transfers, you don't normally use curl to 489 perform FTP commands without transferring anything. Therefore you must 490 always specify a URL to transfer to/from even when doing custom FTP 491 commands, or use -I which implies the "no body" option sent to libcurl. 492 493 3.5 How can I disable the Accept: */* header? 494 495 You can change all internally generated headers by adding a replacement with 496 the -H/--header option. By adding a header with empty contents you safely 497 disable that one. Use -H "Accept:" to disable that specific header. 498 499 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 500 501 To curl, all contents are alike. It doesn't matter how the page was 502 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain HTML 503 files. There's no difference to curl and it doesn't even know what kind of 504 language that generated the page. 505 506 See also item 3.14 regarding javascript. 507 508 3.7 Can I use curl to delete/rename a file through FTP? 509 510 Yes. You specify custom FTP commands with -Q/--quote. 511 512 One example would be to delete a file after you have downloaded it: 513 514 curl -O ftp://download.com/coolfile -Q '-DELE coolfile' 515 516 or rename a file after upload: 517 518 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname" 519 520 3.8 How do I tell curl to follow HTTP redirects? 521 522 Curl does not follow so-called redirects by default. The Location: header 523 that informs the client about this is only interpreted if you're using the 524 -L/--location option. As in: 525 526 curl -L http://redirector.com 527 528 Not all redirects are HTTP ones, see 4.14 529 530 3.9 How do I use curl in my favorite programming language? 531 532 There exist many language interfaces/bindings for curl that integrates it 533 better with various languages. If you are fluid in a script language, you 534 may very well opt to use such an interface instead of using the command line 535 tool. 536 537 Find out more about which languages that support curl directly, and how to 538 install and use them, in the libcurl section of the curl web site: 539 http://curl.haxx.se/libcurl/ 540 541 All the various bindings to libcurl are made by other projects and people, 542 outside of the cURL project. The cURL project itself only produces libcurl 543 with its plain C API. If you don't find anywhere else to ask you can ask 544 about bindings on the curl-library list too, but be prepared that people on 545 that list may not know anything about bindings. 546 547 In October 2009, there were interfaces available for the following 548 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Dylan, Eiffel, Euphoria, 549 Ferite, Gambas, glib/GTK+, Haskell, ILE/RPG, Java, Lisp, Lua, Mono, .NET, 550 Object-Pascal, O'Caml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ruby, 551 Scheme, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro, 552 Q, wxwidgets and XBLite. By the time you read this, additional ones may have 553 appeared! 554 555 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 556 557 Curl adheres to the HTTP spec, which basically means you can play with *any* 558 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and 559 XML-RPC are all such ones. You can use -X to set custom requests and -H to 560 set custom headers (or replace internally generated ones). 561 562 Using libcurl is of course just as fine and you'd just use the proper 563 library options to do the same. 564 565 3.11 How do I POST with a different Content-Type? 566 567 You can always replace the internally generated headers with -H/--header. 568 To make a simple HTTP POST with text/xml as content-type, do something like: 569 570 curl -d "datatopost" -H "Content-Type: text/xml" [URL] 571 572 3.12 Why do FTP specific features over HTTP proxy fail? 573 574 Because when you use a HTTP proxy, the protocol spoken on the network will 575 be HTTP, even if you specify a FTP URL. This effectively means that you 576 normally can't use FTP specific features such as FTP upload and FTP quote 577 etc. 578 579 There is one exception to this rule, and that is if you can "tunnel through" 580 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p) 581 and is generally not available as proxy admins usually disable tunneling to 582 other ports than 443 (which is used for HTTPS access through proxies). 583 584 3.13 Why does my single/double quotes fail? 585 586 To specify a command line option that includes spaces, you might need to 587 put the entire option within quotes. Like in: 588 589 curl -d " with spaces " url.com 590 591 or perhaps 592 593 curl -d ' with spaces ' url.com 594 595 Exactly what kind of quotes and how to do this is entirely up to the shell 596 or command line interpreter that you are using. For most unix shells, you 597 can more or less pick either single (') or double (") quotes. For 598 Windows/DOS prompts I believe you're forced to use double (") quotes. 599 600 Please study the documentation for your particular environment. Examples in 601 the curl docs will use a mix of both these ones as shown above. You must 602 adjust them to work in your environment. 603 604 Remember that curl works and runs on more operating systems than most single 605 individuals have ever tried. 606 607 3.14 Does curl support Javascript or PAC (automated proxy config)? 608 609 Many web pages do magic stuff using embedded Javascript. Curl and libcurl 610 have no built-in support for that, so it will be treated just like any other 611 contents. 612 613 .pac files are a netscape invention and are sometimes used by organizations 614 to allow them to differentiate which proxies to use. The .pac contents is 615 just a Javascript program that gets invoked by the browser and that returns 616 the name of the proxy to connect to. Since curl doesn't support Javascript, 617 it can't support .pac proxy configuration either. 618 619 Some workarounds usually suggested to overcome this Javascript dependency: 620 621 Depending on the Javascript complexity, write up a script that translates it 622 to another language and execute that. 623 624 Read the Javascript code and rewrite the same logic in another language. 625 626 Implement a Javascript interpreter, people have successfully used the 627 Mozilla Javascript engine in the past. 628 629 Ask your admins to stop this, for a static proxy setup or similar. 630 631 3.15 Can I do recursive fetches with curl? 632 633 No. curl itself has no code that performs recursive operations, such as 634 those performed by wget and similar tools. 635 636 There exist wrapper scripts with that functionality (for example the 637 curlmirror perl script), and you can write programs based on libcurl to do 638 it, but the command line tool curl itself cannot. 639 640 3.16 What certificates do I need when I use SSL? 641 642 There are three different kinds of "certificates" to keep track of when we 643 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl. 644 645 CLIENT CERTIFICATE 646 647 The server you communicate may require that you can provide this in order to 648 prove that you actually are who you claim to be. If the server doesn't 649 require this, you don't need a client certificate. 650 651 A client certificate is always used together with a private key, and the 652 private key has a pass phrase that protects it. 653 654 SERVER CERTIFICATE 655 656 The server you communicate with has a server certificate. You can and should 657 verify this certificate to make sure that you are truly talking to the real 658 server and not a server impersonating it. 659 660 CERTIFICATE AUTHORITY CERTIFICATE ("CA cert") 661 662 You often have several CA certs in a CA cert bundle that can be used to 663 verify a server certificate that was signed by one of the authorities in the 664 bundle. curl does not come with a CA cert bundle but most curl installs 665 provide one. You can also override the default. 666 667 The server certificate verification process is made by using a Certificate 668 Authority certificate ("CA cert") that was used to sign the server 669 certificate. Server certificate verification is enabled by default in curl 670 and libcurl and is often the reason for problems as explained in FAQ entry 671 4.12 and the SSLCERTS document 672 (http://curl.haxx.se/docs/sslcerts.html). Server certificates that are 673 "self-signed" or otherwise signed by a CA that you do not have a CA cert 674 for, cannot be verified. If the verification during a connect fails, you are 675 refused access. You then need to explicitly disable the verification to 676 connect to the server. 677 678 3.17 How do I list the root dir of an FTP server? 679 680 There are two ways. The way defined in the RFC is to use an encoded slash 681 in the first path part. List the "/tmp" dir like this: 682 683 curl ftp://ftp.sunet.se/%2ftmp/ 684 685 or the not-quite-kosher-but-more-readable way, by simply starting the path 686 section of the URL with a slash: 687 688 curl ftp://ftp.sunet.se//tmp/ 689 690 3.18 Can I use curl to send a POST/PUT and not wait for a response? 691 692 No. 693 694 But you could easily write your own program using libcurl to do such stunts. 695 696 3.19 How do I get HTTP from a host using a specific IP address? 697 698 For example, you may be trying out a web site installation that isn't yet in 699 the DNS. Or you have a site using multiple IP addresses for a given host 700 name and you want to address a specific one out of the set. 701 702 Set a custom Host: header that identifies the server name you want to reach 703 but use the target IP address in the URL: 704 705 curl --header "Host: www.example.com" http://127.0.0.1/ 706 707 You can also opt to add faked host name entries to curl with the --resolve 708 option. That has the added benefit that things like redirects will also work 709 properly. The above operation would instead be done as: 710 711 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/ 712 713 3.20 How to SFTP from my user's home directory? 714 715 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to 716 work with. It means that if you don't specify that you want the user's home 717 directory, you get the actual root directory. 718 719 To specify a file in your user's home directory, you need to use the correct 720 URL syntax which for sftp might look similar to: 721 722 curl -O -u user:password sftp://example.com/~/file.txt 723 724 and for SCP it is just a different protocol prefix: 725 726 curl -O -u user:password scp://example.com/~/file.txt 727 728 3.21 Protocol xxx not supported or disabled in libcurl 729 730 When passing on a URL to curl to use, it may respond that the particular 731 protocol is not supported or disabled. The particular way this error message 732 is phrased is because curl doesn't make a distinction internally of whether 733 a particular protocol is not supported (i.e. never got any code added that 734 knows how to speak that protocol) or if it was explicitly disabled. curl can 735 be built to only support a given set of protocols, and the rest would then 736 be disabled or not supported. 737 738 Note that this error will also occur if you pass a wrongly spelled protocol 739 part as in "htpt://example.com" or as in the less evident case if you prefix 740 the protocol part with a space as in " http://example.com/". 741 742 3.22 curl -X gives me HTTP problems 743 744 In normal circumstances, -X should hardly ever be used. 745 746 By default you use curl without explicitly saying which request method to 747 use when the URL identifies a HTTP transfer. If you just pass in a URL like 748 "curl http://example.com" it will use GET. If you use -d or -F curl will use 749 POST, -I will cause a HEAD and -T will make it a PUT. 750 751 If for whatever reason you're not happy with these default choices that curl 752 does for you, you can override those request methods by specifying -X 753 [WHATEVER]. This way you can for example send a DELETE by doing "curl -X 754 DELETE [URL]". 755 756 It is thus pointless to do "curl -XGET [URL]" as GET would be used 757 anyway. In the same vein it is pointless to do "curl -X POST -d data 758 [URL]"... But you can make a fun and somewhat rare request that sends a 759 request-body in a GET request with something like "curl -X GET -d data 760 [URL]" 761 762 Note that -X doesn't change curl's behavior. It only modifies the actual 763 string sent in the request. 764 765 Accordingly, by using -XPOST on a command line that for example would follow 766 a 303 redirect, you will effectively prevent curl from behaving 767 correctly. Be aware. 768 769 7704. Running Problems 771 772 4.1 Problems connecting to SSL servers. 773 774 It took a very long time before we could sort out why curl had problems to 775 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The 776 error sometimes showed up similar to: 777 778 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233: 779 780 It turned out to be because many older SSL servers don't deal with SSLv3 781 requests properly. To correct this problem, tell curl to select SSLv2 from 782 the command line (-2/--sslv2). 783 784 There have also been examples where the remote server didn't like the SSLv2 785 request and instead you had to force curl to use SSLv3 with -3/--sslv3. 786 787 4.2 Why do I get problems when I use & or % in the URL? 788 789 In general unix shells, the & symbol is treated specially and when used, it 790 runs the specified command in the background. To safely send the & as a part 791 of a URL, you should quote the entire URL by using single (') or double (") 792 quotes around it. Similar problems can also occur on some shells with other 793 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL. 794 795 An example that would invoke a remote CGI that uses &-symbols could be: 796 797 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl' 798 799 In Windows, the standard DOS shell treats the percent sign specially and you 800 need to use TWO percent signs for each single one you want to use in the 801 URL. 802 803 If you want a literal percent sign to be part of the data you pass in a POST 804 using -d/--data you must encode it as '%25' (which then also needs the 805 percent sign doubled on Windows machines). 806 807 4.3 How can I use {, }, [ or ] to specify multiple URLs? 808 809 Because those letters have a special meaning to the shell, and to be used in 810 a URL specified to curl you must quote them. 811 812 An example that downloads two URLs (sequentially) would do: 813 814 curl '{curl,www}.haxx.se' 815 816 To be able to use those letters as actual parts of the URL (without using 817 them for the curl URL "globbing" system), use the -g/--globoff option: 818 819 curl -g 'www.site.com/weirdname[].html' 820 821 4.4 Why do I get downloaded data even though the web page doesn't exist? 822 823 Curl asks remote servers for the page you specify. If the page doesn't exist 824 at the server, the HTTP protocol defines how the server should respond and 825 that means that headers and a "page" will be returned. That's simply how 826 HTTP works. 827 828 By using the --fail option you can tell curl explicitly to not get any data 829 if the HTTP return code doesn't say success. 830 831 4.5 Why do I get return code XXX from a HTTP server? 832 833 RFC2616 clearly explains the return codes. This is a short transcript. Go 834 read the RFC for exact details: 835 836 4.5.1 "400 Bad Request" 837 838 The request could not be understood by the server due to malformed 839 syntax. The client SHOULD NOT repeat the request without modifications. 840 841 4.5.2 "401 Unauthorized" 842 843 The request requires user authentication. 844 845 4.5.3 "403 Forbidden" 846 847 The server understood the request, but is refusing to fulfil it. 848 Authorization will not help and the request SHOULD NOT be repeated. 849 850 4.5.4 "404 Not Found" 851 852 The server has not found anything matching the Request-URI. No indication 853 is given of whether the condition is temporary or permanent. 854 855 4.5.5 "405 Method Not Allowed" 856 857 The method specified in the Request-Line is not allowed for the resource 858 identified by the Request-URI. The response MUST include an Allow header 859 containing a list of valid methods for the requested resource. 860 861 4.5.6 "301 Moved Permanently" 862 863 If you get this return code and an HTML output similar to this: 864 865 <H1>Moved Permanently</H1> The document has moved <A 866 HREF="http://same_url_now_with_a_trailing_slash/">here</A>. 867 868 it might be because you request a directory URL but without the trailing 869 slash. Try the same operation again _with_ the trailing URL, or use the 870 -L/--location option to follow the redirection. 871 872 4.6 Can you tell me what error code 142 means? 873 874 All curl error codes are described at the end of the man page, in the 875 section called "EXIT CODES". 876 877 Error codes that are larger than the highest documented error code means 878 that curl has exited due to a crash. This is a serious error, and we 879 appreciate a detailed bug report from you that describes how we could go 880 ahead and repeat this! 881 882 4.7 How do I keep user names and passwords secret in Curl command lines? 883 884 This problem has two sides: 885 886 The first part is to avoid having clear-text passwords in the command line 887 so that they don't appear in 'ps' outputs and similar. That is easily 888 avoided by using the "-K" option to tell curl to read parameters from a file 889 or stdin to which you can pass the secret info. curl itself will also 890 attempt to "hide" the given password by blanking out the option - this 891 doesn't work on all platforms. 892 893 To keep the passwords in your account secret from the rest of the world is 894 not a task that curl addresses. You could of course encrypt them somehow to 895 at least hide them from being read by human eyes, but that is not what 896 anyone would call security. 897 898 Also note that regular HTTP (using Basic authentication) and FTP passwords 899 are sent in clear across the network. All it takes for anyone to fetch them 900 is to listen on the network. Eavesdropping is very easy. Use more secure 901 authentication methods (like Digest, Negotiate or even NTLM) or consider the 902 SSL-based alternatives HTTPS and FTPS. 903 904 4.8 I found a bug! 905 906 It is not a bug if the behavior is documented. Read the docs first. 907 Especially check out the KNOWN_BUGS file, it may be a documented bug! 908 909 If it is a problem with a binary you've downloaded or a package for your 910 particular platform, try contacting the person who built the package/archive 911 you have. 912 913 If there is a bug, read the BUGS document first. Then report it as described 914 in there. 915 916 4.9 Curl can't authenticate to the server that requires NTLM? 917 918 NTLM support requires OpenSSL, GnuTLS, NSS, Secure Transport, or Microsoft 919 Windows libraries at build-time to provide this functionality. 920 921 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You 922 should not use such ones. 923 924 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work! 925 926 Many web servers allow or demand that the administrator configures the 927 server properly for these requests to work on the web server. 928 929 Some servers seem to support HEAD only on certain kinds of URLs. 930 931 To fully grasp this, try the documentation for the particular server 932 software you're trying to interact with. This is not anything curl can do 933 anything about. 934 935 4.11 Why does my HTTP range requests return the full document? 936 937 Because the range may not be supported by the server, or the server may 938 choose to ignore it and return the full document anyway. 939 940 4.12 Why do I get "certificate verify failed" ? 941 942 You invoke curl 7.10 or later to communicate on a https:// URL and get an 943 error back looking something similar to this: 944 945 curl: (35) SSL: error:14090086:SSL routines: 946 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed 947 948 Then it means that curl couldn't verify that the server's certificate was 949 good. Curl verifies the certificate using the CA cert bundle that comes with 950 the curl installation. 951 952 To disable the verification (which makes it act like curl did before 7.10), 953 use -k. This does however enable man-in-the-middle attacks. 954 955 If you get this failure but are having a CA cert bundle installed and used, 956 the server's certificate is not signed by one of the CA's in the bundle. It 957 might for example be self-signed. You then correct this problem by obtaining 958 a valid CA cert for the server. Or again, decrease the security by disabling 959 this check. 960 961 Details are also in the SSLCERTS file in the release archives, found online 962 here: http://curl.haxx.se/docs/sslcerts.html 963 964 4.13 Why is curl -R on Windows one hour off? 965 966 During daylight savings time, when -R is used, curl will set a time that 967 appears one hour off. This happens due to a flaw in how Windows stores and 968 uses file modification times and it is not easily worked around. For details 969 on this problem, read this: http://www.codeproject.com/datetime/dstbugs.asp 970 971 4.14 Redirects work in browser but not with curl! 972 973 curl supports HTTP redirects fine (see item 3.8). Browsers generally support 974 at least two other ways to perform redirects that curl does not: 975 976 Meta tags. You can write a HTML tag that will cause the browser to redirect 977 to another given URL after a certain time. 978 979 Javascript. You can write a Javascript program embedded in a HTML page that 980 redirects the browser to another given URL. 981 982 There is no way to make curl follow these redirects. You must either 983 manually figure out what the page is set to do, or you write a script that 984 parses the results and fetches the new URL. 985 986 4.15 FTPS doesn't work 987 988 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit 989 mode. 990 991 When a URL is used that starts with FTPS://, curl assumes implicit SSL on 992 the control connection and will therefore immediately connect and try to 993 speak SSL. FTPS:// connections default to port 990. 994 995 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one 996 of its related flavours). This is the most common method, and the one 997 mandated by RFC4217. This kind of connection then of course uses the 998 standard FTP port 21 by default. 999 1000 4.16 My HTTP POST or PUT requests are slow! 1001 1002 libcurl makes all POST and PUT requests (except for POST requests with a 1003 very tiny request body) use the "Expect: 100-continue" header. This header 1004 allows the server to deny the operation early so that libcurl can bail out 1005 already before having to send any data. This is useful in authentication 1006 cases and others. 1007 1008 However, many servers don't implement the Expect: stuff properly and if the 1009 server doesn't respond (positively) within 1 second libcurl will continue 1010 and send off the data anyway. 1011 1012 You can disable libcurl's use of the Expect: header the same way you disable 1013 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0. 1014 1015 4.17 Non-functional connect timeouts 1016 1017 In most Windows setups having a timeout longer than 21 seconds make no 1018 difference, as it will only send 3 TCP SYN packets and no more. The second 1019 packet sent three seconds after the first and the third six seconds after 1020 the second. No more than three packets are sent, no matter how long the 1021 timeout is set. 1022 1023 See option TcpMaxConnectRetransmissions on this page: 1024 http://support.microsoft.com/?scid=kb%3Ben-us%3B175523&x=6&y=7 1025 1026 Also, even on non-Windows systems there may run a firewall or anti-virus 1027 software or similar that accepts the connection but does not actually do 1028 anything else. This will make (lib)curl to consider the connection connected 1029 and thus the connect timeout won't trigger. 1030 1031 4.18 file:// URLs containing drive letters (Windows, NetWare) 1032 1033 When using cURL to try to download a local file, one might use a URL 1034 in this format: 1035 1036 file://D:/blah.txt 1037 1038 You'll find that even if D:\blah.txt does exist, cURL returns a 'file 1039 not found' error. 1040 1041 According to RFC 1738 (http://www.faqs.org/rfcs/rfc1738.html), 1042 file:// URLs must contain a host component, but it is ignored by 1043 most implementations. In the above example, 'D:' is treated as the 1044 host component, and is taken away. Thus, cURL tries to open '/blah.txt'. 1045 If your system is installed to drive C:, that will resolve to 'C:\blah.txt', 1046 and if that doesn't exist you will get the not found error. 1047 1048 To fix this problem, use file:// URLs with *three* leading slashes: 1049 1050 file:///D:/blah.txt 1051 1052 Alternatively, if it makes more sense, specify 'localhost' as the host 1053 component: 1054 1055 file://localhost/D:/blah.txt 1056 1057 In either case, cURL should now be looking for the correct file. 1058 1059 4.19 Why doesn't cURL return an error when the network cable is unplugged? 1060 1061 Unplugging a cable is not an error situation. The TCP/IP protocol stack 1062 was designed to be fault tolerant, so even though there may be a physical 1063 break somewhere the connection shouldn't be affected, just possibly 1064 delayed. Eventually, the physical break will be fixed or the data will be 1065 re-routed around the physical problem through another path. 1066 1067 In such cases, the TCP/IP stack is responsible for detecting when the 1068 network connection is irrevocably lost. Since with some protocols it is 1069 perfectly legal for the client wait indefinitely for data, the stack may 1070 never report a problem, and even when it does, it can take up to 20 minutes 1071 for it to detect an issue. The curl option --keepalive-time enables 1072 keep-alive support in the TCP/IP stack which makes it periodically probe the 1073 connection to make sure it is still available to send data. That should 1074 reliably detect any TCP/IP network failure. 1075 1076 But even that won't detect the network going down before the TCP/IP 1077 connection is established (e.g. during a DNS lookup) or using protocols that 1078 don't use TCP. To handle those situations, curl offers a number of timeouts 1079 on its own. --speed-limit/--speed-time will abort if the data transfer rate 1080 falls too low, and --connect-timeout and --max-time can be used to put an 1081 overall timeout on the connection phase or the entire transfer. 1082 1083 A libcurl-using application running in a known physical environment (e.g. 1084 an embedded device with only a single network connection) may want to act 1085 immediately if its lone network connection goes down. That can be achieved 1086 by having the application monitor the network connection on its own using an 1087 OS-specific mechanism, then signalling libcurl to abort (see also item 5.13). 1088 1089 10905. libcurl Issues 1091 1092 5.1 Is libcurl thread-safe? 1093 1094 Yes. 1095 1096 We have written the libcurl code specifically adjusted for multi-threaded 1097 programs. libcurl will use thread-safe functions instead of non-safe ones if 1098 your system has such. Note that you must never share the same handle in 1099 multiple threads. 1100 1101 1102 If you use a OpenSSL-powered libcurl in a multi-threaded environment, you 1103 need to provide one or two locking functions: 1104 1105 http://www.openssl.org/docs/crypto/threads.html 1106 1107 If you use a GnuTLS-powered libcurl in a multi-threaded environment, you 1108 need to provide locking function(s) for libgcrypt (which is used by GnuTLS 1109 for the crypto functions). 1110 1111 http://www.gnu.org/software/gnutls/manual/html_node/Multi_002dthreaded-applications.html 1112 1113 No special locking is needed with a NSS-powered libcurl. NSS is thread-safe. 1114 1115 5.2 How can I receive all data into a large memory chunk? 1116 1117 [ See also the examples/getinmemory.c source ] 1118 1119 You are in full control of the callback function that gets called every time 1120 there is data received from the remote server. You can make that callback do 1121 whatever you want. You do not have to write the received data to a file. 1122 1123 One solution to this problem could be to have a pointer to a struct that you 1124 pass to the callback function. You set the pointer using the 1125 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback 1126 instead of a FILE * to a file: 1127 1128 /* imaginary struct */ 1129 struct MemoryStruct { 1130 char *memory; 1131 size_t size; 1132 }; 1133 1134 /* imaginary callback function */ 1135 size_t 1136 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data) 1137 { 1138 size_t realsize = size * nmemb; 1139 struct MemoryStruct *mem = (struct MemoryStruct *)data; 1140 1141 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1); 1142 if (mem->memory) { 1143 memcpy(&(mem->memory[mem->size]), ptr, realsize); 1144 mem->size += realsize; 1145 mem->memory[mem->size] = 0; 1146 } 1147 return realsize; 1148 } 1149 1150 5.3 How do I fetch multiple files with libcurl? 1151 1152 libcurl has excellent support for transferring multiple files. You should 1153 just repeatedly set new URLs with curl_easy_setopt() and then transfer it 1154 with curl_easy_perform(). The handle you get from curl_easy_init() is not 1155 only reusable, but you're even encouraged to reuse it if you can, as that 1156 will enable libcurl to use persistent connections. 1157 1158 5.4 Does libcurl do Winsock initialization on win32 systems? 1159 1160 Yes, if told to in the curl_global_init() call. 1161 1162 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ? 1163 1164 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have 1165 that DLL use the FILE * (as the DLL and the client application cannot access 1166 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must 1167 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the 1168 file, even if that simply writes the data to the specified FILE *. 1169 Similarly, if you use CURLOPT_READDATA you must also specify 1170 CURLOPT_READFUNCTION. 1171 1172 5.6 What about Keep-Alive or persistent connections? 1173 1174 curl and libcurl have excellent support for persistent connections when 1175 transferring several files from the same server. Curl will attempt to reuse 1176 connections for all URLs specified on the same command line/config file, and 1177 libcurl will reuse connections for all transfers that are made using the 1178 same libcurl handle. 1179 1180 When you use the easy interface, the connection cache is kept within the 1181 easy handle. If you instead use the multi interface, the connection cache 1182 will be kept within the multi handle and will be shared among all the easy 1183 handles that are used within the same multi handle. 1184 1185 5.7 Link errors when building libcurl on Windows! 1186 1187 You need to make sure that your project, and all the libraries (both static 1188 and dynamic) that it links against, are compiled/linked against the same run 1189 time library. 1190 1191 This is determined by the /MD, /ML, /MT (and their corresponding /M?d) 1192 options to the command line compiler. /MD (linking against MSVCRT dll) seems 1193 to be the most commonly used option. 1194 1195 When building an application that uses the static libcurl library, you must 1196 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for 1197 dynamic import symbols. If you're using Visual Studio, you need to instead 1198 add CURL_STATICLIB in the "Preprocessor Definitions" section. 1199 1200 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you 1201 have linked against the wrong (static) library. If you want to use the 1202 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of 1203 the import libraries below. These are the libraries produced by the various 1204 lib/Makefile.* files: 1205 1206 Target: static lib. import lib for libcurl*.dll. 1207 ----------------------------------------------------------- 1208 MingW: libcurl.a libcurldll.a 1209 MSVC (release): libcurl.lib libcurl_imp.lib 1210 MSVC (debug): libcurld.lib libcurld_imp.lib 1211 Borland: libcurl.lib libcurl_imp.lib 1212 1213 5.8 libcurl.so.X: open failed: No such file or directory 1214 1215 This is an error message you might get when you try to run a program linked 1216 with a shared version of libcurl and your run-time linker (ld.so) couldn't 1217 find the shared library named libcurl.so.X. (Where X is the number of the 1218 current libcurl ABI, typically 3 or 4). 1219 1220 You need to make sure that ld.so finds libcurl.so.X. You can do that 1221 multiple ways, and it differs somewhat between different operating systems, 1222 but they are usually: 1223 1224 * Add an option to the linker command line that specify the hard-coded path 1225 the run-time linker should check for the lib (usually -R) 1226 1227 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so 1228 should check for libs 1229 1230 * Adjust the system's config to check for libs in the directory where you've 1231 put the dir (like Linux's /etc/ld.so.conf) 1232 1233 'man ld.so' and 'man ld' will tell you more details 1234 1235 5.9 How does libcurl resolve host names? 1236 1237 libcurl supports a large a number of different name resolve functions. One 1238 of them is picked at build-time and will be used unconditionally. Thus, if 1239 you want to change name resolver function you must rebuild libcurl and tell 1240 it to use a different function. 1241 1242 - The non-ipv6 resolver that can use one out of four host name resolve calls 1243 (depending on what your system supports): 1244 1245 A - gethostbyname() 1246 B - gethostbyname_r() with 3 arguments 1247 C - gethostbyname_r() with 5 arguments 1248 D - gethostbyname_r() with 6 arguments 1249 1250 - The ipv6-resolver that uses getaddrinfo() 1251 1252 - The c-ares based name resolver that uses the c-ares library for resolves. 1253 Using this offers asynchronous name resolves. 1254 1255 - The threaded resolver (default option on Windows). It uses: 1256 1257 A - gethostbyname() on plain ipv4 hosts 1258 B - getaddrinfo() on ipv6-enabled hosts 1259 1260 Also note that libcurl never resolves or reverse-lookups addresses given as 1261 pure numbers, such as 127.0.0.1 or ::1. 1262 1263 5.10 How do I prevent libcurl from writing the response to stdout? 1264 1265 libcurl provides a default built-in write function that writes received data 1266 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly 1267 set CURLOPT_WRITEDATA to a different FILE * handle. 1268 1269 5.11 How do I make libcurl not receive the whole HTTP response? 1270 1271 You make the write callback (or progress callback) return an error and 1272 libcurl will then abort the transfer. 1273 1274 5.12 Can I make libcurl fake or hide my real IP address? 1275 1276 No. libcurl operates on a higher level. Besides, faking IP address would 1277 imply sending IP packet with a made-up source address, and then you normally 1278 get a problem with receiving the packet sent back as they would then not be 1279 routed to you! 1280 1281 If you use a proxy to access remote sites, the sites will not see your local 1282 IP address but instead the address of the proxy. 1283 1284 Also note that on many networks NATs or other IP-munging techniques are used 1285 that makes you see and use a different IP address locally than what the 1286 remote server will see you coming from. You may also consider using 1287 http://www.torproject.org . 1288 1289 5.13 How do I stop an ongoing transfer? 1290 1291 With the easy interface you make sure to return the correct error code from 1292 one of the callbacks, but none of them are instant. There is no function you 1293 can call from another thread or similar that will stop it immediately. 1294 Instead, you need to make sure that one of the callbacks you use returns an 1295 appropriate value that will stop the transfer. Suitable callbacks that you 1296 can do this with include the progress callback, the read callback and the 1297 write callback. 1298 1299 If you're using the multi interface, you can also stop a transfer by 1300 removing the particular easy handle from the multi stack at any moment you 1301 think the transfer is done or when you wish to abort the transfer. 1302 1303 5.14 Using C++ non-static functions for callbacks? 1304 1305 libcurl is a C library, it doesn't know anything about C++ member functions. 1306 1307 You can overcome this "limitation" with a relative ease using a static 1308 member function that is passed a pointer to the class: 1309 1310 // f is the pointer to your object. 1311 static YourClass::func(void *buffer, size_t sz, size_t n, void *f) 1312 { 1313 // Call non-static member function. 1314 static_cast<YourClass*>(f)->nonStaticFunction(); 1315 } 1316 1317 // This is how you pass pointer to the static function: 1318 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass:func); 1319 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this); 1320 1321 5.15 How do I get an FTP directory listing? 1322 1323 If you end the FTP URL you request with a slash, libcurl will provide you 1324 with a directory listing of that given directory. You can also set 1325 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use 1326 to list the files. 1327 1328 The follow-up question that tend to follow the previous one, is how a 1329 program is supposed to parse the directory listing. How does it know what's 1330 a file and what's a dir and what's a symlink etc. The harsh reality is that 1331 FTP provides no such fine and easy-to-parse output. The output format FTP 1332 servers respond to LIST commands are entirely at the server's own liking and 1333 the NLST output doesn't reveal any types and in many cases don't even 1334 include all the directory entries. Also, both LIST and NLST tend to hide 1335 unix-style hidden files (those that start with a dot) by default so you need 1336 to do "LIST -a" or similar to see them. 1337 1338 The application thus needs to parse the LIST output. One such existing 1339 list parser is available at http://cr.yp.to/ftpparse.html Versions of 1340 libcurl since 7.21.0 also provide the ability to specify a wildcard to 1341 download multiple files from one FTP directory. 1342 1343 5.16 I want a different time-out! 1344 1345 Time and time again users realize that CURLOPT_TIMEOUT and 1346 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all 1347 the various use cases and scenarios applications end up with. 1348 1349 libcurl offers many more ways to time-out operations. A common alternative 1350 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to 1351 specify the lowest possible speed to accept before to consider the transfer 1352 timed out. 1353 1354 The most flexible way is by writing your own time-out logic and using 1355 CURLOPT_PROGRESSFUNCTION (perhaps in combination with other callbacks) and 1356 use that to figure out exactly when the right condition is met when the 1357 transfer should get stopped. 1358 1359 5.17 Can I write a server with libcurl? 1360 1361 No. libcurl offers no functions or building blocks to build any kind of 1362 internet protocol server. libcurl is only a client-side library. For server 1363 libraries, you need to continue your search elsewhere but there exist many 1364 good open source ones out there for most protocols you could possibly want a 1365 server for. And there are really good stand-alone ones that have been tested 1366 and proven for many years. There's no need for you to reinvent them! 1367 1368 13696. License Issues 1370 1371 Curl and libcurl are released under a MIT/X derivate license. The license is 1372 very liberal and should not impose a problem for your project. This section 1373 is just a brief summary for the cases we get the most questions. (Parts of 1374 this section was much enhanced by Bjorn Reese.) 1375 1376 We are not lawyers and this is not legal advice. You should probably consult 1377 one if you want true and accurate legal insights without our prejudice. Note 1378 especially that this section concerns the libcurl license only; compiling in 1379 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect 1380 the licensing obligations of your application. 1381 1382 6.1 I have a GPL program, can I use the libcurl library? 1383 1384 Yes! 1385 1386 Since libcurl may be distributed under the MIT/X derivate license, it can be 1387 used together with GPL in any software. 1388 1389 6.2 I have a closed-source program, can I use the libcurl library? 1390 1391 Yes! 1392 1393 libcurl does not put any restrictions on the program that uses the library. 1394 1395 6.3 I have a BSD licensed program, can I use the libcurl library? 1396 1397 Yes! 1398 1399 libcurl does not put any restrictions on the program that uses the library. 1400 1401 6.4 I have a program that uses LGPL libraries, can I use libcurl? 1402 1403 Yes! 1404 1405 The LGPL license doesn't clash with other licenses. 1406 1407 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 1408 1409 Yes! 1410 1411 The MIT/X derivate license practically allows you to do almost anything with 1412 the sources, on the condition that the copyright texts in the sources are 1413 left intact. 1414 1415 6.6 Can you please change the curl/libcurl license to XXXX? 1416 1417 No. 1418 1419 We have carefully picked this license after years of development and 1420 discussions and a large amount of people have contributed with source code 1421 knowing that this is the license we use. This license puts the restrictions 1422 we want on curl/libcurl and it does not spread to other programs or 1423 libraries that use it. It should be possible for everyone to use libcurl or 1424 curl in their projects, no matter what license they already have in use. 1425 1426 6.7 What are my obligations when using libcurl in my commercial apps? 1427 1428 Next to none. All you need to adhere to is the MIT-style license (stated in 1429 the COPYING file) which basically says you have to include the copyright 1430 notice in "all copies" and that you may not use the copyright holder's name 1431 when promoting your software. 1432 1433 You do not have to release any of your source code. 1434 1435 You do not have to reveal or make public any changes to the libcurl source 1436 code. 1437 1438 You do not have to broadcast to the world that you are using libcurl within 1439 your app. 1440 1441 All we ask is that you disclose "the copyright notice and this permission 1442 notice" somewhere. Most probably like in the documentation or in the section 1443 where other third party dependencies already are mentioned and acknowledged. 1444 1445 As can be seen here: http://curl.haxx.se/docs/companies.html and elsewhere, 1446 more and more companies are discovering the power of libcurl and take 1447 advantage of it even in commercial environments. 1448 1449 14507. PHP/CURL Issues 1451 1452 7.1 What is PHP/CURL? 1453 1454 The module for PHP that makes it possible for PHP programs to access curl- 1455 functions from within PHP. 1456 1457 In the cURL project we call this module PHP/CURL to differentiate it from 1458 curl the command line tool and libcurl the library. The PHP team however 1459 does not refer to it like this (for unknown reasons). They call it plain 1460 CURL (often using all caps) or sometimes ext/curl, but both cause much 1461 confusion to users which in turn gives us a higher question load. 1462 1463 7.2 Who wrote PHP/CURL? 1464 1465 PHP/CURL is a module that comes with the regular PHP package. It depends and 1466 uses libcurl, so you need to have libcurl installed properly first before 1467 PHP/CURL can be used. PHP/CURL was initially written by Sterling Hughes. 1468 1469 7.3 Can I perform multiple requests using the same handle? 1470 1471 Yes - at least in PHP version 4.3.8 and later (this has been known to not 1472 work in earlier versions, but the exact version when it started to work is 1473 unknown to me). 1474 1475 After a transfer, you just set new options in the handle and make another 1476 transfer. This will make libcurl to re-use the same connection if it can. 1477