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 1.15 How do I port libcurl to my OS? 25 26 2. Install Related Problems 27 2.1 configure doesn't find OpenSSL even when it is installed 28 2.1.1 native linker doesn't find OpenSSL 29 2.1.2 only the libssl lib is missing 30 2.2 Does curl work/build with other SSL libraries? 31 2.3 Where can I find a copy of LIBEAY32.DLL? 32 2.4 Does curl support SOCKS (RFC 1928) ? 33 34 3. Usage Problems 35 3.1 curl: (1) SSL is disabled, https: not supported 36 3.2 How do I tell curl to resume a transfer? 37 3.3 Why doesn't my posting using -F work? 38 3.4 How do I tell curl to run custom FTP commands? 39 3.5 How can I disable the Accept: */* header? 40 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 41 3.7 Can I use curl to delete/rename a file through FTP? 42 3.8 How do I tell curl to follow HTTP redirects? 43 3.9 How do I use curl in my favorite programming language? 44 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 45 3.11 How do I POST with a different Content-Type? 46 3.12 Why do FTP-specific features over HTTP proxy fail? 47 3.13 Why do my single/double quotes fail? 48 3.14 Does curl support Javascript or PAC (automated proxy config)? 49 3.15 Can I do recursive fetches with curl? 50 3.16 What certificates do I need when I use SSL? 51 3.17 How do I list the root dir of an FTP server? 52 3.18 Can I use curl to send a POST/PUT and not wait for a response? 53 3.19 How do I get HTTP from a host using a specific IP address? 54 3.20 How to SFTP from my user's home directory? 55 3.21 Protocol xxx not supported or disabled in libcurl 56 3.22 curl -X gives me HTTP problems 57 58 4. Running Problems 59 4.1 Problems connecting to SSL servers. 60 4.2 Why do I get problems when I use & or % in the URL? 61 4.3 How can I use {, }, [ or ] to specify multiple URLs? 62 4.4 Why do I get downloaded data even though the web page doesn't exist? 63 4.5 Why do I get return code XXX from a HTTP server? 64 4.5.1 "400 Bad Request" 65 4.5.2 "401 Unauthorized" 66 4.5.3 "403 Forbidden" 67 4.5.4 "404 Not Found" 68 4.5.5 "405 Method Not Allowed" 69 4.5.6 "301 Moved Permanently" 70 4.6 Can you tell me what error code 142 means? 71 4.7 How do I keep user names and passwords secret in Curl command lines? 72 4.8 I found a bug! 73 4.9 Curl can't authenticate to the server that requires NTLM? 74 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work! 75 4.11 Why do my HTTP range requests return the full document? 76 4.12 Why do I get "certificate verify failed" ? 77 4.13 Why is curl -R on Windows one hour off? 78 4.14 Redirects work in browser but not with curl! 79 4.15 FTPS doesn't work 80 4.16 My HTTP POST or PUT requests are slow! 81 4.17 Non-functional connect timeouts on Windows 82 4.18 file:// URLs containing drive letters (Windows, NetWare) 83 4.19 Why doesn't curl return an error when the network cable is unplugged? 84 4.20 curl doesn't return error for HTTP non-200 responses! 85 4.21 Why is there a HTTP/1.1 in my HTTP/2 request? 86 87 5. libcurl Issues 88 5.1 Is libcurl thread-safe? 89 5.2 How can I receive all data into a large memory chunk? 90 5.3 How do I fetch multiple files with libcurl? 91 5.4 Does libcurl do Winsock initing on win32 systems? 92 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ? 93 5.6 What about Keep-Alive or persistent connections? 94 5.7 Link errors when building libcurl on Windows! 95 5.8 libcurl.so.X: open failed: No such file or directory 96 5.9 How does libcurl resolve host names? 97 5.10 How do I prevent libcurl from writing the response to stdout? 98 5.11 How do I make libcurl not receive the whole HTTP response? 99 5.12 Can I make libcurl fake or hide my real IP address? 100 5.13 How do I stop an ongoing transfer? 101 5.14 Using C++ non-static functions for callbacks? 102 5.15 How do I get an FTP directory listing? 103 5.16 I want a different time-out! 104 5.17 Can I write a server with libcurl? 105 5.18 Does libcurl use threads? 106 107 6. License Issues 108 6.1 I have a GPL program, can I use the libcurl library? 109 6.2 I have a closed-source program, can I use the libcurl library? 110 6.3 I have a BSD licensed program, can I use the libcurl library? 111 6.4 I have a program that uses LGPL libraries, can I use libcurl? 112 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 113 6.6 Can you please change the curl/libcurl license to XXXX? 114 6.7 What are my obligations when using libcurl in my commercial apps? 115 116 7. PHP/CURL Issues 117 7.1 What is PHP/CURL? 118 7.2 Who wrote PHP/CURL? 119 7.3 Can I perform multiple requests using the same handle? 120 7.4 Does PHP/CURL have dependencies? 121 122============================================================================== 123 1241. Philosophy 125 126 1.1 What is cURL? 127 128 cURL is the name of the project. The name is a play on 'Client for URLs', 129 originally with URL spelled in uppercase to make it obvious it deals with 130 URLs. The fact it can also be pronounced 'see URL' also helped, it works as 131 an abbreviation for "Client URL Request Library" or why not the recursive 132 version: "Curl URL Request Library". 133 134 The cURL project produces two products: 135 136 libcurl 137 138 A free and easy-to-use client-side URL transfer library, supporting DICT, 139 FILE, FTP, FTPS, GOPHER, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, POP3, 140 POP3S, RTMP, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET and TFTP. 141 142 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, 143 Kerberos, SPNEGO, HTTP form based upload, proxies, cookies, user+password 144 authentication, file transfer resume, http proxy tunneling and more! 145 146 libcurl is highly portable, it builds and works identically on numerous 147 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HP-UX, 148 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, BeOS, Mac 149 OS X, Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF, 150 Android, Minix, IBM TPF and more... 151 152 libcurl is free, thread-safe, IPv6 compatible, feature rich, well 153 supported and fast. 154 155 curl 156 157 A command line tool for getting or sending files using URL syntax. 158 159 Since curl uses libcurl, curl supports the same wide range of common 160 Internet protocols that libcurl does. 161 162 We pronounce curl with an initial k sound. It rhymes with words like girl 163 and earl. This is a short WAV file to help you: 164 165 https://media.merriam-webster.com/soundc11/c/curl0001.wav 166 167 There are numerous sub-projects and related projects that also use the word 168 curl in the project names in various combinations, but you should take 169 notice that this FAQ is directed at the command-line tool named curl (and 170 libcurl the library), and may therefore not be valid for other curl-related 171 projects. (There is however a small section for the PHP/CURL in this FAQ.) 172 173 1.2 What is libcurl? 174 175 libcurl is a reliable and portable library which provides you with an easy 176 interface to a range of common Internet protocols. 177 178 You can use libcurl for free in your application, be it open source, 179 commercial or closed-source. 180 181 libcurl is most probably the most portable, most powerful and most often 182 used C-based multi-platform file transfer library on this planet - be it 183 open source or commercial. 184 185 1.3 What is curl not? 186 187 Curl is not a wget clone. That is a common misconception. Never, during 188 curl's development, have we intended curl to replace wget or compete on its 189 market. Curl is targeted at single-shot file transfers. 190 191 Curl is not a web site mirroring program. If you want to use curl to mirror 192 something: fine, go ahead and write a script that wraps around curl to make 193 it reality (like curlmirror.pl does). 194 195 Curl is not an FTP site mirroring program. Sure, get and send FTP with curl 196 but if you want systematic and sequential behavior you should write a 197 script (or write a new program that interfaces libcurl) and do it. 198 199 Curl is not a PHP tool, even though it works perfectly well when used from 200 or with PHP (when using the PHP/CURL module). 201 202 Curl is not a program for a single operating system. Curl exists, compiles, 203 builds and runs under a wide range of operating systems, including all 204 modern Unixes (and a bunch of older ones too), Windows, Amiga, BeOS, OS/2, 205 OS X, QNX etc. 206 207 1.4 When will you make curl do XXXX ? 208 209 We love suggestions of what to change in order to make curl and libcurl 210 better. We do however believe in a few rules when it comes to the future of 211 curl: 212 213 Curl -- the command line tool -- is to remain a non-graphical command line 214 tool. If you want GUIs or fancy scripting capabilities, you should look for 215 another tool that uses libcurl. 216 217 We do not add things to curl that other small and available tools already do 218 very well at the side. Curl's output can be piped into another program or 219 redirected to another file for the next program to interpret. 220 221 We focus on protocol related issues and improvements. If you want to do more 222 magic with the supported protocols than curl currently does, chances are good 223 we will agree. If you want to add more protocols, we may very well agree. 224 225 If you want someone else to do all the work while you wait for us to 226 implement it for you, that is not a very friendly attitude. We spend a 227 considerable time already on maintaining and developing curl. In order to 228 get more out of us, you should consider trading in some of your time and 229 effort in return. Simply go to the GitHub repo which resides at 230 https://github.com/curl/curl, fork the project, and create pull requests 231 with your proposed changes. 232 233 If you write the code, chances are better that it will get into curl faster. 234 235 1.5 Who makes curl? 236 237 curl and libcurl are not made by any single individual. Daniel Stenberg is 238 project leader and main developer, but other persons' submissions are 239 important and crucial. Anyone can contribute and post their changes and 240 improvements and have them inserted in the main sources (of course on the 241 condition that developers agree that the fixes are good). 242 243 The full list of all contributors is found in the docs/THANKS file. 244 245 curl is developed by a community, with Daniel at the wheel. 246 247 1.6 What do you get for making curl? 248 249 Project cURL is entirely free and open. No person gets paid for developing 250 curl full time. We do this voluntarily, mostly in our spare time. 251 Occasionally companies pay individual developers to work on curl, but that's 252 up to each company and developer. This is not controlled by nor supervised in 253 any way by the project. 254 255 We still get help from companies. Haxx provides web site, bandwidth, mailing 256 lists etc, GitHub hosts the primary git repository and other services like 257 the bug tracker at https://github.com/curl/curl. Also again, some companies 258 have sponsored certain parts of the development in the past and I hope some 259 will continue to do so in the future. 260 261 If you want to support our project, consider a donation or a banner-program 262 or even better: by helping us with coding, documenting or testing etc. 263 264 1.7 What about CURL from curl.com? 265 266 During the summer of 2001, curl.com was busy advertising their client-side 267 programming language for the web, named CURL. 268 269 We are in no way associated with curl.com or their CURL programming 270 language. 271 272 Our project name curl has been in effective use since 1998. We were not the 273 first computer related project to use the name "curl" and do not claim any 274 rights to the name. 275 276 We recognize that we will be living in parallel with curl.com and wish them 277 every success. 278 279 1.8 I have a problem whom do I mail? 280 281 Please do not mail any single individual unless you really need to. Keep 282 curl-related questions on a suitable mailing list. All available mailing 283 lists are listed in the MANUAL document and online at 284 https://curl.haxx.se/mail/ 285 286 Keeping curl-related questions and discussions on mailing lists allows 287 others to join in and help, to share their ideas, to contribute their 288 suggestions and to spread their wisdom. Keeping discussions on public mailing 289 lists also allows for others to learn from this (both current and future 290 users thanks to the web based archives of the mailing lists), thus saving us 291 from having to repeat ourselves even more. Thanks for respecting this. 292 293 If you have found or simply suspect a security problem in curl or libcurl, 294 mail curl-security at haxx.se (closed list of receivers, mails are not 295 disclosed) and tell. Then we can produce a fix in a timely manner before the 296 flaw is announced to the world, thus lessen the impact the problem will have 297 on existing users. 298 299 1.9 Where do I buy commercial support for curl? 300 301 curl is fully open source. It means you can hire any skilled engineer to fix 302 your curl-related problems. 303 304 We list available alternatives on the curl web site: 305 https://curl.haxx.se/support.html 306 307 1.10 How many are using curl? 308 309 It is impossible to tell. 310 311 We don't know how many users that knowingly have installed and use curl. 312 313 We don't know how many users that use curl without knowing that they are in 314 fact using it. 315 316 We don't know how many users that downloaded or installed curl and then 317 never use it. 318 319 In May 2012 Daniel did a counting game and came up with a number that may 320 be completely wrong or somewhat accurate. Over 500 million! 321 322 See https://daniel.haxx.se/blog/2012/05/16/300m-users/ 323 324 1.11 Why don't you update ca-bundle.crt 325 326 The ca cert bundle that used to be shipped with curl was very outdated and 327 must be replaced with an up-to-date version by anyone who wants to verify 328 peers. It is no longer provided by curl. The last curl release that ever 329 shipped a ca cert bundle was curl 7.18.0. 330 331 In the cURL project we've decided not to attempt to keep this file updated 332 (or even present anymore) since deciding what to add to a ca cert bundle is 333 an undertaking we've not been ready to accept, and the one we can get from 334 Mozilla is perfectly fine so there's no need to duplicate that work. 335 336 Today, with many services performed over HTTPS, every operating system 337 should come with a default ca cert bundle that can be deemed somewhat 338 trustworthy and that collection (if reasonably updated) should be deemed to 339 be a lot better than a private curl version. 340 341 If you want the most recent collection of ca certs that Mozilla Firefox 342 uses, we recommend that you extract the collection yourself from Mozilla 343 Firefox (by running 'make ca-bundle), or by using our online service setup 344 for this purpose: https://curl.haxx.se/docs/caextract.html 345 346 1.12 I have a problem who can I chat with? 347 348 There's a bunch of friendly people hanging out in the #curl channel on the 349 IRC network irc.freenode.net. If you're polite and nice, chances are good 350 that you can get -- or provide -- help instantly. 351 352 1.13 curl's ECCN number? 353 354 The US government restricts exports of software that contains or uses 355 cryptography. When doing so, the Export Control Classification Number (ECCN) 356 is used to identify the level of export control etc. 357 358 Apache Software Foundation gives a good explanation of ECCNs at 359 https://www.apache.org/dev/crypto.html 360 361 We believe curl's number might be ECCN 5D002, another possibility is 362 5D992. It seems necessary to write them (the authority that administers ECCN 363 numbers), asking to confirm. 364 365 Comprehensible explanations of the meaning of such numbers and how to obtain 366 them (resp.) are here 367 368 https://www.bis.doc.gov/licensing/exportingbasics.htm 369 https://www.bis.doc.gov/licensing/do_i_needaneccn.html 370 371 An incomprehensible description of the two numbers above is here 372 https://www.bis.doc.gov/index.php/documents/new-encryption/1653-ccl5-pt2-3 373 374 1.14 How do I submit my patch? 375 376 When you have made a patch or a change of whatever sort, and want to submit 377 that to the project, there are a few different ways we prefer: 378 379 o send a patch to the curl-library mailing list. We're many subscribers 380 there and there are lots of people who can review patches, comment on them 381 and "receive" them properly. 382 383 o if your patch changes or fixes a bug, you can also opt to submit a bug 384 report in the bug tracker and attach your patch there. There are less 385 people involved there. 386 387 Lots of more details are found in the CONTRIBUTE and INTERNALS docs. 388 389 1.15 How do I port libcurl to my OS? 390 391 Here's a rough step-by-step: 392 393 1. copy a suitable lib/config-*.h file as a start to lib/config-[youros].h 394 395 2. edit lib/config-[youros].h to match your OS and setup 396 397 3. edit lib/curl_setup.h to include config-[youros].h when your OS is 398 detected by the preprocessor, in the style others already exist 399 400 4. compile lib/*.c and make them into a library 401 402 4032. Install Related Problems 404 405 2.1 configure doesn't find OpenSSL even when it is installed 406 407 This may be because of several reasons. 408 409 2.1.1 native linker doesn't find openssl 410 411 Affected platforms: 412 Solaris (native cc compiler) 413 HPUX (native cc compiler) 414 SGI IRIX (native cc compiler) 415 SCO UNIX (native cc compiler) 416 417 When configuring curl, I specify --with-ssl. OpenSSL is installed in 418 /usr/local/ssl Configure reports SSL in /usr/local/ssl, but fails to find 419 CRYPTO_lock in -lcrypto 420 421 Cause: The cc for this test places the -L/usr/local/ssl/lib AFTER 422 -lcrypto, so ld can't find the library. This is due to a bug in the GNU 423 autoconf tool. 424 425 Workaround: Specifying "LDFLAGS=-L/usr/local/ssl/lib" in front of 426 ./configure places the -L/usr/local/ssl/lib early enough in the command 427 line to make things work 428 429 2.1.2 only the libssl lib is missing 430 431 If all include files and the libcrypto lib is present, with only the 432 libssl being missing according to configure, this is most likely because 433 a few functions are left out from the libssl. 434 435 If the function names missing include RSA or RSAREF you can be certain 436 that this is because libssl requires the RSA and RSAREF libs to build. 437 438 See the INSTALL file section that explains how to add those libs to 439 configure. Make sure that you remove the config.cache file before you 440 rerun configure with the new flags. 441 442 2.2 Does curl work/build with other SSL libraries? 443 444 Curl has been written to use a generic SSL function layer internally, and 445 that SSL functionality can then be provided by one out of many different SSL 446 backends. 447 448 curl can be built to use one of the following SSL alternatives: OpenSSL, 449 libressl, BoringSSL, GnuTLS, wolfSSL, NSS, mbedTLS, MesaLink, Secure 450 Transport (native iOS/OS X), Schannel (native Windows) or GSKit (native IBM 451 i). They all have their pros and cons, and we try to maintain a comparison 452 of them here: https://curl.haxx.se/docs/ssl-compared.html 453 454 2.3 Where can I find a copy of LIBEAY32.DLL? 455 456 That is an OpenSSL binary built for Windows. 457 458 Curl can be built with OpenSSL to do the SSL stuff. The LIBEAY32.DLL is then 459 what curl needs on a windows machine to do https:// etc. Check out the curl 460 web site to find accurate and up-to-date pointers to recent OpenSSL DLLs and 461 other binary packages. 462 463 2.4 Does curl support SOCKS (RFC 1928) ? 464 465 Yes, SOCKS 4 and 5 are supported. 466 467 4683. Usage problems 469 470 3.1 curl: (1) SSL is disabled, https: not supported 471 472 If you get this output when trying to get anything from a https:// server, 473 it means that the instance of curl/libcurl that you're using was built 474 without support for this protocol. 475 476 This could've happened if the configure script that was run at build time 477 couldn't find all libs and include files curl requires for SSL to work. If 478 the configure script fails to find them, curl is simply built without SSL 479 support. 480 481 To get the https:// support into a curl that was previously built but that 482 reports that https:// is not supported, you should dig through the document 483 and logs and check out why the configure script doesn't find the SSL libs 484 and/or include files. 485 486 Also, check out the other paragraph in this FAQ labeled "configure doesn't 487 find OpenSSL even when it is installed". 488 489 3.2 How do I tell curl to resume a transfer? 490 491 Curl supports resumed transfers both ways on both FTP and HTTP. 492 Try the -C option. 493 494 3.3 Why doesn't my posting using -F work? 495 496 You can't arbitrarily use -F or -d, the choice between -F or -d depends on the 497 HTTP operation you need curl to do and what the web server that will receive 498 your post expects. 499 500 If the form you're trying to submit uses the type 'multipart/form-data', then 501 and only then you must use the -F type. In all the most common cases, you 502 should use -d which then causes a posting with the type 503 'application/x-www-form-urlencoded'. 504 505 This is described in some detail in the MANUAL and TheArtOfHttpScripting 506 documents, and if you don't understand it the first time, read it again 507 before you post questions about this to the mailing list. Also, try reading 508 through the mailing list archives for old postings and questions regarding 509 this. 510 511 3.4 How do I tell curl to run custom FTP commands? 512 513 You can tell curl to perform optional commands both before and/or after a 514 file transfer. Study the -Q/--quote option. 515 516 Since curl is used for file transfers, you don't normally use curl to 517 perform FTP commands without transferring anything. Therefore you must 518 always specify a URL to transfer to/from even when doing custom FTP 519 commands, or use -I which implies the "no body" option sent to libcurl. 520 521 3.5 How can I disable the Accept: */* header? 522 523 You can change all internally generated headers by adding a replacement with 524 the -H/--header option. By adding a header with empty contents you safely 525 disable that one. Use -H "Accept:" to disable that specific header. 526 527 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 528 529 To curl, all contents are alike. It doesn't matter how the page was 530 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain HTML 531 files. There's no difference to curl and it doesn't even know what kind of 532 language that generated the page. 533 534 See also item 3.14 regarding javascript. 535 536 3.7 Can I use curl to delete/rename a file through FTP? 537 538 Yes. You specify custom FTP commands with -Q/--quote. 539 540 One example would be to delete a file after you have downloaded it: 541 542 curl -O ftp://download.com/coolfile -Q '-DELE coolfile' 543 544 or rename a file after upload: 545 546 curl -T infile ftp://upload.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname" 547 548 3.8 How do I tell curl to follow HTTP redirects? 549 550 Curl does not follow so-called redirects by default. The Location: header 551 that informs the client about this is only interpreted if you're using the 552 -L/--location option. As in: 553 554 curl -L http://redirector.com 555 556 Not all redirects are HTTP ones, see 4.14 557 558 3.9 How do I use curl in my favorite programming language? 559 560 Many programming languages have interfaces/bindings that allow you to use 561 curl without having to use the command line tool. If you are fluent in such 562 a language, you may prefer to use one of these interfaces instead. 563 564 Find out more about which languages that support curl directly, and how to 565 install and use them, in the libcurl section of the curl web site: 566 https://curl.haxx.se/libcurl/ 567 568 All the various bindings to libcurl are made by other projects and people, 569 outside of the cURL project. The cURL project itself only produces libcurl 570 with its plain C API. If you don't find anywhere else to ask you can ask 571 about bindings on the curl-library list too, but be prepared that people on 572 that list may not know anything about bindings. 573 574 In February 2019, there were interfaces available for the following 575 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Delphi, Dylan, Eiffel, 576 Euphoria, Falcon, Ferite, Gambas, glib/GTK+, Go, Guile, Harbour, Haskell, 577 Java, Julia, Lisp, Lua, Mono, .NET, node.js, Object-Pascal, OCaml, Pascal, 578 Perl, PHP, PostgreSQL, Python, R, Rexx, Ring, RPG, Ruby, Rust, Scheme, 579 Scilab, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro, 580 Q, wxwidgets, XBLite and Xoho. By the time you read this, additional ones 581 may have appeared! 582 583 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 584 585 Curl adheres to the HTTP spec, which basically means you can play with *any* 586 protocol that is built on top of HTTP. Protocols such as SOAP, WEBDAV and 587 XML-RPC are all such ones. You can use -X to set custom requests and -H to 588 set custom headers (or replace internally generated ones). 589 590 Using libcurl is of course just as good and you'd just use the proper 591 library options to do the same. 592 593 3.11 How do I POST with a different Content-Type? 594 595 You can always replace the internally generated headers with -H/--header. 596 To make a simple HTTP POST with text/xml as content-type, do something like: 597 598 curl -d "datatopost" -H "Content-Type: text/xml" [URL] 599 600 3.12 Why do FTP-specific features over HTTP proxy fail? 601 602 Because when you use a HTTP proxy, the protocol spoken on the network will 603 be HTTP, even if you specify a FTP URL. This effectively means that you 604 normally can't use FTP-specific features such as FTP upload and FTP quote 605 etc. 606 607 There is one exception to this rule, and that is if you can "tunnel through" 608 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p) 609 and is generally not available as proxy admins usually disable tunneling to 610 ports other than 443 (which is used for HTTPS access through proxies). 611 612 3.13 Why do my single/double quotes fail? 613 614 To specify a command line option that includes spaces, you might need to 615 put the entire option within quotes. Like in: 616 617 curl -d " with spaces " url.com 618 619 or perhaps 620 621 curl -d ' with spaces ' url.com 622 623 Exactly what kind of quotes and how to do this is entirely up to the shell 624 or command line interpreter that you are using. For most unix shells, you 625 can more or less pick either single (') or double (") quotes. For 626 Windows/DOS prompts I believe you're forced to use double (") quotes. 627 628 Please study the documentation for your particular environment. Examples in 629 the curl docs will use a mix of both of these as shown above. You must 630 adjust them to work in your environment. 631 632 Remember that curl works and runs on more operating systems than most single 633 individuals have ever tried. 634 635 3.14 Does curl support Javascript or PAC (automated proxy config)? 636 637 Many web pages do magic stuff using embedded Javascript. Curl and libcurl 638 have no built-in support for that, so it will be treated just like any other 639 contents. 640 641 .pac files are a netscape invention and are sometimes used by organizations 642 to allow them to differentiate which proxies to use. The .pac contents is 643 just a Javascript program that gets invoked by the browser and that returns 644 the name of the proxy to connect to. Since curl doesn't support Javascript, 645 it can't support .pac proxy configuration either. 646 647 Some workarounds usually suggested to overcome this Javascript dependency: 648 649 Depending on the Javascript complexity, write up a script that translates it 650 to another language and execute that. 651 652 Read the Javascript code and rewrite the same logic in another language. 653 654 Implement a Javascript interpreter, people have successfully used the 655 Mozilla Javascript engine in the past. 656 657 Ask your admins to stop this, for a static proxy setup or similar. 658 659 3.15 Can I do recursive fetches with curl? 660 661 No. curl itself has no code that performs recursive operations, such as 662 those performed by wget and similar tools. 663 664 There exists wrapper scripts with that functionality (for example the 665 curlmirror perl script), and you can write programs based on libcurl to do 666 it, but the command line tool curl itself cannot. 667 668 3.16 What certificates do I need when I use SSL? 669 670 There are three different kinds of "certificates" to keep track of when we 671 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl. 672 673 CLIENT CERTIFICATE 674 675 The server you communicate with may require that you can provide this in 676 order to prove that you actually are who you claim to be. If the server 677 doesn't require this, you don't need a client certificate. 678 679 A client certificate is always used together with a private key, and the 680 private key has a pass phrase that protects it. 681 682 SERVER CERTIFICATE 683 684 The server you communicate with has a server certificate. You can and should 685 verify this certificate to make sure that you are truly talking to the real 686 server and not a server impersonating it. 687 688 CERTIFICATE AUTHORITY CERTIFICATE ("CA cert") 689 690 You often have several CA certs in a CA cert bundle that can be used to 691 verify a server certificate that was signed by one of the authorities in the 692 bundle. curl does not come with a CA cert bundle but most curl installs 693 provide one. You can also override the default. 694 695 The server certificate verification process is made by using a Certificate 696 Authority certificate ("CA cert") that was used to sign the server 697 certificate. Server certificate verification is enabled by default in curl 698 and libcurl and is often the reason for problems as explained in FAQ entry 699 4.12 and the SSLCERTS document 700 (https://curl.haxx.se/docs/sslcerts.html). Server certificates that are 701 "self-signed" or otherwise signed by a CA that you do not have a CA cert 702 for, cannot be verified. If the verification during a connect fails, you are 703 refused access. You then need to explicitly disable the verification to 704 connect to the server. 705 706 3.17 How do I list the root dir of an FTP server? 707 708 There are two ways. The way defined in the RFC is to use an encoded slash 709 in the first path part. List the "/tmp" dir like this: 710 711 curl ftp://ftp.sunet.se/%2ftmp/ 712 713 or the not-quite-kosher-but-more-readable way, by simply starting the path 714 section of the URL with a slash: 715 716 curl ftp://ftp.sunet.se//tmp/ 717 718 3.18 Can I use curl to send a POST/PUT and not wait for a response? 719 720 No. 721 722 But you could easily write your own program using libcurl to do such stunts. 723 724 3.19 How do I get HTTP from a host using a specific IP address? 725 726 For example, you may be trying out a web site installation that isn't yet in 727 the DNS. Or you have a site using multiple IP addresses for a given host 728 name and you want to address a specific one out of the set. 729 730 Set a custom Host: header that identifies the server name you want to reach 731 but use the target IP address in the URL: 732 733 curl --header "Host: www.example.com" http://127.0.0.1/ 734 735 You can also opt to add faked host name entries to curl with the --resolve 736 option. That has the added benefit that things like redirects will also work 737 properly. The above operation would instead be done as: 738 739 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/ 740 741 3.20 How to SFTP from my user's home directory? 742 743 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to 744 work with. It means that if you don't specify that you want the user's home 745 directory, you get the actual root directory. 746 747 To specify a file in your user's home directory, you need to use the correct 748 URL syntax which for SFTP might look similar to: 749 750 curl -O -u user:password sftp://example.com/~/file.txt 751 752 and for SCP it is just a different protocol prefix: 753 754 curl -O -u user:password scp://example.com/~/file.txt 755 756 3.21 Protocol xxx not supported or disabled in libcurl 757 758 When passing on a URL to curl to use, it may respond that the particular 759 protocol is not supported or disabled. The particular way this error message 760 is phrased is because curl doesn't make a distinction internally of whether 761 a particular protocol is not supported (i.e. never got any code added that 762 knows how to speak that protocol) or if it was explicitly disabled. curl can 763 be built to only support a given set of protocols, and the rest would then 764 be disabled or not supported. 765 766 Note that this error will also occur if you pass a wrongly spelled protocol 767 part as in "htpt://example.com" or as in the less evident case if you prefix 768 the protocol part with a space as in " http://example.com/". 769 770 3.22 curl -X gives me HTTP problems 771 772 In normal circumstances, -X should hardly ever be used. 773 774 By default you use curl without explicitly saying which request method to 775 use when the URL identifies a HTTP transfer. If you just pass in a URL like 776 "curl http://example.com" it will use GET. If you use -d or -F curl will use 777 POST, -I will cause a HEAD and -T will make it a PUT. 778 779 If for whatever reason you're not happy with these default choices that curl 780 does for you, you can override those request methods by specifying -X 781 [WHATEVER]. This way you can for example send a DELETE by doing "curl -X 782 DELETE [URL]". 783 784 It is thus pointless to do "curl -XGET [URL]" as GET would be used 785 anyway. In the same vein it is pointless to do "curl -X POST -d data 786 [URL]"... But you can make a fun and somewhat rare request that sends a 787 request-body in a GET request with something like "curl -X GET -d data 788 [URL]" 789 790 Note that -X doesn't actually change curl's behavior as it only modifies the 791 actual string sent in the request, but that may of course trigger a 792 different set of events. 793 794 Accordingly, by using -XPOST on a command line that for example would follow 795 a 303 redirect, you will effectively prevent curl from behaving 796 correctly. Be aware. 797 798 7994. Running Problems 800 801 4.1 Problems connecting to SSL servers. 802 803 It took a very long time before we could sort out why curl had problems to 804 connect to certain SSL servers when using SSLeay or OpenSSL v0.9+. The 805 error sometimes showed up similar to: 806 807 16570:error:1407D071:SSL routines:SSL2_READ:bad mac decode:s2_pkt.c:233: 808 809 It turned out to be because many older SSL servers don't deal with SSLv3 810 requests properly. To correct this problem, tell curl to select SSLv2 from 811 the command line (-2/--sslv2). 812 813 There have also been examples where the remote server didn't like the SSLv2 814 request and instead you had to force curl to use SSLv3 with -3/--sslv3. 815 816 4.2 Why do I get problems when I use & or % in the URL? 817 818 In general unix shells, the & symbol is treated specially and when used, it 819 runs the specified command in the background. To safely send the & as a part 820 of a URL, you should quote the entire URL by using single (') or double (") 821 quotes around it. Similar problems can also occur on some shells with other 822 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL. 823 824 An example that would invoke a remote CGI that uses &-symbols could be: 825 826 curl 'http://www.altavista.com/cgi-bin/query?text=yes&q=curl' 827 828 In Windows, the standard DOS shell treats the percent sign specially and you 829 need to use TWO percent signs for each single one you want to use in the 830 URL. 831 832 If you want a literal percent sign to be part of the data you pass in a POST 833 using -d/--data you must encode it as '%25' (which then also needs the 834 percent sign doubled on Windows machines). 835 836 4.3 How can I use {, }, [ or ] to specify multiple URLs? 837 838 Because those letters have a special meaning to the shell, to be used in 839 a URL specified to curl you must quote them. 840 841 An example that downloads two URLs (sequentially) would be: 842 843 curl '{curl,www}.haxx.se' 844 845 To be able to use those characters as actual parts of the URL (without using 846 them for the curl URL "globbing" system), use the -g/--globoff option: 847 848 curl -g 'www.site.com/weirdname[].html' 849 850 4.4 Why do I get downloaded data even though the web page doesn't exist? 851 852 Curl asks remote servers for the page you specify. If the page doesn't exist 853 at the server, the HTTP protocol defines how the server should respond and 854 that means that headers and a "page" will be returned. That's simply how 855 HTTP works. 856 857 By using the --fail option you can tell curl explicitly to not get any data 858 if the HTTP return code doesn't say success. 859 860 4.5 Why do I get return code XXX from a HTTP server? 861 862 RFC2616 clearly explains the return codes. This is a short transcript. Go 863 read the RFC for exact details: 864 865 4.5.1 "400 Bad Request" 866 867 The request could not be understood by the server due to malformed 868 syntax. The client SHOULD NOT repeat the request without modifications. 869 870 4.5.2 "401 Unauthorized" 871 872 The request requires user authentication. 873 874 4.5.3 "403 Forbidden" 875 876 The server understood the request, but is refusing to fulfill it. 877 Authorization will not help and the request SHOULD NOT be repeated. 878 879 4.5.4 "404 Not Found" 880 881 The server has not found anything matching the Request-URI. No indication 882 is given of whether the condition is temporary or permanent. 883 884 4.5.5 "405 Method Not Allowed" 885 886 The method specified in the Request-Line is not allowed for the resource 887 identified by the Request-URI. The response MUST include an Allow header 888 containing a list of valid methods for the requested resource. 889 890 4.5.6 "301 Moved Permanently" 891 892 If you get this return code and an HTML output similar to this: 893 894 <H1>Moved Permanently</H1> The document has moved <A 895 HREF="http://same_url_now_with_a_trailing_slash/">here</A>. 896 897 it might be because you requested a directory URL but without the trailing 898 slash. Try the same operation again _with_ the trailing URL, or use the 899 -L/--location option to follow the redirection. 900 901 4.6 Can you tell me what error code 142 means? 902 903 All curl error codes are described at the end of the man page, in the 904 section called "EXIT CODES". 905 906 Error codes that are larger than the highest documented error code means 907 that curl has exited due to a crash. This is a serious error, and we 908 appreciate a detailed bug report from you that describes how we could go 909 ahead and repeat this! 910 911 4.7 How do I keep user names and passwords secret in Curl command lines? 912 913 This problem has two sides: 914 915 The first part is to avoid having clear-text passwords in the command line 916 so that they don't appear in 'ps' outputs and similar. That is easily 917 avoided by using the "-K" option to tell curl to read parameters from a file 918 or stdin to which you can pass the secret info. curl itself will also 919 attempt to "hide" the given password by blanking out the option - this 920 doesn't work on all platforms. 921 922 To keep the passwords in your account secret from the rest of the world is 923 not a task that curl addresses. You could of course encrypt them somehow to 924 at least hide them from being read by human eyes, but that is not what 925 anyone would call security. 926 927 Also note that regular HTTP (using Basic authentication) and FTP passwords 928 are sent as cleartext across the network. All it takes for anyone to fetch 929 them is to listen on the network. Eavesdropping is very easy. Use more secure 930 authentication methods (like Digest, Negotiate or even NTLM) or consider the 931 SSL-based alternatives HTTPS and FTPS. 932 933 4.8 I found a bug! 934 935 It is not a bug if the behavior is documented. Read the docs first. 936 Especially check out the KNOWN_BUGS file, it may be a documented bug! 937 938 If it is a problem with a binary you've downloaded or a package for your 939 particular platform, try contacting the person who built the package/archive 940 you have. 941 942 If there is a bug, read the BUGS document first. Then report it as described 943 in there. 944 945 4.9 Curl can't authenticate to the server that requires NTLM? 946 947 NTLM support requires OpenSSL, GnuTLS, mbedTLS, NSS, Secure Transport, or 948 Microsoft Windows libraries at build-time to provide this functionality. 949 950 NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You 951 should not use such ones. 952 953 4.10 My HTTP request using HEAD, PUT or DELETE doesn't work! 954 955 Many web servers allow or demand that the administrator configures the 956 server properly for these requests to work on the web server. 957 958 Some servers seem to support HEAD only on certain kinds of URLs. 959 960 To fully grasp this, try the documentation for the particular server 961 software you're trying to interact with. This is not anything curl can do 962 anything about. 963 964 4.11 Why do my HTTP range requests return the full document? 965 966 Because the range may not be supported by the server, or the server may 967 choose to ignore it and return the full document anyway. 968 969 4.12 Why do I get "certificate verify failed" ? 970 971 You invoke curl 7.10 or later to communicate on a https:// URL and get an 972 error back looking something similar to this: 973 974 curl: (35) SSL: error:14090086:SSL routines: 975 SSL3_GET_SERVER_CERTIFICATE:certificate verify failed 976 977 Then it means that curl couldn't verify that the server's certificate was 978 good. Curl verifies the certificate using the CA cert bundle that comes with 979 the curl installation. 980 981 To disable the verification (which makes it act like curl did before 7.10), 982 use -k. This does however enable man-in-the-middle attacks. 983 984 If you get this failure but are having a CA cert bundle installed and used, 985 the server's certificate is not signed by one of the CA's in the bundle. It 986 might for example be self-signed. You then correct this problem by obtaining 987 a valid CA cert for the server. Or again, decrease the security by disabling 988 this check. 989 990 Details are also in the SSLCERTS file in the release archives, found online 991 here: https://curl.haxx.se/docs/sslcerts.html 992 993 4.13 Why is curl -R on Windows one hour off? 994 995 Since curl 7.53.0 this issue should be fixed as long as curl was built with 996 any modern compiler that allows for a 64-bit curl_off_t type. For older 997 compilers or prior curl versions it may set a time that appears one hour off. 998 This happens due to a flaw in how Windows stores and uses file modification 999 times and it is not easily worked around. For more details read this: 1000 https://www.codeproject.com/Articles/1144/Beating-the-Daylight-Savings-Time-bug-and-getting 1001 1002 4.14 Redirects work in browser but not with curl! 1003 1004 curl supports HTTP redirects well (see item 3.8). Browsers generally support 1005 at least two other ways to perform redirects that curl does not: 1006 1007 Meta tags. You can write a HTML tag that will cause the browser to redirect 1008 to another given URL after a certain time. 1009 1010 Javascript. You can write a Javascript program embedded in a HTML page that 1011 redirects the browser to another given URL. 1012 1013 There is no way to make curl follow these redirects. You must either 1014 manually figure out what the page is set to do, or write a script that parses 1015 the results and fetches the new URL. 1016 1017 4.15 FTPS doesn't work 1018 1019 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit 1020 mode. 1021 1022 When a URL is used that starts with FTPS://, curl assumes implicit SSL on 1023 the control connection and will therefore immediately connect and try to 1024 speak SSL. FTPS:// connections default to port 990. 1025 1026 To use explicit FTPS, you use a FTP:// URL and the --ftp-ssl option (or one 1027 of its related flavors). This is the most common method, and the one 1028 mandated by RFC4217. This kind of connection will then of course use the 1029 standard FTP port 21 by default. 1030 1031 4.16 My HTTP POST or PUT requests are slow! 1032 1033 libcurl makes all POST and PUT requests (except for POST requests with a 1034 very tiny request body) use the "Expect: 100-continue" header. This header 1035 allows the server to deny the operation early so that libcurl can bail out 1036 before having to send any data. This is useful in authentication 1037 cases and others. 1038 1039 However, many servers don't implement the Expect: stuff properly and if the 1040 server doesn't respond (positively) within 1 second libcurl will continue 1041 and send off the data anyway. 1042 1043 You can disable libcurl's use of the Expect: header the same way you disable 1044 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0. 1045 1046 4.17 Non-functional connect timeouts 1047 1048 In most Windows setups having a timeout longer than 21 seconds make no 1049 difference, as it will only send 3 TCP SYN packets and no more. The second 1050 packet sent three seconds after the first and the third six seconds after 1051 the second. No more than three packets are sent, no matter how long the 1052 timeout is set. 1053 1054 See option TcpMaxConnectRetransmissions on this page: 1055 https://support.microsoft.com/en-us/kb/175523/en-us 1056 1057 Also, even on non-Windows systems there may run a firewall or anti-virus 1058 software or similar that accepts the connection but does not actually do 1059 anything else. This will make (lib)curl to consider the connection connected 1060 and thus the connect timeout won't trigger. 1061 1062 4.18 file:// URLs containing drive letters (Windows, NetWare) 1063 1064 When using curl to try to download a local file, one might use a URL 1065 in this format: 1066 1067 file://D:/blah.txt 1068 1069 You'll find that even if D:\blah.txt does exist, curl returns a 'file 1070 not found' error. 1071 1072 According to RFC 1738 (https://www.ietf.org/rfc/rfc1738.txt), 1073 file:// URLs must contain a host component, but it is ignored by 1074 most implementations. In the above example, 'D:' is treated as the 1075 host component, and is taken away. Thus, curl tries to open '/blah.txt'. 1076 If your system is installed to drive C:, that will resolve to 'C:\blah.txt', 1077 and if that doesn't exist you will get the not found error. 1078 1079 To fix this problem, use file:// URLs with *three* leading slashes: 1080 1081 file:///D:/blah.txt 1082 1083 Alternatively, if it makes more sense, specify 'localhost' as the host 1084 component: 1085 1086 file://localhost/D:/blah.txt 1087 1088 In either case, curl should now be looking for the correct file. 1089 1090 4.19 Why doesn't curl return an error when the network cable is unplugged? 1091 1092 Unplugging a cable is not an error situation. The TCP/IP protocol stack 1093 was designed to be fault tolerant, so even though there may be a physical 1094 break somewhere the connection shouldn't be affected, just possibly 1095 delayed. Eventually, the physical break will be fixed or the data will be 1096 re-routed around the physical problem through another path. 1097 1098 In such cases, the TCP/IP stack is responsible for detecting when the 1099 network connection is irrevocably lost. Since with some protocols it is 1100 perfectly legal for the client to wait indefinitely for data, the stack may 1101 never report a problem, and even when it does, it can take up to 20 minutes 1102 for it to detect an issue. The curl option --keepalive-time enables 1103 keep-alive support in the TCP/IP stack which makes it periodically probe the 1104 connection to make sure it is still available to send data. That should 1105 reliably detect any TCP/IP network failure. 1106 1107 But even that won't detect the network going down before the TCP/IP 1108 connection is established (e.g. during a DNS lookup) or using protocols that 1109 don't use TCP. To handle those situations, curl offers a number of timeouts 1110 on its own. --speed-limit/--speed-time will abort if the data transfer rate 1111 falls too low, and --connect-timeout and --max-time can be used to put an 1112 overall timeout on the connection phase or the entire transfer. 1113 1114 A libcurl-using application running in a known physical environment (e.g. 1115 an embedded device with only a single network connection) may want to act 1116 immediately if its lone network connection goes down. That can be achieved 1117 by having the application monitor the network connection on its own using an 1118 OS-specific mechanism, then signaling libcurl to abort (see also item 5.13). 1119 1120 4.20 curl doesn't return error for HTTP non-200 responses! 1121 1122 Correct. Unless you use -f (--fail). 1123 1124 When doing HTTP transfers, curl will perform exactly what you're asking it 1125 to do and if successful it will not return an error. You can use curl to 1126 test your web server's "file not found" page (that gets 404 back), you can 1127 use it to check your authentication protected web pages (that gets a 401 1128 back) and so on. 1129 1130 The specific HTTP response code does not constitute a problem or error for 1131 curl. It simply sends and delivers HTTP as you asked and if that worked, 1132 everything is fine and dandy. The response code is generally providing more 1133 higher level error information that curl doesn't care about. The error was 1134 not in the HTTP transfer. 1135 1136 If you want your command line to treat error codes in the 400 and up range 1137 as errors and thus return a non-zero value and possibly show an error 1138 message, curl has a dedicated option for that: -f (CURLOPT_FAILONERROR in 1139 libcurl speak). 1140 1141 You can also use the -w option and the variable %{response_code} to extract 1142 the exact response code that was returned in the response. 1143 1144 4.21 Why is there a HTTP/1.1 in my HTTP/2 request? 1145 1146 If you use verbose to see the HTTP request when you send off a HTTP/2 1147 request, it will still say 1.1. 1148 1149 The reason for this is that we first generate the request to send using the 1150 old 1.1 style and show that request in the verbose output, and then we 1151 convert it over to the binary header-compressed HTTP/2 style. The actual 1152 "1.1" part from that request is then not actually used in the transfer. 1153 The binary HTTP/2 headers are not human readable. 1154 11555. libcurl Issues 1156 1157 5.1 Is libcurl thread-safe? 1158 1159 Yes. 1160 1161 We have written the libcurl code specifically adjusted for multi-threaded 1162 programs. libcurl will use thread-safe functions instead of non-safe ones if 1163 your system has such. Note that you must never share the same handle in 1164 multiple threads. 1165 1166 There may be some exceptions to thread safety depending on how libcurl was 1167 built. Please review the guidelines for thread safety to learn more: 1168 https://curl.haxx.se/libcurl/c/threadsafe.html 1169 1170 5.2 How can I receive all data into a large memory chunk? 1171 1172 [ See also the examples/getinmemory.c source ] 1173 1174 You are in full control of the callback function that gets called every time 1175 there is data received from the remote server. You can make that callback do 1176 whatever you want. You do not have to write the received data to a file. 1177 1178 One solution to this problem could be to have a pointer to a struct that you 1179 pass to the callback function. You set the pointer using the 1180 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback 1181 instead of a FILE * to a file: 1182 1183 /* imaginary struct */ 1184 struct MemoryStruct { 1185 char *memory; 1186 size_t size; 1187 }; 1188 1189 /* imaginary callback function */ 1190 size_t 1191 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data) 1192 { 1193 size_t realsize = size * nmemb; 1194 struct MemoryStruct *mem = (struct MemoryStruct *)data; 1195 1196 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1); 1197 if (mem->memory) { 1198 memcpy(&(mem->memory[mem->size]), ptr, realsize); 1199 mem->size += realsize; 1200 mem->memory[mem->size] = 0; 1201 } 1202 return realsize; 1203 } 1204 1205 5.3 How do I fetch multiple files with libcurl? 1206 1207 libcurl has excellent support for transferring multiple files. You should 1208 just repeatedly set new URLs with curl_easy_setopt() and then transfer it 1209 with curl_easy_perform(). The handle you get from curl_easy_init() is not 1210 only reusable, but you're even encouraged to reuse it if you can, as that 1211 will enable libcurl to use persistent connections. 1212 1213 5.4 Does libcurl do Winsock initialization on win32 systems? 1214 1215 Yes, if told to in the curl_global_init() call. 1216 1217 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ? 1218 1219 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have 1220 that DLL use the FILE * (as the DLL and the client application cannot access 1221 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must 1222 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the 1223 file, even if that simply writes the data to the specified FILE *. 1224 Similarly, if you use CURLOPT_READDATA you must also specify 1225 CURLOPT_READFUNCTION. 1226 1227 5.6 What about Keep-Alive or persistent connections? 1228 1229 curl and libcurl have excellent support for persistent connections when 1230 transferring several files from the same server. Curl will attempt to reuse 1231 connections for all URLs specified on the same command line/config file, and 1232 libcurl will reuse connections for all transfers that are made using the 1233 same libcurl handle. 1234 1235 When you use the easy interface the connection cache is kept within the easy 1236 handle. If you instead use the multi interface, the connection cache will be 1237 kept within the multi handle and will be shared among all the easy handles 1238 that are used within the same multi handle. 1239 1240 5.7 Link errors when building libcurl on Windows! 1241 1242 You need to make sure that your project, and all the libraries (both static 1243 and dynamic) that it links against, are compiled/linked against the same run 1244 time library. 1245 1246 This is determined by the /MD, /ML, /MT (and their corresponding /M?d) 1247 options to the command line compiler. /MD (linking against MSVCRT dll) seems 1248 to be the most commonly used option. 1249 1250 When building an application that uses the static libcurl library, you must 1251 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for 1252 dynamic import symbols. If you're using Visual Studio, you need to instead 1253 add CURL_STATICLIB in the "Preprocessor Definitions" section. 1254 1255 If you get linker error like "unknown symbol __imp__curl_easy_init ..." you 1256 have linked against the wrong (static) library. If you want to use the 1257 libcurl.dll and import lib, you don't need any extra CFLAGS, but use one of 1258 the import libraries below. These are the libraries produced by the various 1259 lib/Makefile.* files: 1260 1261 Target: static lib. import lib for libcurl*.dll. 1262 ----------------------------------------------------------- 1263 MingW: libcurl.a libcurldll.a 1264 MSVC (release): libcurl.lib libcurl_imp.lib 1265 MSVC (debug): libcurld.lib libcurld_imp.lib 1266 Borland: libcurl.lib libcurl_imp.lib 1267 1268 5.8 libcurl.so.X: open failed: No such file or directory 1269 1270 This is an error message you might get when you try to run a program linked 1271 with a shared version of libcurl and your run-time linker (ld.so) couldn't 1272 find the shared library named libcurl.so.X. (Where X is the number of the 1273 current libcurl ABI, typically 3 or 4). 1274 1275 You need to make sure that ld.so finds libcurl.so.X. You can do that 1276 multiple ways, and it differs somewhat between different operating systems, 1277 but they are usually: 1278 1279 * Add an option to the linker command line that specify the hard-coded path 1280 the run-time linker should check for the lib (usually -R) 1281 1282 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so 1283 should check for libs 1284 1285 * Adjust the system's config to check for libs in the directory where you've 1286 put the dir (like Linux's /etc/ld.so.conf) 1287 1288 'man ld.so' and 'man ld' will tell you more details 1289 1290 5.9 How does libcurl resolve host names? 1291 1292 libcurl supports a large a number of different name resolve functions. One 1293 of them is picked at build-time and will be used unconditionally. Thus, if 1294 you want to change name resolver function you must rebuild libcurl and tell 1295 it to use a different function. 1296 1297 - The non-IPv6 resolver that can use one of four different host name resolve 1298 calls (depending on what your system supports): 1299 1300 A - gethostbyname() 1301 B - gethostbyname_r() with 3 arguments 1302 C - gethostbyname_r() with 5 arguments 1303 D - gethostbyname_r() with 6 arguments 1304 1305 - The IPv6-resolver that uses getaddrinfo() 1306 1307 - The c-ares based name resolver that uses the c-ares library for resolves. 1308 Using this offers asynchronous name resolves. 1309 1310 - The threaded resolver (default option on Windows). It uses: 1311 1312 A - gethostbyname() on plain IPv4 hosts 1313 B - getaddrinfo() on IPv6 enabled hosts 1314 1315 Also note that libcurl never resolves or reverse-lookups addresses given as 1316 pure numbers, such as 127.0.0.1 or ::1. 1317 1318 5.10 How do I prevent libcurl from writing the response to stdout? 1319 1320 libcurl provides a default built-in write function that writes received data 1321 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly 1322 set CURLOPT_WRITEDATA to a different FILE * handle. 1323 1324 5.11 How do I make libcurl not receive the whole HTTP response? 1325 1326 You make the write callback (or progress callback) return an error and 1327 libcurl will then abort the transfer. 1328 1329 5.12 Can I make libcurl fake or hide my real IP address? 1330 1331 No. libcurl operates on a higher level. Besides, faking IP address would 1332 imply sending IP packets with a made-up source address, and then you normally 1333 get a problem with receiving the packet sent back as they would then not be 1334 routed to you! 1335 1336 If you use a proxy to access remote sites, the sites will not see your local 1337 IP address but instead the address of the proxy. 1338 1339 Also note that on many networks NATs or other IP-munging techniques are used 1340 that makes you see and use a different IP address locally than what the 1341 remote server will see you coming from. You may also consider using 1342 https://www.torproject.org/ . 1343 1344 5.13 How do I stop an ongoing transfer? 1345 1346 With the easy interface you make sure to return the correct error code from 1347 one of the callbacks, but none of them are instant. There is no function you 1348 can call from another thread or similar that will stop it immediately. 1349 Instead, you need to make sure that one of the callbacks you use returns an 1350 appropriate value that will stop the transfer. Suitable callbacks that you 1351 can do this with include the progress callback, the read callback and the 1352 write callback. 1353 1354 If you're using the multi interface, you can also stop a transfer by 1355 removing the particular easy handle from the multi stack at any moment you 1356 think the transfer is done or when you wish to abort the transfer. 1357 1358 5.14 Using C++ non-static functions for callbacks? 1359 1360 libcurl is a C library, it doesn't know anything about C++ member functions. 1361 1362 You can overcome this "limitation" with relative ease using a static 1363 member function that is passed a pointer to the class: 1364 1365 // f is the pointer to your object. 1366 static size_t YourClass::func(void *buffer, size_t sz, size_t n, void *f) 1367 { 1368 // Call non-static member function. 1369 static_cast<YourClass*>(f)->nonStaticFunction(); 1370 } 1371 1372 // This is how you pass pointer to the static function: 1373 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass::func); 1374 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this); 1375 1376 5.15 How do I get an FTP directory listing? 1377 1378 If you end the FTP URL you request with a slash, libcurl will provide you 1379 with a directory listing of that given directory. You can also set 1380 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use 1381 to list the files. 1382 1383 The follow-up question tends to be how is a program supposed to parse the 1384 directory listing. How does it know what's a file and what's a dir and what's 1385 a symlink etc. If the FTP server supports the MLSD command then it will 1386 return data in a machine-readable format that can be parsed for type. The 1387 types are specified by RFC3659 section 7.5.1. If MLSD is not supported then 1388 you have to work with what you're given. The LIST output format is entirely 1389 at the server's own liking and the NLST output doesn't reveal any types and 1390 in many cases doesn't even include all the directory entries. Also, both LIST 1391 and NLST tend to hide unix-style hidden files (those that start with a dot) 1392 by default so you need to do "LIST -a" or similar to see them. 1393 1394 Example - List only directories. 1395 ftp.funet.fi supports MLSD and ftp.kernel.org does not: 1396 1397 curl -s ftp.funet.fi/pub/ -X MLSD | \ 1398 perl -lne 'print if s/(?:^|;)type=dir;[^ ]+ (.+)$/$1/' 1399 1400 curl -s ftp.kernel.org/pub/linux/kernel/ | \ 1401 perl -lne 'print if s/^d[-rwx]{9}(?: +[^ ]+){7} (.+)$/$1/' 1402 1403 If you need to parse LIST output in libcurl one such existing 1404 list parser is available at https://cr.yp.to/ftpparse.html Versions of 1405 libcurl since 7.21.0 also provide the ability to specify a wildcard to 1406 download multiple files from one FTP directory. 1407 1408 5.16 I want a different time-out! 1409 1410 Time and time again users realize that CURLOPT_TIMEOUT and 1411 CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all 1412 the various use cases and scenarios applications end up with. 1413 1414 libcurl offers many more ways to time-out operations. A common alternative 1415 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to 1416 specify the lowest possible speed to accept before to consider the transfer 1417 timed out. 1418 1419 The most flexible way is by writing your own time-out logic and using 1420 CURLOPT_XFERINFOFUNCTION (perhaps in combination with other callbacks) and 1421 use that to figure out exactly when the right condition is met when the 1422 transfer should get stopped. 1423 1424 5.17 Can I write a server with libcurl? 1425 1426 No. libcurl offers no functions or building blocks to build any kind of 1427 internet protocol server. libcurl is only a client-side library. For server 1428 libraries, you need to continue your search elsewhere but there exist many 1429 good open source ones out there for most protocols you could possibly want a 1430 server for. And there are really good stand-alone ones that have been tested 1431 and proven for many years. There's no need for you to reinvent them! 1432 1433 5.18 Does libcurl use threads? 1434 1435 Put simply: no, libcurl will execute in the same thread you call it in. All 1436 callbacks will be called in the same thread as the one you call libcurl in. 1437 1438 If you want to avoid your thread to be blocked by the libcurl call, you make 1439 sure you use the non-blocking API which will do transfers asynchronously - 1440 but still in the same single thread. 1441 1442 libcurl will potentially internally use threads for name resolving, if it 1443 was built to work like that, but in those cases it'll create the child 1444 threads by itself and they will only be used and then killed internally by 1445 libcurl and never exposed to the outside. 1446 14476. License Issues 1448 1449 Curl and libcurl are released under a MIT/X derivate license. The license is 1450 very liberal and should not impose a problem for your project. This section 1451 is just a brief summary for the cases we get the most questions. (Parts of 1452 this section was much enhanced by Bjorn Reese.) 1453 1454 We are not lawyers and this is not legal advice. You should probably consult 1455 one if you want true and accurate legal insights without our prejudice. Note 1456 especially that this section concerns the libcurl license only; compiling in 1457 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect 1458 the licensing obligations of your application. 1459 1460 6.1 I have a GPL program, can I use the libcurl library? 1461 1462 Yes! 1463 1464 Since libcurl may be distributed under the MIT/X derivate license, it can be 1465 used together with GPL in any software. 1466 1467 6.2 I have a closed-source program, can I use the libcurl library? 1468 1469 Yes! 1470 1471 libcurl does not put any restrictions on the program that uses the library. 1472 1473 6.3 I have a BSD licensed program, can I use the libcurl library? 1474 1475 Yes! 1476 1477 libcurl does not put any restrictions on the program that uses the library. 1478 1479 6.4 I have a program that uses LGPL libraries, can I use libcurl? 1480 1481 Yes! 1482 1483 The LGPL license doesn't clash with other licenses. 1484 1485 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 1486 1487 Yes! 1488 1489 The MIT/X derivate license practically allows you to do almost anything with 1490 the sources, on the condition that the copyright texts in the sources are 1491 left intact. 1492 1493 6.6 Can you please change the curl/libcurl license to XXXX? 1494 1495 No. 1496 1497 We have carefully picked this license after years of development and 1498 discussions and a large amount of people have contributed with source code 1499 knowing that this is the license we use. This license puts the restrictions 1500 we want on curl/libcurl and it does not spread to other programs or 1501 libraries that use it. It should be possible for everyone to use libcurl or 1502 curl in their projects, no matter what license they already have in use. 1503 1504 6.7 What are my obligations when using libcurl in my commercial apps? 1505 1506 Next to none. All you need to adhere to is the MIT-style license (stated in 1507 the COPYING file) which basically says you have to include the copyright 1508 notice in "all copies" and that you may not use the copyright holder's name 1509 when promoting your software. 1510 1511 You do not have to release any of your source code. 1512 1513 You do not have to reveal or make public any changes to the libcurl source 1514 code. 1515 1516 You do not have to broadcast to the world that you are using libcurl within 1517 your app. 1518 1519 All we ask is that you disclose "the copyright notice and this permission 1520 notice" somewhere. Most probably like in the documentation or in the section 1521 where other third party dependencies already are mentioned and acknowledged. 1522 1523 As can be seen here: https://curl.haxx.se/docs/companies.html and elsewhere, 1524 more and more companies are discovering the power of libcurl and take 1525 advantage of it even in commercial environments. 1526 1527 15287. PHP/CURL Issues 1529 1530 7.1 What is PHP/CURL? 1531 1532 The module for PHP that makes it possible for PHP programs to access curl- 1533 functions from within PHP. 1534 1535 In the cURL project we call this module PHP/CURL to differentiate it from 1536 curl the command line tool and libcurl the library. The PHP team however 1537 does not refer to it like this (for unknown reasons). They call it plain 1538 CURL (often using all caps) or sometimes ext/curl, but both cause much 1539 confusion to users which in turn gives us a higher question load. 1540 1541 7.2 Who wrote PHP/CURL? 1542 1543 PHP/CURL was initially written by Sterling Hughes. 1544 1545 7.3 Can I perform multiple requests using the same handle? 1546 1547 Yes - at least in PHP version 4.3.8 and later (this has been known to not 1548 work in earlier versions, but the exact version when it started to work is 1549 unknown to me). 1550 1551 After a transfer, you just set new options in the handle and make another 1552 transfer. This will make libcurl re-use the same connection if it can. 1553 1554 7.4 Does PHP/CURL have dependencies? 1555 1556 PHP/CURL is a module that comes with the regular PHP package. It depends on 1557 and uses libcurl, so you need to have libcurl installed properly before 1558 PHP/CURL can be used. 1559