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 do you not 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 fails when using static libraries 28 2.2 Does curl work/build with other SSL libraries? 29 2.3 How do I upgrade curl.exe in Windows? 30 2.4 Does curl support SOCKS (RFC 1928) ? 31 32 3. Usage Problems 33 3.1 curl: (1) SSL is disabled, https: not supported 34 3.2 How do I tell curl to resume a transfer? 35 3.3 Why does my posting using -F not work? 36 3.4 How do I tell curl to run custom FTP commands? 37 3.5 How can I disable the Accept: */* header? 38 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 39 3.7 Can I use curl to delete/rename a file through FTP? 40 3.8 How do I tell curl to follow HTTP redirects? 41 3.9 How do I use curl in my favorite programming language? 42 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 43 3.11 How do I POST with a different Content-Type? 44 3.12 Why do FTP-specific features over HTTP proxy fail? 45 3.13 Why do my single/double quotes fail? 46 3.14 Does curl support JavaScript or PAC (automated proxy config)? 47 3.15 Can I do recursive fetches with curl? 48 3.16 What certificates do I need when I use SSL? 49 3.17 How do I list the root directory of an FTP server? 50 3.18 Can I use curl to send a POST/PUT and not wait for a response? 51 3.19 How do I get HTTP from a host using a specific IP address? 52 3.20 How to SFTP from my user's home directory? 53 3.21 Protocol xxx not supported or disabled in libcurl 54 3.22 curl -X gives me HTTP problems 55 56 4. Running Problems 57 4.2 Why do I get problems when I use & or % in the URL? 58 4.3 How can I use {, }, [ or ] to specify multiple URLs? 59 4.4 Why do I get downloaded data even though the webpage does not exist? 60 4.5 Why do I get return code XXX from an HTTP server? 61 4.5.1 "400 Bad Request" 62 4.5.2 "401 Unauthorized" 63 4.5.3 "403 Forbidden" 64 4.5.4 "404 Not Found" 65 4.5.5 "405 Method Not Allowed" 66 4.5.6 "301 Moved Permanently" 67 4.6 Can you tell me what error code 142 means? 68 4.7 How do I keep usernames and passwords secret in curl command lines? 69 4.8 I found a bug 70 4.9 curl cannot authenticate to a server that requires NTLM? 71 4.10 My HTTP request using HEAD, PUT or DELETE does not work 72 4.11 Why do my HTTP range requests return the full document? 73 4.12 Why do I get "certificate verify failed" ? 74 4.13 Why is curl -R on Windows one hour off? 75 4.14 Redirects work in browser but not with curl 76 4.15 FTPS does not work 77 4.16 My HTTP POST or PUT requests are slow 78 4.17 Non-functional connect timeouts on Windows 79 4.18 file:// URLs containing drive letters (Windows, NetWare) 80 4.19 Why does not curl return an error when the network cable is unplugged? 81 4.20 curl does not return error for HTTP non-200 responses 82 83 5. libcurl Issues 84 5.1 Is libcurl thread-safe? 85 5.2 How can I receive all data into a large memory chunk? 86 5.3 How do I fetch multiple files with libcurl? 87 5.4 Does libcurl do Winsock initialization on Win32 systems? 88 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on Win32 ? 89 5.6 What about Keep-Alive or persistent connections? 90 5.7 Link errors when building libcurl on Windows 91 5.8 libcurl.so.X: open failed: No such file or directory 92 5.9 How does libcurl resolve hostnames? 93 5.10 How do I prevent libcurl from writing the response to stdout? 94 5.11 How do I make libcurl not receive the whole HTTP response? 95 5.12 Can I make libcurl fake or hide my real IP address? 96 5.13 How do I stop an ongoing transfer? 97 5.14 Using C++ non-static functions for callbacks? 98 5.15 How do I get an FTP directory listing? 99 5.16 I want a different time-out 100 5.17 Can I write a server with libcurl? 101 5.18 Does libcurl use threads? 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 7.4 Does PHP/CURL have dependencies? 117 118 8. Development 119 8.1 Why does curl use C89? 120 8.2 Will curl be rewritten? 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 read as '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 client-side URL transfer library, supporting DICT, FILE, FTP, FTPS, 139 GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, POP3, POP3S, 140 RTMP, RTMPS, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET, TFTP, WS 141 and WSS. 142 143 libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, 144 Kerberos, SPNEGO, HTTP form based upload, proxies, cookies, user+password 145 authentication, file transfer resume, http proxy tunneling and more. 146 147 libcurl is highly portable, it builds and works identically on numerous 148 platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HP-UX, 149 IRIX, AIX, Tru64, Linux, UnixWare, HURD, Windows, Amiga, OS/2, macOS, 150 Ultrix, QNX, OpenVMS, RISC OS, Novell NetWare, DOS, Symbian, OSF, Android, 151 Minix, IBM TPF and more... 152 153 libcurl is free, thread-safe, IPv6 compatible, feature rich, well 154 supported and fast. 155 156 curl 157 158 A command line tool for getting or sending data using URL syntax. 159 160 Since curl uses libcurl, curl supports the same wide range of common 161 Internet protocols that libcurl does. 162 163 We pronounce curl with an initial k sound. It rhymes with words like girl 164 and earl. This is a short WAV file to help you: 165 166 https://media.merriam-webster.com/soundc11/c/curl0001.wav 167 168 There are numerous sub-projects and related projects that also use the word 169 curl in the project names in various combinations, but you should take 170 notice that this FAQ is directed at the command-line tool named curl (and 171 libcurl the library), and may therefore not be valid for other curl-related 172 projects. (There is however a small section for the PHP/CURL in this FAQ.) 173 174 1.2 What is libcurl? 175 176 libcurl is a reliable and portable library for doing Internet data transfers 177 using one or more of its supported Internet protocols. 178 179 You can use libcurl freely in your application, be it open source, 180 commercial or closed-source. 181 182 libcurl is most probably the most portable, most powerful and most often 183 used C-based multi-platform file transfer library on this planet - be it 184 open source or commercial. 185 186 1.3 What is curl not? 187 188 curl is not a wget clone. That is a common misconception. Never, during 189 curl's development, have we intended curl to replace wget or compete on its 190 market. curl is targeted at single-shot file transfers. 191 192 curl is not a website mirroring program. If you want to use curl to mirror 193 something: fine, go ahead and write a script that wraps around curl or use 194 libcurl to make it reality. 195 196 curl is not an FTP site mirroring program. Sure, get and send FTP with curl 197 but if you want systematic and sequential behavior you should write a 198 script (or write a new program that interfaces libcurl) and do it. 199 200 curl is not a PHP tool, even though it works perfectly well when used from 201 or with PHP (when using the PHP/CURL module). 202 203 curl is not a program for a single operating system. curl exists, compiles, 204 builds and runs under a wide range of operating systems, including all 205 modern Unixes (and a bunch of older ones too), Windows, Amiga, OS/2, macOS, 206 QNX etc. 207 208 1.4 When will you make curl do XXXX ? 209 210 We love suggestions of what to change in order to make curl and libcurl 211 better. We do however believe in a few rules when it comes to the future of 212 curl: 213 214 curl -- the command line tool -- is to remain a non-graphical command line 215 tool. If you want GUIs or fancy scripting capabilities, you should look for 216 another tool that uses libcurl. 217 218 We do not add things to curl that other small and available tools already do 219 well at the side. curl's output can be piped into another program or 220 redirected to another file for the next program to interpret. 221 222 We focus on protocol related issues and improvements. If you want to do more 223 magic with the supported protocols than curl currently does, chances are 224 good we will agree. If you want to add more protocols, we may agree. 225 226 If you want someone else to do all the work while you wait for us to 227 implement it for you, that is not a friendly attitude. We spend a 228 considerable time already on maintaining and developing curl. In order to 229 get more out of us, you should consider trading in some of your time and 230 effort in return. Simply go to the GitHub repository which resides at 231 https://github.com/curl/curl, fork the project, and create pull requests 232 with your proposed changes. 233 234 If you write the code, chances are better that it will get into curl faster. 235 236 1.5 Who makes curl? 237 238 curl and libcurl are not made by any single individual. Daniel Stenberg is 239 project leader and main developer, but other persons' submissions are 240 important and crucial. Anyone can contribute and post their changes and 241 improvements and have them inserted in the main sources (of course on the 242 condition that developers agree that the fixes are good). 243 244 The full list of all contributors is found in the docs/THANKS file. 245 246 curl is developed by a community, with Daniel at the wheel. 247 248 1.6 What do you get for making curl? 249 250 Project cURL is entirely free and open. We do this voluntarily, mostly in 251 our spare time. Companies may pay individual developers to work on curl. 252 This is not controlled by nor supervised in any way by the curl project. 253 254 We get help from companies. Haxx provides website, bandwidth, mailing lists 255 etc, GitHub hosts the primary git repository and other services like the bug 256 tracker at https://github.com/curl/curl. Also again, some companies have 257 sponsored certain parts of the development in the past and I hope some will 258 continue to do so in the future. 259 260 If you want to support our project, consider a donation or a banner-program 261 or even better: by helping us with coding, documenting or testing etc. 262 263 See also: https://curl.se/sponsors.html 264 265 1.7 What about CURL from curl.com? 266 267 During the summer of 2001, curl.com was busy advertising their client-side 268 programming language for the web, named CURL. 269 270 We are in no way associated with curl.com or their CURL programming 271 language. 272 273 Our project name curl has been in effective use since 1998. We were not the 274 first computer related project to use the name "curl" and do not claim any 275 rights to the name. 276 277 We recognize that we will be living in parallel with curl.com and wish them 278 every success. 279 280 1.8 I have a problem, who do I mail? 281 282 Please do not mail any single individual unless you really need to. Keep 283 curl-related questions on a suitable mailing list. All available mailing 284 lists are listed in the MANUAL document and online at 285 https://curl.se/mail/ 286 287 Keeping curl-related questions and discussions on mailing lists allows 288 others to join in and help, to share their ideas, to contribute their 289 suggestions and to spread their wisdom. Keeping discussions on public mailing 290 lists also allows for others to learn from this (both current and future 291 users thanks to the web based archives of the mailing lists), thus saving us 292 from having to repeat ourselves even more. Thanks for respecting this. 293 294 If you have found or simply suspect a security problem in curl or libcurl, 295 submit all the details at https://hackerone.one/curl. On there we keep the 296 issue private while we investigate, confirm it, work and validate a fix and 297 agree on a time schedule for publication etc. That way we produce a fix in a 298 timely manner before the flaw is announced to the world, reducing the impact 299 the problem risks having on existing users. 300 301 Security issues can also be taking to the curl security team by emailing 302 security at curl.se (closed list of receivers, mails are not disclosed). 303 304 1.9 Where do I buy commercial support for curl? 305 306 curl is fully open source. It means you can hire any skilled engineer to fix 307 your curl-related problems. 308 309 We list available alternatives on the curl website: 310 https://curl.se/support.html 311 312 1.10 How many are using curl? 313 314 It is impossible to tell. 315 316 We do not know how many users that knowingly have installed and use curl. 317 318 We do not know how many users that use curl without knowing that they are in 319 fact using it. 320 321 We do not know how many users that downloaded or installed curl and then 322 never use it. 323 324 In 2020, we estimate that curl runs in roughly ten billion installations 325 world wide. 326 327 1.11 Why do you not update ca-bundle.crt 328 329 In the cURL project we have decided not to attempt to keep this file updated 330 (or even present) since deciding what to add to a ca cert bundle is an 331 undertaking we have not been ready to accept, and the one we can get from 332 Mozilla is perfectly fine so there is no need to duplicate that work. 333 334 Today, with many services performed over HTTPS, every operating system 335 should come with a default ca cert bundle that can be deemed somewhat 336 trustworthy and that collection (if reasonably updated) should be deemed to 337 be a lot better than a private curl version. 338 339 If you want the most recent collection of ca certs that Mozilla Firefox 340 uses, we recommend that you extract the collection yourself from Mozilla 341 Firefox (by running 'make ca-bundle), or by using our online service setup 342 for this purpose: https://curl.se/docs/caextract.html 343 344 1.12 I have a problem who, can I chat with? 345 346 There is a bunch of friendly people hanging out in the #curl channel on the 347 IRC network libera.chat. If you are polite and nice, chances are good that 348 you can get -- or provide -- help instantly. 349 350 1.13 curl's ECCN number? 351 352 The US government restricts exports of software that contains or uses 353 cryptography. When doing so, the Export Control Classification Number (ECCN) 354 is used to identify the level of export control etc. 355 356 Apache Software Foundation gives a good explanation of ECCNs at 357 https://www.apache.org/dev/crypto.html 358 359 We believe curl's number might be ECCN 5D002, another possibility is 360 5D992. It seems necessary to write them (the authority that administers ECCN 361 numbers), asking to confirm. 362 363 Comprehensible explanations of the meaning of such numbers and how to obtain 364 them (resp.) are here 365 366 https://www.bis.doc.gov/licensing/exportingbasics.htm 367 https://www.bis.doc.gov/licensing/do_i_needaneccn.html 368 369 An incomprehensible description of the two numbers above is here 370 https://www.bis.doc.gov/index.php/documents/new-encryption/1653-ccl5-pt2-3 371 372 1.14 How do I submit my patch? 373 374 We strongly encourage you to submit changes and improvements directly as 375 "pull requests" on GitHub: https://github.com/curl/curl/pulls 376 377 If you for any reason cannot or will not deal with GitHub, send your patch to 378 the curl-library mailing list. We are many subscribers there and there are 379 lots of people who can review patches, comment on them and "receive" them 380 properly. 381 382 Lots of more details are found in the CONTRIBUTE.md and INTERNALS.md 383 documents. 384 385 1.15 How do I port libcurl to my OS? 386 387 Here's a rough step-by-step: 388 389 1. copy a suitable lib/config-*.h file as a start to lib/config-[youros].h 390 391 2. edit lib/config-[youros].h to match your OS and setup 392 393 3. edit lib/curl_setup.h to include config-[youros].h when your OS is 394 detected by the preprocessor, in the style others already exist 395 396 4. compile lib/*.c and make them into a library 397 398 3992. Install Related Problems 400 401 2.1 configure fails when using static libraries 402 403 You may find that configure fails to properly detect the entire dependency 404 chain of libraries when you provide static versions of the libraries that 405 configure checks for. 406 407 The reason why static libraries is much harder to deal with is that for them 408 we do not get any help but the script itself must know or check what more 409 libraries that are needed (with shared libraries, that dependency "chain" is 410 handled automatically). This is an error-prone process and one that also 411 tends to vary over time depending on the release versions of the involved 412 components and may also differ between operating systems. 413 414 For that reason, configure does few attempts to actually figure this out and 415 you are instead encouraged to set LIBS and LDFLAGS accordingly when you 416 invoke configure, and point out the needed libraries and set the necessary 417 flags yourself. 418 419 2.2 Does curl work with other SSL libraries? 420 421 curl has been written to use a generic SSL function layer internally, and 422 that SSL functionality can then be provided by one out of many different SSL 423 backends. 424 425 curl can be built to use one of the following SSL alternatives: OpenSSL, 426 LibreSSL, BoringSSL, AWS-LC, GnuTLS, wolfSSL, mbedTLS, Secure Transport 427 (native iOS/macOS), Schannel (native Windows), BearSSL or Rustls. They all 428 have their pros and cons, and we try to maintain a comparison of them here: 429 https://curl.se/docs/ssl-compared.html 430 431 2.3 How do I upgrade curl.exe in Windows? 432 433 The curl tool that is shipped as an integrated component of Windows 10 and 434 Windows 11 is managed by Microsoft. If you were to delete the file or 435 replace it with a newer version downloaded from https://curl.se/windows, 436 then Windows Update will cease to work on your system. 437 438 There is no way to independently force an upgrade of the curl.exe that is 439 part of Windows other than through the regular Windows update process. There 440 is also nothing the curl project itself can do about this, since this is 441 managed and controlled entirely by Microsoft as owners of the operating 442 system. 443 444 You can always download and install the latest version of curl for Windows 445 from https://curl.se/windows into a separate location. 446 447 2.4 Does curl support SOCKS (RFC 1928) ? 448 449 Yes, SOCKS 4 and 5 are supported. 450 4513. Usage problems 452 453 3.1 curl: (1) SSL is disabled, https: not supported 454 455 If you get this output when trying to get anything from an HTTPS server, it 456 means that the instance of curl/libcurl that you are using was built without 457 support for this protocol. 458 459 This could have happened if the configure script that was run at build time 460 could not find all libs and include files curl requires for SSL to work. If 461 the configure script fails to find them, curl is simply built without SSL 462 support. 463 464 To get HTTPS support into a curl that was previously built but that reports 465 that HTTPS is not supported, you should dig through the document and logs 466 and check out why the configure script does not find the SSL libs and/or 467 include files. 468 469 Also, check out the other paragraph in this FAQ labeled "configure does not 470 find OpenSSL even when it is installed". 471 472 3.2 How do I tell curl to resume a transfer? 473 474 curl supports resumed transfers both ways on both FTP and HTTP. 475 Try the -C option. 476 477 3.3 Why does my posting using -F not work? 478 479 You cannot arbitrarily use -F or -d, the choice between -F or -d depends on 480 the HTTP operation you need curl to do and what the web server that will 481 receive your post expects. 482 483 If the form you are trying to submit uses the type 'multipart/form-data', 484 then and only then you must use the -F type. In all the most common cases, 485 you should use -d which then causes a posting with the type 486 'application/x-www-form-urlencoded'. 487 488 This is described in some detail in the MANUAL and TheArtOfHttpScripting 489 documents, and if you do not understand it the first time, read it again 490 before you post questions about this to the mailing list. Also, try reading 491 through the mailing list archives for old postings and questions regarding 492 this. 493 494 3.4 How do I tell curl to run custom FTP commands? 495 496 You can tell curl to perform optional commands both before and/or after a 497 file transfer. Study the -Q/--quote option. 498 499 Since curl is used for file transfers, you do not normally use curl to 500 perform FTP commands without transferring anything. Therefore you must 501 always specify a URL to transfer to/from even when doing custom FTP 502 commands, or use -I which implies the "no body" option sent to libcurl. 503 504 3.5 How can I disable the Accept: */* header? 505 506 You can change all internally generated headers by adding a replacement with 507 the -H/--header option. By adding a header with empty contents you safely 508 disable that one. Use -H "Accept:" to disable that specific header. 509 510 3.6 Does curl support ASP, XML, XHTML or HTML version Y? 511 512 To curl, all contents are alike. It does not matter how the page was 513 generated. It may be ASP, PHP, Perl, shell-script, SSI or plain HTML 514 files. There is no difference to curl and it does not even know what kind of 515 language that generated the page. 516 517 See also item 3.14 regarding JavaScript. 518 519 3.7 Can I use curl to delete/rename a file through FTP? 520 521 Yes. You specify custom FTP commands with -Q/--quote. 522 523 One example would be to delete a file after you have downloaded it: 524 525 curl -O ftp://example.com/coolfile -Q '-DELE coolfile' 526 527 or rename a file after upload: 528 529 curl -T infile ftp://example.com/dir/ -Q "-RNFR infile" -Q "-RNTO newname" 530 531 3.8 How do I tell curl to follow HTTP redirects? 532 533 curl does not follow so-called redirects by default. The Location: header 534 that informs the client about this is only interpreted if you are using the 535 -L/--location option. As in: 536 537 curl -L http://example.com 538 539 Not all redirects are HTTP ones, see 4.14 540 541 3.9 How do I use curl in my favorite programming language? 542 543 Many programming languages have interfaces/bindings that allow you to use 544 curl without having to use the command line tool. If you are fluent in such 545 a language, you may prefer to use one of these interfaces instead. 546 547 Find out more about which languages that support curl directly, and how to 548 install and use them, in the libcurl section of the curl website: 549 https://curl.se/libcurl/ 550 551 All the various bindings to libcurl are made by other projects and people, 552 outside of the cURL project. The cURL project itself only produces libcurl 553 with its plain C API. If you do not find anywhere else to ask you can ask 554 about bindings on the curl-library list too, but be prepared that people on 555 that list may not know anything about bindings. 556 557 In December 2021, there were interfaces available for the following 558 languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Delphi, Dylan, Eiffel, 559 Euphoria, Falcon, Ferite, Gambas, glib/GTK+, Go, Guile, Harbour, Haskell, 560 Java, Julia, Lisp, Lua, Mono, .NET, node.js, Object-Pascal, OCaml, Pascal, 561 Perl, PHP, PostgreSQL, Python, R, Rexx, Ring, RPG, Ruby, Rust, Scheme, 562 Scilab, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro, 563 Q, wxwidgets, XBLite and Xoho. By the time you read this, additional ones 564 may have appeared. 565 566 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? 567 568 curl adheres to the HTTP spec, which basically means you can play with *any* 569 protocol that is built on top of HTTP. Protocols such as SOAP, WebDAV and 570 XML-RPC are all such ones. You can use -X to set custom requests and -H to 571 set custom headers (or replace internally generated ones). 572 573 Using libcurl is of course just as good and you would just use the proper 574 library options to do the same. 575 576 3.11 How do I POST with a different Content-Type? 577 578 You can always replace the internally generated headers with -H/--header. 579 To make a simple HTTP POST with text/xml as content-type, do something like: 580 581 curl -d "datatopost" -H "Content-Type: text/xml" [URL] 582 583 3.12 Why do FTP-specific features over HTTP proxy fail? 584 585 Because when you use an HTTP proxy, the protocol spoken on the network will 586 be HTTP, even if you specify an FTP URL. This effectively means that you 587 normally cannot use FTP-specific features such as FTP upload and FTP quote 588 etc. 589 590 There is one exception to this rule, and that is if you can "tunnel through" 591 the given HTTP proxy. Proxy tunneling is enabled with a special option (-p) 592 and is generally not available as proxy admins usually disable tunneling to 593 ports other than 443 (which is used for HTTPS access through proxies). 594 595 3.13 Why do my single/double quotes fail? 596 597 To specify a command line option that includes spaces, you might need to 598 put the entire option within quotes. Like in: 599 600 curl -d " with spaces " example.com 601 602 or perhaps 603 604 curl -d ' with spaces ' example.com 605 606 Exactly what kind of quotes and how to do this is entirely up to the shell 607 or command line interpreter that you are using. For most Unix shells, you 608 can more or less pick either single (') or double (") quotes. For 609 Windows/DOS command prompts you must use double (") quotes, and if the 610 option string contains inner double quotes you can escape them with a 611 backslash. 612 613 For Windows powershell the arguments are not always passed on as expected 614 because curl is not a powershell script. You may or may not be able to use 615 single quotes. To escape inner double quotes seems to require a 616 backslash-backtick escape sequence and the outer quotes as double quotes. 617 618 Please study the documentation for your particular environment. Examples in 619 the curl docs will use a mix of both of these as shown above. You must 620 adjust them to work in your environment. 621 622 Remember that curl works and runs on more operating systems than most single 623 individuals have ever tried. 624 625 3.14 Does curl support JavaScript or PAC (automated proxy config)? 626 627 Many webpages do magic stuff using embedded JavaScript. curl and libcurl 628 have no built-in support for that, so it will be treated just like any other 629 contents. 630 631 .pac files are a Netscape invention and are sometimes used by organizations 632 to allow them to differentiate which proxies to use. The .pac contents is 633 just a JavaScript program that gets invoked by the browser and that returns 634 the name of the proxy to connect to. Since curl does not support JavaScript, 635 it cannot support .pac proxy configuration either. 636 637 Some workarounds usually suggested to overcome this JavaScript dependency: 638 639 Depending on the JavaScript complexity, write up a script that translates it 640 to another language and execute that. 641 642 Read the JavaScript code and rewrite the same logic in another language. 643 644 Implement a JavaScript interpreter, people have successfully used the 645 Mozilla JavaScript engine in the past. 646 647 Ask your admins to stop this, for a static proxy setup or similar. 648 649 3.15 Can I do recursive fetches with curl? 650 651 No. curl itself has no code that performs recursive operations, such as 652 those performed by wget and similar tools. 653 654 There exists wrapper scripts with that functionality (for example the 655 curlmirror perl script), and you can write programs based on libcurl to do 656 it, but the command line tool curl itself cannot. 657 658 3.16 What certificates do I need when I use SSL? 659 660 There are three different kinds of "certificates" to keep track of when we 661 talk about using SSL-based protocols (HTTPS or FTPS) using curl or libcurl. 662 663 CLIENT CERTIFICATE 664 665 The server you communicate with may require that you can provide this in 666 order to prove that you actually are who you claim to be. If the server 667 does not require this, you do not need a client certificate. 668 669 A client certificate is always used together with a private key, and the 670 private key has a pass phrase that protects it. 671 672 SERVER CERTIFICATE 673 674 The server you communicate with has a server certificate. You can and should 675 verify this certificate to make sure that you are truly talking to the real 676 server and not a server impersonating it. 677 678 CERTIFICATE AUTHORITY CERTIFICATE ("CA cert") 679 680 You often have several CA certs in a CA cert bundle that can be used to 681 verify a server certificate that was signed by one of the authorities in the 682 bundle. curl does not come with a CA cert bundle but most curl installs 683 provide one. You can also override the default. 684 685 The server certificate verification process is made by using a Certificate 686 Authority certificate ("CA cert") that was used to sign the server 687 certificate. Server certificate verification is enabled by default in curl 688 and libcurl and is often the reason for problems as explained in FAQ entry 689 4.12 and the SSLCERTS document 690 (https://curl.se/docs/sslcerts.html). Server certificates that are 691 "self-signed" or otherwise signed by a CA that you do not have a CA cert 692 for, cannot be verified. If the verification during a connect fails, you are 693 refused access. You then need to explicitly disable the verification to 694 connect to the server. 695 696 3.17 How do I list the root directory of an FTP server? 697 698 There are two ways. The way defined in the RFC is to use an encoded slash 699 in the first path part. List the "/tmp" directory like this: 700 701 curl ftp://ftp.example.com/%2ftmp/ 702 703 or the not-quite-kosher-but-more-readable way, by simply starting the path 704 section of the URL with a slash: 705 706 curl ftp://ftp.example.com//tmp/ 707 708 3.18 Can I use curl to send a POST/PUT and not wait for a response? 709 710 No. 711 712 You can easily write your own program using libcurl to do such stunts. 713 714 3.19 How do I get HTTP from a host using a specific IP address? 715 716 For example, you may be trying out a website installation that is not yet in 717 the DNS. Or you have a site using multiple IP addresses for a given host 718 name and you want to address a specific one out of the set. 719 720 Set a custom Host: header that identifies the server name you want to reach 721 but use the target IP address in the URL: 722 723 curl --header "Host: www.example.com" http://127.0.0.1/ 724 725 You can also opt to add faked hostname entries to curl with the --resolve 726 option. That has the added benefit that things like redirects will also work 727 properly. The above operation would instead be done as: 728 729 curl --resolve www.example.com:80:127.0.0.1 http://www.example.com/ 730 731 3.20 How to SFTP from my user's home directory? 732 733 Contrary to how FTP works, SFTP and SCP URLs specify the exact directory to 734 work with. It means that if you do not specify that you want the user's home 735 directory, you get the actual root directory. 736 737 To specify a file in your user's home directory, you need to use the correct 738 URL syntax which for SFTP might look similar to: 739 740 curl -O -u user:password sftp://example.com/~/file.txt 741 742 and for SCP it is just a different protocol prefix: 743 744 curl -O -u user:password scp://example.com/~/file.txt 745 746 3.21 Protocol xxx not supported or disabled in libcurl 747 748 When passing on a URL to curl to use, it may respond that the particular 749 protocol is not supported or disabled. The particular way this error message 750 is phrased is because curl does not make a distinction internally of whether 751 a particular protocol is not supported (i.e. never got any code added that 752 knows how to speak that protocol) or if it was explicitly disabled. curl can 753 be built to only support a given set of protocols, and the rest would then 754 be disabled or not supported. 755 756 Note that this error will also occur if you pass a wrongly spelled protocol 757 part as in "htpt://example.com" or as in the less evident case if you prefix 758 the protocol part with a space as in " http://example.com/". 759 760 3.22 curl -X gives me HTTP problems 761 762 In normal circumstances, -X should hardly ever be used. 763 764 By default you use curl without explicitly saying which request method to 765 use when the URL identifies an HTTP transfer. If you just pass in a URL like 766 "curl http://example.com" it will use GET. If you use -d or -F curl will use 767 POST, -I will cause a HEAD and -T will make it a PUT. 768 769 If for whatever reason you are not happy with these default choices that curl 770 does for you, you can override those request methods by specifying -X 771 [WHATEVER]. This way you can for example send a DELETE by doing "curl -X 772 DELETE [URL]". 773 774 It is thus pointless to do "curl -XGET [URL]" as GET would be used anyway. 775 In the same vein it is pointless to do "curl -X POST -d data [URL]". You can 776 make a fun and somewhat rare request that sends a request-body in a GET 777 request with something like "curl -X GET -d data [URL]" 778 779 Note that -X does not actually change curl's behavior as it only modifies the 780 actual string sent in the request, but that may of course trigger a 781 different set of events. 782 783 Accordingly, by using -XPOST on a command line that for example would follow 784 a 303 redirect, you will effectively prevent curl from behaving 785 correctly. Be aware. 786 787 7884. Running Problems 789 790 4.2 Why do I get problems when I use & or % in the URL? 791 792 In general Unix shells, the & symbol is treated specially and when used, it 793 runs the specified command in the background. To safely send the & as a part 794 of a URL, you should quote the entire URL by using single (') or double (") 795 quotes around it. Similar problems can also occur on some shells with other 796 characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL. 797 798 An example that would invoke a remote CGI that uses &-symbols could be: 799 800 curl 'http://www.example.com/cgi-bin/query?text=yes&q=curl' 801 802 In Windows, the standard DOS shell treats the percent sign specially and you 803 need to use TWO percent signs for each single one you want to use in the 804 URL. 805 806 If you want a literal percent sign to be part of the data you pass in a POST 807 using -d/--data you must encode it as '%25' (which then also needs the 808 percent sign doubled on Windows machines). 809 810 4.3 How can I use {, }, [ or ] to specify multiple URLs? 811 812 Because those letters have a special meaning to the shell, to be used in 813 a URL specified to curl you must quote them. 814 815 An example that downloads two URLs (sequentially) would be: 816 817 curl '{curl,www}.haxx.se' 818 819 To be able to use those characters as actual parts of the URL (without using 820 them for the curl URL "globbing" system), use the -g/--globoff option: 821 822 curl -g 'www.example.com/weirdname[].html' 823 824 4.4 Why do I get downloaded data even though the webpage does not exist? 825 826 curl asks remote servers for the page you specify. If the page does not exist 827 at the server, the HTTP protocol defines how the server should respond and 828 that means that headers and a "page" will be returned. That is simply how 829 HTTP works. 830 831 By using the --fail option you can tell curl explicitly to not get any data 832 if the HTTP return code does not say success. 833 834 4.5 Why do I get return code XXX from an HTTP server? 835 836 RFC 2616 clearly explains the return codes. This is a short transcript. Go 837 read the RFC for exact details: 838 839 4.5.1 "400 Bad Request" 840 841 The request could not be understood by the server due to malformed 842 syntax. The client SHOULD NOT repeat the request without modifications. 843 844 4.5.2 "401 Unauthorized" 845 846 The request requires user authentication. 847 848 4.5.3 "403 Forbidden" 849 850 The server understood the request, but is refusing to fulfill it. 851 Authorization will not help and the request SHOULD NOT be repeated. 852 853 4.5.4 "404 Not Found" 854 855 The server has not found anything matching the Request-URI. No indication 856 is given as to whether the condition is temporary or permanent. 857 858 4.5.5 "405 Method Not Allowed" 859 860 The method specified in the Request-Line is not allowed for the resource 861 identified by the Request-URI. The response MUST include an Allow header 862 containing a list of valid methods for the requested resource. 863 864 4.5.6 "301 Moved Permanently" 865 866 If you get this return code and an HTML output similar to this: 867 868 <H1>Moved Permanently</H1> The document has moved <A 869 HREF="http://same_url_now_with_a_trailing_slash/">here</A>. 870 871 it might be because you requested a directory URL but without the trailing 872 slash. Try the same operation again _with_ the trailing URL, or use the 873 -L/--location option to follow the redirection. 874 875 4.6 Can you tell me what error code 142 means? 876 877 All curl error codes are described at the end of the man page, in the 878 section called "EXIT CODES". 879 880 Error codes that are larger than the highest documented error code means 881 that curl has exited due to a crash. This is a serious error, and we 882 appreciate a detailed bug report from you that describes how we could go 883 ahead and repeat this. 884 885 4.7 How do I keep usernames and passwords secret in curl command lines? 886 887 This problem has two sides: 888 889 The first part is to avoid having clear-text passwords in the command line 890 so that they do not appear in 'ps' outputs and similar. That is easily 891 avoided by using the "-K" option to tell curl to read parameters from a file 892 or stdin to which you can pass the secret info. curl itself will also 893 attempt to "hide" the given password by blanking out the option - this 894 does not work on all platforms. 895 896 To keep the passwords in your account secret from the rest of the world is 897 not a task that curl addresses. You could of course encrypt them somehow to 898 at least hide them from being read by human eyes, but that is not what 899 anyone would call security. 900 901 Also note that regular HTTP (using Basic authentication) and FTP passwords 902 are sent as cleartext across the network. All it takes for anyone to fetch 903 them is to listen on the network. Eavesdropping is easy. Use more secure 904 authentication methods (like Digest, Negotiate or even NTLM) or consider the 905 SSL-based alternatives HTTPS and FTPS. 906 907 4.8 I found a bug 908 909 It is not a bug if the behavior is documented. Read the docs first. 910 Especially check out the KNOWN_BUGS file, it may be a documented bug. 911 912 If it is a problem with a binary you have downloaded or a package for your 913 particular platform, try contacting the person who built the package/archive 914 you have. 915 916 If there is a bug, read the BUGS document first. Then report it as described 917 in there. 918 919 4.9 curl cannot authenticate to a server that requires NTLM? 920 921 NTLM support requires OpenSSL, GnuTLS, mbedTLS, Secure Transport, or 922 Microsoft Windows libraries at build-time to provide this functionality. 923 924 4.10 My HTTP request using HEAD, PUT or DELETE does not 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 are trying to interact with. This is not anything curl can do 933 anything about. 934 935 4.11 Why do 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 When you invoke curl and get an error 60 error back it means that curl 943 could not verify that the server's certificate was good. curl verifies the 944 certificate using the CA cert bundle and verifying for which names the 945 certificate has been granted. 946 947 To completely disable the certificate verification, use -k. This does 948 however enable man-in-the-middle attacks and makes the transfer INSECURE. 949 We strongly advise against doing this for more than experiments. 950 951 If you get this failure with a CA cert bundle installed and used, the 952 server's certificate might not be signed by one of the CA's in your CA 953 store. It might for example be self-signed. You then correct this problem by 954 obtaining a valid CA cert for the server. Or again, decrease the security by 955 disabling this check. 956 957 At times, you find that the verification works in your favorite browser but 958 fails in curl. When this happens, the reason is usually that the server 959 sends an incomplete cert chain. The server is mandated to send all 960 "intermediate certificates" but does not. This typically works with browsers 961 anyway since they A) cache such certs and B) supports AIA which downloads 962 such missing certificates on demand. This is a server misconfiguration. A 963 good way to figure out if this is the case it to use the SSL Labs server 964 test and check the certificate chain: https://www.ssllabs.com/ssltest/ 965 966 Details are also in the SSLCERTS.md document, found online here: 967 https://curl.se/docs/sslcerts.html 968 969 4.13 Why is curl -R on Windows one hour off? 970 971 Since curl 7.53.0 this issue should be fixed as long as curl was built with 972 any modern compiler that allows for a 64-bit curl_off_t type. For older 973 compilers or prior curl versions it may set a time that appears one hour off. 974 This happens due to a flaw in how Windows stores and uses file modification 975 times and it is not easily worked around. For more details read this: 976 https://www.codeproject.com/Articles/1144/Beating-the-Daylight-Savings-Time-bug-and-getting 977 978 4.14 Redirects work in browser but not with curl 979 980 curl supports HTTP redirects well (see item 3.8). Browsers generally support 981 at least two other ways to perform redirects that curl does not: 982 983 Meta tags. You can write an HTML tag that will cause the browser to redirect 984 to another given URL after a certain time. 985 986 JavaScript. You can write a JavaScript program embedded in an HTML page that 987 redirects the browser to another given URL. 988 989 There is no way to make curl follow these redirects. You must either 990 manually figure out what the page is set to do, or write a script that parses 991 the results and fetches the new URL. 992 993 4.15 FTPS does not work 994 995 curl supports FTPS (sometimes known as FTP-SSL) both implicit and explicit 996 mode. 997 998 When a URL is used that starts with FTPS://, curl assumes implicit SSL on 999 the control connection and will therefore immediately connect and try to 1000 speak SSL. FTPS:// connections default to port 990. 1001 1002 To use explicit FTPS, you use an FTP:// URL and the --ftp-ssl option (or one 1003 of its related flavors). This is the most common method, and the one 1004 mandated by RFC 4217. This kind of connection will then of course use the 1005 standard FTP port 21 by default. 1006 1007 4.16 My HTTP POST or PUT requests are slow 1008 1009 libcurl makes all POST and PUT requests (except for requests with a small 1010 request body) use the "Expect: 100-continue" header. This header allows the 1011 server to deny the operation early so that libcurl can bail out before having 1012 to send any data. This is useful in authentication cases and others. 1013 1014 However, many servers do not implement the Expect: stuff properly and if the 1015 server does not respond (positively) within 1 second libcurl will continue 1016 and send off the data anyway. 1017 1018 You can disable libcurl's use of the Expect: header the same way you disable 1019 any header, using -H / CURLOPT_HTTPHEADER, or by forcing it to use HTTP 1.0. 1020 1021 4.17 Non-functional connect timeouts 1022 1023 In most Windows setups having a timeout longer than 21 seconds make no 1024 difference, as it will only send 3 TCP SYN packets and no more. The second 1025 packet sent three seconds after the first and the third six seconds after 1026 the second. No more than three packets are sent, no matter how long the 1027 timeout is set. 1028 1029 See option TcpMaxConnectRetransmissions on this page: 1030 https://support.microsoft.com/en-us/kb/175523/en-us 1031 1032 Also, even on non-Windows systems there may run a firewall or anti-virus 1033 software or similar that accepts the connection but does not actually do 1034 anything else. This will make (lib)curl to consider the connection connected 1035 and thus the connect timeout will not trigger. 1036 1037 4.18 file:// URLs containing drive letters (Windows, NetWare) 1038 1039 When using curl to try to download a local file, one might use a URL 1040 in this format: 1041 1042 file://D:/blah.txt 1043 1044 you will find that even if D:\blah.txt does exist, curl returns a 'file 1045 not found' error. 1046 1047 According to RFC 1738 (https://www.ietf.org/rfc/rfc1738.txt), 1048 file:// URLs must contain a host component, but it is ignored by 1049 most implementations. In the above example, 'D:' is treated as the 1050 host component, and is taken away. Thus, curl tries to open '/blah.txt'. 1051 If your system is installed to drive C:, that will resolve to 'C:\blah.txt', 1052 and if that does not exist you will get the not found error. 1053 1054 To fix this problem, use file:// URLs with *three* leading slashes: 1055 1056 file:///D:/blah.txt 1057 1058 Alternatively, if it makes more sense, specify 'localhost' as the host 1059 component: 1060 1061 file://localhost/D:/blah.txt 1062 1063 In either case, curl should now be looking for the correct file. 1064 1065 4.19 Why does not curl return an error when the network cable is unplugged? 1066 1067 Unplugging a cable is not an error situation. The TCP/IP protocol stack 1068 was designed to be fault tolerant, so even though there may be a physical 1069 break somewhere the connection should not be affected, just possibly 1070 delayed. Eventually, the physical break will be fixed or the data will be 1071 re-routed around the physical problem through another path. 1072 1073 In such cases, the TCP/IP stack is responsible for detecting when the 1074 network connection is irrevocably lost. Since with some protocols it is 1075 perfectly legal for the client to wait indefinitely for data, the stack may 1076 never report a problem, and even when it does, it can take up to 20 minutes 1077 for it to detect an issue. The curl option --keepalive-time enables 1078 keep-alive support in the TCP/IP stack which makes it periodically probe the 1079 connection to make sure it is still available to send data. That should 1080 reliably detect any TCP/IP network failure. 1081 1082 TCP keep alive will not detect the network going down before the TCP/IP 1083 connection is established (e.g. during a DNS lookup) or using protocols that 1084 do not use TCP. To handle those situations, curl offers a number of timeouts 1085 on its own. --speed-limit/--speed-time will abort if the data transfer rate 1086 falls too low, and --connect-timeout and --max-time can be used to put an 1087 overall timeout on the connection phase or the entire transfer. 1088 1089 A libcurl-using application running in a known physical environment (e.g. 1090 an embedded device with only a single network connection) may want to act 1091 immediately if its lone network connection goes down. That can be achieved 1092 by having the application monitor the network connection on its own using an 1093 OS-specific mechanism, then signaling libcurl to abort (see also item 5.13). 1094 1095 4.20 curl does not return error for HTTP non-200 responses 1096 1097 Correct. Unless you use -f (--fail). 1098 1099 When doing HTTP transfers, curl will perform exactly what you are asking it 1100 to do and if successful it will not return an error. You can use curl to 1101 test your web server's "file not found" page (that gets 404 back), you can 1102 use it to check your authentication protected webpages (that gets a 401 1103 back) and so on. 1104 1105 The specific HTTP response code does not constitute a problem or error for 1106 curl. It simply sends and delivers HTTP as you asked and if that worked, 1107 everything is fine and dandy. The response code is generally providing more 1108 higher level error information that curl does not care about. The error was 1109 not in the HTTP transfer. 1110 1111 If you want your command line to treat error codes in the 400 and up range 1112 as errors and thus return a non-zero value and possibly show an error 1113 message, curl has a dedicated option for that: -f (CURLOPT_FAILONERROR in 1114 libcurl speak). 1115 1116 You can also use the -w option and the variable %{response_code} to extract 1117 the exact response code that was returned in the response. 1118 11195. libcurl Issues 1120 1121 5.1 Is libcurl thread-safe? 1122 1123 Yes. 1124 1125 We have written the libcurl code specifically adjusted for multi-threaded 1126 programs. libcurl will use thread-safe functions instead of non-safe ones if 1127 your system has such. Note that you must never share the same handle in 1128 multiple threads. 1129 1130 There may be some exceptions to thread safety depending on how libcurl was 1131 built. Please review the guidelines for thread safety to learn more: 1132 https://curl.se/libcurl/c/threadsafe.html 1133 1134 5.2 How can I receive all data into a large memory chunk? 1135 1136 [ See also the examples/getinmemory.c source ] 1137 1138 You are in full control of the callback function that gets called every time 1139 there is data received from the remote server. You can make that callback do 1140 whatever you want. You do not have to write the received data to a file. 1141 1142 One solution to this problem could be to have a pointer to a struct that you 1143 pass to the callback function. You set the pointer using the 1144 CURLOPT_WRITEDATA option. Then that pointer will be passed to the callback 1145 instead of a FILE * to a file: 1146 1147 /* imaginary struct */ 1148 struct MemoryStruct { 1149 char *memory; 1150 size_t size; 1151 }; 1152 1153 /* imaginary callback function */ 1154 size_t 1155 WriteMemoryCallback(void *ptr, size_t size, size_t nmemb, void *data) 1156 { 1157 size_t realsize = size * nmemb; 1158 struct MemoryStruct *mem = (struct MemoryStruct *)data; 1159 1160 mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1); 1161 if (mem->memory) { 1162 memcpy(&(mem->memory[mem->size]), ptr, realsize); 1163 mem->size += realsize; 1164 mem->memory[mem->size] = 0; 1165 } 1166 return realsize; 1167 } 1168 1169 5.3 How do I fetch multiple files with libcurl? 1170 1171 libcurl has excellent support for transferring multiple files. You should 1172 just repeatedly set new URLs with curl_easy_setopt() and then transfer it 1173 with curl_easy_perform(). The handle you get from curl_easy_init() is not 1174 only reusable, but you are even encouraged to reuse it if you can, as that 1175 will enable libcurl to use persistent connections. 1176 1177 5.4 Does libcurl do Winsock initialization on Win32 systems? 1178 1179 Yes, if told to in the curl_global_init() call. 1180 1181 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on Win32 ? 1182 1183 Yes, but you cannot open a FILE * and pass the pointer to a DLL and have 1184 that DLL use the FILE * (as the DLL and the client application cannot access 1185 each others' variable memory areas). If you set CURLOPT_WRITEDATA you must 1186 also use CURLOPT_WRITEFUNCTION as well to set a function that writes the 1187 file, even if that simply writes the data to the specified FILE *. 1188 Similarly, if you use CURLOPT_READDATA you must also specify 1189 CURLOPT_READFUNCTION. 1190 1191 5.6 What about Keep-Alive or persistent connections? 1192 1193 curl and libcurl have excellent support for persistent connections when 1194 transferring several files from the same server. curl will attempt to reuse 1195 connections for all URLs specified on the same command line/config file, and 1196 libcurl will reuse connections for all transfers that are made using the 1197 same libcurl handle. 1198 1199 When you use the easy interface the connection cache is kept within the easy 1200 handle. If you instead use the multi interface, the connection cache will be 1201 kept within the multi handle and will be shared among all the easy handles 1202 that are used within the same multi handle. 1203 1204 5.7 Link errors when building libcurl on Windows 1205 1206 You need to make sure that your project, and all the libraries (both static 1207 and dynamic) that it links against, are compiled/linked against the same run 1208 time library. 1209 1210 This is determined by the /MD, /ML, /MT (and their corresponding /M?d) 1211 options to the command line compiler. /MD (linking against MSVCRT dll) seems 1212 to be the most commonly used option. 1213 1214 When building an application that uses the static libcurl library, you must 1215 add -DCURL_STATICLIB to your CFLAGS. Otherwise the linker will look for 1216 dynamic import symbols. If you are using Visual Studio, you need to instead 1217 add CURL_STATICLIB in the "Preprocessor Definitions" section. 1218 1219 If you get a linker error like "unknown symbol __imp__curl_easy_init ..." you 1220 have linked against the wrong (static) library. If you want to use the 1221 libcurl.dll and import lib, you do not need any extra CFLAGS, but use one of 1222 the import libraries below. These are the libraries produced by the various 1223 lib/Makefile.* files: 1224 1225 Target: static lib. import lib for libcurl*.dll. 1226 ----------------------------------------------------------- 1227 MinGW: libcurl.a libcurldll.a 1228 MSVC (release): libcurl.lib libcurl_imp.lib 1229 MSVC (debug): libcurld.lib libcurld_imp.lib 1230 Borland: libcurl.lib libcurl_imp.lib 1231 1232 5.8 libcurl.so.X: open failed: No such file or directory 1233 1234 This is an error message you might get when you try to run a program linked 1235 with a shared version of libcurl and your runtime linker (ld.so) could not 1236 find the shared library named libcurl.so.X. (Where X is the number of the 1237 current libcurl ABI, typically 3 or 4). 1238 1239 You need to make sure that ld.so finds libcurl.so.X. You can do that 1240 multiple ways, and it differs somewhat between different operating systems. 1241 They are usually: 1242 1243 * Add an option to the linker command line that specify the hard-coded path 1244 the runtime linker should check for the lib (usually -R) 1245 1246 * Set an environment variable (LD_LIBRARY_PATH for example) where ld.so 1247 should check for libs 1248 1249 * Adjust the system's config to check for libs in the directory where you have 1250 put the library (like Linux's /etc/ld.so.conf) 1251 1252 'man ld.so' and 'man ld' will tell you more details 1253 1254 5.9 How does libcurl resolve hostnames? 1255 1256 libcurl supports a large number of name resolve functions. One of them is 1257 picked at build-time and will be used unconditionally. Thus, if you want to 1258 change name resolver function you must rebuild libcurl and tell it to use a 1259 different function. 1260 1261 - The non-IPv6 resolver that can use one of four different hostname resolve 1262 calls (depending on what your system supports): 1263 1264 A - gethostbyname() 1265 B - gethostbyname_r() with 3 arguments 1266 C - gethostbyname_r() with 5 arguments 1267 D - gethostbyname_r() with 6 arguments 1268 1269 - The IPv6-resolver that uses getaddrinfo() 1270 1271 - The c-ares based name resolver that uses the c-ares library for resolves. 1272 Using this offers asynchronous name resolves. 1273 1274 - The threaded resolver (default option on Windows). It uses: 1275 1276 A - gethostbyname() on plain IPv4 hosts 1277 B - getaddrinfo() on IPv6 enabled hosts 1278 1279 Also note that libcurl never resolves or reverse-lookups addresses given as 1280 pure numbers, such as 127.0.0.1 or ::1. 1281 1282 5.10 How do I prevent libcurl from writing the response to stdout? 1283 1284 libcurl provides a default built-in write function that writes received data 1285 to stdout. Set the CURLOPT_WRITEFUNCTION to receive the data, or possibly 1286 set CURLOPT_WRITEDATA to a different FILE * handle. 1287 1288 5.11 How do I make libcurl not receive the whole HTTP response? 1289 1290 You make the write callback (or progress callback) return an error and 1291 libcurl will then abort the transfer. 1292 1293 5.12 Can I make libcurl fake or hide my real IP address? 1294 1295 No. libcurl operates on a higher level. Besides, faking IP address would 1296 imply sending IP packets with a made-up source address, and then you normally 1297 get a problem with receiving the packet sent back as they would then not be 1298 routed to you. 1299 1300 If you use a proxy to access remote sites, the sites will not see your local 1301 IP address but instead the address of the proxy. 1302 1303 Also note that on many networks NATs or other IP-munging techniques are used 1304 that makes you see and use a different IP address locally than what the 1305 remote server will see you coming from. You may also consider using 1306 https://www.torproject.org/ . 1307 1308 5.13 How do I stop an ongoing transfer? 1309 1310 With the easy interface you make sure to return the correct error code from 1311 one of the callbacks, but none of them are instant. There is no function you 1312 can call from another thread or similar that will stop it immediately. 1313 Instead, you need to make sure that one of the callbacks you use returns an 1314 appropriate value that will stop the transfer. Suitable callbacks that you 1315 can do this with include the progress callback, the read callback and the 1316 write callback. 1317 1318 If you are using the multi interface, you can also stop a transfer by 1319 removing the particular easy handle from the multi stack at any moment you 1320 think the transfer is done or when you wish to abort the transfer. 1321 1322 5.14 Using C++ non-static functions for callbacks? 1323 1324 libcurl is a C library, it does not know anything about C++ member functions. 1325 1326 You can overcome this "limitation" with relative ease using a static 1327 member function that is passed a pointer to the class: 1328 1329 // f is the pointer to your object. 1330 static size_t YourClass::func(void *buffer, size_t sz, size_t n, void *f) 1331 { 1332 // Call non-static member function. 1333 static_cast<YourClass*>(f)->nonStaticFunction(); 1334 } 1335 1336 // This is how you pass pointer to the static function: 1337 curl_easy_setopt(hcurl, CURLOPT_WRITEFUNCTION, YourClass::func); 1338 curl_easy_setopt(hcurl, CURLOPT_WRITEDATA, this); 1339 1340 5.15 How do I get an FTP directory listing? 1341 1342 If you end the FTP URL you request with a slash, libcurl will provide you 1343 with a directory listing of that given directory. You can also set 1344 CURLOPT_CUSTOMREQUEST to alter what exact listing command libcurl would use 1345 to list the files. 1346 1347 The follow-up question tends to be how is a program supposed to parse the 1348 directory listing. How does it know what's a file and what's a directory and 1349 what's a symlink etc. If the FTP server supports the MLSD command then it 1350 will return data in a machine-readable format that can be parsed for type. 1351 The types are specified by RFC 3659 section 7.5.1. If MLSD is not supported 1352 then you have to work with what you are given. The LIST output format is 1353 entirely at the server's own liking and the NLST output does not reveal any 1354 types and in many cases does not even include all the directory entries. 1355 Also, both LIST and NLST tend to hide Unix-style hidden files (those that 1356 start with a dot) by default so you need to do "LIST -a" or similar to see 1357 them. 1358 1359 Example - List only directories. 1360 ftp.funet.fi supports MLSD and ftp.kernel.org does not: 1361 1362 curl -s ftp.funet.fi/pub/ -X MLSD | \ 1363 perl -lne 'print if s/(?:^|;)type=dir;[^ ]+ (.+)$/$1/' 1364 1365 curl -s ftp.kernel.org/pub/linux/kernel/ | \ 1366 perl -lne 'print if s/^d[-rwx]{9}(?: +[^ ]+){7} (.+)$/$1/' 1367 1368 If you need to parse LIST output in libcurl one such existing 1369 list parser is available at https://cr.yp.to/ftpparse.html Versions of 1370 libcurl since 7.21.0 also provide the ability to specify a wildcard to 1371 download multiple files from one FTP directory. 1372 1373 5.16 I want a different time-out 1374 1375 Sometimes users realize that CURLOPT_TIMEOUT and CURLOPT_CONNECTIMEOUT are 1376 not sufficiently advanced or flexible to cover all the various use cases and 1377 scenarios applications end up with. 1378 1379 libcurl offers many more ways to time-out operations. A common alternative 1380 is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to 1381 specify the lowest possible speed to accept before to consider the transfer 1382 timed out. 1383 1384 The most flexible way is by writing your own time-out logic and using 1385 CURLOPT_XFERINFOFUNCTION (perhaps in combination with other callbacks) and 1386 use that to figure out exactly when the right condition is met when the 1387 transfer should get stopped. 1388 1389 5.17 Can I write a server with libcurl? 1390 1391 No. libcurl offers no functions or building blocks to build any kind of 1392 Internet protocol server. libcurl is only a client-side library. For server 1393 libraries, you need to continue your search elsewhere but there exist many 1394 good open source ones out there for most protocols you could want a server 1395 for. There are also really good stand-alone servers that have been tested 1396 and proven for many years. There is no need for you to reinvent them. 1397 1398 5.18 Does libcurl use threads? 1399 1400 Put simply: no, libcurl will execute in the same thread you call it in. All 1401 callbacks will be called in the same thread as the one you call libcurl in. 1402 1403 If you want to avoid your thread to be blocked by the libcurl call, you make 1404 sure you use the non-blocking multi API which will do transfers 1405 asynchronously - still in the same single thread. 1406 1407 libcurl will potentially internally use threads for name resolving, if it 1408 was built to work like that, but in those cases it will create the child 1409 threads by itself and they will only be used and then killed internally by 1410 libcurl and never exposed to the outside. 1411 14126. License Issues 1413 1414 curl and libcurl are released under a MIT/X derivative license. The license 1415 is liberal and should not impose a problem for your project. This section is 1416 just a brief summary for the cases we get the most questions. (Parts of this 1417 section was much enhanced by Bjorn Reese.) 1418 1419 We are not lawyers and this is not legal advice. You should probably consult 1420 one if you want true and accurate legal insights without our prejudice. Note 1421 especially that this section concerns the libcurl license only; compiling in 1422 features of libcurl that depend on other libraries (e.g. OpenSSL) may affect 1423 the licensing obligations of your application. 1424 1425 6.1 I have a GPL program, can I use the libcurl library? 1426 1427 Yes 1428 1429 Since libcurl may be distributed under the MIT/X derivative license, it can 1430 be used together with GPL in any software. 1431 1432 6.2 I have a closed-source program, can I use the libcurl library? 1433 1434 Yes 1435 1436 libcurl does not put any restrictions on the program that uses the library. 1437 1438 6.3 I have a BSD licensed program, can I use the libcurl library? 1439 1440 Yes 1441 1442 libcurl does not put any restrictions on the program that uses the library. 1443 1444 6.4 I have a program that uses LGPL libraries, can I use libcurl? 1445 1446 Yes 1447 1448 The LGPL license does not clash with other licenses. 1449 1450 6.5 Can I modify curl/libcurl for my program and keep the changes secret? 1451 1452 Yes 1453 1454 The MIT/X derivative license practically allows you to do almost anything 1455 with the sources, on the condition that the copyright texts in the sources 1456 are left intact. 1457 1458 6.6 Can you please change the curl/libcurl license to XXXX? 1459 1460 No. 1461 1462 We have carefully picked this license after years of development and 1463 discussions and a large amount of people have contributed with source code 1464 knowing that this is the license we use. This license puts the restrictions 1465 we want on curl/libcurl and it does not spread to other programs or 1466 libraries that use it. It should be possible for everyone to use libcurl or 1467 curl in their projects, no matter what license they already have in use. 1468 1469 6.7 What are my obligations when using libcurl in my commercial apps? 1470 1471 Next to none. All you need to adhere to is the MIT-style license (stated in 1472 the COPYING file) which basically says you have to include the copyright 1473 notice in "all copies" and that you may not use the copyright holder's name 1474 when promoting your software. 1475 1476 You do not have to release any of your source code. 1477 1478 You do not have to reveal or make public any changes to the libcurl source 1479 code. 1480 1481 You do not have to broadcast to the world that you are using libcurl within 1482 your app. 1483 1484 All we ask is that you disclose "the copyright notice and this permission 1485 notice" somewhere. Most probably like in the documentation or in the section 1486 where other third party dependencies already are mentioned and acknowledged. 1487 1488 As can be seen here: https://curl.se/docs/companies.html and elsewhere, 1489 more and more companies are discovering the power of libcurl and take 1490 advantage of it even in commercial environments. 1491 1492 14937. PHP/CURL Issues 1494 1495 7.1 What is PHP/CURL? 1496 1497 The module for PHP that makes it possible for PHP programs to access curl- 1498 functions from within PHP. 1499 1500 In the cURL project we call this module PHP/CURL to differentiate it from 1501 curl the command line tool and libcurl the library. The PHP team however 1502 does not refer to it like this (for unknown reasons). They call it plain 1503 CURL (often using all caps) or sometimes ext/curl, but both cause much 1504 confusion to users which in turn gives us a higher question load. 1505 1506 7.2 Who wrote PHP/CURL? 1507 1508 PHP/CURL was initially written by Sterling Hughes. 1509 1510 7.3 Can I perform multiple requests using the same handle? 1511 1512 Yes - at least in PHP version 4.3.8 and later (this has been known to not 1513 work in earlier versions, but the exact version when it started to work is 1514 unknown to me). 1515 1516 After a transfer, you just set new options in the handle and make another 1517 transfer. This will make libcurl reuse the same connection if it can. 1518 1519 7.4 Does PHP/CURL have dependencies? 1520 1521 PHP/CURL is a module that comes with the regular PHP package. It depends on 1522 and uses libcurl, so you need to have libcurl installed properly before 1523 PHP/CURL can be used. 1524 15258. Development 1526 1527 8.1 Why does curl use C89? 1528 1529 As with everything in curl, there is a history and we keep using what we have 1530 used before until someone brings up the subject and argues for and works on 1531 changing it. 1532 1533 We started out using C89 in the 1990s because that was the only way to write 1534 a truly portable C program and have it run as widely as possible. C89 was for 1535 a long time even necessary to make things work on otherwise considered modern 1536 platforms such as Windows. Today, we do not really know how many users that 1537 still require the use of a C89 compiler. 1538 1539 We will continue to use C89 for as long as nobody brings up a strong enough 1540 reason for us to change our minds. The core developers of the project do not 1541 feel restricted by this and we are not convinced that going C99 will offer us 1542 enough of a benefit to warrant the risk of cutting off a share of users. 1543 1544 8.2 Will curl be rewritten? 1545 1546 In one go: no. Little by little over time? Maybe. 1547 1548 Over the years, new languages and clever operating environments come and go. 1549 Every now and then the urge apparently arises to request that we rewrite curl 1550 in another language. 1551 1552 Some the most important properties in curl are maintaining the API and ABI 1553 for libcurl and keeping the behavior for the command line tool. As long as we 1554 can do that, everything else is up for discussion. To maintain the ABI, we 1555 probably have to maintain a certain amount of code in C, and to remain rock 1556 stable, we will never risk anything by rewriting a lot of things in one go. 1557 That said, we can certainly offer more and more optional backends written in 1558 other languages, as long as those backends can be plugged in at build-time. 1559 Backends can be written in any language, but should probably provide APIs 1560 usable from C to ease integration and transition. 1561