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Diffstat (limited to 'docs/FAQ')
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1 files changed, 63 insertions, 65 deletions
@@ -65,19 +65,19 @@ FAQ 4.5.6 "301 Moved Permanently" 4.6 Can you tell me what error code 142 means? 4.7 How do I keep user names and passwords secret in curl command lines? - 4.8 I found a bug! + 4.8 I found a bug 4.9 curl cannot authenticate to the server that requires NTLM? - 4.10 My HTTP request using HEAD, PUT or DELETE does not work! + 4.10 My HTTP request using HEAD, PUT or DELETE does not work 4.11 Why do my HTTP range requests return the full document? 4.12 Why do I get "certificate verify failed" ? 4.13 Why is curl -R on Windows one hour off? - 4.14 Redirects work in browser but not with curl! + 4.14 Redirects work in browser but not with curl 4.15 FTPS does not work - 4.16 My HTTP POST or PUT requests are slow! + 4.16 My HTTP POST or PUT requests are slow 4.17 Non-functional connect timeouts on Windows 4.18 file:// URLs containing drive letters (Windows, NetWare) 4.19 Why does not curl return an error when the network cable is unplugged? - 4.20 curl does not return error for HTTP non-200 responses! + 4.20 curl does not return error for HTTP non-200 responses 5. libcurl Issues 5.1 Is libcurl thread-safe? @@ -86,7 +86,7 @@ FAQ 5.4 Does libcurl do Winsock initialization on win32 systems? 5.5 Does CURLOPT_WRITEDATA and CURLOPT_READDATA work on win32 ? 5.6 What about Keep-Alive or persistent connections? - 5.7 Link errors when building libcurl on Windows! + 5.7 Link errors when building libcurl on Windows 5.8 libcurl.so.X: open failed: No such file or directory 5.9 How does libcurl resolve host names? 5.10 How do I prevent libcurl from writing the response to stdout? @@ -95,7 +95,7 @@ FAQ 5.13 How do I stop an ongoing transfer? 5.14 Using C++ non-static functions for callbacks? 5.15 How do I get an FTP directory listing? - 5.16 I want a different time-out! + 5.16 I want a different time-out 5.17 Can I write a server with libcurl? 5.18 Does libcurl use threads? @@ -134,14 +134,13 @@ FAQ libcurl - A free and easy-to-use client-side URL transfer library, supporting DICT, - FILE, FTP, FTPS, GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, - MQTT, POP3, POP3S, RTMP, RTMPS, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, - TELNET and TFTP. + A client-side URL transfer library, supporting DICT, FILE, FTP, FTPS, + GOPHER, GOPHERS, HTTP, HTTPS, IMAP, IMAPS, LDAP, LDAPS, MQTT, POP3, POP3S, + RTMP, RTMPS, RTSP, SCP, SFTP, SMB, SMBS, SMTP, SMTPS, TELNET and TFTP. libcurl supports HTTPS certificates, HTTP POST, HTTP PUT, FTP uploading, Kerberos, SPNEGO, HTTP form based upload, proxies, cookies, user+password - authentication, file transfer resume, http proxy tunneling and more! + authentication, file transfer resume, http proxy tunneling and more. libcurl is highly portable, it builds and works identically on numerous platforms, including Solaris, NetBSD, FreeBSD, OpenBSD, Darwin, HP-UX, @@ -175,7 +174,7 @@ FAQ libcurl is a reliable and portable library for doing Internet data transfers using one or more of its supported Internet protocols. - You can use libcurl for free in your application, be it open source, + You can use libcurl freely in your application, be it open source, commercial or closed-source. libcurl is most probably the most portable, most powerful and most often @@ -184,7 +183,7 @@ FAQ 1.3 What is curl not? - curl is not a wget clone. That is a common misconception. Never, during + curl is not a wget clone. That is a common misconception. Never, during curl's development, have we intended curl to replace wget or compete on its market. curl is targeted at single-shot file transfers. @@ -247,9 +246,8 @@ FAQ 1.6 What do you get for making curl? Project cURL is entirely free and open. We do this voluntarily, mostly in - our spare time. Companies may pay individual developers to work on curl, - but that is up to each company and developer. This is not controlled by nor - supervised in any way by the curl project. + our spare time. Companies may pay individual developers to work on curl. + This is not controlled by nor supervised in any way by the curl project. We get help from companies. Haxx provides website, bandwidth, mailing lists etc, GitHub hosts the primary git repository and other services like the bug @@ -538,14 +536,14 @@ FAQ about bindings on the curl-library list too, but be prepared that people on that list may not know anything about bindings. - In February 2019, there were interfaces available for the following + In December 2021, there were interfaces available for the following languages: Ada95, Basic, C, C++, Ch, Cocoa, D, Delphi, Dylan, Eiffel, Euphoria, Falcon, Ferite, Gambas, glib/GTK+, Go, Guile, Harbour, Haskell, Java, Julia, Lisp, Lua, Mono, .NET, node.js, Object-Pascal, OCaml, Pascal, Perl, PHP, PostgreSQL, Python, R, Rexx, Ring, RPG, Ruby, Rust, Scheme, Scilab, S-Lang, Smalltalk, SP-Forth, SPL, Tcl, Visual Basic, Visual FoxPro, Q, wxwidgets, XBLite and Xoho. By the time you read this, additional ones - may have appeared! + may have appeared. 3.10 What about SOAP, WebDAV, XML-RPC or similar protocols over HTTP? @@ -640,7 +638,7 @@ FAQ CLIENT CERTIFICATE The server you communicate with may require that you can provide this in - order to prove that you actually are who you claim to be. If the server + order to prove that you actually are who you claim to be. If the server does not require this, you do not need a client certificate. A client certificate is always used together with a private key, and the @@ -686,7 +684,7 @@ FAQ No. - But you could easily write your own program using libcurl to do such stunts. + You can easily write your own program using libcurl to do such stunts. 3.19 How do I get HTTP from a host using a specific IP address? @@ -771,7 +769,7 @@ FAQ runs the specified command in the background. To safely send the & as a part of a URL, you should quote the entire URL by using single (') or double (") quotes around it. Similar problems can also occur on some shells with other - characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL. + characters, including ?*!$~(){}<>\|;`. When in doubt, quote the URL. An example that would invoke a remote CGI that uses &-symbols could be: @@ -858,7 +856,7 @@ FAQ Error codes that are larger than the highest documented error code means that curl has exited due to a crash. This is a serious error, and we appreciate a detailed bug report from you that describes how we could go - ahead and repeat this! + ahead and repeat this. 4.7 How do I keep user names and passwords secret in curl command lines? @@ -882,10 +880,10 @@ FAQ authentication methods (like Digest, Negotiate or even NTLM) or consider the SSL-based alternatives HTTPS and FTPS. - 4.8 I found a bug! + 4.8 I found a bug It is not a bug if the behavior is documented. Read the docs first. - Especially check out the KNOWN_BUGS file, it may be a documented bug! + Especially check out the KNOWN_BUGS file, it may be a documented bug. If it is a problem with a binary you have downloaded or a package for your particular platform, try contacting the person who built the package/archive @@ -902,7 +900,7 @@ FAQ NTLM is a Microsoft proprietary protocol. Proprietary formats are evil. You should not use such ones. - 4.10 My HTTP request using HEAD, PUT or DELETE does not work! + 4.10 My HTTP request using HEAD, PUT or DELETE does not work Many web servers allow or demand that the administrator configures the server properly for these requests to work on the web server. @@ -956,7 +954,7 @@ FAQ times and it is not easily worked around. For more details read this: https://www.codeproject.com/Articles/1144/Beating-the-Daylight-Savings-Time-bug-and-getting - 4.14 Redirects work in browser but not with curl! + 4.14 Redirects work in browser but not with curl curl supports HTTP redirects well (see item 3.8). Browsers generally support at least two other ways to perform redirects that curl does not: @@ -985,7 +983,7 @@ FAQ mandated by RFC4217. This kind of connection will then of course use the standard FTP port 21 by default. - 4.16 My HTTP POST or PUT requests are slow! + 4.16 My HTTP POST or PUT requests are slow libcurl makes all POST and PUT requests (except for POST requests with a tiny request body) use the "Expect: 100-continue" header. This header @@ -1005,7 +1003,7 @@ FAQ In most Windows setups having a timeout longer than 21 seconds make no difference, as it will only send 3 TCP SYN packets and no more. The second packet sent three seconds after the first and the third six seconds after - the second. No more than three packets are sent, no matter how long the + the second. No more than three packets are sent, no matter how long the timeout is set. See option TcpMaxConnectRetransmissions on this page: @@ -1049,32 +1047,32 @@ FAQ Unplugging a cable is not an error situation. The TCP/IP protocol stack was designed to be fault tolerant, so even though there may be a physical break somewhere the connection should not be affected, just possibly - delayed. Eventually, the physical break will be fixed or the data will be + delayed. Eventually, the physical break will be fixed or the data will be re-routed around the physical problem through another path. In such cases, the TCP/IP stack is responsible for detecting when the network connection is irrevocably lost. Since with some protocols it is perfectly legal for the client to wait indefinitely for data, the stack may never report a problem, and even when it does, it can take up to 20 minutes - for it to detect an issue. The curl option --keepalive-time enables + for it to detect an issue. The curl option --keepalive-time enables keep-alive support in the TCP/IP stack which makes it periodically probe the connection to make sure it is still available to send data. That should reliably detect any TCP/IP network failure. - But even that will not detect the network going down before the TCP/IP + TCP keep alive will not detect the network going down before the TCP/IP connection is established (e.g. during a DNS lookup) or using protocols that - do not use TCP. To handle those situations, curl offers a number of timeouts + do not use TCP. To handle those situations, curl offers a number of timeouts on its own. --speed-limit/--speed-time will abort if the data transfer rate falls too low, and --connect-timeout and --max-time can be used to put an overall timeout on the connection phase or the entire transfer. A libcurl-using application running in a known physical environment (e.g. an embedded device with only a single network connection) may want to act - immediately if its lone network connection goes down. That can be achieved + immediately if its lone network connection goes down. That can be achieved by having the application monitor the network connection on its own using an OS-specific mechanism, then signaling libcurl to abort (see also item 5.13). - 4.20 curl does not return error for HTTP non-200 responses! + 4.20 curl does not return error for HTTP non-200 responses Correct. Unless you use -f (--fail). @@ -1106,7 +1104,7 @@ FAQ We have written the libcurl code specifically adjusted for multi-threaded programs. libcurl will use thread-safe functions instead of non-safe ones if - your system has such. Note that you must never share the same handle in + your system has such. Note that you must never share the same handle in multiple threads. There may be some exceptions to thread safety depending on how libcurl was @@ -1183,7 +1181,7 @@ FAQ kept within the multi handle and will be shared among all the easy handles that are used within the same multi handle. - 5.7 Link errors when building libcurl on Windows! + 5.7 Link errors when building libcurl on Windows You need to make sure that your project, and all the libraries (both static and dynamic) that it links against, are compiled/linked against the same run @@ -1199,7 +1197,7 @@ FAQ add CURL_STATICLIB in the "Preprocessor Definitions" section. If you get linker error like "unknown symbol __imp__curl_easy_init ..." you - have linked against the wrong (static) library. If you want to use the + have linked against the wrong (static) library. If you want to use the libcurl.dll and import lib, you do not need any extra CFLAGS, but use one of the import libraries below. These are the libraries produced by the various lib/Makefile.* files: @@ -1219,8 +1217,8 @@ FAQ current libcurl ABI, typically 3 or 4). You need to make sure that ld.so finds libcurl.so.X. You can do that - multiple ways, and it differs somewhat between different operating systems, - but they are usually: + multiple ways, and it differs somewhat between different operating systems. + They are usually: * Add an option to the linker command line that specify the hard-coded path the run-time linker should check for the lib (usually -R) @@ -1235,10 +1233,10 @@ FAQ 5.9 How does libcurl resolve host names? - libcurl supports a large a number of different name resolve functions. One - of them is picked at build-time and will be used unconditionally. Thus, if - you want to change name resolver function you must rebuild libcurl and tell - it to use a different function. + libcurl supports a large number of name resolve functions. One of them is + picked at build-time and will be used unconditionally. Thus, if you want to + change name resolver function you must rebuild libcurl and tell it to use a + different function. - The non-IPv6 resolver that can use one of four different host name resolve calls (depending on what your system supports): @@ -1277,7 +1275,7 @@ FAQ No. libcurl operates on a higher level. Besides, faking IP address would imply sending IP packets with a made-up source address, and then you normally get a problem with receiving the packet sent back as they would then not be - routed to you! + routed to you. If you use a proxy to access remote sites, the sites will not see your local IP address but instead the address of the proxy. @@ -1293,7 +1291,7 @@ FAQ one of the callbacks, but none of them are instant. There is no function you can call from another thread or similar that will stop it immediately. Instead, you need to make sure that one of the callbacks you use returns an - appropriate value that will stop the transfer. Suitable callbacks that you + appropriate value that will stop the transfer. Suitable callbacks that you can do this with include the progress callback, the read callback and the write callback. @@ -1351,11 +1349,11 @@ FAQ libcurl since 7.21.0 also provide the ability to specify a wildcard to download multiple files from one FTP directory. - 5.16 I want a different time-out! + 5.16 I want a different time-out - Time and time again users realize that CURLOPT_TIMEOUT and - CURLOPT_CONNECTIMEOUT are not sufficiently advanced or flexible to cover all - the various use cases and scenarios applications end up with. + Sometimes users realize that CURLOPT_TIMEOUT and CURLOPT_CONNECTIMEOUT are + not sufficiently advanced or flexible to cover all the various use cases and + scenarios applications end up with. libcurl offers many more ways to time-out operations. A common alternative is to use the CURLOPT_LOW_SPEED_LIMIT and CURLOPT_LOW_SPEED_TIME options to @@ -1372,9 +1370,9 @@ FAQ No. libcurl offers no functions or building blocks to build any kind of internet protocol server. libcurl is only a client-side library. For server libraries, you need to continue your search elsewhere but there exist many - good open source ones out there for most protocols you could possibly want a - server for. And there are really good stand-alone ones that have been tested - and proven for many years. There's no need for you to reinvent them! + good open source ones out there for most protocols you could want a server + for. There are also really good stand-alone servers that have been tested + and proven for many years. There's no need for you to reinvent them. 5.18 Does libcurl use threads? @@ -1382,8 +1380,8 @@ FAQ callbacks will be called in the same thread as the one you call libcurl in. If you want to avoid your thread to be blocked by the libcurl call, you make - sure you use the non-blocking API which will do transfers asynchronously - - but still in the same single thread. + sure you use the non-blocking multi API which will do transfers + asynchronously - still in the same single thread. libcurl will potentially internally use threads for name resolving, if it was built to work like that, but in those cases it will create the child @@ -1405,36 +1403,36 @@ FAQ 6.1 I have a GPL program, can I use the libcurl library? - Yes! + Yes - Since libcurl may be distributed under the MIT/X derivative license, it can be - used together with GPL in any software. + Since libcurl may be distributed under the MIT/X derivative license, it can + be used together with GPL in any software. 6.2 I have a closed-source program, can I use the libcurl library? - Yes! + Yes libcurl does not put any restrictions on the program that uses the library. 6.3 I have a BSD licensed program, can I use the libcurl library? - Yes! + Yes libcurl does not put any restrictions on the program that uses the library. 6.4 I have a program that uses LGPL libraries, can I use libcurl? - Yes! + Yes The LGPL license does not clash with other licenses. 6.5 Can I modify curl/libcurl for my program and keep the changes secret? - Yes! + Yes - The MIT/X derivative license practically allows you to do almost anything with - the sources, on the condition that the copyright texts in the sources are - left intact. + The MIT/X derivative license practically allows you to do almost anything + with the sources, on the condition that the copyright texts in the sources + are left intact. 6.6 Can you please change the curl/libcurl license to XXXX? |