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<!DOCTYPE HTML> <html lang="en" class="light" dir="ltr"> <head>  <meta charset="UTF-8"> <title>Connection reuse - everything curl</title>  <meta name="description" content="everything there is to know about curl, libcurl and the cURL project"> <meta name="viewport" content="width=device-width, initial-scale=1"> <meta name="theme-color" content="#ffffff"> <link rel="icon" href="../../favicon.svg"> <link rel="shortcut icon" href="../../favicon.png"> <link rel="stylesheet" href="../../css/variables.css"> <link rel="stylesheet" href="../../css/general.css"> <link rel="stylesheet" href="../../css/chrome.css"> <link rel="stylesheet" href="../../css/print.css" media="print">  <link rel="stylesheet" href="../../FontAwesome/css/font-awesome.css"> <link rel="stylesheet" href="../../fonts/fonts.css">  <link rel="stylesheet" href="../../highlight.css"> <link rel="stylesheet" href="../../tomorrow-night.css"> <link rel="stylesheet" href="../../ayu-highlight.css">  </head> <body class="sidebar-visible no-js"> <div id="body-container">  <script> var path_to_root = "../../"; var default_theme = window.matchMedia("(prefers-color-scheme: dark)").matches ? 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document.getElementById("sidebar-toggle-anchor"); if (document.body.clientWidth >= 1080) { try { sidebar = localStorage.getItem('mdbook-sidebar'); } catch(e) { } sidebar = sidebar || 'visible'; } else { sidebar = 'hidden'; } sidebar_toggle.checked = sidebar === 'visible'; body.classList.remove('sidebar-visible'); body.classList.add("sidebar-" + sidebar); </script> <nav id="sidebar" class="sidebar" aria-label="Table of contents"> <div class="sidebar-scrollbox"> <ol class="chapter"><li class="chapter-item "><a href="../../index.html"><strong aria-hidden="true">1.</strong> Everything curl</a></li><li class="chapter-item "><a href="../../how-to-read.html"><strong aria-hidden="true">2.</strong> How to read</a></li><li class="chapter-item "><a href="../../project/index.html"><strong aria-hidden="true">3.</strong> The cURL project</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../project/started.html"><strong aria-hidden="true">3.1.</strong> How it started</a></li><li class="chapter-item "><a href="../../project/name.html"><strong aria-hidden="true">3.2.</strong> The name</a></li><li class="chapter-item "><a href="../../project/does.html"><strong aria-hidden="true">3.3.</strong> What does curl do?</a></li><li class="chapter-item "><a href="../../project/comm.html"><strong aria-hidden="true">3.4.</strong> Project communication</a></li><li class="chapter-item "><a href="../../project/etiquette.html"><strong aria-hidden="true">3.5.</strong> Mailing list etiquette</a></li><li class="chapter-item "><a href="../../project/maillists.html"><strong aria-hidden="true">3.6.</strong> Mailing lists</a></li><li class="chapter-item "><a href="../../project/bugs.html"><strong aria-hidden="true">3.7.</strong> Reporting bugs</a></li><li class="chapter-item "><a href="../../project/support.html"><strong aria-hidden="true">3.8.</strong> Commercial support</a></li><li class="chapter-item "><a href="../../project/releases.html"><strong aria-hidden="true">3.9.</strong> Releases</a></li><li class="chapter-item "><a href="../../project/security.html"><strong aria-hidden="true">3.10.</strong> Security</a></li><li class="chapter-item "><a href="../../project/trust.html"><strong aria-hidden="true">3.11.</strong> Trust</a></li><li class="chapter-item "><a href="../../project/coc.html"><strong aria-hidden="true">3.12.</strong> Code of Conduct</a></li><li class="chapter-item "><a href="../../project/devel.html"><strong aria-hidden="true">3.13.</strong> Development</a></li><li class="chapter-item "><a href="../../project/devteam.html"><strong aria-hidden="true">3.14.</strong> The development team</a></li><li class="chapter-item "><a href="../../project/users.html"><strong aria-hidden="true">3.15.</strong> Users of curl</a></li><li class="chapter-item "><a href="../../project/future.html"><strong aria-hidden="true">3.16.</strong> Future</a></li></ol></li><li class="chapter-item "><a href="../../protocols/index.html"><strong aria-hidden="true">4.</strong> Network and protocols</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../protocols/network.html"><strong aria-hidden="true">4.1.</strong> Networking simplified</a></li><li class="chapter-item "><a href="../../protocols/protocols.html"><strong aria-hidden="true">4.2.</strong> Protocols</a></li><li class="chapter-item "><a href="../../protocols/curl.html"><strong aria-hidden="true">4.3.</strong> curl protocols</a></li><li class="chapter-item "><a href="../../protocols/http.html"><strong aria-hidden="true">4.4.</strong> HTTP basics</a></li></ol></li><li class="chapter-item "><a href="../../install/index.html"><strong aria-hidden="true">5.</strong> Install curl and libcurl</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../install/linux.html"><strong aria-hidden="true">5.1.</strong> Linux</a></li><li class="chapter-item "><a href="../../install/windows/index.html"><strong aria-hidden="true">5.2.</strong> Windows</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../install/windows/win-msys2.html"><strong aria-hidden="true">5.2.1.</strong> MSYS2</a></li><li class="chapter-item "><a href="../../install/windows/win-vcpkg.html"><strong aria-hidden="true">5.2.2.</strong> vcpkg</a></li></ol></li><li class="chapter-item "><a href="../../install/macos.html"><strong aria-hidden="true">5.3.</strong> macOS</a></li><li class="chapter-item "><a href="../../install/container.html"><strong aria-hidden="true">5.4.</strong> Container</a></li></ol></li><li class="chapter-item "><a href="../../source/index.html"><strong aria-hidden="true">6.</strong> Source code</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../source/opensource/index.html"><strong aria-hidden="true">6.1.</strong> Open Source</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../source/opensource/license.html"><strong aria-hidden="true">6.1.1.</strong> License</a></li><li class="chapter-item "><a href="../../source/opensource/copyright.html"><strong aria-hidden="true">6.1.2.</strong> Copyright</a></li></ol></li><li class="chapter-item "><a href="../../source/layout.html"><strong aria-hidden="true">6.2.</strong> Code layout</a></li><li class="chapter-item "><a href="../../source/options.html"><strong aria-hidden="true">6.3.</strong> Handling build options</a></li><li class="chapter-item "><a href="../../source/style.html"><strong aria-hidden="true">6.4.</strong> Code style</a></li><li class="chapter-item "><a href="../../source/contributing.html"><strong aria-hidden="true">6.5.</strong> Contributing</a></li><li class="chapter-item "><a href="../../source/reportvuln.html"><strong aria-hidden="true">6.6.</strong> Reporting vulnerabilities</a></li><li class="chapter-item "><a href="../../source/web.html"><strong aria-hidden="true">6.7.</strong> Website</a></li></ol></li><li class="chapter-item "><a href="../../build/index.html"><strong aria-hidden="true">7.</strong> Build curl and libcurl</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../build/autotools.html"><strong aria-hidden="true">7.1.</strong> Autotools</a></li><li class="chapter-item "><a href="../../build/cmake.html"><strong aria-hidden="true">7.2.</strong> CMake</a></li><li class="chapter-item "><a href="../../build/separate.html"><strong aria-hidden="true">7.3.</strong> Separate install</a></li><li class="chapter-item "><a href="../../build/windows.html"><strong aria-hidden="true">7.4.</strong> Windows</a></li><li class="chapter-item "><a href="../../build/deps.html"><strong aria-hidden="true">7.5.</strong> Dependencies</a></li><li class="chapter-item "><a href="../../build/tls.html"><strong aria-hidden="true">7.6.</strong> TLS libraries</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../build/boringssl.html"><strong aria-hidden="true">7.6.1.</strong> BoringSSL</a></li></ol></li></ol></li><li class="chapter-item "><a href="../../cmdline/index.html"><strong aria-hidden="true">8.</strong> Command line concepts</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cmdline/differences.html"><strong aria-hidden="true">8.1.</strong> Differences</a></li><li class="chapter-item "><a href="../../cmdline/options/index.html"><strong aria-hidden="true">8.2.</strong> Command line options</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cmdline/options/short.html"><strong aria-hidden="true">8.2.1.</strong> Short options</a></li><li class="chapter-item "><a href="../../cmdline/options/long.html"><strong aria-hidden="true">8.2.2.</strong> Long options</a></li><li class="chapter-item "><a href="../../cmdline/options/args.html"><strong aria-hidden="true">8.2.3.</strong> Arguments to options</a></li><li class="chapter-item "><a href="../../cmdline/options/negative.html"><strong aria-hidden="true">8.2.4.</strong> Negative options</a></li></ol></li><li class="chapter-item "><a href="../../cmdline/help.html"><strong aria-hidden="true">8.3.</strong> Help</a></li><li class="chapter-item "><a href="../../cmdline/versions.html"><strong aria-hidden="true">8.4.</strong> Options depend on version</a></li><li class="chapter-item "><a href="../../cmdline/urls/index.html"><strong aria-hidden="true">8.5.</strong> URLs</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../cmdline/urls/scheme.html"><strong aria-hidden="true">8.5.1.</strong> Scheme</a></li><li class="chapter-item "><a href="../../cmdline/urls/auth.html"><strong aria-hidden="true">8.5.2.</strong> Name and password</a></li><li class="chapter-item "><a href="../../cmdline/urls/host.html"><strong aria-hidden="true">8.5.3.</strong> Host</a></li><li class="chapter-item "><a href="../../cmdline/urls/port.html"><strong aria-hidden="true">8.5.4.</strong> Port number</a></li><li class="chapter-item "><a href="../../cmdline/urls/path.html"><strong aria-hidden="true">8.5.5.</strong> Path</a></li><li class="chapter-item "><a href="../../cmdline/urls/query.html"><strong aria-hidden="true">8.5.6.</strong> Query</a></li><li class="chapter-item "><a href="../../cmdline/urls/ftptype.html"><strong aria-hidden="true">8.5.7.</strong> FTP type</a></li><li class="chapter-item "><a href="../../cmdline/urls/fragment.html"><strong aria-hidden="true">8.5.8.</strong> Fragment</a></li><li class="chapter-item "><a href="../../cmdline/urls/browsers.html"><strong aria-hidden="true">8.5.9.</strong> Browsers</a></li><li class="chapter-item "><a href="../../cmdline/urls/options.html"><strong aria-hidden="true">8.5.10.</strong> Many options and URLs</a></li><li class="chapter-item "><a href="../../cmdline/urls/globbing.html"><strong aria-hidden="true">8.5.11.</strong> URL globbing</a></li><li class="chapter-item "><a href="../../cmdline/urls/connreuse.html"><strong aria-hidden="true">8.5.12.</strong> Connection reuse</a></li><li class="chapter-item "><a href="../../cmdline/urls/parallel.html"><strong aria-hidden="true">8.5.13.</strong> Parallel transfers</a></li><li class="chapter-item "><a href="../../cmdline/urls/trurl.html"><strong aria-hidden="true">8.5.14.</strong> trurl</a></li></ol></li><li class="chapter-item "><a href="../../cmdline/configfile.html"><strong aria-hidden="true">8.6.</strong> Config file</a></li><li class="chapter-item "><a href="../../cmdline/variables.html"><strong aria-hidden="true">8.7.</strong> Variables</a></li><li class="chapter-item "><a href="../../cmdline/passwords.html"><strong aria-hidden="true">8.8.</strong> Passwords</a></li><li class="chapter-item "><a href="../../cmdline/progressmeter.html"><strong aria-hidden="true">8.9.</strong> Progress meter</a></li><li class="chapter-item "><a href="../../cmdline/curlver.html"><strong aria-hidden="true">8.10.</strong> Version</a></li><li class="chapter-item "><a href="../../cmdline/exitcode.html"><strong aria-hidden="true">8.11.</strong> Exit code</a></li><li class="chapter-item "><a href="../../cmdline/copyas.html"><strong aria-hidden="true">8.12.</strong> Copy as curl</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/index.html"><strong aria-hidden="true">9.</strong> Command line transfers</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/verbose/index.html"><strong aria-hidden="true">9.1.</strong> Verbose</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/verbose/trace.html"><strong aria-hidden="true">9.1.1.</strong> Trace options</a></li><li class="chapter-item "><a href="../../usingcurl/verbose/writeout.html"><strong aria-hidden="true">9.1.2.</strong> Write out</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/downloads/index.html"><strong aria-hidden="true">9.2.</strong> Downloads</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/downloads/whatis.html"><strong aria-hidden="true">9.2.1.</strong> What is downloading?</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/storing.html"><strong aria-hidden="true">9.2.2.</strong> Storing downloads</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/url-named.html"><strong aria-hidden="true">9.2.3.</strong> Download to a file named by the URL</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/content-disp.html"><strong aria-hidden="true">9.2.4.</strong> Use the target filename from the server</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/charsets.html"><strong aria-hidden="true">9.2.5.</strong> HTML and charsets</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/redirects.html"><strong aria-hidden="true">9.2.6.</strong> Shell redirects</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/multiple.html"><strong aria-hidden="true">9.2.7.</strong> Multiple downloads</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/browsers.html"><strong aria-hidden="true">9.2.8.</strong> My browser shows something else</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/max-filesize.html"><strong aria-hidden="true">9.2.9.</strong> Maximum filesize</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/metadata-fs.html"><strong aria-hidden="true">9.2.10.</strong> Storing metadata in file system</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/raw.html"><strong aria-hidden="true">9.2.11.</strong> Raw</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/retry.html"><strong aria-hidden="true">9.2.12.</strong> Retry</a></li><li class="chapter-item "><a href="../../usingcurl/downloads/resume.html"><strong aria-hidden="true">9.2.13.</strong> Resuming and ranges</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/uploads.html"><strong aria-hidden="true">9.3.</strong> Uploads</a></li><li class="chapter-item "><a href="../../usingcurl/transfers/index.html"><strong aria-hidden="true">9.4.</strong> Transfer controls</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/transfers/tooslow.html"><strong aria-hidden="true">9.4.1.</strong> Stop slow transfers</a></li><li class="chapter-item "><a href="../../usingcurl/transfers/rate-limiting.html"><strong aria-hidden="true">9.4.2.</strong> Rate limiting</a></li><li class="chapter-item "><a href="../../usingcurl/transfers/request-rate.html"><strong aria-hidden="true">9.4.3.</strong> Request rate limiting</a></li><li class="chapter-item "><a href="../../usingcurl/transfers/compression.html"><strong aria-hidden="true">9.4.4.</strong> Compression</a></li><li class="chapter-item "><a href="../../usingcurl/transfers/skip.html"><strong aria-hidden="true">9.4.5.</strong> Skip download if already done</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/connections/index.html"><strong aria-hidden="true">9.5.</strong> Connections</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/connections/setup.html"><strong aria-hidden="true">9.5.1.</strong> Setup</a></li><li class="chapter-item "><a href="../../usingcurl/connections/name.html"><strong aria-hidden="true">9.5.2.</strong> Name resolve tricks</a></li><li class="chapter-item "><a href="../../usingcurl/connections/timeout.html"><strong aria-hidden="true">9.5.3.</strong> Connection timeout</a></li><li class="chapter-item "><a href="../../usingcurl/connections/happy.html"><strong aria-hidden="true">9.5.4.</strong> Happy Eyeballs</a></li><li class="chapter-item "><a href="../../usingcurl/connections/interface.html"><strong aria-hidden="true">9.5.5.</strong> Network interface</a></li><li class="chapter-item "><a href="../../usingcurl/connections/local-port.html"><strong aria-hidden="true">9.5.6.</strong> Local port number</a></li><li class="chapter-item "><a href="../../usingcurl/connections/keepalive.html"><strong aria-hidden="true">9.5.7.</strong> Keep alive</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/timeouts.html"><strong aria-hidden="true">9.6.</strong> Timeouts</a></li><li class="chapter-item "><a href="../../usingcurl/netrc.html"><strong aria-hidden="true">9.7.</strong> .netrc</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/index.html"><strong aria-hidden="true">9.8.</strong> Proxies</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/proxies/discover.html"><strong aria-hidden="true">9.8.1.</strong> Discover your proxy</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/pac.html"><strong aria-hidden="true">9.8.2.</strong> PAC</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/captive.html"><strong aria-hidden="true">9.8.3.</strong> Captive portals</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/type.html"><strong aria-hidden="true">9.8.4.</strong> Proxy type</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/http.html"><strong aria-hidden="true">9.8.5.</strong> HTTP proxy</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/socks.html"><strong aria-hidden="true">9.8.6.</strong> SOCKS proxy</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/mitm.html"><strong aria-hidden="true">9.8.7.</strong> MITM proxy</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/auth.html"><strong aria-hidden="true">9.8.8.</strong> Proxy authentication</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/https.html"><strong aria-hidden="true">9.8.9.</strong> HTTPS proxy</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/env.html"><strong aria-hidden="true">9.8.10.</strong> Proxy environment variables</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/headers.html"><strong aria-hidden="true">9.8.11.</strong> Proxy headers</a></li><li class="chapter-item "><a href="../../usingcurl/proxies/haproxy.html"><strong aria-hidden="true">9.8.12.</strong> haproxy</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/tls.html"><strong aria-hidden="true">9.9.</strong> TLS</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/tls/ciphers.html"><strong aria-hidden="true">9.9.1.</strong> Ciphers</a></li><li class="chapter-item "><a href="../../usingcurl/tls/enable.html"><strong aria-hidden="true">9.9.2.</strong> Enable TLS</a></li><li class="chapter-item "><a href="../../usingcurl/tls/versions.html"><strong aria-hidden="true">9.9.3.</strong> TLS versions</a></li><li class="chapter-item "><a href="../../usingcurl/tls/verify.html"><strong aria-hidden="true">9.9.4.</strong> Verifying server certificates</a></li><li class="chapter-item "><a href="../../usingcurl/tls/pinning.html"><strong aria-hidden="true">9.9.5.</strong> Certificate pinning</a></li><li class="chapter-item "><a href="../../usingcurl/tls/stapling.html"><strong aria-hidden="true">9.9.6.</strong> OCSP stapling</a></li><li class="chapter-item "><a href="../../usingcurl/tls/clientcert.html"><strong aria-hidden="true">9.9.7.</strong> Client certificates</a></li><li class="chapter-item "><a href="../../usingcurl/tls/auth.html"><strong aria-hidden="true">9.9.8.</strong> TLS auth</a></li><li class="chapter-item "><a href="../../usingcurl/tls/backends.html"><strong aria-hidden="true">9.9.9.</strong> TLS backends</a></li><li class="chapter-item "><a href="../../usingcurl/tls/sslkeylogfile.html"><strong aria-hidden="true">9.9.10.</strong> SSLKEYLOGFILE</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/ssh/index.html"><strong aria-hidden="true">9.10.</strong> SCP and SFTP</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../usingcurl/ssh/url.html"><strong aria-hidden="true">9.10.1.</strong> URLs</a></li><li class="chapter-item "><a href="../../usingcurl/ssh/auth.html"><strong aria-hidden="true">9.10.2.</strong> Authentication</a></li><li class="chapter-item "><a href="../../usingcurl/ssh/knownhosts.html"><strong aria-hidden="true">9.10.3.</strong> Known hosts</a></li></ol></li><li class="chapter-item "><a href="../../usingcurl/reademail.html"><strong aria-hidden="true">9.11.</strong> Reading email</a></li><li class="chapter-item "><a href="../../usingcurl/smtp.html"><strong aria-hidden="true">9.12.</strong> Sending email</a></li><li class="chapter-item "><a href="../../usingcurl/dict.html"><strong aria-hidden="true">9.13.</strong> DICT</a></li><li class="chapter-item "><a href="../../usingcurl/ipfs.html"><strong aria-hidden="true">9.14.</strong> IPFS</a></li><li class="chapter-item "><a href="../../usingcurl/mqtt.html"><strong aria-hidden="true">9.15.</strong> MQTT</a></li><li class="chapter-item "><a href="../../usingcurl/telnet.html"><strong aria-hidden="true">9.16.</strong> TELNET</a></li><li class="chapter-item "><a href="../../usingcurl/tftp.html"><strong aria-hidden="true">9.17.</strong> TFTP</a></li></ol></li><li class="chapter-item "><a href="../../http/index.html"><strong aria-hidden="true">10.</strong> Command line HTTP</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../http/method.html"><strong aria-hidden="true">10.1.</strong> Method</a></li><li class="chapter-item "><a href="../../http/response.html"><strong aria-hidden="true">10.2.</strong> Responses</a></li><li class="chapter-item "><a href="../../http/auth.html"><strong aria-hidden="true">10.3.</strong> Authentication</a></li><li class="chapter-item "><a href="../../http/versions/index.html"><strong aria-hidden="true">10.4.</strong> HTTP versions</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../http/versions/http09.html"><strong aria-hidden="true">10.4.1.</strong> HTTP/0.9</a></li><li class="chapter-item "><a href="../../http/versions/http2.html"><strong aria-hidden="true">10.4.2.</strong> HTTP/2</a></li><li class="chapter-item "><a href="../../http/versions/http3.html"><strong aria-hidden="true">10.4.3.</strong> HTTP/3</a></li></ol></li><li class="chapter-item "><a href="../../http/post/index.html"><strong aria-hidden="true">10.5.</strong> HTTP POST</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../http/post/simple.html"><strong aria-hidden="true">10.5.1.</strong> Simple POST</a></li><li class="chapter-item "><a href="../../http/post/content-type.html"><strong aria-hidden="true">10.5.2.</strong> Content-Type</a></li><li class="chapter-item "><a href="../../http/post/binary.html"><strong aria-hidden="true">10.5.3.</strong> Posting binary</a></li><li class="chapter-item "><a href="../../http/post/json.html"><strong aria-hidden="true">10.5.4.</strong> JSON</a></li><li class="chapter-item "><a href="../../http/post/url-encode.html"><strong aria-hidden="true">10.5.5.</strong> URL encode data</a></li><li class="chapter-item "><a href="../../http/post/convert-to-get.html"><strong aria-hidden="true">10.5.6.</strong> Convert to GET</a></li><li class="chapter-item "><a href="../../http/post/expect100.html"><strong aria-hidden="true">10.5.7.</strong> Expect 100-continue</a></li><li class="chapter-item "><a href="../../http/post/chunked.html"><strong aria-hidden="true">10.5.8.</strong> Chunked encoded POSTs</a></li><li class="chapter-item "><a href="../../http/post/hiddenfields.html"><strong aria-hidden="true">10.5.9.</strong> Hidden form fields</a></li><li class="chapter-item "><a href="../../http/post/browsersends.html"><strong aria-hidden="true">10.5.10.</strong> Figure out what a browser sends</a></li><li class="chapter-item "><a href="../../http/post/javascript.html"><strong aria-hidden="true">10.5.11.</strong> JavaScript and forms</a></li><li class="chapter-item "><a href="../../http/post/multipart.html"><strong aria-hidden="true">10.5.12.</strong> Multipart formposts</a></li><li class="chapter-item "><a href="../../http/post/postvspost.html"><strong aria-hidden="true">10.5.13.</strong> -d vs -F</a></li></ol></li><li class="chapter-item "><a href="../../http/put.html"><strong aria-hidden="true">10.6.</strong> HTTP PUT</a></li><li class="chapter-item "><a href="../../http/redirects.html"><strong aria-hidden="true">10.7.</strong> Redirects</a></li><li class="chapter-item "><a href="../../http/modify/index.html"><strong aria-hidden="true">10.8.</strong> Customize your HTTP</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../http/modify/method.html"><strong aria-hidden="true">10.8.1.</strong> Request method</a></li><li class="chapter-item "><a href="../../http/modify/target.html"><strong aria-hidden="true">10.8.2.</strong> Request target</a></li><li class="chapter-item "><a href="../../http/modify/fragment.html"><strong aria-hidden="true">10.8.3.</strong> Fragment</a></li><li class="chapter-item "><a href="../../http/modify/headers.html"><strong aria-hidden="true">10.8.4.</strong> Customize headers</a></li><li class="chapter-item "><a href="../../http/modify/referer.html"><strong aria-hidden="true">10.8.5.</strong> Referer</a></li><li class="chapter-item "><a href="../../http/modify/user-agent.html"><strong aria-hidden="true">10.8.6.</strong> User-agent</a></li><li class="chapter-item "><a href="../../http/modify/ranges.html"><strong aria-hidden="true">10.8.7.</strong> Ranges</a></li><li class="chapter-item "><a href="../../http/modify/conditionals.html"><strong aria-hidden="true">10.8.8.</strong> Conditionals</a></li><li class="chapter-item "><a href="../../http/modify/compression.html"><strong aria-hidden="true">10.8.9.</strong> Compression</a></li></ol></li><li class="chapter-item "><a href="../../http/cookies/index.html"><strong aria-hidden="true">10.9.</strong> Cookies</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../http/cookies/engine.html"><strong aria-hidden="true">10.9.1.</strong> Cookie engine</a></li><li class="chapter-item "><a href="../../http/cookies/reading.html"><strong aria-hidden="true">10.9.2.</strong> Reading cookies from file</a></li><li class="chapter-item "><a href="../../http/cookies/writing.html"><strong aria-hidden="true">10.9.3.</strong> Writing cookies to file</a></li><li class="chapter-item "><a href="../../http/cookies/newsession.html"><strong aria-hidden="true">10.9.4.</strong> New cookie session</a></li><li class="chapter-item "><a href="../../http/cookies/fileformat.html"><strong aria-hidden="true">10.9.5.</strong> Cookie file format</a></li></ol></li><li class="chapter-item "><a href="../../http/https.html"><strong aria-hidden="true">10.10.</strong> HTTPS</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../http/https/hsts.html"><strong aria-hidden="true">10.10.1.</strong> HSTS</a></li><li class="chapter-item "><a href="../../http/https/altsvc.html"><strong aria-hidden="true">10.10.2.</strong> Alternative Services</a></li></ol></li><li class="chapter-item "><a href="../../http/browserlike.html"><strong aria-hidden="true">10.11.</strong> Scripting browser-like tasks</a></li></ol></li><li class="chapter-item "><a href="../../ftp/index.html"><strong aria-hidden="true">11.</strong> Command line FTP</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../ftp/dirlist.html"><strong aria-hidden="true">11.1.</strong> FTP Directory listing</a></li><li class="chapter-item "><a href="../../ftp/upload.html"><strong aria-hidden="true">11.2.</strong> Uploading with FTP</a></li><li class="chapter-item "><a href="../../ftp/cmds.html"><strong aria-hidden="true">11.3.</strong> Custom FTP commands</a></li><li class="chapter-item "><a href="../../ftp/twoconnections.html"><strong aria-hidden="true">11.4.</strong> Two connections</a></li><li class="chapter-item "><a href="../../ftp/traversedir.html"><strong aria-hidden="true">11.5.</strong> Directory traversing</a></li><li class="chapter-item "><a href="../../ftp/ftps.html"><strong aria-hidden="true">11.6.</strong> FTPS</a></li></ol></li><li class="chapter-item "><a href="../../libcurl/index.html"><strong aria-hidden="true">12.</strong> libcurl</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../libcurl/headers.html"><strong aria-hidden="true">12.1.</strong> Header files</a></li><li class="chapter-item "><a href="../../libcurl/globalinit.html"><strong aria-hidden="true">12.2.</strong> Global initialization</a></li><li class="chapter-item "><a href="../../libcurl/api.html"><strong aria-hidden="true">12.3.</strong> API compatibility</a></li><li class="chapter-item "><a href="../../libcurl/--libcurl.html"><strong aria-hidden="true">12.4.</strong> --libcurl</a></li><li class="chapter-item "><a href="../../libcurl/threading.html"><strong aria-hidden="true">12.5.</strong> multi-threading</a></li><li class="chapter-item "><a href="../../libcurl/curlcode.html"><strong aria-hidden="true">12.6.</strong> CURLcode return codes</a></li><li class="chapter-item "><a href="../../libcurl/verbose.html"><strong aria-hidden="true">12.7.</strong> Verbose operations</a></li><li class="chapter-item "><a href="../../libcurl/caches.html"><strong aria-hidden="true">12.8.</strong> Caches</a></li><li class="chapter-item "><a href="../../libcurl/performance.html"><strong aria-hidden="true">12.9.</strong> Performance</a></li><li class="chapter-item "><a href="../../libcurl/cplusplus.html"><strong aria-hidden="true">12.10.</strong> for C++ programmers</a></li></ol></li><li class="chapter-item expanded "><a href="../../transfers/index.html"><strong aria-hidden="true">13.</strong> libcurl transfers</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../transfers/easyhandle.html"><strong aria-hidden="true">13.1.</strong> Easy handle</a></li><li class="chapter-item "><a href="../../transfers/options/index.html"><strong aria-hidden="true">13.2.</strong> curl easy options</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../transfers/options/num.html"><strong aria-hidden="true">13.2.1.</strong> Set numerical options</a></li><li class="chapter-item "><a href="../../transfers/options/strings.html"><strong aria-hidden="true">13.2.2.</strong> Set string options</a></li><li class="chapter-item "><a href="../../transfers/options/tls.html"><strong aria-hidden="true">13.2.3.</strong> TLS options</a></li><li class="chapter-item "><a href="../../transfers/options/all.html"><strong aria-hidden="true">13.2.4.</strong> All options</a></li><li class="chapter-item "><a href="../../transfers/options/info.html"><strong aria-hidden="true">13.2.5.</strong> Get option information</a></li></ol></li><li class="chapter-item "><a href="../../transfers/drive/index.html"><strong aria-hidden="true">13.3.</strong> Drive transfers</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../transfers/drive/easy.html"><strong aria-hidden="true">13.3.1.</strong> Drive with easy</a></li><li class="chapter-item "><a href="../../transfers/drive/multi.html"><strong aria-hidden="true">13.3.2.</strong> Drive with multi</a></li><li class="chapter-item "><a href="../../transfers/drive/multi-socket.html"><strong aria-hidden="true">13.3.3.</strong> Drive with multi_socket</a></li></ol></li><li class="chapter-item "><a href="../../transfers/callbacks/index.html"><strong aria-hidden="true">13.4.</strong> Callbacks</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../transfers/callbacks/write.html"><strong aria-hidden="true">13.4.1.</strong> Write data</a></li><li class="chapter-item "><a href="../../transfers/callbacks/read.html"><strong aria-hidden="true">13.4.2.</strong> Read data</a></li><li class="chapter-item "><a href="../../transfers/callbacks/progress.html"><strong aria-hidden="true">13.4.3.</strong> Progress information</a></li><li class="chapter-item "><a href="../../transfers/callbacks/header.html"><strong aria-hidden="true">13.4.4.</strong> Header data</a></li><li class="chapter-item "><a href="../../transfers/callbacks/debug.html"><strong aria-hidden="true">13.4.5.</strong> Debug</a></li><li class="chapter-item "><a href="../../transfers/callbacks/sockopt.html"><strong aria-hidden="true">13.4.6.</strong> sockopt</a></li><li class="chapter-item "><a href="../../transfers/callbacks/sslcontext.html"><strong aria-hidden="true">13.4.7.</strong> SSL context</a></li><li class="chapter-item "><a href="../../transfers/callbacks/seek.html"><strong aria-hidden="true">13.4.8.</strong> Seek and ioctl</a></li><li class="chapter-item "><a href="../../transfers/callbacks/conversions.html"><strong aria-hidden="true">13.4.9.</strong> Network data conversion</a></li><li class="chapter-item "><a href="../../transfers/callbacks/openclosesocket.html"><strong aria-hidden="true">13.4.10.</strong> Opensocket and closesocket</a></li><li class="chapter-item "><a href="../../transfers/callbacks/sshkey.html"><strong aria-hidden="true">13.4.11.</strong> SSH key</a></li><li class="chapter-item "><a href="../../transfers/callbacks/rtsp.html"><strong aria-hidden="true">13.4.12.</strong> RTSP interleaved data</a></li><li class="chapter-item "><a href="../../transfers/callbacks/ftpmatch.html"><strong aria-hidden="true">13.4.13.</strong> FTP wildcard matching</a></li><li class="chapter-item "><a href="../../transfers/callbacks/resolver.html"><strong aria-hidden="true">13.4.14.</strong> Resolver start</a></li><li class="chapter-item "><a href="../../transfers/callbacks/trailers.html"><strong aria-hidden="true">13.4.15.</strong> Sending trailers</a></li><li class="chapter-item "><a href="../../transfers/callbacks/hsts.html"><strong aria-hidden="true">13.4.16.</strong> HSTS</a></li><li class="chapter-item "><a href="../../transfers/callbacks/prereq.html"><strong aria-hidden="true">13.4.17.</strong> Prereq</a></li></ol></li><li class="chapter-item expanded "><a href="../../transfers/conn/index.html"><strong aria-hidden="true">13.5.</strong> Connection control</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../transfers/conn/how.html"><strong aria-hidden="true">13.5.1.</strong> How libcurl connects</a></li><li class="chapter-item "><a href="../../transfers/conn/local.html"><strong aria-hidden="true">13.5.2.</strong> Local address and port number</a></li><li class="chapter-item expanded "><a href="../../transfers/conn/reuse.html" class="active"><strong aria-hidden="true">13.5.3.</strong> Connection reuse</a></li><li class="chapter-item "><a href="../../transfers/conn/keepalive.html"><strong aria-hidden="true">13.5.4.</strong> Keep alive</a></li><li class="chapter-item "><a href="../../transfers/conn/names.html"><strong aria-hidden="true">13.5.5.</strong> Name resolving</a></li><li class="chapter-item "><a href="../../transfers/conn/proxies.html"><strong aria-hidden="true">13.5.6.</strong> Proxies</a></li></ol></li><li class="chapter-item "><a href="../../transfers/control/index.html"><strong aria-hidden="true">13.6.</strong> Transfer control</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../transfers/control/stop.html"><strong aria-hidden="true">13.6.1.</strong> Stop</a></li><li class="chapter-item "><a href="../../transfers/control/stopslow.html"><strong aria-hidden="true">13.6.2.</strong> Stop slow transfers</a></li><li class="chapter-item "><a href="../../transfers/control/ratelimit.html"><strong aria-hidden="true">13.6.3.</strong> Rate limit</a></li><li class="chapter-item "><a href="../../transfers/control/meter.html"><strong aria-hidden="true">13.6.4.</strong> Progress meter</a></li><li class="chapter-item "><a href="../../transfers/control/progress-callback.html"><strong aria-hidden="true">13.6.5.</strong> Progress callback</a></li></ol></li><li class="chapter-item "><a href="../../transfers/auth.html"><strong aria-hidden="true">13.7.</strong> Authentication</a></li><li class="chapter-item "><a href="../../transfers/cleanup.html"><strong aria-hidden="true">13.8.</strong> Cleanup</a></li><li class="chapter-item "><a href="../../transfers/getinfo.html"><strong aria-hidden="true">13.9.</strong> Post transfer info</a></li></ol></li><li class="chapter-item "><a href="../../libcurl-http/index.html"><strong aria-hidden="true">14.</strong> libcurl HTTP</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../libcurl-http/responses.html"><strong aria-hidden="true">14.1.</strong> Responses</a></li><li class="chapter-item "><a href="../../libcurl-http/requests.html"><strong aria-hidden="true">14.2.</strong> Requests</a></li><li class="chapter-item "><a href="../../libcurl-http/versions.html"><strong aria-hidden="true">14.3.</strong> Versions</a></li><li class="chapter-item "><a href="../../libcurl-http/ranges.html"><strong aria-hidden="true">14.4.</strong> Ranges</a></li><li class="chapter-item "><a href="../../libcurl-http/auth.html"><strong aria-hidden="true">14.5.</strong> Authentication</a></li><li class="chapter-item "><a href="../../libcurl-http/cookies.html"><strong aria-hidden="true">14.6.</strong> Cookies</a></li><li class="chapter-item "><a href="../../libcurl-http/download.html"><strong aria-hidden="true">14.7.</strong> Download</a></li><li class="chapter-item "><a href="../../libcurl-http/upload.html"><strong aria-hidden="true">14.8.</strong> Upload</a></li><li class="chapter-item "><a href="../../libcurl-http/multiplexing.html"><strong aria-hidden="true">14.9.</strong> Multiplexing</a></li><li class="chapter-item "><a href="../../libcurl-http/hsts.html"><strong aria-hidden="true">14.10.</strong> HSTS</a></li><li class="chapter-item "><a href="../../libcurl-http/alt-svc.html"><strong aria-hidden="true">14.11.</strong> alt-svc</a></li></ol></li><li class="chapter-item "><a href="../../helpers/index.html"><strong aria-hidden="true">15.</strong> libcurl helpers</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../helpers/sharing.html"><strong aria-hidden="true">15.1.</strong> Share data between handles</a></li><li class="chapter-item "><a href="../../helpers/url/index.html"><strong aria-hidden="true">15.2.</strong> URL API</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../helpers/url/include.html"><strong aria-hidden="true">15.2.1.</strong> Include files</a></li><li class="chapter-item "><a href="../../helpers/url/init.html"><strong aria-hidden="true">15.2.2.</strong> Create, cleanup, duplicate</a></li><li class="chapter-item "><a href="../../helpers/url/parse.html"><strong aria-hidden="true">15.2.3.</strong> Parse a URL</a></li><li class="chapter-item "><a href="../../helpers/url/redirect.html"><strong aria-hidden="true">15.2.4.</strong> Redirect to URL</a></li><li class="chapter-item "><a href="../../helpers/url/get.html"><strong aria-hidden="true">15.2.5.</strong> Get a URL</a></li><li class="chapter-item "><a href="../../helpers/url/get-part.html"><strong aria-hidden="true">15.2.6.</strong> Get URL parts</a></li><li class="chapter-item "><a href="../../helpers/url/set-part.html"><strong aria-hidden="true">15.2.7.</strong> Set URL parts</a></li><li class="chapter-item "><a href="../../helpers/url/append-query.html"><strong aria-hidden="true">15.2.8.</strong> Append to the query</a></li><li class="chapter-item "><a href="../../helpers/url/setopt.html"><strong aria-hidden="true">15.2.9.</strong> CURLOPT_CURLU</a></li></ol></li><li class="chapter-item "><a href="../../helpers/ws/index.html"><strong aria-hidden="true">15.3.</strong> WebSocket</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../helpers/ws/support.html"><strong aria-hidden="true">15.3.1.</strong> Support</a></li><li class="chapter-item "><a href="../../helpers/ws/urls.html"><strong aria-hidden="true">15.3.2.</strong> URLs</a></li><li class="chapter-item "><a href="../../helpers/ws/concept.html"><strong aria-hidden="true">15.3.3.</strong> Concept</a></li><li class="chapter-item "><a href="../../helpers/ws/options.html"><strong aria-hidden="true">15.3.4.</strong> Options</a></li><li class="chapter-item "><a href="../../helpers/ws/read.html"><strong aria-hidden="true">15.3.5.</strong> Read</a></li><li class="chapter-item "><a href="../../helpers/ws/meta.html"><strong aria-hidden="true">15.3.6.</strong> Meta</a></li><li class="chapter-item "><a href="../../helpers/ws/write.html"><strong aria-hidden="true">15.3.7.</strong> Write</a></li></ol></li><li class="chapter-item "><a href="../../helpers/headerapi/index.html"><strong aria-hidden="true">15.4.</strong> Headers API</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../helpers/headerapi/struct.html"><strong aria-hidden="true">15.4.1.</strong> Header struct</a></li><li class="chapter-item "><a href="../../helpers/headerapi/get.html"><strong aria-hidden="true">15.4.2.</strong> Get a header</a></li><li class="chapter-item "><a href="../../helpers/headerapi/iterate.html"><strong aria-hidden="true">15.4.3.</strong> Iterate over headers</a></li></ol></li></ol></li><li class="chapter-item "><a href="../../examples/index.html"><strong aria-hidden="true">16.</strong> libcurl examples</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../examples/get.html"><strong aria-hidden="true">16.1.</strong> Get a simple HTTP page</a></li><li class="chapter-item "><a href="../../examples/getinmem.html"><strong aria-hidden="true">16.2.</strong> Get a response into memory</a></li><li class="chapter-item "><a href="../../examples/login.html"><strong aria-hidden="true">16.3.</strong> Submit a login form over HTTP</a></li><li class="chapter-item "><a href="../../examples/ftplist.html"><strong aria-hidden="true">16.4.</strong> Get an FTP directory listing</a></li><li class="chapter-item "><a href="../../examples/http-ul-nonblock.html"><strong aria-hidden="true">16.5.</strong> Non-blocking HTTP form-post</a></li></ol></li><li class="chapter-item "><a href="../../bindings/index.html"><strong aria-hidden="true">17.</strong> libcurl bindings</a></li><li class="chapter-item "><a href="../../internals/index.html"><strong aria-hidden="true">18.</strong> libcurl internals</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../internals/easy.html"><strong aria-hidden="true">18.1.</strong> Easy handles and connections</a></li><li class="chapter-item "><a href="../../internals/multi.html"><strong aria-hidden="true">18.2.</strong> Everything is multi</a></li><li class="chapter-item "><a href="../../internals/statemachines.html"><strong aria-hidden="true">18.3.</strong> State machines</a></li><li class="chapter-item "><a href="../../internals/handler.html"><strong aria-hidden="true">18.4.</strong> Protocol handler</a></li><li class="chapter-item "><a href="../../internals/backends.html"><strong aria-hidden="true">18.5.</strong> Backends</a></li><li class="chapter-item "><a href="../../internals/caches.html"><strong aria-hidden="true">18.6.</strong> Caches and state</a></li><li class="chapter-item "><a href="../../internals/timeouts.html"><strong aria-hidden="true">18.7.</strong> Timeouts</a></li><li class="chapter-item "><a href="../../internals/windows-vs-unix.html"><strong aria-hidden="true">18.8.</strong> Windows vs Unix</a></li><li class="chapter-item "><a href="../../internals/memory-debugging.html"><strong aria-hidden="true">18.9.</strong> Memory debugging</a></li><li class="chapter-item "><a href="../../internals/content-encoding.html"><strong aria-hidden="true">18.10.</strong> Content Encoding</a></li><li class="chapter-item "><a href="../../internals/structs.html"><strong aria-hidden="true">18.11.</strong> Structs</a></li><li class="chapter-item "><a href="../../internals/resolving.html"><strong aria-hidden="true">18.12.</strong> Resolving hostnames</a></li><li class="chapter-item "><a href="../../internals/tests/index.html"><strong aria-hidden="true">18.13.</strong> Tests</a><a class="toggle"><div>❱</div></a></li><li><ol class="section"><li class="chapter-item "><a href="../../internals/tests/file-format.html"><strong aria-hidden="true">18.13.1.</strong> Test file format</a></li><li class="chapter-item "><a href="../../internals/tests/build.html"><strong aria-hidden="true">18.13.2.</strong> Build tests</a></li><li class="chapter-item "><a href="../../internals/tests/run.html"><strong aria-hidden="true">18.13.3.</strong> Run tests</a></li><li class="chapter-item "><a href="../../internals/tests/debug.html"><strong aria-hidden="true">18.13.4.</strong> Debug builds</a></li><li class="chapter-item "><a href="../../internals/tests/servers.html"><strong aria-hidden="true">18.13.5.</strong> Test servers</a></li><li class="chapter-item "><a href="../../internals/tests/curl.html"><strong aria-hidden="true">18.13.6.</strong> curl tests</a></li><li class="chapter-item "><a href="../../internals/tests/libcurl.html"><strong aria-hidden="true">18.13.7.</strong> libcurl tests</a></li><li class="chapter-item "><a href="../../internals/tests/unit.html"><strong aria-hidden="true">18.13.8.</strong> Unit tests</a></li><li class="chapter-item "><a href="../../internals/tests/valgrind.html"><strong aria-hidden="true">18.13.9.</strong> Valgrind</a></li><li class="chapter-item "><a href="../../internals/tests/ci.html"><strong aria-hidden="true">18.13.10.</strong> Continuous Integration</a></li><li class="chapter-item "><a href="../../internals/tests/autobuilds.html"><strong aria-hidden="true">18.13.11.</strong> Autobuilds</a></li><li class="chapter-item "><a href="../../internals/tests/torture.html"><strong aria-hidden="true">18.13.12.</strong> Torture</a></li></ol></li></ol></li><li class="chapter-item "><a href="../../bookindex.html"><strong aria-hidden="true">19.</strong> Index</a></li></ol> </div> <div id="sidebar-resize-handle" class="sidebar-resize-handle"> <div class="sidebar-resize-indicator"></div> </div> </nav>  <script> var sidebarScrollbox = document.querySelector('#sidebar .sidebar-scrollbox'); sidebarScrollbox.addEventListener('click', function(e) { if (e.target.tagName === 'A') { sessionStorage.setItem('sidebar-scroll', sidebarScrollbox.scrollTop); } }, { passive: true }); var sidebarScrollTop = sessionStorage.getItem('sidebar-scroll'); sessionStorage.removeItem('sidebar-scroll'); if (sidebarScrollTop) { // preserve sidebar scroll position when navigating via links within sidebar sidebarScrollbox.scrollTop = sidebarScrollTop; } else { // scroll sidebar to current active section when navigating via "next/previous chapter" buttons var activeSection = document.querySelector('#sidebar .active'); if (activeSection) { activeSection.scrollIntoView({ block: 'center' }); } } </script> <div id="page-wrapper" class="page-wrapper"> <div class="page"> <div id="menu-bar-hover-placeholder"></div> <div id="menu-bar" class="menu-bar sticky"> <div class="left-buttons"> <label id="sidebar-toggle" class="icon-button" for="sidebar-toggle-anchor" title="Toggle Table of Contents" aria-label="Toggle Table of Contents" aria-controls="sidebar"> <i class="fa fa-bars"></i> </label> <button id="theme-toggle" class="icon-button" type="button" title="Change theme" aria-label="Change theme" aria-haspopup="true" aria-expanded="false" 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(Shortkey: s)" aria-label="Toggle Searchbar" aria-expanded="false" aria-keyshortcuts="S" aria-controls="searchbar"> <i class="fa fa-search"></i> </button> </div> <h1 class="menu-title">everything curl</h1> <div class="right-buttons"> <a href="../../print.html" title="Print this book" aria-label="Print this book"> <i id="print-button" class="fa fa-print"></i> </a> </div> </div> <div id="search-wrapper" class="hidden"> <form id="searchbar-outer" class="searchbar-outer"> <input type="search" id="searchbar" name="searchbar" placeholder="Search this book ..." aria-controls="searchresults-outer" aria-describedby="searchresults-header"> </form> <div id="searchresults-outer" class="searchresults-outer hidden"> <div id="searchresults-header" class="searchresults-header"></div> <ul id="searchresults"> </ul> </div> </div>  <script> document.getElementById('sidebar-toggle').setAttribute('aria-expanded', sidebar === 'visible'); document.getElementById('sidebar').setAttribute('aria-hidden', sidebar !== 'visible'); Array.from(document.querySelectorAll('#sidebar a')).forEach(function(link) { link.setAttribute('tabIndex', sidebar === 'visible' ? 0 : -1); }); </script> <div id="content" class="content"> <main> <h1 id="connection-reuse"><a class="header" href="#connection-reuse">Connection reuse</a></h1> <p>libcurl keeps a pool of old connections alive. When one transfer has completed it keeps N connections alive in a connection pool (sometimes also called connection cache) so that a subsequent transfer that happens to be able to reuse one of the existing connections can use it instead of creating a new one. Reusing a connection instead of creating a new one offers significant benefits in speed and required resources.</p> <p>When libcurl is about to make a new connection for the purposes of doing a transfer, it first checks to see if there is an existing connection in the pool that it can reuse instead. The connection re-use check is done before any DNS or other name resolving mechanism is used, so it is purely hostname based. If there is an existing live connection to the right hostname, a lot of other properties (port number, protocol, etc) are also checked to see that it can be used.</p> <h2 id="easy-api-pool"><a class="header" href="#easy-api-pool">Easy API pool</a></h2> <p>When you are using the easy API, or, more specifically, <code>curl_easy_perform()</code>, libcurl keeps the pool associated with the specific easy handle. Then reusing the same easy handle ensures libcurl can reuse its connection.</p> <h2 id="multi-api-pool"><a class="header" href="#multi-api-pool">Multi API pool</a></h2> <p>When you are using the multi API, the connection pool is instead kept associated with the multi handle. This allows you to cleanup and re-create easy handles freely without risking losing the connection pool, and it allows the connection used by one easy handle to get reused by a separate one in a later transfer. Just reuse the multi handle.</p> <h2 id="sharing-the-connection-cache"><a class="header" href="#sharing-the-connection-cache">Sharing the connection cache</a></h2> <p>Since libcurl 7.57.0, applications can use the <a href="../../helpers/sharing.html">share interface</a> to have otherwise independent transfers share the same connection pool.</p> <h2 id="when-connections-are-not-reused-as-you-want"><a class="header" href="#when-connections-are-not-reused-as-you-want">When connections are not reused as you want</a></h2> <p>libcurl will automatically and always try to reuse connections unless explicitly told not to. There are however several reasons why a connection is <em>not</em> used for a subsequent transfer.</p> <ul> <li> <p>The server signals that the connection will be closed after this transfer. For example by using the <code>Connection: close</code> HTTP response header or a HTTP/2 or HTTP/3 "go away" frame.</p> </li> <li> <p>The HTTP/1 response of a transfer is sent in such a way that a connection close is the only way to detect the end of the body. Or just an HTTP/1 receive error that makes curl deem that it cannot safely reuse the connection anymore.</p> </li> <li> <p>The connection is deemed "dead" when libcurl tries to reuse it. It might happen when the server side has closed the connection after the previous transfer was completed. It can also happen if a stateful firewall/NAT or something in the network path drops the connection or if there is HTTP/2 or HTTP/3 traffic (like PING frames) over the connection when unattended.</p> </li> <li> <p>The previous transfer is deemed too old to reuse. If <code>CURLOPT_MAXLIFETIME_CONN</code> is set, libcurl will not reuse a connection that is older than the set value in seconds.</p> </li> <li> <p>The previous transfer is deemed having idled for too long. By default libcurl never attempts to reuse a connection that has been idle for more than 118 seconds. This time can be changed with <code>CURLOPT_MAXAGE_CONN</code>.</p> </li> <li> <p>If the connection pool is full when a transfer ends and a new connection is about to get stored there, the oldest idle connection in the pool is closed and discarded and therefore cannot be reused anymore. Increase the connection pool size with <code>CURLMOPT_MAXCONNECTS</code> or <code>CURLOPT_MAXCONNECTS</code>, depending on which API you are using.</p> </li> <li> <p>When using the multi interface, if the previous transfer has not ended when the next transfer is started, and the previous connection cannot be used for multiplexing.</p> </li> </ul> <p>Etc. Usually you can learn about the reason by enabling <code>CURLOPT_VERBOSE</code> and inspecting what libcurl informs the application.</p> </main> <nav class="nav-wrapper" aria-label="Page navigation">  <a rel="prev" href="../../transfers/conn/local.html" class="mobile-nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> <i class="fa fa-angle-left"></i> </a> <a rel="next prefetch" href="../../transfers/conn/keepalive.html" class="mobile-nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> <i class="fa fa-angle-right"></i> </a> <div style="clear: both"></div> </nav> </div> </div> <nav class="nav-wide-wrapper" aria-label="Page navigation"> <a rel="prev" href="../../transfers/conn/local.html" class="nav-chapters previous" title="Previous chapter" aria-label="Previous chapter" aria-keyshortcuts="Left"> <i class="fa fa-angle-left"></i> </a> <a rel="next prefetch" href="../../transfers/conn/keepalive.html" class="nav-chapters next" title="Next chapter" aria-label="Next chapter" aria-keyshortcuts="Right"> <i class="fa fa-angle-right"></i> </a> </nav> </div> <script> window.playground_copyable = true; </script> <script src="../../elasticlunr.min.js"></script> <script src="../../mark.min.js"></script> <script src="../../searcher.js"></script> <script src="../../clipboard.min.js"></script> <script src="../../highlight.js"></script> <script src="../../book.js"></script>  </div> </body> </html>