HTTP2.md: formatted properly
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Daniel Stenberg
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docs/HTTP2.md
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docs/HTTP2.md
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HTTP2 with libcurl
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HTTP/2 with curl
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================
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Spec: http://www.rfc-editor.org/rfc/rfc7540.txt
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[HTTP/2 Spec](http://www.rfc-editor.org/rfc/rfc7540.txt)
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[http2 explained](http://daniel.haxx.se/http2/)
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Document explaining it: http://daniel.haxx.se/http2/
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Build prerequisites
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Build prerequisites
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-------------------
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- nghttp2
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- OpenSSL, NSS, GnutTLS or PolarSSL with a new enough version
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nghttp2 (https://github.com/tatsuhiro-t/nghttp2)
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[nghttp2](https://nghttp2.org/)
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-------------------------------
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libcurl uses this 3rd party library for the low level protocol handling
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parts. The reason for this is that HTTP/2 is much more complex at that layer
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than HTTP/1.1 (which we implement on our own) and that nghttp2 is an already
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existing and well functional library.
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libcurl uses this 3rd party library for the low level protocol handling
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parts. The reason for this is that HTTP/2 is much more complex at that layer
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than HTTP/1.1 (which we implement on our own) and that nghttp2 is an already
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existing and well functional library.
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We require at least version 1.0.0.
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We require at least version 1.0.0.
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Over an http:// URL
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Over an http:// URL
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-------------------
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If CURLOPT_HTTP_VERSION is set to CURL_HTTP_VERSION_2_0, libcurl will
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include an upgrade header in the initial request to the host to allow
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upgrading to http2.
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If `CURLOPT_HTTP_VERSION` is set to `CURL_HTTP_VERSION_2_0`, libcurl will
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include an upgrade header in the initial request to the host to allow
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upgrading to HTTP/2.
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Possibly we can later introduce an option that will cause libcurl to fail if
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not possible to upgrade. Possibly we introduce an option that makes libcurl
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use http2 at once over http://
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Possibly we can later introduce an option that will cause libcurl to fail if
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not possible to upgrade. Possibly we introduce an option that makes libcurl
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use HTTP/2 at once over http://
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Over an https:// URL
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Over an https:// URL
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--------------------
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If CURLOPT_HTTP_VERSION is set to CURL_HTTP_VERSION_2_0, libcurl will use
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ALPN (or NPN) to negotiate which protocol to continue with. Possibly
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introduce an option that will cause libcurl to fail if not possible to use
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http2. Consider options to explicitly disable ALPN and/or NPN.
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If `CURLOPT_HTTP_VERSION` is set to `CURL_HTTP_VERSION_2_0`, libcurl will use
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ALPN (or NPN) to negotiate which protocol to continue with. Possibly introduce
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an option that will cause libcurl to fail if not possible to use HTTP/2.
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Consider options to explicitly disable ALPN and/or NPN.
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ALPN is the TLS extension that http2 is expected to use. The NPN extension
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is for a similar purpose, was made prior to ALPN and is used for SPDY so
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early http2 servers are implemented using NPN before ALPN support is
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widespread.
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ALPN is the TLS extension that HTTP/2 is expected to use. The NPN extension is
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for a similar purpose, was made prior to ALPN and is used for SPDY so early
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HTTP/2 servers are implemented using NPN before ALPN support is widespread.
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SSL libs
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--------
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The challenge is the ALPN and NPN support and all our different SSL
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backends. You may need a fairly updated SSL library version for it to
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provide the necessary TLS features. Right now we support:
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The challenge is the ALPN and NPN support and all our different SSL
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backends. You may need a fairly updated SSL library version for it to
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provide the necessary TLS features. Right now we support:
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OpenSSL: ALPN and NPN
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NSS: ALPN and NPN
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GnuTLS: ALPN
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PolarSSL: ALPN
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- OpenSSL: ALPN and NPN
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- NSS: ALPN and NPN
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- GnuTLS: ALPN
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- PolarSSL: ALPN
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Multiplexing
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------------
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Starting in 7.43.0, libcurl fully supports HTTP/2 multiplexing, which is the
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term for doing multiple independent transfers over the same physical TCP
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connection.
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Starting in 7.43.0, libcurl fully supports HTTP/2 multiplexing, which is the
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term for doing multiple independent transfers over the same physical TCP
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connection.
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To take advantage of multiplexing, you need to use the multi interface and
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set CURLMOPT_PIPELINING to CURLPIPE_MULTIPLEX. With that bit set, libcurl
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will attempt to re-use existing HTTP/2 connections and just add a new stream
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over that when doing subsequent parallel requests.
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To take advantage of multiplexing, you need to use the multi interface and set
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`CURLMOPT_PIPELINING` to `CURLPIPE_MULTIPLEX`. With that bit set, libcurl will
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attempt to re-use existing HTTP/2 connections and just add a new stream over
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that when doing subsequent parallel requests.
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While libcurl sets up a connection to a HTTP server there is a period during
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which it doesn't know if it can pipeline or do multiplexing and if you add
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new transfers in that period, libcurl will default to start new connections
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for those transfers. With the new option CURLOPT_PIPEWAIT (added in 7.43.0),
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you can ask that a transfer should rather wait and see in case there's a
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connection for the same host in progress that might end up being possible to
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multiplex on. It favours keeping the number of connections low to the cost
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of slightly longer time to first byte transfered.
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While libcurl sets up a connection to a HTTP server there is a period during
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which it doesn't know if it can pipeline or do multiplexing and if you add new
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transfers in that period, libcurl will default to start new connections for
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those transfers. With the new option `CURLOPT_PIPEWAIT` (added in 7.43.0), you
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can ask that a transfer should rather wait and see in case there's a
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connection for the same host in progress that might end up being possible to
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multiplex on. It favours keeping the number of connections low to the cost of
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slightly longer time to first byte transfered.
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Applications
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------------
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We hide http2's binary nature and convert received http2 traffic to headers
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in HTTP 1.1 style. This allows applications to work unmodified.
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We hide HTTP/2's binary nature and convert received HTTP/2 traffic to headers
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in HTTP 1.1 style. This allows applications to work unmodified.
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curl tool
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---------
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curl offers the --http2 command line option to enable use of http2
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curl offers the `--http2` command line option to enable use of HTTP/2
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HTTP Alternative Services
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-------------------------
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Alt-Svc is a suggested extension with a corresponding frame (ALTSVC) in
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http2 that tells the client about an alternative "route" to the same content
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for the same origin server that you get the response from. A browser or
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long-living client can use that hint to create a new connection
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asynchronously. For libcurl, we may introduce a way to bring such clues to
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the applicaton and/or let a subsequent request use the alternate route
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automatically. Spec:
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http://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-05
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Alt-Svc is a suggested extension with a corresponding frame (ALTSVC) in HTTP/2
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that tells the client about an alternative "route" to the same content for the
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same origin server that you get the response from. A browser or long-living
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client can use that hint to create a new connection asynchronously. For
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libcurl, we may introduce a way to bring such clues to the applicaton and/or
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let a subsequent request use the alternate route
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automatically. [Spec](http://tools.ietf.org/html/draft-ietf-httpbis-alt-svc-05)
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TODO:
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TODO
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----
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- Provide API to set priorities / dependencies of individual streams
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@ -38,7 +38,7 @@ EXTRA_DIST = MANUAL BUGS CONTRIBUTE FAQ FEATURES INTERNALS SSLCERTS \
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KNOWN_BUGS BINDINGS $(man_MANS) $(HTMLPAGES) HISTORY INSTALL \
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$(PDFPAGES) LICENSE-MIXING README.netware DISTRO-DILEMMA INSTALL.devcpp \
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MAIL-ETIQUETTE HTTP-COOKIES LIBCURL-STRUCTS SECURITY RELEASE-PROCEDURE \
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SSL-PROBLEMS HTTP2.md
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SSL-PROBLEMS HTTP2.md ROADMAP.md
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MAN2HTML= roffit < $< >$@
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