document http options in new apt-transport-http manpage

We had documentation for the http transport in our "catch-all" apt.conf
manpage, but it seems benefitial to document transports in their own
manpage instead of pushing them all into one.

1 files changed, 138 insertions, 0 deletions

diff --git a/doc/apt-transport-http.1.xml b/doc/apt-transport-http.1.xml
new file mode 100644
index 000000000..546e47761
--- /dev/null
+++ b/doc/apt-transport-http.1.xml
@@ -0,0 +1,138 @@
+<?xml version="1.0" encoding="utf-8" standalone="no"?>
+<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
+  "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd" [
+<!ENTITY % aptent SYSTEM "apt.ent"> %aptent;
+<!ENTITY % aptverbatiment SYSTEM "apt-verbatim.ent"> %aptverbatiment;
+<!ENTITY % aptvendor SYSTEM "apt-vendor.ent"> %aptvendor;
+]>
+
+<refentry>
+
+ <refentryinfo>
+   &apt-author.team;
+   &apt-email;
+   &apt-product;
+   <!-- The last update date -->
+   <date>2017-11-22T00:00:00Z</date>
+ </refentryinfo>
+
+ <refmeta>
+   <refentrytitle>apt-transport-http</refentrytitle>
+   <manvolnum>1</manvolnum>
+   <refmiscinfo class="manual">APT</refmiscinfo>
+ </refmeta>
+
+ <!-- Man page title -->
+ <refnamediv>
+    <refname>apt-transport-http</refname>
+    <refpurpose>APT transport for downloading via the Hypertext Transfer Protocol (HTTP)</refpurpose>
+ </refnamediv>
+
+<refsect1><title>Description</title>
+<para>This APT transport allows the use of repositories accessed via the
+Hypertext Transfer Protocol (HTTP). It is available by default and probably the
+most used of all transports. Note that a transport is never called directly by
+a user but used by APT tools based on user configuration.</para>
+<para>HTTP is an unencrypted transport protocol meaning that the
+whole communication with the remote server (or proxy) can be observed by a
+sufficiently capable attacker referred to commonly as man in the middle (MITM).
+Such an attacker can <emphasis>not</emphasis> modify the communication to compromise
+the security of your system through as APTs data security model is independent of the
+chosen transport method. This is explained in detail in &apt-secure;. An overview over
+available transport methods is given in &sources-list;.</para>
+</refsect1>
+
+<refsect1><title>Options</title>
+<para>Various options are available to modify its behaviour which can be set in
+an &apt-conf; file ranging from proxy configuration to workaround for specific
+server insufficiencies.</para>
+
+<refsect2><title>Proxy Configuration</title>
+<para>The environment variable <envar>http_proxy</envar> is supported for system wide configuration.
+Proxies specific to apt can be configured via the option <literal>Acquire::http::Proxy</literal>.
+Proxies which should be used only for certain hosts can be specified via
+<literal>Acquire::http::Proxy::<replaceable>host</replaceable></literal>. Even more finegrained control
+can be achieved via proxy autodetection detailed further below.
+All these options use the URI format <literal><replaceable>scheme</replaceable>://[[<replaceable>user</replaceable>][:<replaceable>pass</replaceable>]@]<replaceable>host</replaceable>[:<replaceable>port</replaceable>]/</literal>.
+Supported URI schemes are <literal>socks5h</literal> (SOCKS5 with remote DNS resolution), <literal>http</literal> and <literal>https</literal>.
+Authentification details can be supplied via &apt-authconf; instead of including it in the URI directly.</para>
+<para>The various APT configuration options support the special value <literal>DIRECT</literal> meaning that
+no proxy should be used. The environment variable <envar>no_proxy</envar> with the same propose is also supported.</para>
+<para>Further more there are three settings provided for cache control with HTTP/1.1 compliant proxy caches:
+<literal>Acquire::http::No-Cache</literal> tells the proxy not to use its
+cached response under any circumstances.
+<literal>Acquire::http::Max-Age</literal> sets the allowed maximum age (in
+seconds) of an index file in the cache of the proxy.
+<literal>Acquire::http::No-Store</literal> specifies that the proxy should not
+store the requested archive files in its cache, which can be used to prevent
+the proxy from polluting its cache with (big) .deb files.</para>
+</refsect2>
+
+<refsect2><title>Automatic Proxy Configuration</title>
+<para><literal>Acquire::http::Proxy-Auto-Detect</literal> can be used to
+specify an external command to discover the http proxy to use. The first
+and only parameter is an URI denoting the host to be contacted to allow
+for host-specific configuration. APT expects the command to output the
+proxy on stdout as a single line in the previously specified URI format
+or the word <literal>DIRECT</literal> if no proxy should be used. No output
+indicates that the generic proxy settings should be used.</para>
+<para>Note that auto-detection will not be used for a host if a host-specific proxy
+configuration is already set via <literal>Acquire::http::Proxy::<replaceable>host</replaceable></literal>.</para>
+<para>See the &squid-deb-proxy-client; and &auto-apt-proxy; packages for example implementations.</para>
+<para>This option takes precedence over the legacy option name <literal>Acquire::http::ProxyAutoDetect</literal>.</para>
+</refsect2>
+
+<refsect2><title>Connection Configuration</title>
+<para>The option <literal>Acquire::http::Timeout</literal> sets the timeout timer used by the method;
+this value applies to the connection as well as the data timeout.</para>
+<para>The used bandwidth can be limited with
+<literal>Acquire::http::Dl-Limit</literal> which accepts integer values in
+kilobytes per second. The default value is 0 which deactivates the limit and
+tries to use all available bandwidth. Note that this option implicitly
+disables downloading from multiple servers at the same time.</para>
+<para>The setting <literal>Acquire::http::Pipeline-Depth</literal> can be used to
+enable HTTP pipelining (RFC 2616 section 8.1.2.2) which can be beneficial e.g. on
+high-latency connections. It specifies how many requests are sent in a pipeline.
+APT tries to detect and workaround misbehaving webservers and proxies at runtime, but
+if you know that yours does not conform to the HTTP/1.1 specification pipelining can
+be disabled by setting the value to 0. It is enabled by default with the value 10.</para>
+<para><literal>Acquire::http::AllowRedirect</literal> controls whether APT will follow
+redirects, which is enabled by default.</para>
+<para><literal>Acquire::http::User-Agent</literal> can be used to set a different
+User-Agent for the http download method as some proxies allow access for clients
+only if the client uses a known identifier.</para>
+<para><literal>Acquire::http::SendAccept</literal> is enabled by default and
+sends a <literal>Accept: text/*</literal> header field to the server for
+requests without file extensions to prevent the server from attempting content
+negotiation.</para>
+</refsect2>
+</refsect1>
+
+<refsect1><title>Examples</title>
+<literallayout>
+Acquire::http {
+	Proxy::example.org "DIRECT";
+	Proxy "socks5h://apt:pass@localhost:9050";
+	Proxy-Auto-Detect "/usr/local/bin/apt-http-proxy-auto-detect";
+	No-Cache "true";
+	Max-Age "3600";
+	No-Store "true";
+	Timeout "10";
+	Dl-Limit "42";
+	Pipeline-Depth "0";
+	AllowRedirect "false";
+	User-Agent "My APT-HTTP";
+	SendAccept "false";
+};
+</literallayout>
+</refsect1>
+
+<refsect1>
+<title>See Also</title>
+<para>&apt-conf; &apt-authconf; &sources-list;
+</para>
+</refsect1>
+
+ &manbugs;
+
+</refentry>