reenable pipelining via hashsum reordering support

Now that methods have the expected hashes available they can check if
the response from the server is what they expected. Pipelining is one of
those areas in which servers can mess up by not supporting it properly,
which forced us to disable it for the time being. Now, we check if
we got a response out of order, which we can not only use to disable
pipelining automatically for the next requests, but we can fix it up
just like the server responded in proper order for the current requests.

To ensure that this little trick works pipelining is only attempt if we
have hashsums for all the files in the chain which in theory reduces the
use of pipelining usage even on the many servers which work properly,
but in practice only the InRelease file (or similar such) will be
requested without a hashsum – and as it is the only file requested in
that stage it can't be pipelined even if we wanted to.

Some minor annoyances remain: The display of the progress we have
doesn't reflect this change, so it looks like the same package gets
downloaded multiple times while others aren't at all. Further more,
partial files are not supported in this recovery as the received data
was appended to the wrong file, so the hashsum doesn't match.

Both seem to be minor enough to reenable pipelining by default until
further notice through to test if it really solves the problem.
This therefore reverts commit 8221431757c775ee875a061b184b5f6f2330f928.

1 files changed, 3 insertions, 3 deletions

diff --git a/doc/apt.conf.5.xml b/doc/apt.conf.5.xml
index fcbf20dac..21878e262 100644
--- a/doc/apt.conf.5.xml
+++ b/doc/apt.conf.5.xml
@@ -390,9 +390,9 @@ DPkg::Pre-Install-Pkgs {"/usr/sbin/dpkg-preconfigure --apt";};
      <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.
-     Previous APT versions had a default of 10 for this setting, but the default value
-     is now 0 (= disabled) to avoid problems with the ever-growing amount of webservers
-     and proxies which choose to not conform to the HTTP/1.1 specification.</para>
+     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>