httppeer: extract code for HTTP header spanning A second consumer of HTTP header spanning will soon be introduced. Factor out the code to do this so it can be reused.

commands: config option to control bundle compression level Currently, bundle compression uses the default compression level for the active compression engine. The default compression level is tuned as a compromise between speed and size. Some scenarios may call for a different compression level. For example, with clone bundles, bundles are generated once and used several times. Since the cost to generate is paid infrequently, server operators may wish to trade extra CPU time for better compression ratios. This patch introduces an experimental and undocumented config option to control the bundle compression level. As the inline comment says, this approach is a bit hacky. I'd prefer for the compression level to be encoded in the bundle spec. e.g. "zstd-v2;complevel=15." However, given that the 4.1 freeze is imminent, I'm not comfortable implementing this user-facing change without much time to test and consider the implications. So, we're going with the quick and dirty solution for now. Having this option in the 4.1 release will enable Mozilla to easily produce and test zlib and zstd bundles with non-default compression levels in production. This will help drive future development of the feature and zstd integration with Mercurial.

bundle2: allow compression options to be passed to compressor Compression engines allow options to be passed to them to control behavior. This patch exposes an argument to bundle2.writebundle() that passes options to the compression engine when writing compressed bundles. The argument is honored for both bundle1 and bundle2, the latter requiring a bit of plumbing to pass the value around.