macro_rules! try_old_curl_http2_pipewait { ($multiplexing:expr, $handle:expr) => { ... }; }
Expand description
Enable HTTP/2 and pipewait to be used as it’ll allow true multiplexing which makes downloads much faster.
Currently Cargo requests the http2 feature of the curl crate which
means it should always be built in. On OSX, however, we ship cargo still
linked against the system libcurl. Building curl with ALPN support for
HTTP/2 requires newer versions of OSX (the SecureTransport API) than we
want to ship Cargo for. By linking Cargo against the system libcurl then
older curl installations won’t use HTTP/2 but newer ones will. All that to
basically say we ignore errors here on OSX, but consider this a fatal error
to not activate HTTP/2 on all other platforms.
pipewait is an option which indicates that if there’s a bunch of parallel
requests to the same host they all wait until the pipelining status of the
host is known. This means that we won’t initiate dozens of connections but
rather only one. Once the main one is opened we realized that pipelining is
possible and multiplexing is possible. All in all this reduces the number
of connections down to a more manageable state.