On Tue, Feb 06, 2018 at 05:12:49PM -0800, Brandon Williams wrote: > +In protocol v2 communication is command oriented. When first contacting a > +server a list of capabilities will advertised. Some of these capabilities > +will be commands which a client can request be executed. Once a command > +has completed, a client can reuse the connection and request that other > +commands be executed.
If I understand this correctly, we'll potentially have a lot more round-trips between the client and server (one per "command"). And for git-over-http, each one will be its own HTTP request? We've traditionally tried to minimize HTTP requests, but I guess it's not too bad if we can keep the connection open in most cases. Then we just suffer some extra framing bytes, but we don't have to re-establish the TCP connection each time. I do wonder if the extra round trips will be noticeable in high-latency conditions. E.g., if I'm 200ms away, converting the current ref-advertisement spew to "capabilities, then the client asks for refs, then we spew the refs" is going to cost an extra 200ms, even if the fetch just ends up being a noop. I'm not sure how bad that is in the grand scheme of things (after all, the TCP handshake involves some round-trips, too). > + Capability Advertisement > +-------------------------- > + > +A server which decides to communicate (based on a request from a client) > +using protocol version 2, notifies the client by sending a version string > +in its initial response followed by an advertisement of its capabilities. > +Each capability is a key with an optional value. Clients must ignore all > +unknown keys. Semantics of unknown values are left to the definition of > +each key. Some capabilities will describe commands which can be requested > +to be executed by the client. > + > + capability-advertisement = protocol-version > + capability-list > + flush-pkt > + > + protocol-version = PKT-LINE("version 2" LF) > + capability-list = *capability > + capability = PKT-LINE(key[=value] LF) > + > + key = 1*CHAR > + value = 1*CHAR > + CHAR = 1*(ALPHA / DIGIT / "-" / "_") > + > +A client then responds to select the command it wants with any particular > +capabilities or arguments. There is then an optional section where the > +client can provide any command specific parameters or queries. > + > + command-request = command > + capability-list > + (command-args) > + flush-pkt > + command = PKT-LINE("command=" key LF) > + command-args = delim-pkt > + *arg > + arg = 1*CHAR For a single stateful TCP connection like git:// or git-over-ssh, the client would get the capabilities once and then issue a series of commands. For git-over-http, how does it work? The client speaks first in HTTP, so we'd first make a request to get just the capabilities from the server? And then proceed from there with a series of requests, assuming that the capabilities for each server we subsequently contact are the same? That's probably reasonable (and certainly the existing http protocol makes that capabilities assumption). I don't see any documentation on how this all works with http. But reading patch 34, it looks like we just do the usual service=git-upload-pack request (with the magic request for v2), and then the server would send us capabilities. Which follows my line of thinking in the paragraph above. -Peff