Re: Returning error message from custom smart http server

> On Sat, May 17, 2014 at 9:01 AM, brian m. carlson
> <sandals@crustytoothpaste.net> wrote:
> > On Tue, May 13, 2014 at 09:39:59AM +0200, "Ákos, Tajti" wrote:
> >> Dear List,
> >>
> >> we implemented our own git smart http server to be able to check permissions
> >> and other thing before pushes. It works fine, however, the error messages we
> >> generate on the server side are not displayed by the command line client. On
> >> the server we generate error messages like this:
> >>
> >>         response.setStatus(HttpServletResponse.SC_UNAUTHORIZED);
> >>         response.getWriter().write(msg);
> >>
> >> On the command line we get this:
> >>
> >> Total 0 (delta 0), reused 0 (delta 0)
> >> POST git-receive-pack (290 bytes)
> >> efrror: RPC failed; result=22, HTTP code = 401
> >> atal: The remote end hung up unexpectedly
> >> fatal: The remote end hung up unexpectedly
> >>
> >> The server message is completely missing. Is there a solution for this?
> 
> You should not need a patched git; the wire protocol itself has a
> mechanism for sending "smart" error messages. It's not particularly
> _obvious_, but it's there.
> 
> For starters, to return an error message, your status must be 200 OK.
> You can't return any other status code or Git will interpret your
> error as some form of _HTTP_ error rather than a _git_ error.
> 
> In the smart protocol the client sends a service to the server as a
> query parameter, like "?service=git-receive-pack". For such a request,
> you need to:
> - Set the content type to "application/x-<service>-advertisement"
> (e.g. "application/x-git-receive-pack-advertisement") (Not all command
> line Git versions require this, but JGit does)
> - Set the status code as 200 OK
> - Write back a payload where the first 4 bytes are the hex-encoded
> length of the text (where "FFFF" is max length for a single packet).
> Note that the 4 bytes for the size are _part_ of that length, so if
> you're writing "Test" the length is 8, not 4
> - After the size, you write "# service=<service>" (e.g. "#
> service=git-receive-pack"; note the space after the #) This is the
> metadata. For an error, you don't really have much to say.
> - After that, an empty packet, which is "0000" (four zeros) This
> separates the metadata from the ref advertisement
> - After that you can write your message, beginning with "ERR " (note
> the trailing space there). The "ERR " tells Git what you're writing
> isn't a ref, it's an error. I'd recommend appending a newline (and add
> 1 more to your length for it), because when Git echoes your error
> message it doesn't seem to do that
> 
> I'm not sure whether there's a document that describes all of this; I
> found it by digging into the Git source code (you can find the "ERR"
> handling in connect.c, get_remote_heads). This may be exploiting the
> protocol, I'll leave that to someone more knowledgeable on how they
> _intended_ this all to be used, but it works for us.
> 
> A full example looks something like this: "0036#
> service=git-receive-pack0000ERR This is a test\n"