ssh: add capability detection at startup

Because older servers don't return any output for unknown commands,
it's tricky to add new commands. The approach is this: we add a
"hello" command that reports any interesting capabilities (and other
things that might be of interest in the future). To detect whether
this new command is supported, we issue both it and our startup
detection command ("between") at the beginning of a connection.

mercurial/sshrepo.py

@@ -1,154 +1,162 b''
 # sshrepo.py - ssh repository proxy class for mercurial
 #
 # Copyright 2005 Matt Mackall <[e-mail]>
 #
 # This software may be used and distributed according to the terms
 # of the GNU General Public License, incorporated herein by reference.
 
 from node import *
 from remoterepo import *
 from i18n import gettext as _
 from demandload import *
 demandload(globals(), "hg os re stat util")
 
 class sshrepository(remoterepository):
     def __init__(self, ui, path):
         self.url = path
         self.ui = ui
 
         m = re.match(r'ssh://(([^@]+)@)?([^:/]+)(:(\d+))?(/(.*))?', path)
         if not m:
             raise hg.RepoError(_("couldn't parse destination %s") % path)
 
         self.user = m.group(2)
         self.host = m.group(3)
         self.port = m.group(5)
         self.path = m.group(7) or "."
 
         args = self.user and ("%s@%s" % (self.user, self.host)) or self.host
         args = self.port and ("%s -p %s") % (args, self.port) or args
 
         sshcmd = self.ui.config("ui", "ssh", "ssh")
         remotecmd = self.ui.config("ui", "remotecmd", "hg")
         cmd = '%s %s "%s -R %s serve --stdio"'
         cmd = cmd % (sshcmd, args, remotecmd, self.path)
 
         ui.note('running %s\n' % cmd)
         self.pipeo, self.pipei, self.pipee = os.popen3(cmd, 'b')
 
         # skip any noise generated by remote shell
+        self.do_cmd("hello")
         r = self.do_cmd("between", pairs=("%s-%s" % ("0"*40, "0"*40)))
         lines = ["", "dummy"]
         max_noise = 500
         while lines[-1] and max_noise:
             l = r.readline()
             self.readerr()
             if lines[-1] == "1\n" and l == "\n":
                 break
             if l:
                 ui.debug(_("remote: "), l)
             lines.append(l)
             max_noise -= 1
         else:
             if l1:
                 ui.debug(_("remote: "), l1)
             raise hg.RepoError(_("no response from remote hg"))
 
+        self.capabilities = ()
+        lines.reverse()
+        for l in lines:
+            if l.startswith("capabilities:"):
+                self.capabilities = l[:-1].split(":")[1].split()
+                break
+
     def readerr(self):
         while 1:
             size = util.fstat(self.pipee).st_size
             if size == 0: break
             l = self.pipee.readline()
             if not l: break
             self.ui.status(_("remote: "), l)
 
     def __del__(self):
         try:
             self.pipeo.close()
             self.pipei.close()
             # read the error descriptor until EOF
             for l in self.pipee:
                 self.ui.status(_("remote: "), l)
             self.pipee.close()
         except:
             pass
 
     def dev(self):
         return -1
 
     def do_cmd(self, cmd, **args):
         self.ui.debug(_("sending %s command\n") % cmd)
         self.pipeo.write("%s\n" % cmd)
         for k, v in args.items():
             self.pipeo.write("%s %d\n" % (k, len(v)))
             self.pipeo.write(v)
         self.pipeo.flush()
 
         return self.pipei
 
     def call(self, cmd, **args):
         r = self.do_cmd(cmd, **args)
         l = r.readline()
         self.readerr()
         try:
             l = int(l)
         except:
             raise hg.RepoError(_("unexpected response '%s'") % l)
         return r.read(l)
 
     def lock(self):
         self.call("lock")
         return remotelock(self)
 
     def unlock(self):
         self.call("unlock")
 
     def heads(self):
         d = self.call("heads")
         try:
             return map(bin, d[:-1].split(" "))
         except:
             raise hg.RepoError(_("unexpected response '%s'") % (d[:400] + "..."))
 
     def branches(self, nodes):
         n = " ".join(map(hex, nodes))
         d = self.call("branches", nodes=n)
         try:
             br = [ tuple(map(bin, b.split(" "))) for b in d.splitlines() ]
             return br
         except:
             raise hg.RepoError(_("unexpected response '%s'") % (d[:400] + "..."))
 
     def between(self, pairs):
         n = "\n".join(["-".join(map(hex, p)) for p in pairs])
         d = self.call("between", pairs=n)
         try:
             p = [ l and map(bin, l.split(" ")) or [] for l in d.splitlines() ]
             return p
         except:
             raise hg.RepoError(_("unexpected response '%s'") % (d[:400] + "..."))
 
     def changegroup(self, nodes, kind):
         n = " ".join(map(hex, nodes))
         f = self.do_cmd("changegroup", roots=n)
         return self.pipei
 
     def addchangegroup(self, cg, source):
         d = self.call("addchangegroup")
         if d:
             raise hg.RepoError(_("push refused: %s"), d)
 
         while 1:
             d = cg.read(4096)
             if not d: break
             self.pipeo.write(d)
             self.readerr()
 
         self.pipeo.flush()
 
         self.readerr()
         l = int(self.pipei.readline())
         r = self.pipei.read(l)
         if not r:
             return 1
         return int(r)