httppeer: change logic around argument handling

The code to process arguments only makes sense if there are
arguments. So change an "else" to "elif args", remove an
"if" that isn't necessary, and add some docs for good measure.

Differential Revision: https://phab.mercurial-scm.org/D2214

mercurial/httppeer.py

@@ -252,6 +252,8 b' class httppeer(wireproto.wirepeer):'
         # with infinite recursion when trying to look up capabilities
         # for the first time.
         postargsok = self._caps is not None and 'httppostargs' in self._caps
+
+        # Send arguments via POST.
         if postargsok and args:
             strargs = urlreq.urlencode(sorted(args.items()))
             if not data:
@@ -265,11 +267,16 b' class httppeer(wireproto.wirepeer):'
                 argsio.length = len(strargs)
                 data = _multifile(argsio, data)
             headers[r'X-HgArgs-Post'] = len(strargs)
-        else:
-            if len(args) > 0:
-                httpheader = self.capable('httpheader')
-                if httpheader:
-                    headersize = int(httpheader.split(',', 1)[0])
+        elif args:
+            # Calling self.capable() can infinite loop if we are calling
+            # "capabilities". But that command should never accept wire
+            # protocol arguments. So this should never happen.
+            assert cmd != 'capabilities'
+            httpheader = self.capable('httpheader')
+            if httpheader:
+                headersize = int(httpheader.split(',', 1)[0])
+
+            # Send arguments via HTTP headers.
             if headersize > 0:
                 # The headers can typically carry more data than the URL.
                 encargs = urlreq.urlencode(sorted(args.items()))
@@ -277,8 +284,10 b' class httppeer(wireproto.wirepeer):'
                                                           headersize):
                     headers[header] = value
                     varyheaders.append(header)
+            # Send arguments via query string (Mercurial <1.9).
             else:
                 q += sorted(args.items())
+
         qs = '?%s' % urlreq.urlencode(q)
         cu = "%s%s" % (self._url, qs)
         size = 0