hgweb: handle CONTENT_LENGTH

PEP 3333 says CONTENT_LENGTH may be set. I /think/ WSGI servers are
allowed to invent this key even if the client didn't send it.

We had code in wireprotoserver looking for this key. So let's
just automagically convert this key to an HTTP request header
when parsing the request.

Differential Revision: https://phab.mercurial-scm.org/D2744

mercurial/hgweb/request.py

@@ -200,6 +200,13 b' def parserequestfromenv(env):'
 
     headers = wsgiheaders.Headers(headers)
 
+    # This is kind of a lie because the HTTP header wasn't explicitly
+    # sent. But for all intents and purposes it should be OK to lie about
+    # this, since a consumer will either either value to determine how many
+    # bytes are available to read.
+    if 'CONTENT_LENGTH' in env and 'HTTP_CONTENT_LENGTH' not in env:
+        headers['Content-Length'] = env['CONTENT_LENGTH']
+
     return parsedrequest(url=fullurl, baseurl=baseurl,
                          advertisedurl=advertisedfullurl,
                          advertisedbaseurl=advertisedbaseurl,

mercurial/wireprotoserver.py

@@ -91,10 +91,9 b' class httpv1protocolhandler(wireprototyp'
         return args
 
     def forwardpayload(self, fp):
-        if b'Content-Length' in self._req.headers:
-            length = int(self._req.headers[b'Content-Length'])
-        else:
-            length = int(self._wsgireq.env[r'CONTENT_LENGTH'])
+        # Existing clients *always* send Content-Length.
+        length = int(self._req.headers[b'Content-Length'])
+
         # If httppostargs is used, we need to read Content-Length
         # minus the amount that was consumed by args.
         length -= int(self._req.headers.get(b'X-HgArgs-Post', 0))