httppeer: don't send empty Vary request header As part of writing test-http-bad-server.t, I noticed that some requests include an empty Vary HTTP request header. The Vary HTTP request header indicates which headers should be taken into account when determining if a cached response can be used. It also accepts the special value of "*". The previous code unconditionally added a Vary header. This could lead to an empty header value. While I don't believe this violates the HTTP spec, this is weird and just wastes bytes. So this patch changes behavior to only send a Vary header when it has a value. Some low-level wire protocol byte reporting tests changed. In some cases, the exact point of data termination changed. However, the behavior being tested - that clients react when the connection is closed in the middle of an HTTP request line or header - remains unchanged.

--- a/mercurial/httppeer.py	Sun Apr 16 21:25:16 2017 -0400
+++ b/mercurial/httppeer.py	Sun Apr 16 11:28:02 2017 -0700
@@ -218,7 +218,9 @@
                 headers[header] = value
                 varyheaders.append(header)
 
-        headers['Vary'] = ','.join(varyheaders)
+        if varyheaders:
+            headers['Vary'] = ','.join(varyheaders)
+
         req = self.requestbuilder(cu, data, headers)
 
         if data is not None: