streamclone: move payload header generation into own function

The stream clone data over the wire protocol contains a header line
indicating total file count and data size. In bundle2, this metadata can
be captured by a part parameter and doesn't need to be in the body.

In preparation for bundle2, have generatev1() return the raw metadata
and move the header generation to its own function.

mercurial/streamclone.py

@@ -164,13 +164,12 b' def _walkstreamfiles(repo):'
 def generatev1(repo):
     """Emit content for version 1 of a streaming clone.
 
-    This is a generator of raw chunks that constitute a streaming clone.
+    This returns a 3-tuple of (file count, byte size, data iterator).
 
-    The stream begins with a line of 2 space-delimited integers containing the
-    number of entries and total bytes size.
+    The data iterator consists of N entries for each file being transferred.
+    Each file entry starts as a line with the file name and integer size
+    delimited by a null byte.
 
-    Next, are N entries for each file being transferred. Each file entry starts
-    as a line with the file name and integer size delimited by a null byte.
     The raw file data follows. Following the raw file data is the next file
     entry, or EOF.
 
@@ -196,13 +195,13 b' def generatev1(repo):'
 
     repo.ui.debug('%d files, %d bytes to transfer\n' %
                   (len(entries), total_bytes))
-    yield '%d %d\n' % (len(entries), total_bytes)
 
     svfs = repo.svfs
     oldaudit = svfs.mustaudit
     debugflag = repo.ui.debugflag
     svfs.mustaudit = False
 
+    def emitrevlogdata():
     try:
         for name, size in entries:
             if debugflag:
@@ -222,6 +221,19 b' def generatev1(repo):'
     finally:
         svfs.mustaudit = oldaudit
 
+    return len(entries), total_bytes, emitrevlogdata()
+
+def generatev1wireproto(repo):
+    """Emit content for version 1 of streaming clone suitable for the wire.
+
+    This is the data output from ``generatev1()`` with a header line
+    indicating file count and byte size.
+    """
+    filecount, bytecount, it = generatev1(repo)
+    yield '%d %d\n' % (filecount, bytecount)
+    for chunk in it:
+        yield chunk
+
 def consumev1(repo, fp, filecount, bytecount):
     """Apply the contents from version 1 of a streaming clone file handle.
 

mercurial/wireproto.py

@@ -718,7 +718,7 b' def stream(repo, proto):'
     try:
         # LockError may be raised before the first result is yielded. Don't
         # emit output until we're sure we got the lock successfully.
-        it = streamclone.generatev1(repo)
+        it = streamclone.generatev1wireproto(repo)
         return streamres(getstream(it))
     except error.LockError:
         return '2\n'