wireprotov2: allow multiple fields to follow revision maps The *data wire protocol commands emit a series of CBOR values. Because revision/delta data may be large, their data is emitted outside the map as a top-level bytestring value. Before this commit, we'd emit a single optional bytestring value after the revision descriptor map. This got the job done. But it was limiting in that we could only send a single field. And, it required the consumer to know that the presence of a key in the map implied the existence of a following bytestring value. This commit changes the encoding strategy so top-level bytestring values in the stream are explicitly denoted in a "fieldsfollowing" key. This key contains an array defining what fields that follow and the expected size of each field. By defining things this way, we can easily send N bytestring values without any ambiguity about their order. In addition, clients only need to know how to parse ``fieldsfollowing`` to know if extra values are present. Because this breaks backwards compatibility, we've bumped the version number of the wire protocol version 2 API endpoint. Differential Revision: https://phab.mercurial-scm.org/D4620

--- a/mercurial/wireprototypes.py	Mon Sep 17 11:54:00 2018 -0700
+++ b/mercurial/wireprototypes.py	Thu Sep 20 12:57:23 2018 -0700
@@ -22,8 +22,8 @@
 SSHV1 = 'ssh-v1'
 # These are advertised over the wire. Increment the counters at the end
 # to reflect BC breakages.
-SSHV2 = 'exp-ssh-v2-0001'
-HTTP_WIREPROTO_V2 = 'exp-http-v2-0001'
+SSHV2 = 'exp-ssh-v2-0002'
+HTTP_WIREPROTO_V2 = 'exp-http-v2-0002'
 
 # All available wire protocol transports.
 TRANSPORTS = {