Adds a function for encoding a Merkle tree leaf in TLS wire format.

net/cert/merkle_tree_leaf.h

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef NET_CERT_MERKLE_TREE_LEAF_H_
 #define NET_CERT_MERKLE_TREE_LEAF_H_
 
 #include <memory>
 #include <string>
 
 #include "base/time/time.h"
 #include "net/base/net_export.h"
 #include "net/cert/signed_certificate_timestamp.h"
 
 namespace net {
 
 class X509Certificate;
 
 namespace ct {
 
 // Represents a MerkleTreeLeaf as defined in RFC6962, section 3.4.
 // Has all the data as the MerkleTreeLeaf defined in the RFC, arranged
 // slightly differently.
 struct NET_EXPORT MerkleTreeLeaf {
+  // Version enum in RFC 6962, Section 3.2.

[Eran Messeri, 2016/05/04 10:29:23]

Nit: I'd inline those in ct_serialization.cc and avoid changing
merkle_tree_leaf.h entirely.
You'd point out that we did this differently for SignedCertificateTimestamp -
and you're right - but now I'm fairly confident there won't be another version /
type of MerkleTreeLeaf for RFC6962.
Since we only care about these values during serialization, then it's simpler to
have them in the serialization code.

[Rob Percival, 2016/05/05 15:45:31]

Done.

+  enum Version { VERSION_1 = 0, };
+  // MerkleLeafType enum in RFC 6962, Section 3.4.
+  enum Type { TYPE_TIMESTAMPED_ENTRY = 0, };
+
   MerkleTreeLeaf();
   ~MerkleTreeLeaf();
 
+  // Version and Merkle leaf type fields are omitted, as there is only one
+  // possible value for each of them in CTv1.
+
   // The log id this leaf belongs to.
   std::string log_id;
 
   // Certificate / Precertificate and indication of entry type.
   LogEntry log_entry;
 
   // Timestamp from the SCT.
   base::Time timestamp;
 
   // Extensions from the SCT.
   std::string extensions;
 };
 
 NET_EXPORT bool GetMerkleTreeLeaf(const X509Certificate* cert,
                                   const SignedCertificateTimestamp* sct,
                                   MerkleTreeLeaf* merkle_tree_leaf);
 
 }  // namespace ct
 
 }  // namespace net
 
 #endif  // NET_CERT_MERKLE_TREE_LEAF_H_