Add functions for DER parsing a BIT STRING.

net/der/parser.cc

Index: net/der/parser.cc
diff --git a/net/der/parser.cc b/net/der/parser.cc
index 1d9cbc51086b00a7470addbe0d0448fdf03ecc90..c42d4200d6e6f721bcc70362db816636ed8d2300 100644
--- a/net/der/parser.cc
+++ b/net/der/parser.cc
@@ -186,6 +186,20 @@ bool Parser::ReadUint64(uint64_t* out) {
   return ParseUint64(encoded_int, out);
 }
 
+bool Parser::ReadBitString(Input* bytes, uint8_t* unused_bits) {
+  Input value;
+  if (!ReadTag(kBitString, &value))
+    return false;
+  return ParseBitString(value, bytes, unused_bits);
+}
+
+bool Parser::ReadBitStringNoUnusedBits(Input* bytes) {
+  uint8_t unused_bits;
+  if (!ReadBitString(bytes, &unused_bits))
+    return false;
+  return unused_bits == 0;

[nharper, 2015/07/21 23:23:47]

This approach results in modifying *bytes even if the method returns false. I
believe that the rest of the Parser methods only modify output parameters if
they return true. (ParseBitString does this correctly by declaring Input bytes
(parse_values.cc:180) and only assigning it to the output parameter if the
function is going to return true (parse_values.cc:195).)

[eroman, 2015/07/22 17:05:23]

Done.

+}
+
 }  // namespace der
 
 }  // namespace net