Adds a listener interface to HpackEncoder. Not used in production. Not protected.

net/spdy/hpack/hpack_encoder.h

Index: net/spdy/hpack/hpack_encoder.h
diff --git a/net/spdy/hpack/hpack_encoder.h b/net/spdy/hpack/hpack_encoder.h
index ce5c9df51ca6653585b09f934f0d2fe01f7efc67..a2085f084f523d97dd0a0f47217ab46bb41ca1d8 100644
--- a/net/spdy/hpack/hpack_encoder.h
+++ b/net/spdy/hpack/hpack_encoder.h
@@ -20,6 +20,8 @@
 #include "net/spdy/hpack/hpack_output_stream.h"
 #include "net/spdy/spdy_protocol.h"
 
+using base::StringPiece;

[Bence, 2016/08/15 13:58:31]

Please remove this using directive.  Unfortunately they are not allowed in
header files.  (See "Do not use Namespace aliases at namespace scope in header
files except in explicitly marked internal-only namespaces" and "Don't put
namespace aliases in your public" at
https://google.github.io/styleguide/cppguide.html.)  This means that in every
header file, we have to spell out base::StringPiece.

+
 // An HpackEncoder encodes header sets as outlined in
 // http://tools.ietf.org/html/rfc7541.
 
@@ -36,6 +38,10 @@ class NET_EXPORT_PRIVATE HpackEncoder {
   using Representation = std::pair<base::StringPiece, base::StringPiece>;
   using Representations = std::vector<Representation>;
 
+  // Callers may provide a HeaderListener to be informed of header name-value
+  // pairs processed by this encoder.
+  typedef std::function<void(StringPiece, StringPiece)> HeaderListener;
+
   // An indexing policy should return true if the provided header name-value
   // pair should be inserted into the HPACK dynamic table.
   using IndexingPolicy =
@@ -73,6 +79,10 @@ class NET_EXPORT_PRIVATE HpackEncoder {
   // name-value pairs into the dynamic table.
   void SetIndexingPolicy(IndexingPolicy policy) { should_index_ = policy; }
 
+  // |listener| will be invoked for each header name-value pair processed by
+  // this encoder.
+  void SetHeaderListener(HeaderListener listener) { listener_ = listener; }
+
   void SetHeaderTableDebugVisitor(
       std::unique_ptr<HpackHeaderTable::DebugVisitorInterface> visitor) {
     header_table_.set_debug_visitor(std::move(visitor));
@@ -114,6 +124,7 @@ class NET_EXPORT_PRIVATE HpackEncoder {
 
   const HpackHuffmanTable& huffman_table_;
   size_t min_table_size_setting_received_;
+  HeaderListener listener_;
   IndexingPolicy should_index_;
   bool allow_huffman_compression_;
   bool should_emit_table_size_;