Implement "clear" keyword in SpdyAltSvcWireFormat.

Note that the "clear" keyword was introduced to the Alternative Services
specification in draft-08.

This CL lands server change 104884972 by bnc.

BUG=392575

Review URL: https://codereview.chromium.org/1402633003

Cr-Commit-Position: refs/heads/master@{#353672}

3 files changed, 24 insertions, 4 deletions

diff --git a/net/spdy/spdy_alt_svc_wire_format.cc b/net/spdy/spdy_alt_svc_wire_format.cc
index 4ac8dc5..ad414ff 100644
--- a/net/spdy/spdy_alt_svc_wire_format.cc
+++ b/net/spdy/spdy_alt_svc_wire_format.cc
@@ -54,7 +54,14 @@ SpdyAltSvcWireFormat::AlternativeService::AlternativeService(
 bool SpdyAltSvcWireFormat::ParseHeaderFieldValue(
     StringPiece value,
     AlternativeServiceVector* altsvc_vector) {
+  // Empty value is invalid according to the specification.
+  if (value.empty()) {
+    return false;
+  }
   altsvc_vector->clear();
+  if (value == StringPiece("clear")) {
+    return true;
+  }
   StringPiece::const_iterator c = value.begin();
   while (c != value.end()) {
     // Parse protocol-id.
@@ -156,6 +163,9 @@ bool SpdyAltSvcWireFormat::ParseHeaderFieldValue(
 // static
 std::string SpdyAltSvcWireFormat::SerializeHeaderFieldValue(
     const AlternativeServiceVector& altsvc_vector) {
+  if (altsvc_vector.empty()) {
+    return std::string("clear");
+  }
   const char kNibbleToHex[] = "0123456789ABCDEF";
   std::string value;
   for (const AlternativeService& altsvc : altsvc_vector) {
diff --git a/net/spdy/spdy_alt_svc_wire_format.h b/net/spdy/spdy_alt_svc_wire_format.h
index 23d9187..8b8a0b1 100644
--- a/net/spdy/spdy_alt_svc_wire_format.h
+++ b/net/spdy/spdy_alt_svc_wire_format.h
@@ -5,7 +5,7 @@
 // This file contains data structures and utility functions used for serializing
 // and parsing alternative service header values, common to HTTP/1.1 header
 // fields and HTTP/2 and QUIC ALTSVC frames.  See specification at
-// https://tools.ietf.org/id/draft-ietf-httpbis-alt-svc-06.html
+// https://httpwg.github.io/http-extensions/alt-svc.html.
 
 #ifndef NET_SPDY_SPDY_ALT_SVC_WIRE_FORMAT_H_
 #define NET_SPDY_SPDY_ALT_SVC_WIRE_FORMAT_H_
@@ -52,6 +52,9 @@ class NET_EXPORT_PRIVATE SpdyAltSvcWireFormat {
              max_age == other.max_age && p == other.p;
     }
   };
+  // An empty vector means alternative services should be cleared for given
+  // origin.  Note that the wire format for this is the string "clear", not an
+  // empty value (which is invalid).
   typedef std::vector<AlternativeService> AlternativeServiceVector;
 
   friend class test::SpdyAltSvcWireFormatPeer;
diff --git a/net/spdy/spdy_alt_svc_wire_format_test.cc b/net/spdy/spdy_alt_svc_wire_format_test.cc
index 550d767..b53db3b 100644
--- a/net/spdy/spdy_alt_svc_wire_format_test.cc
+++ b/net/spdy/spdy_alt_svc_wire_format_test.cc
@@ -159,9 +159,15 @@ TEST(SpdyAltSvcWireFormatTest, DefaultValues) {
   EXPECT_DOUBLE_EQ(1.0, altsvc.p);
 }
 
-TEST(SpdyAltSvcWireFormatTest, ParseEmptyHeaderFieldValue) {
+TEST(SpdyAltSvcWireFormatTest, ParseInvalidEmptyHeaderFieldValue) {
   SpdyAltSvcWireFormat::AlternativeServiceVector altsvc_vector;
-  ASSERT_TRUE(SpdyAltSvcWireFormat::ParseHeaderFieldValue("", &altsvc_vector));
+  ASSERT_FALSE(SpdyAltSvcWireFormat::ParseHeaderFieldValue("", &altsvc_vector));
+}
+
+TEST(SpdyAltSvcWireFormatTest, ParseHeaderFieldValueClear) {
+  SpdyAltSvcWireFormat::AlternativeServiceVector altsvc_vector;
+  ASSERT_TRUE(
+      SpdyAltSvcWireFormat::ParseHeaderFieldValue("clear", &altsvc_vector));
   EXPECT_EQ(0u, altsvc_vector.size());
 }
 
@@ -220,7 +226,8 @@ TEST(SpdyAltSvcWireFormatTest, ParseHeaderFieldValueMultiple) {
 
 TEST(SpdyAltSvcWireFormatTest, SerializeEmptyHeaderFieldValue) {
   SpdyAltSvcWireFormat::AlternativeServiceVector altsvc_vector;
-  EXPECT_EQ("", SpdyAltSvcWireFormat::SerializeHeaderFieldValue(altsvc_vector));
+  EXPECT_EQ("clear",
+            SpdyAltSvcWireFormat::SerializeHeaderFieldValue(altsvc_vector));
 }
 
 // Test SerializeHeaderFieldValue() with and without hostname and each