Support encrypted RTP extensions (RFC 6904)

webrtc/media/base/fakertp.cc

+/*
+ *  Copyright (c) 2017 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include <algorithm>
+
+#include "webrtc/base/gunit.h"
+#include "webrtc/media/base/fakertp.h"
+
+void CompareHeaderExtensions(const char* packet1, const char* packet2,
+    const std::vector<int> encrypted_headers, bool expect_equal) {

[pthatcher1, 2017/05/05 21:26:38]

Shouldn't we be passing in sizes with these packets?  It just feels too unsafe
otherwise, even for unit tests.

[joachim, 2017/05/06 14:52:33]

Done.

+  // RTP extension headers are the same.
+  EXPECT_EQ(0, memcmp(packet1 + 12, packet2 + 12, 4));
+  // Check for one-byte header extensions.
+  EXPECT_EQ('\xBE', packet1[12]);
+  EXPECT_EQ('\xDE', packet1[13]);
+  // Determine position and size of extension headers.
+  size_t extension_words = packet1[14] << 8 | packet1[15];
+  const char* extension_data1 = packet1 + 12 + 4;
+  const char* extension_end1 = extension_data1 + extension_words * 4;
+  const char* extension_data2 = packet2 + 12 + 4;

[pthatcher1, 2017/05/05 21:26:38]

It would be a lot nicer to have something in media/base/rtputils.cc that pulls
out header extensions and then check that here rather than doing it in inline
here.

[joachim, 2017/05/06 14:52:33]

As this is quite some work to implement including tests, I would rather do it in
a separate CL and with that also change other code that parses header extensions
(e.g. also done manually in "UpdateRtpAbsSendTimeExtension" in
media/base/rtputils.cc and probably other places, too).

+  while (extension_data1 < extension_end1) {
+    uint8_t id = (*extension_data1 & 0xf0) >> 4;
+    uint8_t len = (*extension_data1 & 0x0f) +1;
+    extension_data1++;
+    extension_data2++;
+    EXPECT_LE(extension_data1, extension_end1);
+    if (id == 15) {
+      // Finished parsing.
+      break;
+    }
+
+    // The header extension doesn't get encrypted if the id is not in the
+    // list of header extensions to encrypt.
+    if (expect_equal ||
+        std::find(encrypted_headers.begin(), encrypted_headers.end(), id)
+            == encrypted_headers.end()) {
+      EXPECT_EQ(0, memcmp(extension_data1, extension_data2, len));
+    } else {
+      EXPECT_NE(0, memcmp(extension_data1, extension_data2, len));
+    }
+
+    extension_data1 += len;
+    extension_data2 += len;
+    // Skip padding.
+    while (extension_data1 < extension_end1 && *extension_data1 == 0) {
+      extension_data1++;
+      extension_data2++;
+    }
+  }
+}