This is a recommit of

https://webrtc.googlesource.com/src.git/+/26246cac660a95f439b7d1c593edec2929806d3f
that was reverted due to compile error on windows.

Changes since last is an addition of a cast to uint16_t in stun.cc:1018.

---

Add RelayPortFactoryInterface that allows for custom relay (e.g turn) ports

This patch adds a RelayPortFactoryInterface that allows
for custom relay ports. The factor is added as optional argument
to BasicPortAlloctor. If none is provided a default implementation
that mimics existing behavior is created.

The patch also adds 2 stun functions, namely to copy a
StunAttribute and to remove StunAttribute's from a StunMessage.

Bug: webrtc:8640
Change-Id: If23638317130060286f576c94401de55c60a1821
Reviewed-on: https://webrtc-review.googlesource.com/34181
Reviewed-by: Guido Urdaneta <guidou@webrtc.org>
Reviewed-by: Peter Thatcher <pthatcher@webrtc.org>
Commit-Queue: Jonas Oreland <jonaso@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21345}

p2p/base/stun.cc

@@ -92,6 +92,26 @@ void StunMessage::AddAttribute(std::unique_ptr<StunAttribute> attr) {
   attrs_.push_back(std::move(attr));
 }
 
+std::unique_ptr<StunAttribute> StunMessage::RemoveAttribute(int type) {
+  std::unique_ptr<StunAttribute> attribute;
+  for (auto it = attrs_.rbegin(); it != attrs_.rend(); ++it) {
+    if ((* it)->type() == type) {
+      attribute = std::move(* it);
+      attrs_.erase(std::next(it).base());
+      break;
+    }
+  }
+  if (attribute) {
+    attribute->SetOwner(nullptr);
+    size_t attr_length = attribute->length();
+    if (attr_length % 4 != 0) {
+      attr_length += (4 - (attr_length % 4));
+    }
+    length_ -= static_cast<uint16_t>(attr_length + 4);
+  }
+  return attribute;
+}
+
 const StunAddressAttribute* StunMessage::GetAddress(int type) const {
   switch (type) {
     case STUN_ATTR_MAPPED_ADDRESS: {
@@ -984,6 +1004,35 @@ bool ComputeStunCredentialHash(const std::string& username,
   return true;
 }
 
+std::unique_ptr<StunAttribute> CopyStunAttribute(
+    const StunAttribute& attribute,
+    rtc::ByteBufferWriter* tmp_buffer_ptr) {
+  ByteBufferWriter tmpBuffer;
+  if (tmp_buffer_ptr == nullptr) {
+    tmp_buffer_ptr = &tmpBuffer;
+  }
+
+  std::unique_ptr<StunAttribute> copy(
+      StunAttribute::Create(attribute.value_type(),
+                            attribute.type(),
+                            static_cast<uint16_t>(attribute.length()),
+                            nullptr));
+
+  if (!copy) {
+    return nullptr;
+  }
+  tmp_buffer_ptr->Clear();
+  if (!attribute.Write(tmp_buffer_ptr)) {
+    return nullptr;
+  }
+  rtc::ByteBufferReader reader(*tmp_buffer_ptr);
+  if (!copy->Read(&reader)) {
+    return nullptr;
+  }
+
+  return copy;
+}
+
 StunAttributeValueType RelayMessage::GetAttributeValueType(int type) const {
   switch (type) {
     case STUN_ATTR_LIFETIME: