IPC: Add attachment brokering support to the message header.

ipc/brokerable_attachment.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef IPC_BROKERABLE_ATTACHMENT_H_
 #define IPC_BROKERABLE_ATTACHMENT_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "ipc/ipc_export.h"
 #include "ipc/ipc_message_attachment.h"
 
 namespace IPC {
 
 // This subclass of MessageAttachment requires an AttachmentBroker to be
 // attached to a Chrome IPC message.
 class IPC_EXPORT BrokerableAttachment : public MessageAttachment {
  public:
-  static const size_t kNonceSize = 16;
+  static const size_t kNonceSize;

[Tom Sepez, 2015/08/17 18:29:39]

Why did we lose the initianlizer? should be just const size_t, losing the
static.

[erikchen, 2015/08/18 05:59:46]

I looked into this further...the actual problem lies in the implementation of
DCHECK_EQ, and switching DCHECK_EQ(something, kNonceSize) into DCHECK (something
== kNonceSize) fixes the problem.

http://stackoverflow.com/questions/185844/initializing-private-static-members

In C++, inlining the initializer makes this a declaration, but not a definition.
This is fine, as long as nothing attempts to take the address of kNonceSize.
I've reverted back to the inline initializer.

I'm not sure what you mean about removing "static", in this context, "static"
means that the member is a class member, rather than an instance member.

   // An id uniquely identifies an attachment sent via a broker.
   struct IPC_EXPORT AttachmentId {
-    uint8_t nonce[kNonceSize];
+    // The size of this array must match kNonceSize.
+    uint8_t nonce[16];
 
-    bool operator==(const AttachmentId& rhs) const {
-      for (size_t i = 0; i < kNonceSize; ++i) {
-        if (nonce[i] != rhs.nonce[i])
-          return false;
-      }
-      return true;
-    }
+    // Default constructor doesn't initialize nonce.

[Tom Sepez, 2015/08/17 18:29:39]

nit: Seems like a mistake to leave it uninitizlized.

[erikchen, 2015/08/18 05:59:46]

You're right, I've changed the behavior and updated the comment.

+    AttachmentId(){};
 
-    bool operator<(const AttachmentId& rhs) const {
-      for (size_t i = 0; i < kNonceSize; ++i) {
-        if (nonce[i] < rhs.nonce[i])
-          return true;
-        if (nonce[i] > rhs.nonce[i])
-          return false;
-      }
-      return false;
-    }
+    // Constructs an AttachmentId from a buffer.
+    AttachmentId(const char* start_address, size_t size);
+
+    // Writes the nonce into a buffer.
+    void SerializeToBuffer(char* start_address, size_t size);
+
+    bool operator==(const AttachmentId& rhs) const;

[Tom Sepez, 2015/08/17 18:29:39]

probably want to put the code in here to help the compiler inline.

[erikchen, 2015/08/18 05:59:46]

Done.

+
+    bool operator<(const AttachmentId& rhs) const;
   };
 
   enum BrokerableType {
+    PLACEHOLDER,
     WIN_HANDLE,
   };
 
   // The identifier is unique across all Chrome processes.
   AttachmentId GetIdentifier() const;
 
   // Whether the attachment still needs information from the broker before it
   // can be used.
   bool NeedsBrokering() const;
 
-  // Fills in the data of this instance with the data from |attachment|.
-  // This instance must require brokering, |attachment| must be brokered, and
-  // both instances must have the same identifier.
-  virtual void PopulateWithAttachment(
-      const BrokerableAttachment* attachment) = 0;
-
   // Returns TYPE_BROKERABLE_ATTACHMENT
   Type GetType() const override;
 
   virtual BrokerableType GetBrokerableType() const = 0;
 
+// MessageAttachment override.
+#if defined(OS_POSIX)
+  base::PlatformFile TakePlatformFile() override;
+#endif  // OS_POSIX
+
  protected:
   BrokerableAttachment();
-  BrokerableAttachment(const AttachmentId& id, bool needs_brokering);
+  BrokerableAttachment(const AttachmentId& id);
   ~BrokerableAttachment() override;
 
-  void SetNeedsBrokering(bool needs_brokering);
-
  private:
   // This member uniquely identifies a BrokerableAttachment across all Chrome
   // processes.
   const AttachmentId id_;
 
-  // Whether the attachment still needs to be filled in by an AttachmentBroker.
-  bool needs_brokering_;
   DISALLOW_COPY_AND_ASSIGN(BrokerableAttachment);
 };
 
 }  // namespace IPC
 
 #endif  // IPC_BROKERABLE_ATTACHMENT_H_