ipc: Update Message::FindNext to parse brokered attachments.

ipc/ipc_message.h

Index: ipc/ipc_message.h
diff --git a/ipc/ipc_message.h b/ipc/ipc_message.h
index d0e38afc342218365423056330b0eed5b734d8ba..e7cc7d4c230edddb553139cafa9597f807e9b46b 100644
--- a/ipc/ipc_message.h
+++ b/ipc/ipc_message.h
@@ -12,6 +12,7 @@
 #include "base/pickle.h"
 #include "base/trace_event/trace_event.h"
 #include "ipc/attachment_broker.h"
+#include "ipc/brokerable_attachment.h"
 #include "ipc/ipc_export.h"
 
 #if !defined(NDEBUG)
@@ -165,11 +166,33 @@ class IPC_EXPORT Message : public base::Pickle {
   static void Log(std::string* name, const Message* msg, std::string* l) {
   }
 
-  // Find the end of the message data that starts at range_start.  Returns NULL
-  // if the entire message is not found in the given data range.
-  static const char* FindNext(const char* range_start, const char* range_end) {
-    return base::Pickle::FindNext(sizeof(Header), range_start, range_end);
-  }
+  // The static method FindNext() returns several pieces of information, which
+  // are aggregated into an instance of this struct.

[Tom Sepez, 2015/09/01 18:01:54]

nit: this may be complex enough to warrant being a class with protected members.
 Your call.

[erikchen, 2015/09/04 02:13:39]

This is just a wrapper around several different pieces of information being
returned from a function. Making it a class and adding accessors adds
unnecessary complexity.

+  struct NextMessageInfo {
+    NextMessageInfo();
+    ~NextMessageInfo();
+    // Whether an entire message was found in the given memory range.
+    bool message_found;
+    // The parser encountered an unrecoverable error. This will always be false
+    // if |message_found| is true.
+    bool parsing_error;
+    // Only filled in if |message_found| is true.
+    // The start address is passed into FindNext() by the caller, so isn't
+    // repeated in this struct. The end address of the pickle should be used to
+    // construct a base::Pickle.
+    const char* pickle_end;
+    // Only filled in if |message_found| is true.
+    // The end address of the message should be used to determine the start
+    // address of the next message.
+    const char* message_end;
+    // If the message has brokerable attachments, this vector will contain the
+    // ids of the brokerable attachments. The caller of FindNext() is
+    // responsible for adding the attachments to the message.
+    std::vector<BrokerableAttachment::AttachmentId> attachment_ids;
+  };
+
+  static NextMessageInfo FindNext(const char* range_start,
+                                  const char* range_end);
 
   // WriteAttachment appends |attachment| to the end of the set. It returns
   // false iff the set is full.