Avoid trusting the length encoded in the Snapshot if there is an

runtime/vm/snapshot.h

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #ifndef VM_SNAPSHOT_H_
 #define VM_SNAPSHOT_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
@@ skipping 83 matching lines @@
 };
 
 
 enum SerializeState {
   kIsSerialized = 0,
   kIsNotSerialized = 1,
 };
 
 
 // Structure capturing the raw snapshot.
+//
+// TODO(turnidge): Remove this class once the snapshot does not have a
+// header anymore.  This is pending on making the embedder pass in the
+// length of their snapshot.
 class Snapshot {
  public:
   enum Kind {
     kFull = 0,  // Full snapshot of the current dart heap.
     kScript,    // A partial snapshot of only the application script.
     kMessage,   // A partial snapshot used only for isolate messaging.
   };
 
   static const int kHeaderSize = 2 * sizeof(int32_t);
   static const int kLengthIndex = 0;
   static const int kSnapshotFlagIndex = 1;
 
   static const Snapshot* SetupFromBuffer(const void* raw_memory);
 
   // Getters.
   const uint8_t* content() const { return content_; }
   int32_t length() const { return length_; }
   Kind kind() const { return static_cast<Kind>(kind_); }
 
   bool IsMessageSnapshot() const { return kind_ == kMessage; }
   bool IsScriptSnapshot() const { return kind_ == kScript; }
   bool IsFullSnapshot() const { return kind_ == kFull; }
-  int32_t Size() const { return length_ + sizeof(Snapshot); }
   uint8_t* Addr() { return reinterpret_cast<uint8_t*>(this); }
 
   static intptr_t length_offset() { return OFFSET_OF(Snapshot, length_); }
   static intptr_t kind_offset() {
     return OFFSET_OF(Snapshot, kind_);
   }
 
  private:
   Snapshot() : length_(0), kind_(kFull) {}
 
@@ skipping 39 matching lines @@
   }
 
  private:
   ReadStream stream_;  // input stream.
 };
 
 
 // Reads a snapshot into objects.
 class SnapshotReader : public BaseReader {
  public:
-  SnapshotReader(const Snapshot* snapshot, Isolate* isolate);
+  SnapshotReader(const uint8_t* buffer,
+                 intptr_t size,
+                 Snapshot::Kind kind,
+                 Isolate* isolate);
   ~SnapshotReader() { }
 
   Isolate* isolate() const { return isolate_; }
   Heap* heap() const { return isolate_->heap(); }
   ObjectStore* object_store() const { return isolate_->object_store(); }
   ClassTable* class_table() const { return isolate_->class_table(); }
   Object* ObjectHandle() { return &obj_; }
   String* StringHandle() { return &str_; }
   AbstractType* TypeHandle() { return &type_; }
   AbstractTypeArguments* TypeArgumentsHandle() { return &type_arguments_; }
@@ skipping 160 matching lines @@
     value = SerializedHeaderTag::update(kInlined, value);
     value = SerializedHeaderData::update(id, value);
     WriteIntptrValue(value);
   }
 
   // Write out a buffer of bytes.
   void WriteBytes(const uint8_t* addr, intptr_t len) {
     stream_.WriteBytes(addr, len);
   }
 
-  // Finalize the serialized buffer by filling in the header information
-  // which comprises of a flag(snaphot kind) and the length of
-  // serialzed bytes.
-  void FinalizeBuffer(Snapshot::Kind kind) {
-    int32_t* data = reinterpret_cast<int32_t*>(stream_.buffer());
-    data[Snapshot::kLengthIndex] = stream_.bytes_written();
-    data[Snapshot::kSnapshotFlagIndex] = kind;
-  }
-
  protected:
   BaseWriter(uint8_t** buffer, ReAlloc alloc) : stream_(buffer, alloc) {
     ASSERT(buffer != NULL);
     ASSERT(alloc != NULL);
-    // Make room for recording snapshot buffer size.
-    stream_.set_current(*buffer + Snapshot::kHeaderSize);
   }
   ~BaseWriter() { }
 
+  void ReserveHeader() {
+    // Make room for recording snapshot buffer size.
+    stream_.set_current(stream_.buffer() + Snapshot::kHeaderSize);
+  }
+
+  void FillHeader(Snapshot::Kind kind) {
+    int32_t* data = reinterpret_cast<int32_t*>(stream_.buffer());
+    data[Snapshot::kLengthIndex] = stream_.bytes_written();
+    data[Snapshot::kSnapshotFlagIndex] = kind;
+  }
+
  private:
   WriteStream stream_;
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(BaseWriter);
 };
 
 
 class SnapshotWriter : public BaseWriter {
- public:
+ protected:
   SnapshotWriter(Snapshot::Kind kind, uint8_t** buffer, ReAlloc alloc)
       : BaseWriter(buffer, alloc),
         kind_(kind),
         object_store_(Isolate::Current()->object_store()),
         class_table_(Isolate::Current()->class_table()),
         forward_list_() {
   }
-  ~SnapshotWriter() { }
 
+ public:
   // Snapshot kind.
   Snapshot::Kind kind() const { return kind_; }
 
-  // Finalize the serialized buffer by filling in the header information
-  // which comprises of a flag(full/partial snaphot) and the length of
-  // serialzed bytes.
-  void FinalizeBuffer() {
-    BaseWriter::FinalizeBuffer(kind_);
-    UnmarkAll();
-  }
-
   // Serialize an object into the buffer.
   void WriteObject(RawObject* raw);
 
-  // Writes a full snapshot of the Isolate.
-  void WriteFullSnapshot();
-
   uword GetObjectTags(RawObject* raw);
 
- private:
+ protected:
   class ForwardObjectNode : public ZoneAllocated {
    public:
     ForwardObjectNode(RawObject* raw, uword tags, SerializeState state)
         : raw_(raw), tags_(tags), state_(state) {}
     RawObject* raw() const { return raw_; }
     uword tags() const { return tags_; }
     bool is_serialized() const { return state_ == kIsSerialized; }
     void set_state(SerializeState value) { state_ = value; }
 
    private:
@@ skipping 17 matching lines @@
   void WriteForwardedObjects();
   void ArrayWriteTo(intptr_t object_id,
                     intptr_t array_kind,
                     intptr_t tags,
                     RawSmi* length,
                     RawAbstractTypeArguments* type_arguments,
                     RawObject* data[]);
 
   ObjectStore* object_store() const { return object_store_; }
 
+ private:
   Snapshot::Kind kind_;
   ObjectStore* object_store_;  // Object store for common classes.
   ClassTable* class_table_;  // Class table for the class index to class lookup.
   GrowableArray<ForwardObjectNode*> forward_list_;
 
   friend class RawArray;
   friend class RawClass;
   friend class RawGrowableObjectArray;
   friend class RawImmutableArray;
   friend class RawJSRegExp;
   friend class RawLibrary;
   friend class RawLiteralToken;
   friend class RawScript;
   friend class RawTokenStream;
   friend class RawTypeArguments;
   friend class SnapshotWriterVisitor;
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriter);
 };
 
 
+class FullSnapshotWriter : public SnapshotWriter {
+ public:
+  FullSnapshotWriter(uint8_t** buffer, ReAlloc alloc)
+      : SnapshotWriter(Snapshot::kFull, buffer, alloc) {
+    ASSERT(buffer != NULL);
+    ASSERT(alloc != NULL);
+  }
+  ~FullSnapshotWriter() { }
+
+  // Writes a full snapshot of the Isolate.
+  void WriteFullSnapshot();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(FullSnapshotWriter);
+};
+
+
 class ScriptSnapshotWriter : public SnapshotWriter {
  public:
   ScriptSnapshotWriter(uint8_t** buffer, ReAlloc alloc)
       : SnapshotWriter(Snapshot::kScript, buffer, alloc) {
     ASSERT(buffer != NULL);
     ASSERT(alloc != NULL);
   }
   ~ScriptSnapshotWriter() { }
 
   // Writes a partial snapshot of the script.
   void WriteScriptSnapshot(const Library& lib);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ScriptSnapshotWriter);
 };
 
 
+class MessageWriter : public SnapshotWriter {
+ public:
+  MessageWriter(uint8_t** buffer, ReAlloc alloc)
+      : SnapshotWriter(Snapshot::kMessage, buffer, alloc) {
+    ASSERT(buffer != NULL);
+    ASSERT(alloc != NULL);
+  }
+  ~MessageWriter() { }
+
+  void WriteMessage(const Object& obj);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(MessageWriter);
+};
+
+
 // An object pointer visitor implementation which writes out
 // objects to a snap shot.
 class SnapshotWriterVisitor : public ObjectPointerVisitor {
  public:
   explicit SnapshotWriterVisitor(SnapshotWriter* writer)
       : ObjectPointerVisitor(Isolate::Current()),
         writer_(writer),
         as_references_(true) {}
 
   SnapshotWriterVisitor(SnapshotWriter* writer, bool as_references)
       : ObjectPointerVisitor(Isolate::Current()),
         writer_(writer),
         as_references_(as_references) {}
 
   virtual void VisitPointers(RawObject** first, RawObject** last);
 
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_SNAPSHOT_H_