Implementation of message reader for converting a message snapshot into a C structure

runtime/vm/snapshot.cc

Index: runtime/vm/snapshot.cc
diff --git a/runtime/vm/snapshot.cc b/runtime/vm/snapshot.cc
index 8cb504591ee37fe0acab86dcdcf4f1efd995302f..edd9e7ba9a41ed4f9f1718b9047117081bf6c460 100644
--- a/runtime/vm/snapshot.cc
+++ b/runtime/vm/snapshot.cc
@@ -55,8 +55,20 @@ const Snapshot* Snapshot::SetupFromBuffer(const void* raw_memory) {
 }
 
 
+RawSmi* BaseReader::ReadAsSmi() {
+  intptr_t value = ReadIntptrValue();
+  ASSERT((value & kSmiTagMask) == 0);
+  return reinterpret_cast<RawSmi*>(value);
+}
+
+
+intptr_t BaseReader::ReadSmiValue() {
+  return  Smi::Value(ReadAsSmi());
+}
+
+
 SnapshotReader::SnapshotReader(const Snapshot* snapshot, Isolate* isolate)
-    : stream_(snapshot->content(), snapshot->length()),
+    : BaseReader(snapshot->content(), snapshot->length()),
       kind_(snapshot->kind()),
       isolate_(isolate),
       cls_(Class::Handle()),
@@ -425,6 +437,176 @@ RawObject* SnapshotReader::ReadInlinedObject(intptr_t object_id) {
 }
 
 
+MessageReader::MessageReader(const uint8_t* buffer, intptr_t length)
+    : BaseReader(buffer, length) {
+}
+
+
+intptr_t MessageReader::LookupInternalClass(intptr_t class_header) {
+  SerializedHeaderType header_type = SerializedHeaderTag::decode(class_header);
+  ASSERT(header_type == kObjectId);
+  intptr_t header_value = SerializedHeaderData::decode(class_header);
+  return header_value;
+}
+
+
+Dart_Value* MessageReader::AllocateDartValue(Dart_Value::Type type) {
+  Dart_Value* value = reinterpret_cast<Dart_Value*>(malloc(sizeof(Dart_Value)));

[siva, 2012/01/27 01:56:52]

Instead of using regular malloc should we accept an allocator parameter in the
CMessageReader class constructor and use it. That would give some flexibility to
the caller.

[Søren Gjesse, 2012/01/27 14:40:03]

Done.

+  memset(value, 0, sizeof(*value));

[siva, 2012/01/27 01:56:52]

Is this init needed as we are about to deserialize the message into this
structure and it would have all the proper values?

[Søren Gjesse, 2012/01/27 14:40:03]

Not really - removed.

+  value->type = type;
+  return value;
+}
+
+
+Dart_Value* MessageReader::AllocateDartValueNull() {
+  return AllocateDartValue(Dart_Value::kNull);
+}
+
+
+Dart_Value* MessageReader::AllocateDartValueBool(bool val) {
+  Dart_Value* value = AllocateDartValue(Dart_Value::kBool);
+  value->data.bl = val;
+  return value;
+}
+
+
+Dart_Value* MessageReader::AllocateDartValueInt32(int32_t val) {
+  Dart_Value* value = AllocateDartValue(Dart_Value::kInt32);
+  value->data.int32 = val;
+  return value;
+}
+
+
+Dart_Value* MessageReader::AllocateDartValueDouble(double val) {
+  Dart_Value* value = AllocateDartValue(Dart_Value::kDouble);
+  value->data.dbl = val;
+  return value;
+}
+
+
+Dart_Value* MessageReader::AllocateDartValueString(intptr_t length) {
+  Dart_Value* value =
+      reinterpret_cast<Dart_Value*>(malloc(sizeof(Dart_Value) + length + 1));
+  memset(value, 0, sizeof(*value));
+  reinterpret_cast<char*>(value)[sizeof(*value)] = '\0';
+  value->data.str = reinterpret_cast<char*>(value) + sizeof(*value);
+  value->type = Dart_Value::kString;
+  return value;
+}
+
+
+Dart_Value* MessageReader::AllocateDartValueArray(intptr_t length) {
+  // Allocate a Dart_Value structure followed by an array of pointers
+  // to Dart_Value structures.
+  Dart_Value* value =
+      reinterpret_cast<Dart_Value*>(
+          malloc(sizeof(Dart_Value) + length * sizeof(value)));
+  memset(value, 0, sizeof(*value));
+  value->type = Dart_Value::kArray;
+  value->data.array.len = length;
+  value->data.array.values = reinterpret_cast<Dart_Value**>(value + 1);

[siva, 2012/01/27 01:56:52]

If the passed in 'length' is 0 which happens if we send an empty array over then
values will point to some random location instead of NULL

[Søren Gjesse, 2012/01/27 14:40:03]

Set values to NULL for empty arrays. Added test with an empty array.

+  return value;
+}
+
+
+Dart_Value* MessageReader::ReadInlinedObject(intptr_t object_id) {
+  // Read the class header information and lookup the class.
+  intptr_t class_header = ReadIntptrValue();
+  intptr_t tags = ReadIntptrValue();
+  USE(tags);
+  intptr_t class_id;
+
+  // Reading of regular dart instances is not supported.
+  if (SerializedHeaderData::decode(class_header) == kInstanceId) {
+    return NULL;
+  }
+
+  ASSERT((class_header & kSmiTagMask) != 0);
+  class_id = LookupInternalClass(class_header);
+  switch (class_id) {
+    case ObjectStore::kArrayClass: {
+      intptr_t len = ReadSmiValue();
+      // Skip type arguments.
+      Dart_Value* type_arguments = ReadObject();
+      if (type_arguments == NULL || type_arguments->type != Dart_Value::kNull) {
+        return NULL;

[siva, 2012/01/27 01:56:52]

This condition may not be true when you are receiving a message created from the
dart side.

The current C message writer (MessageWrite class) passes in a Null but the dart
message writer passing in an actual type object.

[Søren Gjesse, 2012/01/27 14:40:03]

I have added a test for processing objects from Dart. There is still a TODO for
decoding lists.

+      }
+      Dart_Value* value = AllocateDartValueArray(len);
+      for (int i = 0; i < len; i++) {
+        value->data.array.values[i] = ReadObject();
+      }
+      return value;
+      break;
+    }
+    case ObjectStore::kDoubleClass: {
+      // Read the double value for the object.
+      return AllocateDartValueDouble(Read<double>());
+      break;
+    }
+    case ObjectStore::kOneByteStringClass: {
+      intptr_t len = ReadSmiValue();
+      intptr_t hash = ReadSmiValue();
+      USE(hash);
+      Dart_Value* value = AllocateDartValueString(len);
+      char* p = value->data.str;
+      for (intptr_t i = 0; i < len; i++) {
+        *p = Read<uint8_t>();
+        p++;
+      }
+      *p = '\0';
+      return value;
+      break;
+    }
+    case ObjectStore::kTwoByteStringClass:
+      // Two byte strings not supported.
+      return NULL;
+      break;
+    case ObjectStore::kFourByteStringClass:
+      // Four byte strings not supported.
+      return NULL;
+      break;
+    default:
+      // Everything else not supported.
+      return NULL;
+  }
+}
+
+
+Dart_Value* MessageReader::ReadIndexedObject(intptr_t object_id) {
+  if (object_id == Object::kNullObject) {
+    return AllocateDartValueNull();
+  } else if (object_id == ObjectStore::kTrueValue) {
+    return AllocateDartValueBool(true);
+  } else if (object_id == ObjectStore::kFalseValue) {
+    return AllocateDartValueBool(false);
+  }

[siva, 2012/01/27 01:56:52]

should we have:
else {
  UNREACHABLE();
}

because I don't know if at some point we will have to deal with canonical
objects, i.e if a string is repeated multiple times in a message we might want
to refer to the same string  Dart_value object instead of creating a new one
every time.

[Søren Gjesse, 2012/01/27 14:40:03]

We should definately be able to handle back-references. Put in a TODO and
UNREACHABLE().

+  return NULL;
+}
+
+
+Dart_Value* MessageReader::ReadObjectImpl(intptr_t header) {
+  SerializedHeaderType header_type = SerializedHeaderTag::decode(header);
+  intptr_t header_value = SerializedHeaderData::decode(header);
+
+  if (header_type == kObjectId) {
+    return ReadIndexedObject(header_value);
+  }
+  ASSERT(header_type == kInlined);
+  return ReadInlinedObject(header_value);
+}
+
+
+Dart_Value* MessageReader::ReadObject() {
+  int64_t value = Read<int64_t>();
+  if ((value & kSmiTagMask) == 0) {
+    Dart_Value* dart_value = AllocateDartValueInt32(value >> kSmiTagShift);
+    return dart_value;
+  }
+  ASSERT((value <= kIntptrMax) && (value >= kIntptrMin));
+  return ReadObjectImpl(value);
+}
+
+
 void MessageWriter::WriteMessage(intptr_t field_count, intptr_t *data) {
   // Write out the serialization header value for this object.
   WriteSerializationMarker(kInlined, kMaxPredefinedObjectIds);