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

runtime/include/dart_api.h

Index: runtime/include/dart_api.h
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index 1fc3f4e26902ed9ac4c475f8e3b0515973b04509..6e9be59cc82224bb5f0d85fce1856076d8921c63 100755
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
@@ -1360,4 +1360,28 @@ DART_EXPORT Dart_Handle Dart_SetNativeResolver(
 DART_EXPORT void Dart_InitPprofSupport();
 DART_EXPORT void Dart_GetPprofSymbolInfo(void** buffer, int* buffer_size);
 
+// --- Message encoding/decoding ----
+
+struct Dart_Value {

[turnidge, 2012/01/26 19:48:30]

I'm wondering about what to name this struct.  Dart_Value seems pretty general.

What do you think of something like Dart_CMessage?  We could add a comment at
the top like this:

/**
 * A Dart_CMessage is used for encoding and decoding messages from native code.
*/

[Søren Gjesse, 2012/01/27 14:40:03]

The reason for the name Dart_Value is that it is just a representation of a
value from Dart, but I agree it is a bit generic.

What I have done for is renamed Dart_Value to Dart_CObject as we might start to
represent things which are not just simple values added add a Dart_CMessage
struct for representing the message. The message has an array of Dart_CObjects
as a message can contain more than one object at the top level. The
Dart_CMessage can then also contain some more header information. Maybe we can
also have the Dart_CMessage have a pointer to the binary message and the data
field of a Dart_CValue (e.g. ByteArray) could point directly into the original
message so we don't need to copy all data.

Regarding a message with more that one object on the top level it might be that
this is only used for internal snapshots, and "normal" messages can only have
one top level object. In that case it might be that having separate
Dart_CMessage and Dart_CObject structures is to much.

+  enum Type {
+    kNull,
+    kBool,
+    kInt32,

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

We would need a kInt64 type too?

[Søren Gjesse, 2012/01/27 14:40:03]

I think we do. I have only added the types needed by what is currently
implemented. The only number type currently decoded are Smis.

+    kDouble,
+    kString,
+    kArray
+  };
+  Type type;
+  union {
+    bool bl;
+    int32_t int32;
+    double dbl;
+    char* str;

[turnidge, 2012/01/26 19:48:30]

I might prefer names like "bool_value", "int32_value" here.

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

The code is going to look as follows:
Data_Value myval;
myval.data.bl or myval.data.bool_value as Todd suggests.

maybe if we renamed data to value and bl to asBool we would have:
myval.value.asBool
myval.value.asInt32
myval.value.asDouble
etc.

What do you guys think?

[Søren Gjesse, 2012/01/27 14:40:03]

Changed to value.asXXX as suggested by Siva.

[Søren Gjesse, 2012/01/27 14:40:03]

I like the value.asXXX - used value.as_xxx to stick with the code style.

+    struct {
+      int len;
+      Dart_Value** values;
+    } array;
+  } data;
+};
+
 #endif  // INCLUDE_DART_API_H_