Change snapshot versioning code to use plain strings instead of Dart strings

runtime/vm/snapshot.cc

 // 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.
 
 #include "vm/snapshot.h"
 
 #include "platform/assert.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
@@ skipping 394 matching lines @@
 };
 
 
 RawApiError* SnapshotReader::ReadFullSnapshot() {
   ASSERT(kind_ == Snapshot::kFull);
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate != NULL);
   ObjectStore* object_store = isolate->object_store();
   ASSERT(object_store != NULL);
 
+  // First read the version string, and check that it matches.
+  RawApiError* error = VerifyVersion();
+  if (error != ApiError::null()) {
+    return error;
+  }
+
+  // The version string matches. Read the rest of the snapshot.
+
   // TODO(asiva): Add a check here to ensure we have the right heap
   // size for the full snapshot being read.
-
   {
     NoGCScope no_gc;
     HeapLocker hl(isolate, old_space());
 
-    // First read the version string, and check that it matches.
-    obj_ = ReadObject();
-
-    // If the version string doesn't match, return an error.
-    // NB: New things are allocated only if we're going to return an error.
-    if (!obj_.IsString() ||
-        !String::Cast(obj_).Equals(Version::SnapshotString())) {
-      const intptr_t kMessageBufferSize = 128;
-      char message_buffer[kMessageBufferSize];
-      OS::SNPrint(message_buffer,
-                  kMessageBufferSize,
-                  "Wrong full snapshot version. Found %s expected %s",
-                  obj_.ToCString(),
-                  Version::SnapshotString());
-      const String& msg = String::Handle(String::New(message_buffer));
-      return ApiError::New(msg);
-    }
-
-    // The version string matches. Read the rest of the snapshot.
-
     // Read in all the objects stored in the object store.
     intptr_t num_flds = (object_store->to() - object_store->from());
     for (intptr_t i = 0; i <= num_flds; i++) {
       *(object_store->from() + i) = ReadObjectImpl();
     }
     for (intptr_t i = 0; i < backward_references_.length(); i++) {
       if (!backward_references_[i].is_deserialized()) {
         ReadObjectImpl();
         backward_references_[i].set_state(kIsDeserialized);
       }
     }
 
     // Validate the class table.
 #if defined(DEBUG)
     isolate->ValidateClassTable();
 #endif
 
     // Setup native resolver for bootstrap impl.
     Bootstrap::SetupNativeResolver();
     return ApiError::null();
   }
 }
 
 
 RawObject* SnapshotReader::ReadScriptSnapshot() {
   ASSERT(kind_ == Snapshot::kScript);
 
   // First read the version string, and check that it matches.
-  obj_ = ReadObject();
-
-  // If the version string doesn't match, return an error.
-  // NB: New things are allocated only if we're going to return an error.
-  if (!obj_.IsString() ||
-      !String::Cast(obj_).Equals(Version::SnapshotString())) {
-    const intptr_t kMessageBufferSize = 256;
-    char message_buffer[kMessageBufferSize];
-    OS::SNPrint(message_buffer,
-                kMessageBufferSize,
-                "Wrong script snapshot version. Found %s expected '%s'",
-                obj_.ToCString(),
-                Version::SnapshotString());
-    const String& msg = String::Handle(String::New(message_buffer));
-    return ApiError::New(msg);
+  RawApiError* error = VerifyVersion();
+  if (error != ApiError::null()) {
+    return error;
   }
 
   // The version string matches. Read the rest of the snapshot.
   obj_ = ReadObject();
   if (!obj_.IsLibrary()) {
     if (!obj_.IsError()) {
       const intptr_t kMessageBufferSize = 128;
       char message_buffer[kMessageBufferSize];
       OS::SNPrint(message_buffer,
                   kMessageBufferSize,
                   "Invalid object %s found in script snapshot",
                   obj_.ToCString());
       const String& msg = String::Handle(String::New(message_buffer));
       obj_ = ApiError::New(msg);
     }
   }
   return obj_.raw();
 }
 
 
+RawApiError* SnapshotReader::VerifyVersion() {
+  // If the version string doesn't match, return an error.
+  // Note: New things are allocated only if we're going to return an error.
+
+  const char* expected_version = Version::SnapshotString();
+  ASSERT(expected_version != NULL);
+  const intptr_t version_len = strlen(expected_version);
+  if (PendingBytes() < version_len) {
+    const intptr_t kMessageBufferSize = 128;
+    char message_buffer[kMessageBufferSize];
+    OS::SNPrint(message_buffer,
+                kMessageBufferSize,
+                "No full snapshot version found, expected '%s'",
+                Version::SnapshotString());
+    const String& msg = String::Handle(String::New(message_buffer));
+    return ApiError::New(msg);
+  }
+
+  const char* version = reinterpret_cast<const char*>(CurrentBufferAddress());
+  ASSERT(version != NULL);
+  if (strncmp(version, expected_version, version_len)) {
+    const intptr_t kMessageBufferSize = 256;
+    char message_buffer[kMessageBufferSize];
+    char* actual_version = strndup(version, version_len);
+    OS::SNPrint(message_buffer,
+                kMessageBufferSize,
+                "Wrong full snapshot version, expected '%s' found '%s'",
+                Version::SnapshotString(),
+                actual_version);
+    free(actual_version);
+    const String& msg = String::Handle(String::New(message_buffer));
+    return ApiError::New(msg);
+  }
+  Advance(version_len);
+  return ApiError::null();
+}
+
+
 #define ALLOC_NEW_OBJECT_WITH_LEN(type, length)                                \
   ASSERT(kind_ == Snapshot::kFull);                                            \
   ASSERT(isolate()->no_gc_scope_depth() != 0);                                 \
   Raw##type* obj = reinterpret_cast<Raw##type*>(                               \
       AllocateUninitialized(k##type##Cid, type::InstanceSize(length)));        \
   obj->ptr()->length_ = Smi::New(length);                                      \
   return obj;                                                                  \
 
 
 RawArray* SnapshotReader::NewArray(intptr_t len) {
@@ skipping 729 matching lines @@
 #endif
 
   // Setup for long jump in case there is an exception while writing
   // the snapshot.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     // Reserve space in the output buffer for a snapshot header.
     ReserveHeader();
 
     // Write out the version string.
-    WriteObject(String::New(Version::SnapshotString()));
+    WriteVersion();
 
     // Write out the full snapshot.
     {
       NoGCScope no_gc;
 
       // Write out all the objects in the object store of the isolate which
       // is the root set for all dart allocated objects at this point.
       SnapshotWriterVisitor visitor(this, false);
       object_store->VisitObjectPointers(&visitor);
 
@@ skipping 401 matching lines @@
     const Array& args = Array::Handle(Array::New(1));
     args.SetAt(0, msg_obj);
     Exceptions::ThrowByType(type, args);
   } else {
     Exceptions::ThrowByType(type, Object::empty_array());
   }
   UNREACHABLE();
 }
 
 
+void SnapshotWriter::WriteVersion() {
+  const char* expected_version = Version::SnapshotString();
+  ASSERT(expected_version != NULL);
+  const intptr_t version_len = strlen(expected_version);
+  WriteBytes(reinterpret_cast<const uint8_t*>(expected_version), version_len);
+}
+
+
 void ScriptSnapshotWriter::WriteScriptSnapshot(const Library& lib) {
   ASSERT(kind() == Snapshot::kScript);
   Isolate* isolate = Isolate::Current();
   ASSERT(isolate != NULL);
   ASSERT(ClassFinalizer::AllClassesFinalized());
 
   // Setup for long jump in case there is an exception while writing
   // the snapshot.
   LongJumpScope jump;
   if (setjmp(*jump.Set()) == 0) {
     // Reserve space in the output buffer for a snapshot header.
     ReserveHeader();
 
     // Write out the version string.
-    WriteObject(String::New(Version::SnapshotString()));
+    WriteVersion();
 
     // Write out the library object.
     {
       NoGCScope no_gc;
 
       // Write out the library object.
       WriteObject(lib.raw());
 
       FillHeader(kind());
       UnmarkAll();
@@ skipping 28 matching lines @@
     NoGCScope no_gc;
     WriteObject(obj.raw());
     UnmarkAll();
   } else {
     ThrowException(exception_type(), exception_msg());
   }
 }
 
 
 }  // namespace dart