denoland-deno/src/snapshot_creator.cc

// Copyright 2018 Ryan Dahl <ry@tinyclouds.org>
// All rights reserved. MIT License.
// Hint: --trace_serializer is a useful debugging flag.
#include "deno_internal.h"
#include "file_util.h"
#include "include/deno.h"
#include "v8/include/v8.h"
#include "v8/src/base/logging.h"

namespace deno {

v8::StartupData SerializeInternalFields(v8::Local<v8::Object> holder, int index,
                                        void* data) {
  DCHECK_EQ(data, nullptr);
  InternalFieldData* embedder_field = static_cast<InternalFieldData*>(
      holder->GetAlignedPointerFromInternalField(index));
  if (embedder_field == nullptr) return {nullptr, 0};
  int size = sizeof(*embedder_field);
  char* payload = new char[size];
  // We simply use memcpy to serialize the content.
  memcpy(payload, embedder_field, size);
  return {payload, size};
}

v8::StartupData MakeSnapshot(const char* js_filename, const char* js_source) {
  auto* creator = new v8::SnapshotCreator(external_references);
  auto* isolate = creator->GetIsolate();
  v8::Isolate::Scope isolate_scope(isolate);
  {
    v8::HandleScope handle_scope(isolate);
    auto context = v8::Context::New(isolate);
    InitializeContext(isolate, context, js_filename, js_source);
    creator->SetDefaultContext(context, v8::SerializeInternalFieldsCallback(
                                            SerializeInternalFields, nullptr));
  }

  // Note that using kKeep here will cause segfaults. This is demoed in the
  // "SnapshotBug" test case.
  auto snapshot_blob =
      creator->CreateBlob(v8::SnapshotCreator::FunctionCodeHandling::kClear);

  return snapshot_blob;
}

// Wrap the js_source in an IIFE to work around a bug in the V8 snapshot
// serializer. Without it, CreateBlob() triggers the following assert:
//   Debug check failed : outer_scope_info()->IsScopeInfo() || is_toplevel().
//   ==== C stack trace ====
//   v8::internal::SharedFunctionInfo::FlushCompiled
//   v8::SnapshotCreator::CreateBlob
//   deno::MakeSnapshot
// Avoid misaligning the source map, and ensure that the sourceMappingUrl
// comment remains at the last line.
// Try removing this when this bug is fixed:
// https://bugs.chromium.org/p/v8/issues/detail?id=7857
std::string WrapSourceCode(const std::string& js_source) {
  auto smu_offset = js_source.rfind("//# sourceMappingURL=");
  std::string tail =
      smu_offset == std::string::npos ? "" : js_source.substr(smu_offset);
  auto wrapped_js_source =
      "(function() {" + js_source.substr(0, smu_offset) + "\n})();\n" + tail;
  // Double check that the source mapping url comment is at the last line.
  auto last_line = wrapped_js_source.substr(wrapped_js_source.rfind('\n'));
  CHECK(smu_offset == std::string::npos ||
        last_line.find("sourceMappingURL") != std::string::npos);
  return wrapped_js_source;
}

}  // namespace deno

int main(int argc, char** argv) {
  const char* js_fn = argv[1];
  const char* snapshot_out_cc = argv[2];

  v8::V8::SetFlagsFromCommandLine(&argc, argv, true);

  CHECK_EQ(argc, 3);
  CHECK_NE(js_fn, nullptr);
  CHECK_NE(snapshot_out_cc, nullptr);

  std::string js_source;
  CHECK(deno::ReadFileToString(js_fn, &js_source));

  auto wrapped_js_source = deno::WrapSourceCode(js_source);

  deno_init();
  auto snapshot_blob = deno::MakeSnapshot(js_fn, wrapped_js_source.c_str());
  std::string snapshot_str(snapshot_blob.data, snapshot_blob.raw_size);

  CHECK(deno::WriteDataAsCpp("snapshot", snapshot_out_cc, snapshot_str));
}