tools: refactor snapshot builder

This patch:

- Moves the snapshot building code to src/ so that we can reuse it
  later when generating custom snapshots from an entry point accepted
  by the node binary.
- Create a SnapshotData struct that incorporates all the data useful
  for a snapshot blob, including both the V8 data and the Node.js
  data.

PR-URL: https://github.com/nodejs/node/pull/38902
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>

1 files changed, 165 insertions, 0 deletions

diff --git a/src/node_snapshotable.cc b/src/node_snapshotable.cc
index 216a0a9a725..1871cef443f 100644
--- a/src/node_snapshotable.cc
+++ b/src/node_snapshotable.cc
@@ -1,16 +1,181 @@
 
 #include "node_snapshotable.h"
+#include <iostream>
+#include <sstream>
 #include "base_object-inl.h"
 #include "debug_utils-inl.h"
+#include "env-inl.h"
+#include "node_errors.h"
+#include "node_external_reference.h"
 #include "node_file.h"
+#include "node_internals.h"
+#include "node_main_instance.h"
 #include "node_v8.h"
+#include "node_v8_platform-inl.h"
 
 namespace node {
 
+using v8::Context;
+using v8::HandleScope;
+using v8::Isolate;
 using v8::Local;
 using v8::Object;
 using v8::SnapshotCreator;
 using v8::StartupData;
+using v8::TryCatch;
+using v8::Value;
+
+template <typename T>
+void WriteVector(std::ostringstream* ss, const T* vec, size_t size) {
+  for (size_t i = 0; i < size; i++) {
+    *ss << std::to_string(vec[i]) << (i == size - 1 ? '\n' : ',');
+  }
+}
+
+std::string FormatBlob(SnapshotData* data) {
+  std::ostringstream ss;
+
+  ss << R"(#include <cstddef>
+#include "env.h"
+#include "node_main_instance.h"
+#include "v8.h"
+
+// This file is generated by tools/snapshot. Do not edit.
+
+namespace node {
+
+static const char blob_data[] = {
+)";
+  WriteVector(&ss, data->blob.data, data->blob.raw_size);
+  ss << R"(};
+
+static const int blob_size = )"
+     << data->blob.raw_size << R"(;
+static v8::StartupData blob = { blob_data, blob_size };
+)";
+
+  ss << R"(v8::StartupData* NodeMainInstance::GetEmbeddedSnapshotBlob() {
+  return &blob;
+}
+
+static const std::vector<size_t> isolate_data_indices {
+)";
+  WriteVector(&ss,
+              data->isolate_data_indices.data(),
+              data->isolate_data_indices.size());
+  ss << R"(};
+
+const std::vector<size_t>* NodeMainInstance::GetIsolateDataIndices() {
+  return &isolate_data_indices;
+}
+
+static const EnvSerializeInfo env_info )"
+     << data->env_info << R"(;
+
+const EnvSerializeInfo* NodeMainInstance::GetEnvSerializeInfo() {
+  return &env_info;
+}
+
+}  // namespace node
+)";
+
+  return ss.str();
+}
+
+void SnapshotBuilder::Generate(SnapshotData* out,
+                               const std::vector<std::string> args,
+                               const std::vector<std::string> exec_args) {
+  Isolate* isolate = Isolate::Allocate();
+  isolate->SetCaptureStackTraceForUncaughtExceptions(
+      true, 10, v8::StackTrace::StackTraceOptions::kDetailed);
+  per_process::v8_platform.Platform()->RegisterIsolate(isolate,
+                                                       uv_default_loop());
+  std::unique_ptr<NodeMainInstance> main_instance;
+  std::string result;
+
+  {
+    const std::vector<intptr_t>& external_references =
+        NodeMainInstance::CollectExternalReferences();
+    SnapshotCreator creator(isolate, external_references.data());
+    Environment* env;
+    {
+      main_instance =
+          NodeMainInstance::Create(isolate,
+                                   uv_default_loop(),
+                                   per_process::v8_platform.Platform(),
+                                   args,
+                                   exec_args);
+
+      HandleScope scope(isolate);
+      creator.SetDefaultContext(Context::New(isolate));
+      out->isolate_data_indices =
+          main_instance->isolate_data()->Serialize(&creator);
+
+      // Run the per-context scripts
+      Local<Context> context;
+      {
+        TryCatch bootstrapCatch(isolate);
+        context = NewContext(isolate);
+        if (bootstrapCatch.HasCaught()) {
+          PrintCaughtException(isolate, context, bootstrapCatch);
+          abort();
+        }
+      }
+      Context::Scope context_scope(context);
+
+      // Create the environment
+      env = new Environment(main_instance->isolate_data(),
+                            context,
+                            args,
+                            exec_args,
+                            nullptr,
+                            node::EnvironmentFlags::kDefaultFlags,
+                            {});
+      // Run scripts in lib/internal/bootstrap/
+      {
+        TryCatch bootstrapCatch(isolate);
+        v8::MaybeLocal<Value> result = env->RunBootstrapping();
+        if (bootstrapCatch.HasCaught()) {
+          PrintCaughtException(isolate, context, bootstrapCatch);
+        }
+        result.ToLocalChecked();
+      }
+
+      if (per_process::enabled_debug_list.enabled(DebugCategory::MKSNAPSHOT)) {
+        env->PrintAllBaseObjects();
+        printf("Environment = %p\n", env);
+      }
+
+      // Serialize the native states
+      out->env_info = env->Serialize(&creator);
+      // Serialize the context
+      size_t index = creator.AddContext(
+          context, {SerializeNodeContextInternalFields, env});
+      CHECK_EQ(index, NodeMainInstance::kNodeContextIndex);
+    }
+
+    // Must be out of HandleScope
+    out->blob =
+        creator.CreateBlob(SnapshotCreator::FunctionCodeHandling::kClear);
+    CHECK(out->blob.CanBeRehashed());
+    // Must be done while the snapshot creator isolate is entered i.e. the
+    // creator is still alive.
+    FreeEnvironment(env);
+    main_instance->Dispose();
+  }
+
+  per_process::v8_platform.Platform()->UnregisterIsolate(isolate);
+}
+
+std::string SnapshotBuilder::Generate(
+    const std::vector<std::string> args,
+    const std::vector<std::string> exec_args) {
+  SnapshotData data;
+  Generate(&data, args, exec_args);
+  std::string result = FormatBlob(&data);
+  delete[] data.blob.data;
+  return result;
+}
 
 SnapshotableObject::SnapshotableObject(Environment* env,
                                        Local<Object> wrap,