vm: include vm context in the embeded snapshot

Include a minimally initialized contextify context in the embeded
snapshot. This paves the way for user-land vm context snapshots.

src/env.h

@@ -1002,7 +1002,8 @@ struct SnapshotData {
   enum class DataOwnership { kOwned, kNotOwned };
 
   static const uint32_t kMagic = 0x143da19;
-  static const SnapshotIndex kNodeBaseContextIndex = 0;
+  static const SnapshotIndex kNodeVMContextIndex = 0;
+  static const SnapshotIndex kNodeBaseContextIndex = kNodeVMContextIndex + 1;
   static const SnapshotIndex kNodeMainContextIndex = kNodeBaseContextIndex + 1;
 
   DataOwnership data_ownership = DataOwnership::kOwned;

src/node_contextify.cc

@@ -28,6 +28,7 @@
 #include "node_errors.h"
 #include "node_external_reference.h"
 #include "node_internals.h"
+#include "node_snapshot_builder.h"
 #include "node_watchdog.h"
 #include "util-inl.h"
 
@@ -118,14 +119,17 @@ ContextifyContext::ContextifyContext(
     object_template = CreateGlobalTemplate(env->isolate());
     env->set_contextify_global_template(object_template);
   }
+  bool use_node_snapshot = per_process::cli_options->node_snapshot;
+  const SnapshotData* snapshot_data =
+      use_node_snapshot ? SnapshotBuilder::GetEmbeddedSnapshotData() : nullptr;
 
   MicrotaskQueue* queue =
       microtask_queue()
           ? microtask_queue().get()
           : env->isolate()->GetCurrentContext()->GetMicrotaskQueue();
 
   Local<Context> v8_context;
-  if (!(CreateV8Context(env->isolate(), object_template, queue)
+  if (!(CreateV8Context(env->isolate(), object_template, snapshot_data, queue)
             .ToLocal(&v8_context)) ||
       !InitializeContext(v8_context, env, sandbox_obj, options)) {
     // Allocation failure, maximum call stack size reached, termination, etc.
@@ -190,17 +194,28 @@ Local<ObjectTemplate> ContextifyContext::CreateGlobalTemplate(
 MaybeLocal<Context> ContextifyContext::CreateV8Context(
     Isolate* isolate,
     Local<ObjectTemplate> object_template,
+    const SnapshotData* snapshot_data,
     MicrotaskQueue* queue) {
   EscapableHandleScope scope(isolate);
 
-  Local<Context> ctx = Context::New(isolate,
-                                    nullptr,  // extensions
-                                    object_template,
-                                    {},  // global object
-                                    {},  // deserialization callback
-                                    queue);
-  if (ctx.IsEmpty()) return MaybeLocal<Context>();
-
+  Local<Context> ctx;
+  if (snapshot_data == nullptr) {
+    ctx = Context::New(isolate,
+                       nullptr,  // extensions
+                       object_template,
+                       {},  // global object
+                       {},  // deserialization callback
+                       queue);
+    if (ctx.IsEmpty()) return MaybeLocal<Context>();
+  } else if (!Context::FromSnapshot(isolate,
+                             SnapshotData::kNodeVMContextIndex,
+                             {},       // deserialization callback
+                             nullptr,  // extensions
+                             {},       // global object
+                             queue)
+           .ToLocal(&ctx)) {
+    return MaybeLocal<Context>();
+  }
   return scope.Escape(ctx);
 }
 

src/node_contextify.h

@@ -53,6 +53,7 @@ class ContextifyContext {
   static v8::MaybeLocal<v8::Context> CreateV8Context(
       v8::Isolate* isolate,
       v8::Local<v8::ObjectTemplate> object_template,
+      const SnapshotData* snapshot_data,
       v8::MicrotaskQueue* queue);
   bool InitializeContext(v8::Local<v8::Context> ctx,
                          Environment* env,

src/node_snapshotable.cc

@@ -7,6 +7,7 @@
 #include "env-inl.h"
 #include "node_blob.h"
 #include "node_builtins.h"
+#include "node_contextify.h"
 #include "node_errors.h"
 #include "node_external_reference.h"
 #include "node_file.h"
@@ -31,6 +32,7 @@ using v8::HandleScope;
 using v8::Isolate;
 using v8::Local;
 using v8::Object;
+using v8::ObjectTemplate;
 using v8::ScriptCompiler;
 using v8::ScriptOrigin;
 using v8::SnapshotCreator;
@@ -1030,6 +1032,19 @@ int SnapshotBuilder::Generate(SnapshotData* out,
     // The default context with only things created by V8.
     Local<Context> default_context = Context::New(isolate);
 
+    // The context used by the vm module.
+    Local<Context> vm_context;
+    {
+      Local<ObjectTemplate> global_template =
+          main_instance->isolate_data()->contextify_global_template();
+      CHECK(!global_template.IsEmpty());
+      if (!contextify::ContextifyContext::CreateV8Context(
+               isolate, global_template, nullptr, nullptr)
+               .ToLocal(&vm_context)) {
+        return SNAPSHOT_ERROR;
+      }
+    }
+
     // The Node.js-specific context with primodials, can be used by workers
     // TODO(joyeecheung): investigate if this can be used by vm contexts
     // without breaking compatibility.
@@ -1111,7 +1126,9 @@ int SnapshotBuilder::Generate(SnapshotData* out,
     // blob is created. So initialize all the contexts before adding them.
     // TODO(joyeecheung): figure out how to remove this restriction.
     creator.SetDefaultContext(default_context);
-    size_t index = creator.AddContext(base_context);
+    size_t index = creator.AddContext(vm_context);
+    CHECK_EQ(index, SnapshotData::kNodeVMContextIndex);
+    index = creator.AddContext(base_context);
     CHECK_EQ(index, SnapshotData::kNodeBaseContextIndex);
     index = creator.AddContext(main_context,
                                {SerializeNodeContextInternalFields, env});