bootstrap: handle snapshot errors gracefully

This patch refactors the SnapshotBuilder::Generate() routines
so that when running into errors during the snapshot building
process, they can exit gracefully by printing the error
and return a non-zero exit code. If the error is likely to
be caused by internal scripts, the return code would be 12,
if the error is caused by user scripts the return code would
be 1. In addition this refactors the generation of embedded
snapshots and directly writes to the output file stream
instead of producing an intermediate string with string
streams.

PR-URL: #43531
Refs: #35711
Reviewed-By: Chengzhong Wu <legendecas@gmail.com>
Reviewed-By: Darshan Sen <raisinten@gmail.com>

doc/api/process.md

@@ -3822,6 +3822,9 @@ cases:
   options were set, but the port number chosen was invalid or unavailable.
 * `13` **Unfinished Top-Level Await**: `await` was used outside of a function
   in the top-level code, but the passed `Promise` never resolved.
+* `14` **Snapshot Failure**: Node.js was started to build a V8 startup
+  snapshot and it failed because certain requirements of the state of
+  the application were not met.
 * `>128` **Signal Exits**: If Node.js receives a fatal signal such as
   `SIGKILL` or `SIGHUP`, then its exit code will be `128` plus the
   value of the signal code. This is a standard POSIX practice, since

src/env.h

@@ -963,13 +963,17 @@ struct EnvSerializeInfo {
 };
 
 struct SnapshotData {
-  // The result of v8::SnapshotCreator::CreateBlob() during the snapshot
-  // building process.
-  v8::StartupData v8_snapshot_blob_data;
+  enum class DataOwnership { kOwned, kNotOwned };
 
   static const size_t kNodeBaseContextIndex = 0;
   static const size_t kNodeMainContextIndex = kNodeBaseContextIndex + 1;
 
+  DataOwnership data_ownership = DataOwnership::kOwned;
+
+  // The result of v8::SnapshotCreator::CreateBlob() during the snapshot
+  // building process.
+  v8::StartupData v8_snapshot_blob_data{nullptr, 0};
+
   std::vector<size_t> isolate_data_indices;
   // TODO(joyeecheung): there should be a vector of env_info once we snapshot
   // the worker environments.
@@ -979,6 +983,15 @@ struct SnapshotData {
   // read only space. We use native_module::CodeCacheInfo because
   // v8::ScriptCompiler::CachedData is not copyable.
   std::vector<native_module::CodeCacheInfo> code_cache;
+
+  ~SnapshotData();
+
+  SnapshotData(const SnapshotData&) = delete;
+  SnapshotData& operator=(const SnapshotData&) = delete;
+  SnapshotData(SnapshotData&&) = delete;
+  SnapshotData& operator=(SnapshotData&&) = delete;
+
+  SnapshotData() = default;
 };
 
 class Environment : public MemoryRetainer {

src/node_snapshot_builder.h

@@ -15,13 +15,14 @@ struct SnapshotData;
 
 class NODE_EXTERN_PRIVATE SnapshotBuilder {
  public:
-  static std::string Generate(const std::vector<std::string> args,
-                              const std::vector<std::string> exec_args);
+  static int Generate(std::ostream& out,
+                      const std::vector<std::string> args,
+                      const std::vector<std::string> exec_args);
 
   // Generate the snapshot into out.
-  static void Generate(SnapshotData* out,
-                       const std::vector<std::string> args,
-                       const std::vector<std::string> exec_args);
+  static int Generate(SnapshotData* out,
+                      const std::vector<std::string> args,
+                      const std::vector<std::string> exec_args);
 
   // If nullptr is returned, the binary is not built with embedded
   // snapshot.