Add patch file support to Dart embedder

mojo/dart/embedder/builtin.cc

Index: mojo/dart/embedder/builtin.cc
diff --git a/mojo/dart/embedder/builtin.cc b/mojo/dart/embedder/builtin.cc
index dcbb33514b6f42f8867e747a8f93de9afd25cd3f..63e158fa9224764a88275fcd7a61adde023d89f2 100644
--- a/mojo/dart/embedder/builtin.cc
+++ b/mojo/dart/embedder/builtin.cc
@@ -4,6 +4,8 @@
 
 #include <stdio.h>
 
+#include "base/files/file_enumerator.h"
+#include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/i18n/icu_util.h"
 #include "dart/runtime/include/dart_api.h"
@@ -13,11 +15,21 @@
 namespace mojo {
 namespace dart {
 
+extern const uint8_t* snapshot_buffer;
+
+static bool EmbedderRunningFromSnapshot() {
+  return snapshot_buffer != nullptr;
+}
+
 Builtin::builtin_lib_props Builtin::builtin_libraries_[] = {
-    /* { url_, has_natives_, native_symbol_, native_resolver_ } */
-    {"dart:mojo_builtin", true, Builtin::NativeSymbol, Builtin::NativeLookup},
-    {"dart:mojo_bindings", false, nullptr, nullptr},
-    {"dart:mojo_core", true, MojoNativeSymbol, MojoNativeLookup},
+    /* { url_, has_natives_, native_symbol_, native_resolver_,
+         patch_url_, patch_paths_ } */
+    {"dart:mojo_builtin", true, Builtin::NativeSymbol, Builtin::NativeLookup,
+      nullptr, nullptr },
+    {"dart:mojo_bindings", false, nullptr, nullptr,
+      nullptr, nullptr },
+    {"dart:mojo_core", true, MojoNativeSymbol, MojoNativeLookup,
+     "dart:mojo_core-patch", mojo_core_patch_paths_ },
 };
 
 uint8_t Builtin::snapshot_magic_number[] = {0xf5, 0xf5, 0xdc, 0xdc};
@@ -25,7 +37,7 @@ uint8_t Builtin::snapshot_magic_number[] = {0xf5, 0xf5, 0xdc, 0xdc};
 Dart_Handle Builtin::NewError(const char* format, ...) {
   va_list args;
   va_start(args, format);
-  intptr_t len = vsnprintf(NULL, 0, format, args);
+  intptr_t len = vsnprintf(nullptr, 0, format, args);
   va_end(args);
 
   char* buffer = reinterpret_cast<char*>(Dart_ScopeAllocate(len + 1));
@@ -54,6 +66,37 @@ void Builtin::SetNativeResolver(BuiltinLibraryId id) {
   }
 }
 
+Dart_Handle Builtin::ReadStringFromFile(const char* file) {
+  base::FilePath path(base::FilePath::FromUTF8Unsafe(std::string(file)));
+  std::string source;
+  if (ReadFileToString(path, &source)) {
+    const uint8_t* text_buffer =
+        reinterpret_cast<const uint8_t*>(source.c_str());
+    const intptr_t len = source.length();
+    return Dart_NewStringFromUTF8(text_buffer, len);
+  }
+  return NewError("Could not load %s", file);
+}
+
+// Patch all the specified patch files in the array 'patch_files' into the
+// library specified in 'library'.
+void Builtin::LoadPatchFiles(Dart_Handle library,
+                           const char* patch_uri,
+                           const char** patch_files) {
+  for (intptr_t j = 0; patch_files[j] != NULL; j += 2) {
+    Dart_Handle patch_src = ReadStringFromFile(patch_files[j + 1]);
+    DART_CHECK_VALID(patch_src);
+    // Prepend the patch library URI to form a unique script URI for the patch.
+    intptr_t len = snprintf(NULL, 0, "%s/%s", patch_uri, patch_files[j]);
+    char* patch_filename = reinterpret_cast<char*>(malloc(len + 1));
+    snprintf(patch_filename, len + 1, "%s/%s", patch_uri, patch_files[j]);
+    Dart_Handle patch_file_uri = Dart_NewStringFromCString(patch_filename);
+    DART_CHECK_VALID(patch_file_uri);
+    free(patch_filename);
+    DART_CHECK_VALID(Dart_LibraryLoadPatch(library, patch_file_uri, patch_src));
+  }
+}
+
 Dart_Handle Builtin::LoadAndCheckLibrary(BuiltinLibraryId id) {
   static_assert((sizeof(builtin_libraries_) / sizeof(builtin_lib_props)) ==
                 kInvalidLibrary, "Unexpected number of builtin libraries");
@@ -62,6 +105,17 @@ Dart_Handle Builtin::LoadAndCheckLibrary(BuiltinLibraryId id) {
   Dart_Handle url = Dart_NewStringFromCString(builtin_libraries_[id].url_);
   Dart_Handle library = Dart_LookupLibrary(url);
   DART_CHECK_VALID(library);
+  SetNativeResolver(id);
+  if (EmbedderRunningFromSnapshot()) {
+    // Patch files are included in the snapshot.
+    return library;
+  }
+  if (builtin_libraries_[id].patch_url_ != nullptr) {
+    DCHECK(builtin_libraries_[id].patch_paths_ != nullptr);
+    LoadPatchFiles(library,
+                   builtin_libraries_[id].patch_url_,
+                   builtin_libraries_[id].patch_paths_);
+  }
   return library;
 }