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src: fix performance regression in node_file.cc #31343

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src: fix performance regression in node_file.cc #31343

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44 changes: 35 additions & 9 deletions src/node_file.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -829,20 +829,46 @@ static void InternalModuleReadJSON(const FunctionCallbackInfo<Value>& args) {
}

const size_t size = offset - start;
if (size == 0 || (
size == SearchString(&chars[start], size, "\"name\"") &&
size == SearchString(&chars[start], size, "\"main\"") &&
size == SearchString(&chars[start], size, "\"exports\"") &&
size == SearchString(&chars[start], size, "\"type\""))) {
args.GetReturnValue().Set(env->empty_object_string());
} else {
Local<String> chars_string =
char* p = &chars[start];
char* pe = &chars[size];
char* pos[2];
char** ppos = &pos[0];

while (p < pe) {
char c = *p++;
if (c == '"') goto quote; // Keeps code flat and inner loop small.
if (c == '\\' && p < pe && *p == '"') p++;
continue;
quote:
*ppos++ = p;
if (ppos < &pos[2]) continue;
ppos = &pos[0];

char* s = &pos[0][0];
char* se = &pos[1][-1]; // Exclude quote.
size_t n = se - s;

if (n == 4) {
if (0 == memcmp(s, "main", 4)) break;
if (0 == memcmp(s, "name", 4)) break;
if (0 == memcmp(s, "type", 4)) break;
} else if (n == 7) {
if (0 == memcmp(s, "exports", 7)) break;
}
}

Local<String> return_value;
if (p < pe) {
return_value =
String::NewFromUtf8(isolate,
&chars[start],
v8::NewStringType::kNormal,
size).ToLocalChecked();
args.GetReturnValue().Set(chars_string);
} else {
return_value = env->empty_object_string();
}

args.GetReturnValue().Set(return_value);
}

// Used to speed up module loading. Returns 0 if the path refers to
Expand Down