src: expose uv.errmap to binding

Add a errno -> [error code, uv error message] map to the uv binding
so the error message can be assembled in the JS layer.

PR-URL: https://github.com/nodejs/node/pull/17338
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

src/uv.cc

@@ -27,10 +27,15 @@
 namespace node {
 namespace {
 
+using v8::Array;
 using v8::Context;
 using v8::FunctionCallbackInfo;
+using v8::Integer;
+using v8::Isolate;
 using v8::Local;
+using v8::Map;
 using v8::Object;
+using v8::String;
 using v8::Value;
 
 
@@ -47,14 +52,30 @@ void InitializeUV(Local<Object> target,
                   Local<Value> unused,
                   Local<Context> context) {
   Environment* env = Environment::GetCurrent(context);
-  target->Set(FIXED_ONE_BYTE_STRING(env->isolate(), "errname"),
+  Isolate* isolate = env->isolate();
+  target->Set(FIXED_ONE_BYTE_STRING(isolate, "errname"),
               env->NewFunctionTemplate(ErrName)->GetFunction());
 
 #define V(name, _) NODE_DEFINE_CONSTANT(target, UV_##name);
   UV_ERRNO_MAP(V)
 #undef V
-}
 
+  Local<Map> err_map = Map::New(isolate);
+
+#define V(name, msg) do {                                                     \
+  Local<Array> arr = Array::New(isolate, 2);                                  \
+  arr->Set(0, OneByteString(isolate, #name));                                 \
+  arr->Set(1, OneByteString(isolate, msg));                                   \
+  err_map->Set(context,                                                       \
+               Integer::New(isolate, UV_##name),                              \
+               arr).ToLocalChecked();                                         \
+} while (0);
+  UV_ERRNO_MAP(V)
+#undef V
+
+  target->Set(context, FIXED_ONE_BYTE_STRING(isolate, "errmap"),
+              err_map).FromJust();
+}
 
 }  // anonymous namespace
 }  // namespace node

test/parallel/test-uv-binding-constant.js

@@ -9,10 +9,10 @@ const uv = process.binding('uv');
 
 const keys = Object.keys(uv);
 keys.forEach((key) => {
-  if (key === 'errname')
+  if (key.startsWith('UV_')) {
-    return; // skip this
     const val = uv[key];
     assert.throws(() => uv[key] = 1,
                   /^TypeError: Cannot assign to read only property/);
     assert.strictEqual(uv[key], val);
+  }
 });

test/parallel/test-uv-errno.js

@@ -8,7 +8,7 @@ const uv = process.binding('uv');
 const keys = Object.keys(uv);
 
 keys.forEach((key) => {
-  if (key === 'errname')
+  if (!key.startsWith('UV_'))
     return;
 
   assert.doesNotThrow(() => {