Feature: report Go code error

build.mk

@@ -1,4 +1,6 @@
 TOOLS ?= ./tools
+PUBLIC_DIR ?= $(UI)/public
+WEBWORKER_PKG ?= ./cmd/webworker
 
 .PHONY: clean
 clean:
@@ -25,8 +27,14 @@ build-ui:
 	@echo "- Building UI..."
 	cd $(UI) && yarn build
 
+.PHONY:build-webworker
+build-webworker:
+	@echo "Building Go Webworker module..." && \
+	GOOS=js GOARCH=wasm go build -o $(PUBLIC_DIR)/worker.wasm $(WEBWORKER_PKG) && \
+	cp "$$(go env GOROOT)/misc/wasm/wasm_exec.js" $(PUBLIC_DIR)
+
 .PHONY: build
-build: clean preinstall collect-meta build-server build-ui
+build: clean preinstall collect-meta build-server build-webworker build-ui
 	@echo "- Copying assets..."
 	cp -rf ./data $(TARGET)/data
 	mv $(UI)/build $(TARGET)/public

build/Dockerfile

@@ -1,8 +1,8 @@
 FROM node:13-alpine as ui-build
 COPY web /tmp/web
 WORKDIR /tmp/web
-ARG APP_VERSION="1.0.0"
-ARG GITHUB_URL="https://github.com/x1unix/go-playground"
+ARG APP_VERSION=1.0.0
+ARG GITHUB_URL=https://github.com/x1unix/go-playground
 RUN yarn install --silent && REACT_APP_VERSION=$APP_VERSION REACT_APP_GITHUB_URL=$GITHUB_URL yarn build
 
 FROM golang:1.13-alpine as build
@@ -11,7 +11,9 @@ COPY cmd ./cmd
 COPY pkg ./pkg
 COPY go.mod .
 COPY go.sum .
-RUN go build -o server ./cmd/playground
+RUN go build -o server ./cmd/playground && \
+    GOOS=js GOARCH=wasm go build -o ./worker.wasm ./cmd/webworker && \
+    cp $(go env GOROOT)/misc/wasm/wasm_exec.js .
 
 FROM golang:1.13-alpine as production
 WORKDIR /opt/playground
@@ -21,5 +23,7 @@ ENV APP_DEBUG=false
 COPY data ./data
 COPY --from=ui-build /tmp/web/build ./public
 COPY --from=build /tmp/playground/server .
+COPY --from=build /tmp/playground/worker.wasm ./public
+COPY --from=build /tmp/playground/wasm_exec.js ./public
 EXPOSE 8000
 ENTRYPOINT /opt/playground/server -f=/opt/playground/data/packages.json -addr=:8000 -clean-interval=${APP_CLEAN_INTERVAL} -debug=${APP_DEBUG}

cmd/webworker/README.md

@@ -0,0 +1,6 @@
+# WebWorker
+
+`webworker` binary exports collection of tools used by UI web worker to analyze Go code and report
+code errors.
+
+Package should be compiled as **WebAssembly** binary and loaded by JS WebWorker. 

cmd/webworker/webworker.go

@@ -0,0 +1,73 @@
+package main
+
+import (
+	"fmt"
+	"os"
+	"syscall/js"
+
+	"github.com/x1unix/go-playground/pkg/analyzer/check"
+
+	"github.com/x1unix/go-playground/pkg/worker"
+)
+
+type void = struct{}
+
+var (
+	done     = make(chan void, 0)
+	onResult js.Value
+)
+
+func main() {
+	entrypoint, err := getEntrypointFunction()
+	if err != nil {
+		panic(err)
+	}
+
+	// prepare exports object
+	analyzeCodeCb := worker.FuncOf(analyzeCode)
+	exitCb := js.FuncOf(exit)
+	module := map[string]interface{}{
+		"analyzeCode": analyzeCodeCb,
+		"exit":        exitCb,
+	}
+
+	defer analyzeCodeCb.Release()
+	defer exitCb.Release()
+
+	entrypoint.Invoke(js.ValueOf(module))
+	<-done
+	fmt.Println("Go: exit")
+}
+
+func getEntrypointFunction() (js.Value, error) {
+	if len(os.Args) < 2 {
+		return js.Value{}, fmt.Errorf("WASM module requires at least 2 arguments: 'js' and entrypoint function name")
+	}
+
+	entrypointName := os.Args[1]
+	entrypoint := js.Global().Get(entrypointName)
+	switch t := entrypoint.Type(); t {
+	case js.TypeFunction:
+		return entrypoint, nil
+	case js.TypeUndefined:
+		return js.Value{}, fmt.Errorf("function %q doesn't exists on global JS scope", entrypointName)
+	default:
+		return js.Value{}, fmt.Errorf("%q should be callable JS function, but got %d instead", entrypointName, t)
+	}
+}
+
+func exit(this js.Value, args []js.Value) interface{} {
+	go func() {
+		done <- void{}
+	}()
+	return nil
+}
+
+func analyzeCode(this js.Value, args worker.Args) (interface{}, error) {
+	var code string
+	if err := args.Bind(&code); err != nil {
+		return nil, err
+	}
+
+	return check.Check(code)
+}

pkg/analyzer/check/check.go

@@ -0,0 +1,22 @@
+package check
+
+import (
+	"go/parser"
+	"go/scanner"
+	"go/token"
+)
+
+// Check checks Go code and returns check result
+func Check(src string) (*Result, error) {
+	fset := token.NewFileSet()
+	_, err := parser.ParseFile(fset, "main.go", src, parser.DeclarationErrors)
+	if err == nil {
+		return &Result{HasErrors: false}, nil
+	}
+
+	if errList, ok := err.(scanner.ErrorList); ok {
+		return &Result{HasErrors: true, Markers: errorsListToMarkers(errList)}, nil
+	}
+
+	return nil, err
+}

pkg/analyzer/check/marker.go

@@ -0,0 +1,46 @@
+// package check checks provided Go code and reports syntax errors
+package check
+
+import "go/scanner"
+
+// MarkerSeverity is equivalent for MarkerSeverity type in monaco-editor
+type MarkerSeverity = int
+
+const (
+	Hint    = MarkerSeverity(1)
+	Info    = MarkerSeverity(2)
+	Warning = MarkerSeverity(3)
+	Error   = MarkerSeverity(8)
+)
+
+// MarkerData is a structure defining a problem/warning/etc.
+// Equivalent to IMarkerData in 'monaco-editor'
+type MarkerData struct {
+	Severity        MarkerSeverity `json:"severity"`
+	StartLineNumber int            `json:"startLineNumber"`
+	StartColumn     int            `json:"startColumn"`
+	EndLineNumber   int            `json:"endLineNumber"`
+	EndColumn       int            `json:"endColumn"`
+	Message         string         `json:"message"`
+}
+
+func errorsListToMarkers(errList scanner.ErrorList) []MarkerData {
+	markers := make([]MarkerData, 0, len(errList))
+	for _, err := range errList {
+		markers = append(markers, MarkerData{
+			Severity:        Error,
+			Message:         err.Msg,
+			StartLineNumber: err.Pos.Line,
+			EndLineNumber:   err.Pos.Line,
+			StartColumn:     err.Pos.Column - 1,
+			EndColumn:       err.Pos.Column,
+		})
+	}
+
+	return markers
+}
+
+type Result struct {
+	HasErrors bool         `json:"hasErrors"`
+	Markers   []MarkerData `json:"markers"`
+}

pkg/worker/args.go

@@ -0,0 +1,75 @@
+package worker
+
+import (
+	"fmt"
+	"syscall/js"
+)
+
+// NewTypeError creates a new type error
+func NewTypeError(expType, gotType js.Type) error {
+	return fmt.Errorf("value type should be %q, but got %q", expType, gotType)
+}
+
+type ValueUnmarshaler interface {
+	UnmarshalValue(js.Value) error
+}
+
+// Args is collection if function call arguments
+type Args []js.Value
+
+// BindIndex binds argument at specified index to passed value
+func (args Args) BindIndex(index int, dest interface{}) error {
+	if len(args) <= index {
+		return fmt.Errorf("function expects %d arguments, but %d were passed", index+1, len(args))
+	}
+
+	return BindValue(args[index], dest)
+}
+
+// Bind binds passed JS arguments to Go values
+//
+// Function supports *int, *bool, *string and ValueUnmarshaler values.
+func (args Args) Bind(targets ...interface{}) error {
+	if len(args) != len(targets) {
+		return fmt.Errorf("function expects %d arguments, but %d were passed", len(targets), len(args))
+	}
+
+	for i, arg := range args {
+		if err := BindValue(arg, targets[i]); err != nil {
+			return fmt.Errorf("invalid argument %d type: %s", err)
+		}
+	}
+
+	return nil
+}
+
+// BindValue binds JS value to specified target
+func BindValue(val js.Value, dest interface{}) error {
+	valType := val.Type()
+	switch v := dest.(type) {
+	case *int:
+		if valType != js.TypeNumber {
+			return NewTypeError(js.TypeNumber, valType)
+		}
+
+		*v = val.Int()
+	case *bool:
+		if valType != js.TypeBoolean {
+			return NewTypeError(js.TypeBoolean, valType)
+		}
+
+		*v = val.Bool()
+	case *string:
+		if valType != js.TypeString {
+			return NewTypeError(js.TypeString, valType)
+		}
+
+		*v = val.String()
+	case ValueUnmarshaler:
+		return v.UnmarshalValue(val)
+	default:
+		return fmt.Errorf("BindValue: unsupported JS type %q", valType)
+	}
+
+	return nil
+}

pkg/worker/callback.go

@@ -0,0 +1,25 @@
+package worker
+
+import "syscall/js"
+
+// Callback is async function callback
+type Callback = func(interface{}, error)
+
+func newCallbackFromValue(val js.Value) (Callback, error) {
+	if typ := val.Type(); typ != js.TypeFunction {
+		return nil, NewTypeError(js.TypeFunction, typ)
+	}
+
+	return func(result interface{}, err error) {
+		if err != nil {
+			val.Invoke(js.ValueOf(NewErrorResponse(err).JSON()))
+		}
+
+		if result == nil {
+			val.Invoke()
+			return
+		}
+
+		val.Invoke(js.ValueOf(NewResponse(result, nil).JSON()))
+	}, nil
+}

pkg/worker/response.go

@@ -0,0 +1,33 @@
+package worker
+
+import (
+	"encoding/json"
+	"fmt"
+)
+
+type Response struct {
+	Error  string      `json:"error,omitempty"`
+	Result interface{} `json:"result,omitempty"`
+}
+
+func (r Response) JSON() string {
+	data, err := json.Marshal(r)
+	if err != nil {
+		// Return manual JSON in case of error
+		return fmt.Sprintf(`{"error": %q}`, err)
+	}
+
+	return string(data)
+}
+
+func NewErrorResponse(err error) Response {
+	return Response{Error: err.Error()}
+}
+
+func NewResponse(result interface{}, err error) Response {
+	if err != nil {
+		return Response{Error: err.Error()}
+	}
+
+	return Response{Result: result}
+}

pkg/worker/worker.go

@@ -0,0 +1,46 @@
+// Package worker contains Go web-worker WASM module bridge methods
+package worker
+
+import (
+	"fmt"
+	"syscall/js"
+)
+
+// Func is worker handler function
+type Func = func(this js.Value, args Args) (interface{}, error)
+
+// ParseArgs parses async call arguments.
+//
+// Function expects the last argument to be a callable JS function
+func ParseArgs(allArgs []js.Value) (Args, Callback, error) {
+	argLen := len(allArgs)
+	if argLen == 0 {
+		return nil, nil, fmt.Errorf("function requires at least 1 argument, but only 0 were passed")
+	}
+
+	lastIndex := len(allArgs) - 1
+	cb, err := newCallbackFromValue(allArgs[lastIndex:][0])
+	if err != nil {
+		return nil, nil, fmt.Errorf("last function argument should be callable (%s)", err)
+	}
+
+	return allArgs[:lastIndex], cb, nil
+}
+
+func callFunc(fn Func, this js.Value, jsArgs []js.Value) {
+	args, callback, err := ParseArgs(jsArgs)
+	if err != nil {
+		js.Global().Get("console").Call("error", fmt.Sprintf("go worker: %s", err))
+		panic(err)
+	}
+
+	callback(fn(this, args))
+}
+
+// FuncOf wraps function into js-compatible async function with callback
+func FuncOf(fn Func) js.Func {
+	return js.FuncOf(func(this js.Value, args []js.Value) interface{} {
+		go callFunc(fn, this, args)
+		return nil
+	})
+}

web/package.json

@@ -22,7 +22,8 @@
     "react-scripts": "3.3.0",
     "redux": "^4.0.5",
     "redux-thunk": "^2.3.0",
-    "typescript": "^3.7.4"
+    "typescript": "^3.7.4",
+    "uuid": "^3.4.0"
   },
   "scripts": {
     "start": "react-app-rewired start",