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// Copyright 2020 The Matrix.org Foundation C.I.C.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//go:build wasm
// +build wasm
package main
import (
"bufio"
"fmt"
"net/http"
"net/http/httptest"
"strings"
"syscall/js"
)
// JSServer exposes an HTTP-like server interface which allows JS to 'send' requests to it.
type JSServer struct {
// The router which will service requests
Mux http.Handler
}
// OnRequestFromJS is the function that JS will invoke when there is a new request.
// The JS function signature is:
// function(reqString: string): Promise<{result: string, error: string}>
// Usage is like:
// const res = await global._go_js_server.fetch(reqString);
// if (res.error) {
// // handle error: this is a 'network' error, not a non-2xx error.
// }
// const rawHttpResponse = res.result;
func (h *JSServer) OnRequestFromJS(this js.Value, args []js.Value) interface{} {
// we HAVE to spawn a new goroutine and return immediately or else Go will deadlock
// if this request blocks at all e.g for /sync calls
httpStr := args[0].String()
promise := js.Global().Get("Promise").New(js.FuncOf(func(pthis js.Value, pargs []js.Value) interface{} {
// The initial callback code for new Promise() is also called on the critical path, which is why
// we need to put this in an immediately invoked goroutine.
go func() {
resolve := pargs[0]
resStr, err := h.handle(httpStr)
errStr := ""
if err != nil {
errStr = err.Error()
}
resolve.Invoke(map[string]interface{}{
"result": resStr,
"error": errStr,
})
}()
return nil
}))
return promise
}
// handle invokes the http.ServeMux for this request and returns the raw HTTP response.
func (h *JSServer) handle(httpStr string) (resStr string, err error) {
req, err := http.ReadRequest(bufio.NewReader(strings.NewReader(httpStr)))
if err != nil {
return
}
w := httptest.NewRecorder()
h.Mux.ServeHTTP(w, req)
res := w.Result()
var resBuffer strings.Builder
err = res.Write(&resBuffer)
return resBuffer.String(), err
}
// ListenAndServe registers a variable in JS-land with the given namespace. This variable is
// a function which JS-land can call to 'send' HTTP requests. The function is attached to
// a global object called "_go_js_server". See OnRequestFromJS for more info.
func (h *JSServer) ListenAndServe(namespace string) {
globalName := "_go_js_server"
// register a hook in JS-land for it to invoke stuff
server := js.Global().Get(globalName)
if !server.Truthy() {
server = js.Global().Get("Object").New()
js.Global().Set(globalName, server)
}
server.Set(namespace, js.FuncOf(h.OnRequestFromJS))
fmt.Printf("Listening for requests from JS on function %s.%s\n", globalName, namespace)
// Block forever to mimic http.ListenAndServe
select {}
}
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