当 Go 编译为 WebAssembly (wasm) 后，使用 http.Client 进行 HTTP GET 请求会引发异常。此问题仅在编译为 wasm 时出现，导致应用程序死锁。解决方法是将 HTTP 请求移动到 Go 例程中运行，避免阻塞主 JavaScript 应用程序中的事件线程。

我想使用 http.client 进行具有相同 x 标头的简单 http get，但在 println("start: getvalues (client.do)") 之后发生异常。

仅当代码编译为 wasm 时才会发生错误。

我需要同样的帮助来理解错误。

代码

println("start: getvalues")
client := &http.client{

}

req, err := http.newrequest("get", "https://abc.azurewebsites.net/api/value", nil)
if err != nil {
    log.println(err.error())
    return nil
}

req.header.add("x-apikey", `abc`)
req.header.add("x-system", `abc`)
req.header.add("x-user", `abc`)

println("start: getvalues (client.do)")
// exception !!!
resp, err := client.do(req)
if err != nil {
    return nil
}

println("start: getvalues (readall)")
data, err := ioutil.readall(resp.body)
if err != nil {
    return nil
}

浏览器日志记录

wasm_exec.js:45 Hello World!
wasm_exec.js:45 WASM Go Initialized
wasm_exec.js:45 
wasm_exec.js:45 Start: GetData
wasm_exec.js:45 Start: getValues
wasm_exec.js:45 Start: getValues (client.Do)
wasm_exec.js:45 fatal error: all goroutines are asleep - deadlock!
wasm_exec.js:45 
wasm_exec.js:45 goroutine 1 [chan receive]:
wasm_exec.js:45 main.main()
wasm_exec.js:45     C:/Git/GoWasmExample/GoWasmExample.go:43 +0xa
wasm_exec.js:45 
wasm_exec.js:45 goroutine 5 [select]:
wasm_exec.js:45 net/http.(*Transport).RoundTrip(0x36b100, 0xc0ba000, 0x0, 0x0, 0x0)
wasm_exec.js:45     C:/Go/src/net/http/roundtrip_js.go:151 +0x44
wasm_exec.js:45 net/http.send(0xc0ba000, 0xbdc80, 0x36b100, 0x0, 0x0, 0x0, 0xc00c068, 0x22, 0xc028de0, 0x1)
wasm_exec.js:45     C:/Go/src/net/http/client.go:250 +0x16
wasm_exec.js:45 net/http.(*Client).send(0xc028d80, 0xc0ba000, 0x0, 0x0, 0x0, 0xc00c068, 0x0, 0x1, 0x40000000000)
wasm_exec.js:45     C:/Go/src/net/http/client.go:174 +0x10
wasm_exec.js:45 net/http.(*Client).do(0xc028d80, 0xc0ba000, 0x0, 0x0, 0x0)
wasm_exec.js:45     C:/Go/src/net/http/client.go:641 +0x17
wasm_exec.js:45 net/http.(*Client).Do(0xc028d80, 0xc0ba000, 0x6, 0x89f48, 0x24)
wasm_exec.js:45     C:/Go/src/net/http/client.go:509 +0x2
wasm_exec.js:45 main.getValues(0x84392, 0x12, 0x0, 0x10b0003d, 0xc048150)
wasm_exec.js:45     C:/Git/GoWasmExample/GoWasmExample.go:124 +0x10
wasm_exec.js:45 main.GetData(0x7ff800000000001f, 0x83468)
wasm_exec.js:45     C:/Git/GoWasmExample/GoWasmExample.go:53 +0x5
wasm_exec.js:45 main.getValue(0xc040240, 0x3, 0x3)
wasm_exec.js:45     C:/Git/GoWasmExample/GoWasmExample.go:161 +0x1d
wasm_exec.js:45 syscall/js.callbackLoop()
wasm_exec.js:45     C:/Go/src/syscall/js/callback.go:116 +0x7
wasm_exec.js:45 created by syscall/js.NewCallback.func1
wasm_exec.js:45     C:/Go/src/syscall/js/callback.go:40 +0x2
wasm_exec.js:67 exit code: 2
exit @ wasm_exec.js:67
runtime.wasmExit @ wasm_exec.js:185
wasm-function[939]
wasm-function[928]
wasm-function[857]
wasm-function[883]
wasm-function[472]
wasm-function[470]
wasm-function[591]
wasm-function[594]
wasm-function[546]
wasm-function[555]
wasm-function[559]
wasm-function[561]
wasm-function[882]
wasm-function[499]
wasm-function[637]
wasm-function[4291]
wasm-function[926]
run @ wasm_exec.js:383
wasm_exec.js:378 Uncaught (in promise) Error: bad callback: Go program has already exited
    at global.Go._resolveCallbackPromise (wasm_exec.js:378)
    at wasm_exec.js:394
_resolveCallbackPromise @ wasm_exec.js:378
(anonymous) @ wasm_exec.js:394

解决方案

因此，http 调用（在 wasm 中）似乎阻塞了我的主 js 应用程序中的事件线程，因此出现了死锁。在 go 例程中运行 http 请求为我解决了这个问题。

https://github.com/golang/go/issues/26382#issuecomment-416926829

对于任何看这里的人来说，这是一个有效的示例:) https://github.com/eduFDiaz/golang-webassembly

到这里，我们也就讲完了《http.Client 在 Go 编译为 wasm 后无法正常工作》的内容了。个人认为，基础知识的学习和巩固，是为了更好的将其运用到项目中，欢迎关注golang学习网公众号，带你了解更多关于的知识点！