unknwon/the-way-to-go_ZH_CN · error

expected GET

Error message

expected GET

What it means

Error from the closure-based validation in the eBook's httpRequestHandler example (16.10.2): the anonymous func checks req.Method != "GET" first and returns errors.New("expected GET") for any other verb; the outer code turns it into a 400 via w.WriteHeader(400) and io.WriteString(w, err). The snippet demonstrates concentrating all request validation in one closure so the handler body stays clean.

Source

Thrown at eBook/16.10.md:50

... err1 := api.Func1()
if err1 != nil {
    fmt.Println("err: " + err.Error())
    return
}
err2 := api.Func2()
if err2 != nil {
...
    return
}    
```

首先，包括在一个初始化的 `if` 语句中对函数的调用。但即使代码中到处都是以 `if` 语句的形式通知错误（通过打印错误信息）。通过这种方式，很难分辨什么是正常的程序逻辑，什么是错误检测或错误通知。还需注意的是，大部分代码都是致力于错误的检测。通常解决此问题的好办法是尽可能以闭包的形式封装你的错误检测，例如下面的代码：

```go
func httpRequestHandler(w http.ResponseWriter, req *http.Request) {
    err := func () error {
        if req.Method != "GET" {
            return errors.New("expected GET")
        }
        if input := parseInput(req); input != "command" {
            return errors.New("malformed command")
        }
        // 可以在此进行其他的错误检测
    } ()

        if err != nil {
            w.WriteHeader(400)
            io.WriteString(w, err)
            return
        }
        doSomething() ...
```

这种方法可以很容易分辨出错误检测、错误通知和正常的程序逻辑（更详细的方式参考[第 13.5 小节](13.5.md)）。

**在开始阅读[第 17 章](17.0.md)前，先回答下列 2 个问题：**

View on GitHub (pinned to 7a54d34d36)

Solutions

1. Fix the client to use GET if the operation is a read: fetch(url) defaults to GET — remove method: 'POST'; drop curl -d
2. If other verbs are legitimate, return 405 Method Not Allowed with an Allow header instead of a bare 400 — 405 is the correct status for a wrong verb
3. Route by verb so the handler is never reached with the wrong method: Go 1.22+ net/http mux patterns like mux.HandleFunc("GET /path", h)
4. Compare against the http.MethodGet constant instead of the literal "GET" to avoid typo class bugs

Example fix

// before (inside the closure)
if req.Method != "GET" {
	return errors.New("expected GET")
}
// ...
if err != nil {
	w.WriteHeader(400)
	io.WriteString(w, err)
	return
}

// after
if req.Method != http.MethodGet {
	w.Header().Set("Allow", http.MethodGet)
	w.WriteHeader(http.StatusMethodNotAllowed)
	io.WriteString(w, "expected GET")
	return nil
}

// register the handler so only GET reaches it (Go 1.22+ method patterns)
mux.HandleFunc("GET /command", httpRequestHandler)

err := func() error {
	if req.Method != http.MethodGet {
		return errors.New("expected GET")
	}
	// further checks...
	return nil
}()
if err != nil {
	http.Error(w, err.Error(), http.StatusBadRequest)
	return
}

When it happens

Trigger: Any non-GET request reaching this handler: POST/PUT/DELETE from a form submission, a CORS preflight OPTIONS, or curl defaulting to POST when given -d. The method check runs before parseInput, so a wrong verb always fails here even with a valid body.

Common situations: Front-end switched to fetch with method POST while the backend still demands GET; health-checkers and proxies sending HEAD; browser CORS preflight OPTIONS hitting the route; copy-pasting the book handler without aligning the allowed method with the client.

Related errors

• expected GET
• I won't be able to do a sqrt of negative number!
• things aren’t good
• malformed command
• key not found

AI-assisted analysis of unknwon/the-way-to-go_ZH_CN@7a54d34d36 (2026-08-15). Data as JSON: /api/errors/fcf6693d55ba6e41. Report an issue: GitHub.