httperroryzer

Static analyzer to catch invalid uses of http.Error without a return statement which can cause expected bugs

Example

An insidious bug could be the following in an HTTP handler

type credentials struct {
	Secret string `json:"secret"`
}

func authenticate(rw http.ResponseWriter, req *http.Request) {
	dec := json.NewDecoder(req.Body)
	defer req.Body.Close()
	creds := new(credentials)
	if err := dec.Decode(creds); err != nil {
		http.Error(rw, "could not parse out the response", http.StatusBadRequest)
	}
	if creds.Secret != "open-sesame" {
		http.Error(rw, "unauthorized", http.StatusUnauthorized)
	}
	rw.Write([]byte(`{"secret_location":"23.4162° N, 25.6628° E"}`))
}

In here, the caller forgot to invoke return after every error and in the end exposed what was supposed to be privileged information only available to those with the right credentials, for example when ran as per https://play.golang.org/p/I7Swd6GBfYe, it'll print out with malformed/malicious input such as { or {"secret":""}

http: superfluous response.WriteHeader call from main.authenticate (secrets.go:45)
could not parse out the response
unauthorized
{"secret_location":"23.4162° N, 25.6628° E"}

Remedy

Let's what would happen if we ran httperroryzer on it

go get github.com/orijtech/httperroryzer/cmd/httperroryzer && httperroryzer secrets.go

/go/src/github.com/orijtech/httperroryzer/sample/secrets.go:42:3: call to http.Error without a terminating statement below it
/go/src/github.com/orijtech/httperroryzer/sample/secrets.go:45:3: call to http.Error without a terminating statement below it

and when corrected

func authenticate(rw http.ResponseWriter, req *http.Request) {
	dec := json.NewDecoder(req.Body)
	defer req.Body.Close()
	creds := new(credentials)
	if err := dec.Decode(creds); err != nil {
		http.Error(rw, "could not parse out the response", http.StatusBadRequest)
		return
	}
	if creds.Secret != "open-sesame" {
		http.Error(rw, "unauthorized", http.StatusUnauthorized)
		return
	}
	rw.Write([]byte(`{"secret_location":"23.4162° N, 25.6628° E"}`))
}