xerrors

Package xerrors provides extended error handling primitives to add a bit more information to errors returning from the function.

go get github.com/eugeneradionov/xerrors

Motivation

Every API that handles HTTP requests, you need to work with error handling. The standard errors package does not bring the easy way to know what the error is and with which code to respond. With xerrors package, you can extend the error with missing information, such as HTTP status code to respond, and better control the application flow.

Usage

XError

Use XError interface instead of standard error

func GetUserByID(id string) (*User, xerrors.XError) {
    user, err := db.GetUserByID(id)
    if err != nil {
        return nil, xhttp.NewInternalServerError(err)
    }

    return user, nil
}

func GetUserHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json;charset=utf-8")    

    user, xErr := GetUserByID("user_id_1")
    if xErr != nil {
        LogXError(xErr)
        SendXError(w, xErr)
        return
    }
}

func SendExtError(w http.ResponseWriter, xErr xerrors.XError) {
    var statusCode = xErr.GetExtra()["http_code"].(int)

    w.Header().Set("Content-Type", "application/json;charset=utf-8")
    errResp, err := json.Marshal(xErr)
    if err != nil {
        statusCode = http.StatusInternalServerError
    }
    
    w.WriteHeader(statusCode)
    w.Write(errResp)
}

func LogXError(xErr xerrors.XError) {
    log.Printf("[ERR] %s: %s", xErr.Error(), xErr.GetInternalExtra()["error"].(error).Error())
}

The same with xerror

func GetUserByID(id string) (*User, xerrors.XError) {
    user, err := db.GetUserByID(id)
    if err != nil {
        return nil, xerrors.New("Internal Server Error",
            xerrors.WithExtra(map[string]interface{}{"http_code": http.StatusInternalServerError}),
            xerrors.WithInternalExtra(map[string]interface{}{"error": err}),
        )
    }

    return user, nil
}

XErrors

Use XErrors for handling multiple errors

func GetUsersHandler(w http.ResponseWriter, r *http.Request) {
    w.Header().Set("Content-Type", "application/json;charset=utf-8")    
    
    xErrs := xerrors.NewXErrs()

    user1, xErr := GetUserByID("user_id_1")
    if xErr != nil {
        xErrs.Add(xErr)
    }

    user2, xErr := GetUserByID("user_id_2")
    if xErr != nil {
        xErrs.Add(xErr)
    }

    SendXErrs(w, http.StatusUnprocessableEntity, xErrs)
}

func SendXErrs(w http.ResponseWriter, statusCode int, xErrs xerrors.XErrs) {
    w.Header().Set("Content-Type", "application/json;charset=utf-8")
    errResp, err := json.Marshal(xErrs)
    if err != nil {
        statusCode = http.StatusInternalServerError
    }
    
    w.WriteHeader(statusCode)
    w.Write(errResp)
}

Caveats

As XError requires implementation of standard error interface to be compatible with it, be careful, when trying to assign function result XError to the variable with standard error type. This could cause unpredictable behavior.