Decode HTTP Query Params into a Struct in Go

Many people use net/http package directly in Go to deal with HTTP requests, including reading URL parameters, HTTP headers, and the request body. It's straightforward and efficient, though. We can still get bored writing so much tedious code for just reading and parsing the URL params. Especially when we were maintaining a service with hundres of APIs.

Let's see a piece of code for dealing with HTTP requests by using net/http package:

// GET /v1/users?page=1&per_page=20&is_member=true
func ListUsers(rw http.ResponseWriter, r *http.Request) {
    page, err := strconv.ParseInt(r.FormValue("page"), 10, 64)
    if err != nil {
        // Invalid parameter: page.
        return
    }
    perPage, err := strconv.ParseInt(r.FormValue("per_page"), 10, 64)
    if err != nil {
        // Invalid parameter: per_page.
        return
    }
    isMember, err := strconv.ParseBool(r.FormValue("is_member"))
    if err != nil {
        // Invalid parameter: is_member.
        return
    }

    // Read database and return the user list.
}

It's okay if there are only a few (usually less than 3) parameters to be parsed. But what if more? Both the number of lots of local variables and the writing of statements of parsing string URL params to target types can kill us. Some "evil" guys even spread these statements all over in an API handler. 🤒

For such cases, what can we do to save a clean and tidy code base?

Use ggicci/httpin

httpin - 🍡 HTTP Input for Go - Decode an HTTP request into a custom struct

ggicci/httpin is an awesome package which helps you easily decoding HTTP reqeusts from:

• Query string (URL parameters), e.g. ?name=john&is_member=true
• Headers, e.g. Authorization: xxx
• Form data, e.g. login=john&password=*****
• JSON/XML body, e.g. POST {"name": "john", "is_member": true}
• Path variables, e.g. /users/{username}
• File uploads

You don't need to write parsing code for each parameter by yourself. You only care about the input struct and in which handler it will be used.

Let's see an example:

// 1. Define you input struct
type ListUsersInput struct {
    Page     int  `in:"form=page"`
    PerPage  int  `in:"form=per_page"`
    IsMember bool `in:"form=is_member"`
}

// 2. Bind this input struct with an HTTP handler
func init() {
    http.Handle("/users", alice.New(
        httpin.NewInput(ListUsersInput{}),
    ).ThenFunc(ListUsers))
}

// 3. Use the input in the handler, all the parsing stuff are handled by httpin
func ListUsers(rw http.ResponseWriter, r *http.Request) {
    input := r.Context().Value(httpin.Input).(*ListUsersInput)
}

You will find that with the help of httpin, you can get the following benefits:

• ⌛️ Saving developer time
• ♻️ Lower code repetition rate
• 📖 Higher readability
• 🔨 Higher maintainability

httpin is well documentated at https://ggicci.github.io/httpin/.

❤️ Have a try with it :)