http.Post Golang example

Hello,

Today, I am going to write small tutorial about basic usage of http.Post method in Golang. Please ignore if there is any mistakes, thank you.

package main

import (
    "bytes"
    "encoding/json"
    "fmt"
    "log"
    "net/http"
)

// Post holds the post data that we send or receive from the API server.
type Post struct {
    ID     string `json:"id,omitempty"`
    Title  string `json:"title"`
    Body   string `json:"Body"`
    UserID string `json:"user_id"`
}

func main() {
    // Before we create resource or post on the API server, we need to see the documentation of the REST API we want to use.
    // Like what is the URL, version, what are the required fields in the resource object.
    // Most of the companies create API docs,  it will have examples in different programming languages along with cURL commands.
    // Companies also create SDKs in different programming languages.
    // Difference between SDK and API: https://addevice.medium.com/difference-between-an-api-and-an-sdk-anyone-can-understand-3a95bf7fc691
    // For example Okta to deal with mangement of users, they are having SDK at:https://github.com/okta/okta-sdk-golang

    // Let's build response body for the server we want to post or create resource
    p := new(Post)
    p.Title = "Title"
    p.Body = "This is body"
    p.UserID = "userID"

    // Now we need erializes Post 'p' to JSON
    b, err := json.Marshal(p)
    if err != nil {
        log.Fatalf("Failed to Serialize to JSON from native Go struct type: %v", err)
    }

    // here http.Post method expects body as 'io.Redear' which should implement Read() method.
    // So, bytes package will take care of that.
    body := bytes.NewBuffer(b)

    // REST APIs means, always think in terms of 'resources'.
    // This is good resource: https://www.practical-go-lessons.com/chap-35-build-an-http-client
    // This post method uses default http client, so timeout is NOT mentioned.
    // Doc of this POST API can be found here: https://jsonplaceholder.typicode.com/guide/.
    postURL := "https://jsonplaceholder.typicode.com/posts"
    resp, err := http.Post(postURL, "application/json; charset=utf-8", body)
    if err != nil {
        log.Fatalf("Failed to create resource at: %s and the error is: %v\n", postURL, err)
    }

    // Always close the response body
    defer resp.Body.Close()

    // Let us just print the response headers info from the server
    log.Printf("Status received from server is: %s", resp.Status)
    log.Printf("StatusCode received from server is: %d", resp.StatusCode)
    log.Printf("Content Type received from Server is: %s", resp.Header["Content-Type"][0])

    // Like I mentioned in my last article,
    // we can read the server response to our native Golang type
    // as the map data structure is close to JSON, we could use it
    // in fact we could use this for most of the wire formats.
    data := make(map[string]interface{})
    if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
        log.Fatalf("Failed to read response body: %v", err)
    }

    // Let's print the map data by iterating over it.
    // Usually in real usecases we use this response to pass to ther functions.
    for key, value := range data {
        fmt.Printf("%s: %v\n", key, value)
    }
    log.Println("We have successfully created resource and read the response from API server.")
}

Thank you.

Comments

[Clavin June]

Great post!

Actually, you can use this snippet below instead of using ioutil.ReadAll and json.Unmarshal

var data map[string]interface{}
if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
    log.Fatalf("Failed to read response body: %v", err)
}