Sending JSON Via an HTTP POST Request in Go

Clive B.

—October 15, 2024

The Problem

You don’t know how to send JSON data in the body of an HTTP request in Go. For example:

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{
  "description": "Buy cheese and bread for breakfast."
}

The Solution

The simplest way to send JSON data in an HTTP request is to use the http.Post function from the http package, which requires only a URL, a content type, and a request body.

Sending a JSON String Via HTTP POST in Go

To send a JSON via an HTTP POST request, use http.Post and wrap your JSON string in a bytes.Buffer.

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package main

import (
    "bytes"
    "log"
    "net/http"
)

func main() {
    // Define the JSON body as a string.
    body := `{"description": "Buy cheese and bread for breakfast."}`

    // Make the request.
    response, err := http.Post("https://example.com/endpoint", "application/json", bytes.NewBufferString(body))
    if err != nil {
        log.Fatalf("POST failed: %s", err)
    }

    // Do something with the response.
    log.Printf("POST returned with %d status", response.StatusCode)
}

Note: The http.Post function requires only a URL, a content type, and a request body. If you want more control over your request, check out http.Client to learn how to set custom headers, timeouts, etc.

Generating JSON From a Struct in Go

If you’d like to generate your JSON programmatically, use Go’s encoding/json package.

The json.Marshal function uses user-defined json struct tags to format its output.

The Go Wiki offers more information about well-known struct tags.

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package main

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

// Task contains the fields that you'd like to marshal (or serialise) as JSON.
type Task struct {
    Title       string `json:"title"`
    Description string `json:"description"`
}

func main() {
    // Define a Task instance.
    task := Task{
        Title:       "Morning task",
        Description: "Buy cheese and bread for breakfast.",
    }

    // Generate a byte slice representing the Task.
    body, err := json.Marshal(&task)
    if err != nil {
        log.Fatalf("Failed to marshal JSON: %s", err)
    }

    // Make the request.
    // Note that this time, `body` is a slice of bytes, so we use `bytes.NewBuffer` instead.
    response, err := http.Post("https://example.com/endpoint", "application/json", bytes.NewBuffer(body))
    if err != nil {
        log.Fatalf("POST failed: %s", err)
    }

    // Do something with the response.
    log.Printf("POST returned with %d status", response.StatusCode)
}

Bi-weekly Intro to Sentry Demo

Sending JSON Via an HTTP POST Request in Go

The Problem

The Solution

Sending a JSON String Via HTTP POST in Go

Generating JSON From a Struct in Go

Further Reading

Bi-weekly Intro to Sentry Demo

Sending JSON Via an HTTP POST Request in Go

The SolutionThe Solution

Sending a JSON String Via HTTP POST in GoSending a JSON String Via HTTP POST in Go

Generating JSON From a Struct in GoGenerating JSON From a Struct in Go

Further ReadingFurther Reading

The Solution

Sending a JSON String Via HTTP POST in Go

Generating JSON From a Struct in Go

Further Reading