Just use the -H and –data params when you request:

Introduction

When working with APIs, sending JSON data to a server using cURL is a common requirement. Whether you’re testing an API, automating tasks, or integrating services, cURL provides a simple way to send HTTP POST requests with JSON data. In this guide, we’ll walk through how to use cURL to send JSON data, including setting headers, handling responses, and troubleshooting common issues.

Step 1: Understanding cURL and JSON

cURL is a command-line tool that allows you to send HTTP requests. JSON (JavaScript Object Notation) is a lightweight format for data exchange commonly used in APIs. Combining these two allows seamless interaction with RESTful web services.

Step 2: Sending JSON Data with cURL POST

To send a JSON payload using cURL, use the following syntax:

curl -X POST 'https://ww.googleapis.com/***' \
	  -H 'Content-Type: application/json'  \
	  -d '{"token":"[CUSTOM_TOKEN]","otherKey":"otherValue"}'

Breaking Down the Command:

  • -X POST: Specifies the HTTP method as POST.
  • -H “Content-Type: application/json”: Sets the request header to indicate JSON data.
  • -d ‘{“token”:"[CUSTOM_TOKEN]",“otherKey”:“otherValue”}’: Defines the JSON data payload.

Step 3: Storing JSON Data in a File

If the JSON data is large or complex, storing it in a file and using @ to reference it is a cleaner approach:

curl -X POST https://api.example.com/endpoint \
     -H "Content-Type: application/json" \
     -d @data.json

Ensure data.json is in the correct format:

{
  "key1": "value1",
  "key2": "value2"
}

Step 4: Handling API Responses

When you send a request, the server responds with a status code and possibly a JSON response. To display the response, use:

curl -X POST https://api.example.com/endpoint \
     -H "Content-Type: application/json" \
     -d '{"key1":"value1"}' -i

Common HTTP Status Codes:

  • 200 OK: Request successful.
  • 201 Created: Resource created successfully.
  • 400 Bad Request: Incorrect or malformed JSON data.
  • 401 Unauthorized: Authentication required.
  • 500 Internal Server Error: Server-side issue.

Step 5: Adding Authentication (Optional)

If the API requires authentication, include an API key or token in the headers:

curl -X POST https://api.example.com/endpoint \
     -H "Content-Type: application/json" \
     -H "Authorization: Bearer YOUR_ACCESS_TOKEN" \
     -d '{"key1":"value1"}'

Troubleshooting Common Issues

  • Invalid JSON Format: Ensure JSON is correctly formatted and enclosed in single or double quotes.
  • Connection Issues: Use -v for verbose mode to debug network problems.
  • SSL Errors: Use -k to bypass SSL verification (not recommended for production).

Conclusion

Using cURL to send JSON data via POST requests is an essential skill for developers working with APIs. By correctly structuring requests, handling responses, and troubleshooting errors, you can efficiently interact with web services. Try it out and integrate cURL into your workflow today!