Azure Functions Documentation

Home > Azure Functions > Bindings > HTTP Output Bindings

HTTP Output Bindings

HTTP output bindings enable your Azure Functions to send HTTP responses back to the caller. This is the fundamental mechanism for creating HTTP-triggered APIs with Azure Functions.

How it Works

When a function is triggered by an HTTP request, you can define an HTTP output binding that will be used to construct and send the response. This binding typically takes the form of an HttpResponseData object in your function code.

Configuration

You configure HTTP output bindings in your function.json file.

Example function.json

JSON 
{
  "scriptFile": "run.csx",
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [
        "get",
        "post"
      ]
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

In this configuration:

Using HTTP Output Bindings in Code

C# Example

C# 
using System.Net;
using System.Net.Http;
using System.Threading.Tasks;
using Microsoft.Azure.Functions.Worker;
using Microsoft.Azure.Functions.Worker.Http;

public static class HttpExample
{
    [Function("HttpExample")]
    public static async Task Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequestData req,
        FunctionContext context)
    {
        var response = req.CreateResponse(HttpStatusCode.OK);
        response.Headers.Add("Content-Type", "text/plain; charset=utf-8");
        await response.WriteStringAsync("Hello from Azure Functions!");

        return response;
    }
}

JavaScript Example

JavaScript 
module.exports = async function (context, req) {
    context.res = {
        status: 200,
        headers: {
            "Content-Type": "text/plain"
        },
        body: "Hello from Azure Functions!"
    };
};

Common Response Scenarios

Returning JSON Data

You can easily return JSON by setting the Content-Type header and providing a JSON string or object as the response body.

Note: When returning JSON, ensure your response body is a valid JSON string. For example, when using Node.js, you might use JSON.stringify().

Setting HTTP Status Codes

You can specify the HTTP status code for your response. The default is usually 200 OK.

C# 
var response = req.CreateResponse(HttpStatusCode.BadRequest); // Example for 400 Bad Request
response.WriteStringAsync("Invalid input provided.");
return response;
JavaScript 
context.res = {
    status: 404, // Example for 404 Not Found
    body: "Resource not found."
};

Custom Headers

Add custom headers to your HTTP response as needed.

C# 
response.Headers.Add("X-Custom-Header", "MyValue");
JavaScript 
context.res = {
    status: 200,
    headers: {
        "Content-Type": "application/json",
        "X-Custom-Header": "MyValue"
    },
    body: { message: "Success" }
};

Handling Errors

For robust API development, it's crucial to handle errors gracefully by returning appropriate error status codes and messages.

Tip: For more advanced scenarios, consider using a library for routing or an API management service in front of your Azure Functions.

Further Reading