Azure Functions Documentation

HTTP Triggers in Azure Functions

HTTP triggers allow you to execute Azure Functions in response to HTTP requests. This is a fundamental building block for creating serverless APIs, webhooks, and microservices with Azure Functions.

What is an HTTP Trigger?

An HTTP trigger defines an Azure Function that is invoked when an HTTP request is received by a specific endpoint. The function can then process the request, perform actions, and return an HTTP response.

Creating an HTTP Trigger

You can create an HTTP trigger in several ways, including using the Azure portal, Azure CLI, Visual Studio, or VS Code. The core configuration involves defining the function's binding, which specifies how it is triggered.

Function.json Configuration (Example)

For Node.js, C#, and other languages, the trigger configuration is often defined in a function.json file.

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

Explanation:

• type: "httpTrigger": Specifies this is an HTTP trigger.
• name: "req": The name of the parameter in your function code that will receive the HTTP request object.
• direction: "in": Indicates this binding is for input.
• methods: ["get", "post"]: Restricts the HTTP methods that can trigger the function.
• authLevel: Controls authorization. Options include anonymous, function, and admin.
• The second binding with type: "http" and direction: "out" is for the HTTP response.

Accessing the HTTP Request

Within your function code, you can access various properties of the incoming HTTP request, such as:

• Query parameters
• Route parameters
• Request body
• Headers
• HTTP method

Example: Node.js HTTP Trigger

Here's a simple Node.js example of an HTTP trigger that echoes a name from the query string or request body.

module.exports = async function (context, req) {
    context.log('JavaScript HTTP trigger function processed a request.');

    const name = (req.query.name || (req.body && req.body.name));
    const responseMessage = name
        ? "Hello, " + name + "!"
        : "This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response.";

    context.res = {
        status: 200,
        body: responseMessage
    };
};

Example: C# HTTP Trigger

And here's a C# equivalent:

using System;
using System.IO;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Newtonsoft.Json;

public static class HttpTriggerCSharp
{
    [FunctionName("HttpTriggerCSharp")]
    public static async Task Run(
        [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");

        string name = req.Query["name"];

        string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
        dynamic data = JsonConvert.DeserializeObject(requestBody);
        name = name ?? data?.name;

        string responseMessage = string.IsNullOrEmpty(name)
            ? "This HTTP triggered function executed successfully. Pass a name in the query string or in the request body for a personalized response."
            : $"Hello, {name}!";

        return new OkObjectResult(responseMessage);
    }
}

HTTP Response

Your function can return an HTTP response. This typically involves setting properties on the context.res object (in Node.js) or returning an IActionResult (in C#).

• Status Code: Set the HTTP status code (e.g., 200 OK, 400 Bad Request, 404 Not Found).
• Headers: Add custom headers to the response.
• Body: Include the content of the response. This can be JSON, HTML, plain text, etc.

Routing

You can define custom routes for your HTTP triggers to create cleaner API endpoints. This is configured using the route property in the function.json or via the Route attribute in C#.

Further Reading

• PowerShell HTTP Trigger Binding
• .NET HTTP Trigger Binding
• Create your first HTTP-triggered function