Azure Functions: HTTP Trigger Input Bindings

Understanding HTTP Trigger Input Bindings

The HTTP trigger for Azure Functions allows you to create serverless APIs that respond to HTTP requests. Input bindings enable your function to easily access data from various sources, including the incoming HTTP request itself. This section details how to access common HTTP request elements like query parameters, route parameters, and request body as input to your function.

Request Body

The request body can be accessed as a string or deserialized into an object, depending on the contentType header. By default, if the contentType is application/json, Azure Functions runtime will attempt to deserialize the body into the target type.

Example: C#

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

public static class HttpTriggerExample
{
    [FunctionName("HttpTriggerWithBody")]
    public static async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = null)] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");

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

        string name = data?.name;
        int? age = data?.age;

        string responseMessage = string.IsNullOrEmpty(name)
            ? "Hello, world! Please pass a name in the request body."
            : $"Hello, {name}! Your age is {age}.";

        return new OkObjectResult(responseMessage);
    }
}
            

Example: JavaScript

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

    const name = (req.body && req.body.name) || (req.query && req.query.name);
    const age = (req.body && req.body.age) || (req.query && req.query.age);

    let responseMessage;
    if (name) {
        responseMessage = `Hello, ${name}! Your age is ${age}.`;
    } else {
        responseMessage = "Hello, world! Please pass a name in the request body or query string.";
    }

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

Query Parameters

Query parameters are accessible directly from the HttpRequest object (in C#) or via req.query (in JavaScript).

Example: C#

using Microsoft.AspNetCore.Http;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.Extensions.Logging;
using System.Threading.Tasks;

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

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

        string responseMessage = string.IsNullOrEmpty(name)
            ? "Hello, world! Please pass a name in the query string."
            : $"Hello, {name}!";

        return new OkObjectResult(responseMessage);
    }
}
            

Example: JavaScript

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);

    let responseMessage;
    if (name) {
        responseMessage = `Hello, ${name}!`;
    } else {
        responseMessage = "Hello, world! Please pass a name in the query string or request body.";
    }

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

Route Parameters

When you define a Route in your trigger attribute, you can specify parameters that will be extracted from the URL path.

Example: C# with Route Parameter

using Microsoft.AspNetCore.Http;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.Extensions.Logging;
using System.Threading.Tasks;

public static class HttpTriggerExample
{
    [FunctionName("HttpTriggerWithRoute")]
    public static async Task<IActionResult> Run(
        [HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = "users/{userId}")] HttpRequest req,
        string userId, // This parameter will be bound from the route
        ILogger log)
    {
        log.LogInformation($"C# HTTP trigger function processed a request for user ID: {userId}");

        string responseMessage = $"Hello, User {userId}!";

        return new OkObjectResult(responseMessage);
    }
}
            

Example: JavaScript with Route Parameter

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

    // The 'userId' parameter is automatically available in context.bindingData
    const userId = context.bindingData.userId;

    let responseMessage;
    if (userId) {
        responseMessage = `Hello, User ${userId}!`;
    } else {
        responseMessage = "Hello, world! User ID not found in route.";
    }

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

HTTP Headers

HTTP headers can be accessed through the HttpRequest object in C# or req.headers in JavaScript.

Example: Accessing Headers

// Inside your C# function...
string contentType = req.Headers["Content-Type"];
log.LogInformation($"Content-Type: {contentType}");
            

// Inside your JavaScript function...
const contentType = req.headers["content-type"];
context.log(`Content-Type: ${contentType}`);