HTTP bindings for Azure Functions

Overview

HTTP bindings let Azure Functions expose a RESTful endpoint or call external HTTP services. The same function can act as an HTTP trigger, an HTTP input binding, and an HTTP output binding.

• Trigger: Defines how the function is invoked via an HTTP request.
• Input: Provides request data (e.g., query string, headers, body) as parameters.
• Output: Generates the HTTP response returned to the caller.

HTTP Trigger

Add an httpTrigger binding in function.json to make the function reachable via HTTP.

{
  "bindings": [
    {
      "authLevel": "function",
      "type": "httpTrigger",
      "direction": "in",
      "name": "req",
      "methods": [ "get", "post" ],
      "route": "items/{id?}"
    },
    {
      "type": "http",
      "direction": "out",
      "name": "res"
    }
  ]
}

HTTP Input binding

You can bind request details directly to function parameters.

public static async Task Run(
    [HttpTrigger(AuthorizationLevel.Function, "get", "post", Route = null)] HttpRequest req,
    ILogger log)
{
    string name = req.Query["name"];
    string requestBody = await new StreamReader(req.Body).ReadToEndAsync();
    // ...
}

HTTP Output binding

Return an IActionResult (C#), HttpResponseMessage (JS), or equivalent to send a response.

return new OkObjectResult(new { message = "Success", id = 123 });

context.res = {
    status: 200,
    body: { message: "Success", id: 123 },
    headers: {
        "Content-Type": "application/json"
    }
};
context.done();

Samples

Below are quick-start samples for common scenarios.

// GET /api/todo/{id}
public static IActionResult GetTodo(
    [HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = "todo/{id}")] HttpRequest req,
    int id,
    ILogger log)
{
    var todo = TodoRepository.Get(id);
    return todo != null ? (IActionResult)new OkObjectResult(todo) : new NotFoundResult();
}

// POST /api/todo
public static async Task CreateTodo(
    [HttpTrigger(AuthorizationLevel.Function, "post", Route = "todo")] HttpRequest req,
    ILogger log)
{
    var data = await new StreamReader(req.Body).ReadToEndAsync();
    var todo = JsonConvert.DeserializeObject(data);
    TodoRepository.Add(todo);
    return new CreatedResult($"/api/todo/{todo.Id}", todo);
}

Best practices

• Use AuthorizationLevel.Function for internal APIs and Anonymous only for public endpoints.
• Validate all request data and return proper status codes (400, 401, 404, 500, etc.).
• Leverage ILogger to log request IDs for traceability.
• Prefer binding to POCO models instead of raw strings when possible.
• Set appropriate Cache-Control and CORS headers in the response.