Functions handlers reference

Reviewed on April 23, 2025

A handler is a routine/function/method that processes specific events. Upon invoking your function, the handler is executed and returns an output.

To learn how to package a function and its dependencies in a zip file, refer to the dedicated documentation.

Handler syntax

For Python functions, the handler must be written in the <folder>/<file>.<function_name> format.

If the handle function is defined in a single file named handler.py: the handler name will be handler.handle.
If the handle function is defined in a file named handler.py in a root folder: the handler will be handler.handle.
If the handle function is defined in a file named handler.py within a folder (for example, myFunction/handler.py): the handler will be myFunction/handler.handle.

Python handler example

def handle(event, context):
return {
    "body": {
        "message": 'Hello, world',
    },
    "statusCode": 200,
}

For Node functions, the handler must be written in the <folder>/<file>.<function_name> format.

If the handle function is defined in a single file named handler.js: the handler name will be handler.handle.
If the handle function is defined in a file named handler.js in a root folder: the handler will be handler.handle.
If the handle function is defined in a file named handler.js within a folder (for example, myFunction/handler.js): the handler will be myFunction/handler.handle.

Node handler example

export {handle};

function handle (event, context, cb) {
    return {
        body: process.version,
        statusCode: 200,
    };
};

For PHP functions, the handler must be written in the <folder>/<file>.<function_name> format.

If the handle function is defined in a single file named handler.php: the handler name will be handler.handle.
If the handle function is defined in a file named handler.php in a root folder: the handler will be handler.handle.
If the handle function is defined in a file named handler.php within a folder (for example, myFunction/handler.php): the handler will be myFunction/handler.handle.

PHP handler example

<?php
function handle($event, $context) {
  return [
    "body" => phpversion(),
    "statusCode" => 200,
  ];
}

For Go, the handler must be written in the <folder>/<function_name> format:

If the Handle function is defined in a handler.go file in a root folder: the handler name will be Handle.
If the Handle function is defined in a handler.go file (for example, myFunction/handler.go): the handler will be myFunction/Handle

Note

With Go, the method name must be capitalized.

Go handler example

package myfunc
  
  import (
      "encoding/json"
      "net/http"
  )
  
  // Handle - Handle event
  func Handle(w http.ResponseWriter, r *http.Request) {
      response := map[string]interface{}{
        "message": "We're all good",
      }
  
      responseBytes, err := json.Marshal(response)
      if err != nil {
        w.WriteHeader(http.StatusInternalServerError)
        return
      }
  
      // Set the header explicitly depending the returned data
      w.Header().Set("Content-Type", "application/json")
  
      // Customize status code.
      w.WriteHeader(http.StatusOK)
  
      // Add content to the response
      _, _ = w.Write(responseBytes)
  }

For Rust, the handler must be written in the <folder>/<function_name> format:

If the handle function is defined in a handler.rs file in a root folder: the handler name will be handle.
If the handle function is defined in a handler.rs file (for example, myFunction/handler.rs): the handler will be myFunction/handle

Note

With Rust, the method must be exported using the pub keyword.

Rust handler example

use axum::{
      body::Body, extract::Request, response::Response,
  };
  use http::StatusCode;
  
  pub async fn handle(_req: Request<Body>) -> Response<Body> {
      Response::builder()
          .status(StatusCode::OK)
          .header("Content-Type", "text/plain")
          .body(Body::from("Hello world!"))
          .unwrap()
  }

Still need help?

Create a support ticket