HTTP 417 Expectation Failed

Overview

The HTTP 417 Expectation Failed status code is a client error response indicating that the expectations specified in the Expect header of the request cannot be met by the server. This status code is often used when a client expects a certain behavior from the server, and the server is unable to fulfill those expectations.

Purpose

The primary purpose of the HTTP 417 response is to inform the client that the server cannot meet the expectations set in the Expect header of the request.

Usage

Client Behavior:

1. Send Request with Expectation: The client includes an Expect header in the request, specifying certain expectations.
2. Receive Response: The client receives the HTTP 417 status code if the server cannot meet the specified expectations.

Server Behavior:

1. Evaluate Expectations: The server evaluates the expectations specified in the Expect header.
2. Send Response: If the expectations cannot be fulfilled, the server responds with a 417 Expectation Failed status code.

Scenarios

• Unmet Expectations: The client requests a behavior or condition from the server using the Expect header, and the server is unable to fulfill those expectations.

Sequence Diagram

Illustrating the process for an HTTP 417 response:

sequenceDiagram
    participant Client
    participant Server as Web Server

    Note over Client: Client sends a request with Expect header
    Client->>Server: POST /resource HTTP/1.1
    Client->>Server: Expect: certain-expectation
    Note over Server: Server evaluates the expectation
    Server->>Client: HTTP/1.1 417 Expectation Failed

Curl Request and Response Example

Sending a request with an Expect header using Curl:

curl -i -H "Expect: certain-expectation" http://example.com/resource
# Expected response: HTTP/1.1 417 Expectation Failed

PHP cURL Request and Response Example

PHP script using cURL to handle a 417 Expectation Failed response:

<?php
$ch = curl_init('http://example.com/resource');
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Expect: certain-expectation'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
if (curl_getinfo($ch, CURLINFO_HTTP_CODE) == 417) {
    echo "Expectation Failed.";
}
curl_close($ch);
?>

Python Request and Response Example

Python script to send a request with an Expect header and handle a 417 response:

import requests
headers = {'Expect': 'certain-expectation'}
response = requests.post('http://example.com/resource', headers=headers)
if response.status_code == 417:
    print("Expectation Failed")

Apache Configuration for HTTP 417 Expectation Failed

Configuring Apache to handle expectations:

<VirtualHost *:80>
    ServerName example.com
    # Additional configurations as needed
</VirtualHost>

NGINX Configuration for HTTP 417 Expectation Failed

Setting up NGINX to handle expectations:

server {
    listen 80;
    server_name example.com;
    # Additional configurations as needed
}

HTTP 416 Requested Range Not Satisfiable HTTP 418 I’m a Teapot (RFC 2324)