HTTP 428 Precondition Required

Overview

The HTTP ~428 Precondition Required~ status code indicates that the server requires the client to apply one or more preconditions to their request headers. It is typically used to enforce certain conditions before processing the request.

Purpose

The HTTP 428 response is used to inform the client that specific preconditions must be met for the server to process the request.

Usage

Client Behavior:

1. Send Request: The client sends an HTTP request to the server.
2. Receive Response: The client receives the HTTP 428 status code, indicating that preconditions are required.
3. Apply Preconditions: The client adjusts the request headers to meet the specified preconditions.
4. Resend Request: The client resends the adjusted request to the server.

Server Behavior:

1. Evaluate Preconditions: The server determines that the request requires certain preconditions to be met.
2. Send Response: The server responds with a ~428 Precondition Required~ status, specifying the required preconditions.

Scenarios

• Conditional Requests: Used when the server wants to enforce specific conditions before processing the request.

Sequence Diagram

Illustrating the process for an HTTP 428 response:

sequenceDiagram
    participant Client
    participant Server as Web Server

    Note over Client: Step 1: Client sends a request
    Client->>Server: HTTP Request (Step 1)

    Note over Server: Step 2: Server evaluates preconditions
    Server->>Client: HTTP/1.1 428 Precondition Required (Step 2)
    Server->>Client: Preconditions: If-Match, If-None-Match (Step 3)

Curl Request and Response Example

Sending a request that requires preconditions using Curl:

curl -i http://example.com/resource
# Expected response: HTTP/1.1 428 Precondition Required
# Preconditions: If-Match, If-None-Match

PHP cURL Request and Response Example

PHP script using cURL to handle a 428 Precondition Required response:

<?php
$ch = curl_init('http://example.com/resource');
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
$response = curl_exec($ch);
if (curl_getinfo($ch, CURLINFO_HTTP_CODE) == 428) {
    $preconditions = curl_getinfo($ch, CURLINFO_PRECONDITION_REQUIRED);
    echo "Precondition required. Preconditions: $preconditions";
}
curl_close($ch);
?>

Python Request and Response Example

Python script to handle a 428 Precondition Required response:

import requests
response = requests.get('http://example.com/resource')
if response.status_code == 428:
    preconditions = response.headers['Preconditions']
    print(f"Precondition required. Preconditions: {preconditions}")

Apache Configuration for HTTP 428 Precondition Required

Configuring Apache to handle scenarios where the server requires preconditions:

<VirtualHost *:80>
    ServerName example.com
    <Location "/resource">
        # Additional configuration to evaluate preconditions
        # ...
        # Return 428 Precondition Required with Preconditions header
        Header always set Preconditions "If-Match, If-None-Match"
        ErrorDocument 428 "HTTP/1.1 428 Precondition Required"
    </Location>
</VirtualHost>

NGINX Configuration for HTTP 428 Precondition Required

Setting up NGINX to handle scenarios where the server requires preconditions:

server {
    listen 80;
    server_name example.com;
    location /resource {
        # Additional configuration to evaluate preconditions
        # ...
        # Return 428 Precondition Required with Preconditions header
        add_header Preconditions "If-Match, If-None-Match";
        return 428 "HTTP/1.1 428 Precondition Required";
    }
}

HTTP 426 Upgrade Required HTTP 429 Too Many Requests