HTTP 101 Switching Protocols

Overview

HTTP 101 Switching Protocols status code is sent in response to a client’s request to change the application protocol. It is primarily used for upgrading from HTTP to a different protocol, like WebSockets.

Purpose

The main purpose of HTTP 101 is to allow efficient switching to more suitable protocols, such as WebSockets for full-duplex communication. This is particularly useful in real-time applications where continuous data exchange occurs.

Usage

Client Behavior:

1. Initial Request: The client sends a request to upgrade the protocol, including the Upgrade header.
2. Awaiting Response: The client waits for the server’s response to confirm the protocol switch.

Server Behavior:

1. Receiving Headers: The server receives the upgrade request.
2. Evaluating: The server evaluates if it can switch to the requested protocol.
3. Responding: The server sends a 101 Switching Protocols response if it agrees to the protocol change.

Scenarios

• WebSocket Upgrade: Commonly used for upgrading an HTTP connection to a WebSocket connection.
• Real-Time Communication: Essential in applications requiring real-time data flow, like chat applications or live data feeds.

Sequence Diagram

sequenceDiagram
    participant Client
    participant Server

    Note over Client: Step 1: Client sends a request to upgrade protocol
    Client->>Server: GET /socket HTTP/1.1 (Upgrade: websocket) (Step 1)
    Client->>Server: Headers (Connection: Upgrade, Upgrade: WebSocket) (Step 2)
    
    Note over Server: Step 3: Server agrees to protocol switch
    Server->>Client: HTTP/1.1 101 Switching Protocols (Step 3)

    Note over Client,Server: Step 4: WebSocket connection established
    Client->>Server: WebSocket Data (Step 4)
    Server->>Client: WebSocket Data (Step 5)

Curl Request and Response Example for HTTP 101

When a client wishes to switch protocols, it can send a request with appropriate headers to indicate the desired protocol. Here’s how you can use Curl to request a protocol upgrade, such as to WebSockets:

# Sample curl request to upgrade to WebSocket
curl -i -H "Upgrade: websocket" -H "Connection: Upgrade" http://example.com/path

# Expected response if the server agrees to switch protocols
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade

PHP cURL Request and Response Example for HTTP 101

In PHP, you can use cURL to make a request that includes headers to request a protocol upgrade. This is especially relevant for situations like upgrading an HTTP connection to a WebSocket.

<?php
// Initialize cURL session
$ch = curl_init('http://example.com/path');

// Set cURL options for protocol upgrade
curl_setopt($ch, CURLOPT_HTTPHEADER, array('Upgrade: websocket', 'Connection: Upgrade'));
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);

// Execute cURL session
$response = curl_exec($ch);

// Check for HTTP 101 Switching Protocols response
if (strpos($response, "HTTP/1.1 101 Switching Protocols") !== false) {
    echo "Protocol successfully upgraded.\n";
} else {
    echo "Failed to upgrade protocol.\n";
}

// Close cURL session
curl_close($ch);
?>

Apache Configuration for HTTP 101 Switching Protocols

Apache does not directly handle WebSocket connections, but it can be configured to proxy these connections to a WebSocket server. The mod_proxy and mod_proxy_wstunnel modules are used for this purpose. Here is an example of how you can configure Apache to handle WebSocket connections:

# Apache Configuration Example for WebSocket Proxy
<VirtualHost *:80>
    ServerName example.com

    # Ensure mod_proxy and mod_proxy_wstunnel are enabled
    ProxyRequests Off
    ProxyPass "/ws/" "ws://websocketserver.example.com/"
    ProxyPassReverse "/ws/" "ws://websocketserver.example.com/"

    # Other configurations...
</VirtualHost>

NGINX Configuration for HTTP 101 Switching Protocols

NGINX can be configured to handle WebSocket upgrades using the HTTP 101 Switching Protocols status code. To set up NGINX as a reverse proxy for WebSocket connections, you need to include specific directives in your NGINX configuration file. Here’s an example:

# NGINX Configuration Example for WebSocket Upgrade
server {
    listen 80;
    server_name example.com;

    location /ws/ {
        proxy_pass http://websocket_backend;

        proxy_http_version 1.1;
        proxy_set_header Upgrade $http_upgrade;
        proxy_set_header Connection "upgrade";

        # Additional proxy settings...
    }
}

HTTP 100 Continue HTTP 102 Processing (WebDAV)