Building a Basic C# HTTP Proxy

Proxies act as intermediaries between clients (like web browsers) and target servers. This article explores how a C# proxy efficiently relays web content.

The Proxy's Role

A client directs its requests to a designated proxy server (specified by IP address and port). The proxy then interprets the HTTP request header to identify the target website and path.

The Relay Process (Three Steps):

1. Client Initiates: The client connects to the proxy, sending its HTTP request.
2. Proxy Processes: The proxy server receives and processes the request (potentially filtering or encrypting). It then establishes a TCP connection with the target server.
3. Response Transfer: The proxy forwards the client's request to the target server. Once the response is received, the proxy simply relays it back to the client. This allows the client to access the content without a direct connection to the server.

Development Considerations

A straightforward C# HTTP proxy needs to handle:

• TCP Port Listening: The proxy must listen on a specified TCP port for incoming client requests.
• Request Parsing: Correctly parse incoming HTTP headers from client requests.
• Target Connection: Establish a TCP connection with the target web server.
• Data Forwarding: Efficiently transfer data between the client and the target server.

While libraries like HttpListener provide some proxy functionality, they may have limitations with features such as Keep-Alive connections and SSL handling. For more robust and flexible proxy behavior, using low-level TCP socket operations is generally preferred.