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Connection.java — One Client's State

📄 File: src/Connection.java 🔗 Back to: Main README

What is this file?

Connection.java is a data container. It holds everything the server needs to know about one specific client currently connected.

Since the server handles many clients at once with a single thread, it needs a way to remember "what stage is Client A at?" and "what has Client B sent so far?". That's exactly what Connection does.

Real-world analogy

Think of a notepad a waiter carries. For each customer at the table, the waiter writes:

  • Table number (which port they came from)
  • What they've ordered so far (HTTP headers/body)
  • Whether the order is complete (has all data arrived?)
  • What's being delivered back (the response buffer)

The Fields Explained

public SocketChannel channel;     // The actual network pipe to this client
public ByteBuffer readBuffer;     // Where we store incoming bytes as they arrive
public ByteBuffer writeBuffer;    // Where we put the response bytes to send out
public long lastActive;           // When did this client last send something?
public int localPort;             // Which port did they connect to? (for virtual hosting)

HTTP parsing state:

public String method;        // "GET", "POST", "DELETE"
public String path;          // "/index.html", "/upload/file.txt"
public String queryString;   // "name=John&age=20" (the part after ?)
public Map<String,String> headers; // All HTTP headers e.g. {"host": "localhost"}
public byte[] body;          // The request body (e.g. uploaded file data)
public boolean chunked;      // Is the body sent in chunks?

CGI script state:

public Process cgiProcess;   // The Python/Shell process currently running
public File cgiOutputFile;   // Temp file where the script writes its output
public File cgiInputFile;    // Temp file with the request body (for POST)

Why track localPort?

The server supports virtual hosting — multiple websites on the same IP but different domain names. To figure out which website a client wants, we need to know:

  1. Which port they connected on
  2. What Host: header they sent

For example:

curl --resolve test.com:8080:127.0.0.1 http://test.com:8080/

The browser connects to port 8080 and sends Host: test.com. With both pieces of info, Config.findServer() knows to serve the test.com website, not localhost.

The Buffer System

The readBuffer is a 16KB chunk of memory. As bytes arrive from the network, they're written here. Once a complete HTTP request is assembled, HttpParser processes it.

[...bytes arriving from network...] → readBuffer → HttpParser

The writeBuffer works in reverse:

Router builds a response → writeBuffer → [...bytes sent to browser...]

updateActivity()

Called every time a client sends data. Resets their idle timer:

public void updateActivity() {
    this.lastActive = System.currentTimeMillis();
}

If this timestamp gets too old, EventLoop.checkTimeouts() will disconnect them.