Abstract WebSocket adapter interface to support multiple libraries

[Copilot]

This PR introduces a WebSocket adapter interface to decouple go-vncproxy from any specific WebSocket library, enabling support for multiple WebSocket implementations while maintaining full backward compatibility.

Problem

Previously, go-vncproxy was tightly coupled to golang.org/x/net/websocket, making it difficult for users to integrate with other popular WebSocket libraries like github.com/gorilla/websocket or github.com/coder/websocket.

Solution

WebSocket Adapter Interface

Introduced two key interfaces:

type WebSocketAdapter interface {
    Read(p []byte) (n int, err error)
    Write(p []byte) (n int, err error)
    Close() error
    RemoteAddr() string
    Request() *http.Request
    SetBinaryMode() error
}

type WebSocketUpgrader interface {
    Upgrade(w http.ResponseWriter, r *http.Request) (WebSocketAdapter, error)
}

Backward Compatibility

All existing code continues to work unchanged:

// This still works exactly as before
vncProxy := vncproxy.New(&vncproxy.Config{...})
r.GET("/ws", func(ctx *gin.Context) {
    h := websocket.Handler(vncProxy.ServeWS)
    h.ServeHTTP(ctx.Writer, ctx.Request)
})

New Extensible API

Users can now easily integrate custom WebSocket libraries:

// Using the new adapter interface
vncProxy := vncproxy.New(&vncproxy.Config{
    WebSocketAdapter: customUpgrader, // Any WebSocket library
})

r.GET("/ws", func(ctx *gin.Context) {
    handler := vncProxy.HTTPHandler()
    handler.ServeHTTP(ctx.Writer, ctx.Request)
})

Custom Adapter Support

The PR includes documentation and examples for implementing custom adapters, such as for Gorilla WebSocket:

type GorillaWebSocketAdapter struct {
    conn *websocket.Conn
    request *http.Request
}

func (a *GorillaWebSocketAdapter) Read(p []byte) (n int, err error) {
    _, data, err := a.conn.ReadMessage()
    if err != nil {
        return 0, err
    }
    return copy(p, data), nil
}
// ... implement other interface methods

Changes Made

• New files:

  • websocket_adapter.go: Core interface definitions
  • net_websocket_adapter.go: Default adapter for golang.org/x/net/websocket
  • websocket_adapter_test.go: Comprehensive test suite
  • example_gorilla_adapter.go: Example adapter implementation

• Modified files:

  • proxy.go: Added adapter support while preserving existing API
  • peer.go: Updated to use WebSocketAdapter interface
  • example/main.go: Enhanced with usage examples
  • README.md: Comprehensive documentation with examples

Benefits

1. 🔌 Library Independence: Support for any WebSocket library
2. 🔄 Zero Breaking Changes: Complete backward compatibility
3. 📦 Batteries Included: Default implementation using existing library
4. 🎯 Minimal Footprint: Surgical changes with maximum extensibility
5. 📚 Well Documented: Clear examples for custom implementations

Testing

Added comprehensive tests including:

• Mock WebSocket adapter implementation
• Integration tests with the default adapter
• Interface compliance verification

All existing tests continue to pass, ensuring no regressions.

This change significantly improves the library's flexibility and extensibility while maintaining its simplicity and backward compatibility.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Abstract a WebSocket adapter interface to support multiple libraries</issue_title>
<issue_description>To improve compatibility with different WebSocket libraries, introduce an abstraction layer via a WebSocket adapter interface. Provide a default implementation using golang.org/x/net/websocket and allow custom adapters for libraries such as github.com/coder/websocket and github.com/gorilla/websocket.

Proposed approach:

• Define a unified WebSocketAdapter interface that covers connect/upgrade, read, write, close, and error handling, including binary/text frames and context cancellation.
• Implement the default adapter based on golang.org/x/net/websocket.
• Expose clear extension points so users can implement adapters for other libraries (e.g., coder/websocket, gorilla/websocket).
• Document how to implement and plug in a custom adapter.

This change increases extensibility and decouples go-vncproxy from any specific WebSocket library.</issue_description>

<agent_instructions>implement this</agent_instructions>

Comments on the Issue (you are @copilot in this section)

Fixes #37

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