feat: add client agent handshake transport

internal/client/agent/websocket.go

@@ -0,0 +1,49 @@
+package agent
+
+import (
+	"context"
+	"errors"
+	"net/http"
+
+	"github.com/coder/websocket"
+)
+
+var ErrUnexpectedMessage = errors.New("agent transport received a non-binary WebSocket message")
+
+type WebSocketTransport struct{ connection *websocket.Conn }
+
+func DialWebSocket(ctx context.Context, address string, client *http.Client) (*WebSocketTransport, error) {
+	connection, _, err := websocket.Dial(ctx, address, &websocket.DialOptions{HTTPClient: client, CompressionMode: websocket.CompressionDisabled})
+	if err != nil {
+		return nil, err
+	}
+	return &WebSocketTransport{connection: connection}, nil
+}
+
+func (transport *WebSocketTransport) Write(ctx context.Context, payload []byte) error {
+	if transport == nil || transport.connection == nil {
+		return ErrSessionClosed
+	}
+	return transport.connection.Write(ctx, websocket.MessageBinary, payload)
+}
+
+func (transport *WebSocketTransport) Read(ctx context.Context) ([]byte, error) {
+	if transport == nil || transport.connection == nil {
+		return nil, ErrSessionClosed
+	}
+	kind, payload, err := transport.connection.Read(ctx)
+	if err != nil {
+		return nil, err
+	}
+	if kind != websocket.MessageBinary {
+		return nil, ErrUnexpectedMessage
+	}
+	return payload, nil
+}
+
+func (transport *WebSocketTransport) Close() error {
+	if transport == nil || transport.connection == nil {
+		return nil
+	}
+	return transport.connection.Close(websocket.StatusNormalClosure, "")
+}