Document compression API

So it begins :)

Author: nhooyr

Diff for: handshake.go

@@ -45,6 +45,12 @@ type AcceptOptions struct {
 	// If you do, remember that if you store secure data in cookies, you wil need to verify the
 	// Origin header yourself otherwise you are exposing yourself to a CSRF attack.
 	InsecureSkipVerify bool
+
+	// Compression sets the WebSocket compression extension options.
+	// If unset, CompressionNoContextTakeover is negotiated with
+	// a threshold of 1024 bytes, flate.BestSpeed and only text messages
+	// are compressed.
+	Compression *CompressionOptions
 }
 
 func verifyClientRequest(w http.ResponseWriter, r *http.Request) error {
@@ -240,8 +246,42 @@ type DialOptions struct {
 
 	// Subprotocols lists the subprotocols to negotiate with the server.
 	Subprotocols []string
+
+	// Compression sets the WebSocket compression extension options.
+	// If unset, CompressionNoContextTakeover is negotiated with
+	// a threshold of 1024 bytes, flate.BestSpeed and only text messages
+	// are compressed.
+	Compression *CompressionOptions
 }
 
+type CompressionOptions struct {
+	// Type sets the WebSocket compression extension type.
+	// Defaults to CompressionNoContextTakeover.
+	Type CompressionType
+
+	// Level controls the compression level negotiated.
+	// Defaults to flate.BestSpeed.
+	Level int
+
+	// Threshold controls the minimum size in bytes of the message
+	// before compression is enabled.
+	// Defaults to 1024.
+	Threshold int
+
+	// Binary controls whether to compression binary messages.
+	Binary bool
+
+	// Text controls whether to compress text messages.
+	Text bool
+}
+
+type CompressionType int
+
+const (
+	CompressionNoContextTakeover CompressionType = iota
+	CompressionContextTakeover
+)
+
 // Dial performs a WebSocket handshake on the given url with the given options.
 // The response is the WebSocket handshake response from the server.
 // If an error occurs, the returned response may be non nil. However, you can only