lib/connections: Add KCP support (fixes #804)

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3489

vendor/github.com/hashicorp/yamux/mux.go

@@ -0,0 +1,87 @@
+package yamux
+
+import (
+	"fmt"
+	"io"
+	"os"
+	"time"
+)
+
+// Config is used to tune the Yamux session
+type Config struct {
+	// AcceptBacklog is used to limit how many streams may be
+	// waiting an accept.
+	AcceptBacklog int
+
+	// EnableKeepalive is used to do a period keep alive
+	// messages using a ping.
+	EnableKeepAlive bool
+
+	// KeepAliveInterval is how often to perform the keep alive
+	KeepAliveInterval time.Duration
+
+	// ConnectionWriteTimeout is meant to be a "safety valve" timeout after
+	// we which will suspect a problem with the underlying connection and
+	// close it. This is only applied to writes, where's there's generally
+	// an expectation that things will move along quickly.
+	ConnectionWriteTimeout time.Duration
+
+	// MaxStreamWindowSize is used to control the maximum
+	// window size that we allow for a stream.
+	MaxStreamWindowSize uint32
+
+	// LogOutput is used to control the log destination
+	LogOutput io.Writer
+}
+
+// DefaultConfig is used to return a default configuration
+func DefaultConfig() *Config {
+	return &Config{
+		AcceptBacklog:          256,
+		EnableKeepAlive:        true,
+		KeepAliveInterval:      30 * time.Second,
+		ConnectionWriteTimeout: 10 * time.Second,
+		MaxStreamWindowSize:    initialStreamWindow,
+		LogOutput:              os.Stderr,
+	}
+}
+
+// VerifyConfig is used to verify the sanity of configuration
+func VerifyConfig(config *Config) error {
+	if config.AcceptBacklog <= 0 {
+		return fmt.Errorf("backlog must be positive")
+	}
+	if config.KeepAliveInterval == 0 {
+		return fmt.Errorf("keep-alive interval must be positive")
+	}
+	if config.MaxStreamWindowSize < initialStreamWindow {
+		return fmt.Errorf("MaxStreamWindowSize must be larger than %d", initialStreamWindow)
+	}
+	return nil
+}
+
+// Server is used to initialize a new server-side connection.
+// There must be at most one server-side connection. If a nil config is
+// provided, the DefaultConfiguration will be used.
+func Server(conn io.ReadWriteCloser, config *Config) (*Session, error) {
+	if config == nil {
+		config = DefaultConfig()
+	}
+	if err := VerifyConfig(config); err != nil {
+		return nil, err
+	}
+	return newSession(config, conn, false), nil
+}
+
+// Client is used to initialize a new client-side connection.
+// There must be at most one client-side connection.
+func Client(conn io.ReadWriteCloser, config *Config) (*Session, error) {
+	if config == nil {
+		config = DefaultConfig()
+	}
+
+	if err := VerifyConfig(config); err != nil {
+		return nil, err
+	}
+	return newSession(config, conn, true), nil
+}