all: Tweak error creation (#6391)

- In the few places where we wrap errors, use the new Go 1.13 "%w"
  construction instead of %s or %v.

- Where we create errors with constant strings, consistently use
  errors.New and not fmt.Errorf.

- Remove capitalization from errors in the few places where we had that.

lib/relay/client/client.go

@@ -38,7 +38,7 @@ type RelayClient interface {
 func NewClient(uri *url.URL, certs []tls.Certificate, invitations chan protocol.SessionInvitation, timeout time.Duration) (RelayClient, error) {
 	factory, ok := supportedSchemes[uri.Scheme]
 	if !ok {
-		return nil, fmt.Errorf("Unsupported scheme: %s", uri.Scheme)
+		return nil, fmt.Errorf("unsupported scheme: %s", uri.Scheme)
 	}
 
 	return factory(uri, certs, invitations, timeout), nil

lib/relay/client/dynamic.go

@@ -6,6 +6,7 @@ import (
 	"context"
 	"crypto/tls"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"net/http"
 	"net/url"
@@ -100,7 +101,7 @@ func (c *dynamicClient) serve(ctx context.Context) error {
 		}
 	}
 	l.Debugln(c, "could not find a connectable relay")
-	return fmt.Errorf("could not find a connectable relay")
+	return errors.New("could not find a connectable relay")
 }
 
 func (c *dynamicClient) Stop() {

lib/relay/client/methods.go

@@ -19,7 +19,7 @@ import (
 
 func GetInvitationFromRelay(ctx context.Context, uri *url.URL, id syncthingprotocol.DeviceID, certs []tls.Certificate, timeout time.Duration) (protocol.SessionInvitation, error) {
 	if uri.Scheme != "relay" {
-		return protocol.SessionInvitation{}, fmt.Errorf("Unsupported relay scheme: %v", uri.Scheme)
+		return protocol.SessionInvitation{}, fmt.Errorf("unsupported relay scheme: %v", uri.Scheme)
 	}
 
 	ctx, cancel := context.WithTimeout(ctx, timeout)
@@ -53,7 +53,7 @@ func GetInvitationFromRelay(ctx context.Context, uri *url.URL, id syncthingproto
 
 	switch msg := message.(type) {
 	case protocol.Response:
-		return protocol.SessionInvitation{}, fmt.Errorf("Incorrect response code %d: %s", msg.Code, msg.Message)
+		return protocol.SessionInvitation{}, fmt.Errorf("incorrect response code %d: %s", msg.Code, msg.Message)
 	case protocol.SessionInvitation:
 		l.Debugln("Received invitation", msg, "via", conn.LocalAddr())
 		ip := net.IP(msg.Address)
@@ -96,7 +96,7 @@ func JoinSession(ctx context.Context, invitation protocol.SessionInvitation) (ne
 	switch msg := message.(type) {
 	case protocol.Response:
 		if msg.Code != 0 {
-			return nil, fmt.Errorf("Incorrect response code %d: %s", msg.Code, msg.Message)
+			return nil, fmt.Errorf("incorrect response code %d: %s", msg.Code, msg.Message)
 		}
 		return conn, nil
 	default:

lib/relay/client/static.go

@@ -73,9 +73,9 @@ func (c *staticClient) serve(ctx context.Context) error {
 	c.mut.Unlock()
 
 	messages := make(chan interface{})
-	errors := make(chan error, 1)
+	errorsc := make(chan error, 1)
 
-	go messageReader(ctx, c.conn, messages, errors)
+	go messageReader(ctx, c.conn, messages, errorsc)
 
 	timeout := time.NewTimer(c.messageTimeout)
 
@@ -102,7 +102,7 @@ func (c *staticClient) serve(ctx context.Context) error {
 
 			case protocol.RelayFull:
 				l.Infof("Disconnected from relay %s due to it becoming full.", c.uri)
-				return fmt.Errorf("relay full")
+				return errors.New("relay full")
 
 			default:
 				l.Infoln("Relay: protocol error: unexpected message %v", msg)
@@ -113,13 +113,13 @@ func (c *staticClient) serve(ctx context.Context) error {
 			l.Debugln(c, "stopping")
 			return nil
 
-		case err := <-errors:
+		case err := <-errorsc:
 			l.Infof("Disconnecting from relay %s due to error: %s", c.uri, err)
 			return err
 
 		case <-timeout.C:
 			l.Debugln(c, "timed out")
-			return fmt.Errorf("timed out")
+			return errors.New("timed out")
 		}
 	}
 }
@@ -205,7 +205,7 @@ func (c *staticClient) join() error {
 		}
 
 	case protocol.RelayFull:
-		return fmt.Errorf("relay full")
+		return errors.New("relay full")
 
 	default:
 		return fmt.Errorf("protocol error: expecting response got %v", msg)
@@ -221,7 +221,7 @@ func performHandshakeAndValidation(conn *tls.Conn, uri *url.URL) error {
 
 	cs := conn.ConnectionState()
 	if !cs.NegotiatedProtocolIsMutual || cs.NegotiatedProtocol != protocol.ProtocolName {
-		return fmt.Errorf("protocol negotiation error")
+		return errors.New("protocol negotiation error")
 	}
 
 	q := uri.Query()

lib/relay/protocol/protocol.go

@@ -3,7 +3,7 @@
 package protocol
 
 import (
-	"fmt"
+	"errors"
 	"io"
 )
 
@@ -53,7 +53,7 @@ func WriteMessage(w io.Writer, message interface{}) error {
 		payload, err = msg.MarshalXDR()
 		header.messageType = messageTypeRelayFull
 	default:
-		err = fmt.Errorf("Unknown message type")
+		err = errors.New("unknown message type")
 	}
 
 	if err != nil {
@@ -84,7 +84,7 @@ func ReadMessage(r io.Reader) (interface{}, error) {
 	}
 
 	if header.magic != magic {
-		return nil, fmt.Errorf("magic mismatch")
+		return nil, errors.New("magic mismatch")
 	}
 
 	buf = make([]byte, int(header.messageLength))
@@ -127,5 +127,5 @@ func ReadMessage(r io.Reader) (interface{}, error) {
 		return msg, err
 	}
 
-	return nil, fmt.Errorf("Unknown message type")
+	return nil, errors.New("unknown message type")
 }