chore: bump golangci version

Fix linting issues.

.version

@@ -1,7 +1,7 @@
 GO_VERSION=1.22.0
 
 X_TOOLS_VERSION=v0.15.0
-GOLANGCI_LINT_VERSION=v1.55.2
+GOLANGCI_LINT_VERSION=v1.56.0
 GORELEASER_VERSION=v1.22.1
 GO_LICENSES_VERSION=v1.6.0
 

bind/flag.go

@@ -289,7 +289,7 @@ func HTTPServerConfig(fs *pflag.FlagSet, cfg *forwarder.HTTPServerConfig, prefix
 func HTTPLogConfig(fs *pflag.FlagSet, cfg []NamedParam[httplog.Mode]) {
 	for _, p := range cfg {
 		if p.Param == nil {
-			panic(fmt.Sprintf("httplog mode is nil for %s", p.Name))
+			panic("httplog mode is nil for %s" + p.Name)
 		}
 	}
 

bind/redact.go

@@ -23,7 +23,7 @@ func RedactUserinfo(ui *url.Userinfo) string {
 		return ""
 	}
 	if _, has := ui.Password(); has {
-		return fmt.Sprintf("%s:xxxxx", ui.Username())
+		return ui.Username() + ":xxxxx"
 	}
 	return ui.Username()
 }

config.go

@@ -7,6 +7,7 @@
 package forwarder
 
 import (
+	"errors"
 	"fmt"
 	"net"
 	"net/netip"
@@ -24,7 +25,7 @@ import (
 // ParseUserinfo parses a user:password string into *url.Userinfo.
 func ParseUserinfo(val string) (*url.Userinfo, error) {
 	if val == "" {
-		return nil, fmt.Errorf("expected username[:password]")
+		return nil, errors.New("expected username[:password]")
 	}
 
 	var ui *url.Userinfo
@@ -46,7 +47,7 @@ func validatedUserInfo(ui *url.Userinfo) error {
 		return nil
 	}
 	if ui.Username() == "" {
-		return fmt.Errorf("username cannot be empty")
+		return errors.New("username cannot be empty")
 	}
 
 	return nil
@@ -63,15 +64,15 @@ func wildcardPortTo0(val string) string {
 // ParseHostPortUser parses a user:password@host:port string into HostUser.
 func ParseHostPortUser(val string) (*HostPortUser, error) {
 	if val == "" {
-		return nil, fmt.Errorf("expected user[:password]@host:port")
+		return nil, errors.New("expected user[:password]@host:port")
 	}
 	if strings.Index(val, "@") != strings.LastIndex(val, "@") {
-		return nil, fmt.Errorf("only one '@' is allowed")
+		return nil, errors.New("only one '@' is allowed")
 	}
 
 	up, hp, ok := strings.Cut(val, "@")
 	if !ok {
-		return nil, fmt.Errorf("expected user[:password]@host:port")
+		return nil, errors.New("expected user[:password]@host:port")
 	}
 
 	ui, err := ParseUserinfo(up)
@@ -104,7 +105,7 @@ func ParseProxyURL(val string) (*url.URL, error) {
 	}
 
 	if strings.Index(hpu, "@") != strings.LastIndex(hpu, "@") {
-		return nil, fmt.Errorf("only one '@' is allowed")
+		return nil, errors.New("only one '@' is allowed")
 	}
 
 	var (
@@ -162,7 +163,7 @@ func validateProxyURL(u *url.URL) error {
 		uu := *u
 		uu.User = nil
 		if uu.String() != c.String() {
-			return fmt.Errorf("unsupported URL elements, format: [<protocol>://]<host>:<port>")
+			return errors.New("unsupported URL elements, format: [<protocol>://]<host>:<port>")
 		}
 	}
 
@@ -182,14 +183,14 @@ func validateProxyURL(u *url.URL) error {
 
 	{
 		if u.Port() == "" {
-			return fmt.Errorf("port is required")
+			return errors.New("port is required")
 		}
 		p, err := strconv.ParseUint(u.Port(), 10, 16)
 		if err != nil {
 			return fmt.Errorf("port: %w", err)
 		}
 		if p == 0 {
-			return fmt.Errorf("port cannot be 0")
+			return errors.New("port cannot be 0")
 		}
 	}
 
@@ -233,7 +234,7 @@ func validateDNSAddress(p netip.AddrPort) error {
 		return fmt.Errorf("IP: %s", p.Addr())
 	}
 	if p.Port() == 0 {
-		return fmt.Errorf("port cannot be 0")
+		return errors.New("port cannot be 0")
 	}
 	return nil
 }

credentials.go

@@ -7,6 +7,7 @@
 package forwarder
 
 import (
+	"errors"
 	"fmt"
 	"net"
 	"net/url"
@@ -22,13 +23,13 @@ type HostPortUser struct {
 
 func (hpu *HostPortUser) Validate() error {
 	if hpu.Host == "" {
-		return fmt.Errorf("missing host")
+		return errors.New("missing host")
 	}
 	if hpu.Port == "" {
-		return fmt.Errorf("missing port")
+		return errors.New("missing port")
 	}
 	if hpu.Userinfo == nil {
-		return fmt.Errorf("missing user")
+		return errors.New("missing user")
 	}
 	return validatedUserInfo(hpu.Userinfo)
 }
@@ -100,7 +101,7 @@ func NewCredentialsMatcher(credentials []*HostPortUser, log log.Logger) (*Creden
 		switch {
 		case hpu.Host == "*" && hpu.Port == "0":
 			if m.global != nil {
-				return nil, withRowInfo(fmt.Errorf("duplicate global input"))
+				return nil, withRowInfo(errors.New("duplicate global input"))
 			}
 			m.global = hpu.Userinfo
 		case hpu.Host == "*":
@@ -116,7 +117,7 @@ func NewCredentialsMatcher(credentials []*HostPortUser, log log.Logger) (*Creden
 		default:
 			hostport := net.JoinHostPort(hpu.Host, hpu.Port)
 			if _, ok := m.hostport[hostport]; ok {
-				return nil, fmt.Errorf("duplicate input")
+				return nil, errors.New("duplicate input")
 			}
 			m.hostport[hostport] = hpu.Userinfo
 		}

e2e/setup/callback.go

@@ -8,6 +8,7 @@ package setup
 
 import (
 	"bytes"
+	"errors"
 	"fmt"
 	"os"
 	"os/exec"
@@ -40,7 +41,7 @@ func makeTestCallback(run string, debug bool) func() error {
 			fmt.Fprintln(os.Stderr, "stderr:")
 			stderr.WriteTo(os.Stderr)
 			fmt.Fprintln(os.Stderr)
-			return fmt.Errorf("unexpected stderr")
+			return errors.New("unexpected stderr")
 		}
 
 		s := strings.Split(stdout.String(), "\n")

http_proxy.go

@@ -190,7 +190,7 @@ func newHTTPProxy(cfg *HTTPProxyConfig, pr PACResolver, cm *CredentialsMatcher,
 		return nil, err
 	}
 	if cfg.UpstreamProxy != nil && pr != nil {
-		return nil, fmt.Errorf("cannot use both upstream proxy and PAC")
+		return nil, errors.New("cannot use both upstream proxy and PAC")
 	}
 
 	// If not set, use http.DefaultTransport.

http_proxy_test.go

@@ -9,7 +9,6 @@ package forwarder
 import (
 	"context"
 	"errors"
-	"fmt"
 	"net"
 	"net/http"
 	"net/http/httptest"
@@ -82,7 +81,7 @@ func TestAbortIf(t *testing.T) {
 }
 
 func TestNopDialer(t *testing.T) {
-	nopDialerErr := fmt.Errorf("nop dialer")
+	nopDialerErr := errors.New("nop dialer")
 
 	tr := &http.Transport{
 		DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {

httplog/httplog.go

@@ -154,7 +154,7 @@ func (w *logWriter) ShortURLLine(e middleware.LogEntry) {
 	if scheme != "" {
 		scheme += "://"
 	}
-	if len(path) > 0 && path[0] != '/' {
+	if path != "" && path[0] != '/' {
 		path = "/" + path
 	}
 

internal/martian/context.go

@@ -17,6 +17,7 @@ package martian
 import (
 	"bufio"
 	"context"
+	"errors"
 	"fmt"
 	"net"
 	"net/http"
@@ -116,7 +117,7 @@ func (s *Session) Hijack() (conn net.Conn, brw *bufio.ReadWriter, err error) {
 	defer s.mu.Unlock()
 
 	if s.hijacked {
-		return nil, nil, fmt.Errorf("session has already been hijacked")
+		return nil, nil, errors.New("session has already been hijacked")
 	}
 	defer func() {
 		s.hijacked = err == nil
@@ -138,15 +139,15 @@ func (s *Session) HijackResponseWriter() (http.ResponseWriter, error) {
 	defer s.mu.Unlock()
 
 	if s.hijacked {
-		return nil, fmt.Errorf("session has already been hijacked")
+		return nil, errors.New("session has already been hijacked")
 	}
 
 	if s.rw != nil {
 		s.hijacked = true
 		return s.rw, nil
 	}
 
-	return nil, fmt.Errorf("session has no response writer")
+	return nil, errors.New("session has no response writer")
 }
 
 // Hijacked returns whether the connection has been hijacked.

internal/martian/h2/h2_test.go

@@ -197,7 +197,7 @@ func (p *plusOne) Message(data []byte, streamEnded bool) error {
 	if err := proto.Unmarshal(data, msg); err != nil {
 		return fmt.Errorf("unmarshalling request: %w", err)
 	}
-	msg.Values = append(msg.Values, 1) //nolint:protogetter // synthetic data
+	msg.Values = append(msg.Values, 1)
 
 	data, err := proto.Marshal(msg)
 	if err != nil {

internal/martian/h2/testing/fixture.go

@@ -98,7 +98,7 @@ func New(spf []h2.StreamProcessorFactory) (*Fixture, error) {
 		}
 		proxyTarget := hostname + ":" + strconv.Itoa(proxyPort)
 		// Sets the HTTPS_PROXY environment variable so that http requests will go through the proxy.
-		os.Setenv("HTTPS_PROXY", fmt.Sprintf("http://%s", proxyTarget))
+		os.Setenv("HTTPS_PROXY", "http://"+proxyTarget)
 		fmt.Printf("proxy at %s\n", proxyTarget)
 	}
 	if f.proxyListener == nil {

internal/martian/header/framing_modifier.go

@@ -15,6 +15,7 @@
 package header
 
 import (
+	"errors"
 	"fmt"
 	"net/http"
 	"strings"
@@ -66,7 +67,7 @@ func NewBadFramingModifier() martian.RequestModifier {
 				// "chunked", else we have no way to determine when the request is
 				// finished.
 				if strings.TrimSpace(last[len(last)-1]) != "chunked" {
-					return fmt.Errorf(`bad request framing: "Transfer-Encoding" header is present, but does not end in "chunked"`)
+					return errors.New(`bad request framing: "Transfer-Encoding" header is present, but does not end in "chunked"`)
 				}
 
 				// Transfer-Encoding "chunked" takes precedence over

internal/martian/proxy_test.go

@@ -708,7 +708,7 @@ func TestIntegrationTLSHandshakeErrorCallback(t *testing.T) {
 	}
 
 	var herr error
-	mc.SetHandshakeErrorCallback(func(_ *http.Request, err error) { herr = fmt.Errorf("handshake error") })
+	mc.SetHandshakeErrorCallback(func(_ *http.Request, err error) { herr = errors.New("handshake error") })
 	p.SetMITM(mc)
 
 	tl, err := net.Listen("tcp", "[::]:0")
@@ -1808,7 +1808,7 @@ func TestServerClosesConnection(t *testing.T) {
 	}
 	defer conn.Close()
 
-	req, err := http.NewRequest(http.MethodConnect, fmt.Sprintf("//%s", dstl.Addr().String()), http.NoBody)
+	req, err := http.NewRequest(http.MethodConnect, "//"+dstl.Addr().String(), http.NoBody)
 	if err != nil {
 		t.Fatalf("http.NewRequest(): got %v, want no error", err)
 	}

internal/martian/proxyutil/proxyutil_test.go

@@ -15,7 +15,7 @@
 package proxyutil
 
 import (
-	"fmt"
+	"errors"
 	"net/http"
 	"strings"
 	"testing"
@@ -57,7 +57,7 @@ func TestNewResponse(t *testing.T) {
 
 func TestWarning(t *testing.T) {
 	hdr := http.Header{}
-	err := fmt.Errorf("modifier error")
+	err := errors.New("modifier error")
 
 	Warning(hdr, err)
 

middleware/prometheus.go

@@ -7,7 +7,7 @@
 package middleware
 
 import (
-	"fmt"
+	"errors"
 	"net/http"
 	"strconv"
 	"time"
@@ -138,7 +138,7 @@ func (p *Prometheus) ModifyResponse(res *http.Response) error {
 		start := t0.(time.Time) //nolint:forcetypeassert // we know it's time
 		elapsed = float64(time.Since(start)) / float64(time.Second)
 	} else {
-		return fmt.Errorf("prometheus duration key not found")
+		return errors.New("prometheus duration key not found")
 	}
 
 	reqSize := computeApproximateRequestSize(r)

mitm.go

@@ -9,7 +9,7 @@ package forwarder
 import (
 	"crypto/tls"
 	"crypto/x509"
-	"fmt"
+	"errors"
 	"time"
 
 	"github.com/saucelabs/forwarder/internal/martian/mitm"
@@ -53,7 +53,7 @@ func newMartianMITMConfig(c *MITMConfig) (*mitm.Config, error) {
 	}
 
 	if !ca.IsCA {
-		return nil, fmt.Errorf("certificate is not a CA")
+		return nil, errors.New("certificate is not a CA")
 	}
 
 	cfg, err := mitm.NewConfig(ca, cert.PrivateKey)

pac/pac.go

@@ -8,6 +8,7 @@ package pac
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -28,7 +29,7 @@ type ProxyResolverConfig struct {
 
 func (c *ProxyResolverConfig) Validate() error {
 	if c.Script == "" {
-		return fmt.Errorf("PAC script is empty")
+		return errors.New("PAC script is empty")
 	}
 	return nil
 }
@@ -82,10 +83,10 @@ func NewProxyResolver(cfg *ProxyResolverConfig, r *net.Resolver, opts ...Option)
 	// Find the FindProxyForURL function.
 	fnx, fn := pr.entryPoint()
 	if fnx == nil && fn == nil {
-		return nil, fmt.Errorf("PAC script: missing required function FindProxyForURL or FindProxyForURLEx")
+		return nil, errors.New("PAC script: missing required function FindProxyForURL or FindProxyForURLEx")
 	}
 	if fnx != nil && fn != nil {
-		return nil, fmt.Errorf("PAC script: ambiguous entry point, both FindProxyForURL and FindProxyForURLEx are defined")
+		return nil, errors.New("PAC script: ambiguous entry point, both FindProxyForURL and FindProxyForURLEx are defined")
 	}
 	if fnx != nil {
 		pr.fn = fnx