ci: enable perfsprint linter

This linter encourages replacing several functions from the fmt package
with faster alternatives. While fixing issues, I also added a few
exported error types rather than returning a naked errors.New().

.golangci.yml

@@ -209,7 +209,7 @@ linters:
     - nolintlint
     - nonamedreturns
     - nosprintfhostport
-    # - perfsprint # TODO https://github.com/gofiber/fiber/issues/2816
+    - perfsprint
     - predeclared
     - promlinter
     - reassign

addon/retry/exponential_backoff_test.go

@@ -1,7 +1,7 @@
 package retry
 
 import (
-	"fmt"
+	"errors"
 	"testing"
 	"time"
 
@@ -44,9 +44,9 @@ func TestExponentialBackoff_Retry(t *testing.T) {
 				MaxRetryCount:   5,
 			},
 			f: func() error {
-				return fmt.Errorf("failed function")
+				return errors.New("failed function")
 			},
-			expErr: fmt.Errorf("failed function"),
+			expErr: errors.New("failed function"),
 		},
 	}
 

app.go

@@ -897,7 +897,7 @@ func (app *App) ShutdownWithContext(ctx context.Context) error {
 	app.mutex.Lock()
 	defer app.mutex.Unlock()
 	if app.server == nil {
-		return fmt.Errorf("shutdown: server is not running")
+		return ErrNotRunning
 	}
 	return app.server.ShutdownWithContext(ctx)
 }
@@ -948,7 +948,7 @@ func (app *App) Test(req *http.Request, msTimeout ...int) (*http.Response, error
 		var returned bool
 		defer func() {
 			if !returned {
-				channel <- fmt.Errorf("runtime.Goexit() called in handler or server panic")
+				channel <- ErrHandlerExited
 			}
 		}()
 
@@ -1071,10 +1071,7 @@ func (app *App) ErrorHandler(ctx Ctx, err error) error {
 // errors before calling the application's error handler method.
 func (app *App) serverErrorHandler(fctx *fasthttp.RequestCtx, err error) {
 	// Acquire Ctx with fasthttp request from pool
-	c, ok := app.AcquireCtx().(*DefaultCtx)
-	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *DefaultCtx"))
-	}
+	c := app.AcquireCtx()
 	c.Reset(fctx)
 
 	defer app.ReleaseCtx(c)

app_test.go

@@ -1672,7 +1672,7 @@ func Test_App_ReadBodyStream(t *testing.T) {
 	require.NoError(t, err, "app.Test(req)")
 	body, err := io.ReadAll(resp.Body)
 	require.NoError(t, err, "io.ReadAll(resp.Body)")
-	require.Equal(t, fmt.Sprintf("true %s", testString), string(body))
+	require.Equal(t, "true "+testString, string(body))
 }
 
 func Test_App_DisablePreParseMultipartForm(t *testing.T) {
@@ -1688,7 +1688,7 @@ func Test_App_DisablePreParseMultipartForm(t *testing.T) {
 			return err
 		}
 		if !req.IsBodyStream() {
-			return fmt.Errorf("not a body stream")
+			return errors.New("not a body stream")
 		}
 		file, err := mpf.File["test"][0].Open()
 		if err != nil {
@@ -1700,7 +1700,7 @@ func Test_App_DisablePreParseMultipartForm(t *testing.T) {
 			return fmt.Errorf("failed to read: %w", err)
 		}
 		if n != len(testString) {
-			return fmt.Errorf("bad read length")
+			return errors.New("bad read length")
 		}
 		return c.Send(buffer)
 	})

bind_test.go

@@ -1556,7 +1556,7 @@ func (*structValidator) ValidateStruct(out any) error {
 	out = reflect.ValueOf(out).Elem().Interface()
 	sq, ok := out.(simpleQuery)
 	if !ok {
-		return fmt.Errorf("failed to type-assert to simpleQuery")
+		return errors.New("failed to type-assert to simpleQuery")
 	}
 
 	if sq.Name != "john" {

client.go

@@ -5,6 +5,7 @@ import (
 	"crypto/tls"
 	"encoding/json"
 	"encoding/xml"
+	"errors"
 	"fmt"
 	"io"
 	"mime/multipart"
@@ -885,7 +886,7 @@ func AcquireClient() *Client {
 	}
 	c, ok := v.(*Client)
 	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *Client"))
+		panic(errors.New("failed to type-assert to *Client"))
 	}
 	return c
 }
@@ -911,7 +912,7 @@ func ReleaseClient(c *Client) {
 func AcquireAgent() *Agent {
 	a, ok := agentPool.Get().(*Agent)
 	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *Agent"))
+		panic(errors.New("failed to type-assert to *Agent"))
 	}
 	return a
 }
@@ -938,7 +939,7 @@ func AcquireResponse() *Response {
 	}
 	r, ok := v.(*Response)
 	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *Response"))
+		panic(errors.New("failed to type-assert to *Response"))
 	}
 	return r
 }
@@ -965,7 +966,7 @@ func AcquireArgs() *Args {
 	}
 	a, ok := v.(*Args)
 	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *Args"))
+		panic(errors.New("failed to type-assert to *Args"))
 	}
 	return a
 }
@@ -990,7 +991,7 @@ func AcquireFormFile() *FormFile {
 	}
 	ff, ok := v.(*FormFile)
 	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *FormFile"))
+		panic(errors.New("failed to type-assert to *FormFile"))
 	}
 	return ff
 }

client_test.go

@@ -8,7 +8,6 @@ import (
 	"encoding/json"
 	"encoding/xml"
 	"errors"
-	"fmt"
 	"io"
 	"mime/multipart"
 	"net"
@@ -630,7 +629,7 @@ type readErrorConn struct {
 }
 
 func (*readErrorConn) Read(_ []byte) (int, error) {
-	return 0, fmt.Errorf("error")
+	return 0, errors.New("error")
 }
 
 func (*readErrorConn) Write(p []byte) (int, error) {

ctx.go

@@ -8,6 +8,7 @@ import (
 	"bytes"
 	"context"
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"io"
 	"mime/multipart"
@@ -615,7 +616,7 @@ func (c *DefaultCtx) Hostname() string {
 func (c *DefaultCtx) Port() string {
 	tcpaddr, ok := c.fasthttp.RemoteAddr().(*net.TCPAddr)
 	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *net.TCPAddr"))
+		panic(errors.New("failed to type-assert to *net.TCPAddr"))
 	}
 	return strconv.Itoa(tcpaddr.Port)
 }
@@ -1108,12 +1109,8 @@ func (c *DefaultCtx) Queries() map[string]string {
 //	age := Query[int](c, "age") // Returns 8
 //	unknown := Query[string](c, "unknown", "default") // Returns "default" since the query parameter "unknown" is not found
 func Query[V QueryType](c Ctx, key string, defaultValue ...V) V {
-	ctx, ok := c.(*DefaultCtx)
-	if !ok {
-		panic(fmt.Errorf("failed to type-assert to *DefaultCtx"))
-	}
 	var v V
-	q := ctx.app.getString(ctx.fasthttp.QueryArgs().Peek(key))
+	q := c.App().getString(c.Context().QueryArgs().Peek(key))
 
 	switch any(v).(type) {
 	case int:
@@ -1151,7 +1148,7 @@ func Query[V QueryType](c Ctx, key string, defaultValue ...V) V {
 		if q == "" && len(defaultValue) > 0 {
 			return defaultValue[0]
 		}
-		return assertValueType[V, []byte](ctx.app.getBytes(q))
+		return assertValueType[V, []byte](c.App().getBytes(q))
 	default:
 		if len(defaultValue) > 0 {
 			return defaultValue[0]

ctx_interface.go

@@ -7,7 +7,7 @@ package fiber
 import (
 	"context"
 	"crypto/tls"
-	"fmt"
+	"errors"
 	"io"
 	"mime/multipart"
 	"sync"
@@ -446,7 +446,7 @@ func (app *App) NewCtx(fctx *fasthttp.RequestCtx) Ctx {
 func (app *App) AcquireCtx() Ctx {
 	ctx, ok := app.pool.Get().(Ctx)
 	if !ok {
-		panic(fmt.Errorf("failed to type-assert to Ctx"))
+		panic(errors.New("failed to type-assert to Ctx"))
 	}
 	return ctx
 }

ctx_test.go

@@ -1271,7 +1271,7 @@ func Test_Ctx_FormValue(t *testing.T) {
 	require.NoError(t, writer.Close())
 
 	req := httptest.NewRequest(MethodPost, "/test", body)
-	req.Header.Set("Content-Type", fmt.Sprintf("multipart/form-data; boundary=%s", writer.Boundary()))
+	req.Header.Set("Content-Type", "multipart/form-data; boundary="+writer.Boundary())
 	req.Header.Set("Content-Length", strconv.Itoa(len(body.Bytes())))
 
 	resp, err := app.Test(req)
@@ -2155,7 +2155,7 @@ func Test_Ctx_MultipartForm(t *testing.T) {
 	require.NoError(t, writer.Close())
 
 	req := httptest.NewRequest(MethodPost, "/test", body)
-	req.Header.Set(HeaderContentType, fmt.Sprintf("multipart/form-data; boundary=%s", writer.Boundary()))
+	req.Header.Set(HeaderContentType, "multipart/form-data; boundary="+writer.Boundary())
 	req.Header.Set(HeaderContentLength, strconv.Itoa(len(body.Bytes())))
 
 	resp, err := app.Test(req)

error.go

@@ -11,9 +11,13 @@ import (
 // Unexported because users will hopefully never need to see it.
 var errUnreachable = errors.New("fiber: unreachable code, please create an issue at github.com/gofiber/fiber")
 
-// Graceful shutdown errors
+// General errors
 var (
 	ErrGracefulTimeout = errors.New("shutdown: graceful timeout has been reached, exiting")
+	// ErrNotRunning indicates that a Shutdown method was called when the server was not running.
+	ErrNotRunning = errors.New("shutdown: server is not running")
+	// ErrHandlerExited is returned by App.Test if a handler panics or calls runtime.Goexit().
+	ErrHandlerExited = errors.New("runtime.Goexit() called in handler or server panic")
 )
 
 // Fiber redirection errors

helpers.go

@@ -7,6 +7,7 @@ package fiber
 import (
 	"bytes"
 	"crypto/tls"
+	"errors"
 	"fmt"
 	"io"
 	"net"
@@ -41,25 +42,27 @@ func getTLSConfig(ln net.Listener) *tls.Config {
 	pointer := reflect.ValueOf(ln)
 
 	// Is it a tls.listener?
-	if pointer.String() == "<*tls.listener Value>" {
-		// Copy value from pointer
-		if val := reflect.Indirect(pointer); val.Type() != nil {
-			// Get private field from value
-			if field := val.FieldByName("config"); field.Type() != nil {
-				// Copy value from pointer field (unsafe)
-				newval := reflect.NewAt(field.Type(), unsafe.Pointer(field.UnsafeAddr())) //nolint:gosec // Probably the only way to extract the *tls.Config from a net.Listener. TODO: Verify there really is no easier way without using unsafe.
-				if newval.Type() != nil {
-					// Get element from pointer
-					if elem := newval.Elem(); elem.Type() != nil {
-						// Cast value to *tls.Config
-						c, ok := elem.Interface().(*tls.Config)
-						//nolint:revive // We need to check if the type assertion was successful
-						if !ok {
-							panic(fmt.Errorf("failed to type-assert to *tls.Config"))
-						}
-						return c
-					}
+	if pointer.String() != "<*tls.listener Value>" {
+		return nil
+	}
+
+	// Copy value from pointer
+	if val := reflect.Indirect(pointer); val.Type() != nil {
+		// Get private field from value
+		if field := val.FieldByName("config"); field.Type() != nil {
+			// Copy value from pointer field (unsafe)
+			newval := reflect.NewAt(field.Type(), unsafe.Pointer(field.UnsafeAddr())) //nolint:gosec // Probably the only way to extract the *tls.Config from a net.Listener. TODO: Verify there really is no easier way without using unsafe.
+			if newval.Type() == nil {
+				return nil
+			}
+			// Get element from pointer
+			if elem := newval.Elem(); elem.Type() != nil {
+				// Cast value to *tls.Config
+				c, ok := elem.Interface().(*tls.Config)
+				if !ok {
+					panic(errors.New("failed to type-assert to *tls.Config"))
 				}
+				return c
 			}
 		}
 	}

middleware/cache/cache_test.go

@@ -50,7 +50,7 @@ func Test_Cache_Expired(t *testing.T) {
 	app.Use(New(Config{Expiration: 2 * time.Second}))
 
 	app.Get("/", func(c fiber.Ctx) error {
-		return c.SendString(fmt.Sprintf("%d", time.Now().UnixNano()))
+		return c.SendString(strconv.FormatInt(time.Now().UnixNano(), 10))
 	})
 
 	resp, err := app.Test(httptest.NewRequest(fiber.MethodGet, "/", nil))
@@ -88,7 +88,7 @@ func Test_Cache(t *testing.T) {
 	app.Use(New())
 
 	app.Get("/", func(c fiber.Ctx) error {
-		now := fmt.Sprintf("%d", time.Now().UnixNano())
+		now := strconv.FormatInt(time.Now().UnixNano(), 10)
 		return c.SendString(now)
 	})
 
@@ -307,7 +307,7 @@ func Test_Cache_Invalid_Expiration(t *testing.T) {
 	app.Use(cache)
 
 	app.Get("/", func(c fiber.Ctx) error {
-		now := fmt.Sprintf("%d", time.Now().UnixNano())
+		now := strconv.FormatInt(time.Now().UnixNano(), 10)
 		return c.SendString(now)
 	})
 
@@ -513,8 +513,7 @@ func Test_CustomExpiration(t *testing.T) {
 
 	app.Get("/", func(c fiber.Ctx) error {
 		c.Response().Header.Add("Cache-Time", "1")
-		now := fmt.Sprintf("%d", time.Now().UnixNano())
-		return c.SendString(now)
+		return c.SendString(strconv.FormatInt(time.Now().UnixNano(), 10))
 	})
 
 	resp, err := app.Test(httptest.NewRequest(fiber.MethodGet, "/", nil))
@@ -620,7 +619,7 @@ func Test_Cache_WithHead(t *testing.T) {
 	app.Use(New())
 
 	handler := func(c fiber.Ctx) error {
-		now := fmt.Sprintf("%d", time.Now().UnixNano())
+		now := strconv.FormatInt(time.Now().UnixNano(), 10)
 		return c.SendString(now)
 	}
 	app.Route("/").Get(handler).Head(handler)

middleware/earlydata/earlydata_test.go

@@ -70,7 +70,7 @@ func appWithConfig(t *testing.T, c *fiber.Config) *fiber.App {
 	}, "/", func(c fiber.Ctx) error {
 		valid, ok := c.Locals(localsKeyTestValid).(bool)
 		if !ok {
-			panic(fmt.Errorf("failed to type-assert to bool"))
+			panic(errors.New("failed to type-assert to bool"))
 		}
 		if !valid {
 			return errors.New("handler called even though validation failed")

middleware/filesystem/utils.go

@@ -1,6 +1,7 @@
 package filesystem
 
 import (
+	"errors"
 	"fmt"
 	"html"
 	"io/fs"
@@ -12,6 +13,11 @@ import (
 	"github.com/gofiber/fiber/v3"
 )
 
+// ErrDirListingNotSupported is returned from the filesystem middleware handler if
+// the given fs.FS does not support directory listing. This is uncommon and may
+// indicate an issue with the FS implementation.
+var ErrDirListingNotSupported = errors.New("failed to type-assert to fs.ReadDirFile")
+
 func getFileExtension(p string) string {
 	n := strings.LastIndexByte(p, '.')
 	if n < 0 {
@@ -23,7 +29,7 @@ func getFileExtension(p string) string {
 func dirList(c fiber.Ctx, f fs.File) error {
 	ff, ok := f.(fs.ReadDirFile)
 	if !ok {
-		return fmt.Errorf("failed to type-assert to fs.ReadDirFile")
+		return ErrDirListingNotSupported
 	}
 	fileinfos, err := ff.ReadDir(-1)
 	if err != nil {