Merge 16857146c8961f809f1a6735e84556d5835eaec9 into d9307dbcbbe796a64d9e0ef23452da888dd7f904

* fix: skip chmod on pre-existing dirs in SaveUploadedFile

Fixes #4622

Prior to this change, SaveUploadedFile unconditionally called
os.Chmod(dir, mode) after os.MkdirAll, even when the target
directory already existed. This caused 'operation not permitted'
errors when saving files into system-owned directories like /tmp
that the current process does not own.

The fix uses os.Stat before MkdirAll to detect whether the
directory already exists, and only calls os.Chmod when the
directory was freshly created by MkdirAll.

This restores the behaviour from v1.10.1 where only os.MkdirAll
was used (which correctly skips permission changes on existing dirs)
while preserving the custom permission feature added in v1.12.0.

Regression test added: TestSaveUploadedFileToExistingDir saves
a file into os.TempDir() (a pre-existing system directory) and
asserts no error is returned.

* test: make SaveUploadedFile #4622 regression test platform-independent

The regression test relied on os.Chmod failing on a pre-existing directory,
which only happens for a non-owner, non-root process. When tests run as root
(common in containers/CI) or with a user-owned $TMPDIR, the buggy chmod
succeeds, so the test passed even against the unfixed code.

Assert the actual contract instead: a pre-existing directory's permissions
are left unchanged. This catches the regression deterministically on every
platform.

Also tighten the SaveUploadedFile doc/comments: the requested perm is enforced
only on the newly created destination directory, not on every directory in the
path.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

context.go

@@ -142,6 +142,16 @@ func (c *Context) Copy() *Context {
 	cp.Params = make([]Param, len(cParams))
 	copy(cp.Params, cParams)
 
+	if c.Errors != nil {
+		cp.Errors = make(errorMsgs, len(c.Errors))
+		copy(cp.Errors, c.Errors)
+	}
+
+	if c.Accepted != nil {
+		cp.Accepted = make([]string, len(c.Accepted))
+		copy(cp.Accepted, c.Accepted)
+	}
+
 	return &cp
 }
 
@@ -620,8 +630,8 @@ func (c *Context) DefaultPostForm(key, defaultValue string) string {
 // For example, during a PATCH request to update the user's email:
 //
 //	    email=mail@example.com  -->  ("mail@example.com", true) := GetPostForm("email") // set email to "mail@example.com"
-//		   email=                  -->  ("", true) := GetPostForm("email") // set email to ""
-//	                            -->  ("", false) := GetPostForm("email") // do nothing with email
+//		email=                  -->  ("", true) := GetPostForm("email")                 // set email to ""
+//	                            -->  ("", false) := GetPostForm("email")                // do nothing with email
 func (c *Context) GetPostForm(key string) (string, bool) {
 	if values, ok := c.GetPostFormArray(key); ok {
 		return values[0], ok
@@ -717,6 +727,11 @@ func (c *Context) MultipartForm() (*multipart.Form, error) {
 }
 
 // SaveUploadedFile uploads the form file to specific dst.
+// An optional perm argument specifies the permission bits used when creating
+// the destination directory. If not provided, the default is 0750. The exact
+// permission is enforced only on the destination directory and only when it is
+// newly created by this call; pre-existing directories (e.g. /tmp) are not
+// modified.
 func (c *Context) SaveUploadedFile(file *multipart.FileHeader, dst string, perm ...fs.FileMode) error {
 	src, err := file.Open()
 	if err != nil {
@@ -729,11 +744,19 @@ func (c *Context) SaveUploadedFile(file *multipart.FileHeader, dst string, perm
 		mode = perm[0]
 	}
 	dir := filepath.Dir(dst)
+	// Record whether the destination directory exists before MkdirAll, so we
+	// only chmod a directory we just created. Chmod'ing a pre-existing directory
+	// the process does not own (e.g. /tmp) fails with "operation not permitted"
+	// (#4622). A non-ErrNotExist stat error also skips chmod and lets MkdirAll
+	// surface the underlying failure.
+	_, statErr := os.Stat(dir)
 	if err = os.MkdirAll(dir, mode); err != nil {
 		return err
 	}
-	if err = os.Chmod(dir, mode); err != nil {
-		return err
+	if errors.Is(statErr, os.ErrNotExist) {
+		if err = os.Chmod(dir, mode); err != nil {
+			return err
+		}
 	}
 
 	out, err := os.Create(dst)
@@ -1052,6 +1075,33 @@ func (c *Context) IsWebsocket() bool {
 	return false
 }
 
+// Scheme returns the HTTP scheme of the request ("http" or "https").
+// When running behind reverse proxies or load balancers `Request.URL.Scheme` is usually empty.
+// the original scheme is commonly forwarded via headers such as X-Forwarded-Proto.
+// Reference:
+// https://developer.mozilla.org/en-US/docs/Web/HTTP/Reference/Headers/X-Forwarded-Proto
+func (c *Context) Scheme() string {
+	if c.Request.TLS != nil {
+		return "https"
+	}
+	if scheme := c.requestHeader("X-Forwarded-Proto"); scheme != "" {
+		return scheme
+	}
+	if scheme := c.requestHeader("X-Forwarded-Protocol"); scheme != "" {
+		return scheme
+	}
+	if ssl := c.requestHeader("X-Forwarded-Ssl"); ssl == "on" {
+		return "https"
+	}
+	if scheme := c.requestHeader("X-Url-Scheme"); scheme != "" {
+		return scheme
+	}
+	if scheme := c.Request.URL.Scheme; scheme != "" {
+		return scheme
+	}
+	return "http"
+}
+
 func (c *Context) requestHeader(key string) string {
 	return c.Request.Header.Get(key)
 }

context_test.go

@@ -7,6 +7,7 @@ package gin
 import (
 	"bytes"
 	"context"
+	"crypto/tls"
 	"errors"
 	"fmt"
 	"html/template"
@@ -248,13 +249,11 @@ func TestSaveUploadedFileWithPermission(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "permission_test", f.Filename)
 	var mode fs.FileMode = 0o755
-	require.NoError(t, c.SaveUploadedFile(f, "permission_test", mode))
-	t.Cleanup(func() {
-		assert.NoError(t, os.Remove("permission_test"))
-	})
-	info, err := os.Stat(filepath.Dir("permission_test"))
+	dst := filepath.Join(t.TempDir(), "subdir", "permission_test")
+	require.NoError(t, c.SaveUploadedFile(f, dst, mode))
+	info, err := os.Stat(filepath.Dir(dst))
 	require.NoError(t, err)
-	assert.Equal(t, info.Mode().Perm(), mode)
+	assert.Equal(t, mode, info.Mode().Perm())
 }
 
 func TestSaveUploadedFileWithPermissionFailed(t *testing.T) {
@@ -272,7 +271,52 @@ func TestSaveUploadedFileWithPermissionFailed(t *testing.T) {
 	require.NoError(t, err)
 	assert.Equal(t, "permission_test", f.Filename)
 	var mode fs.FileMode = 0o644
-	require.Error(t, c.SaveUploadedFile(f, "test/permission_test", mode))
+	dst := filepath.Join(t.TempDir(), "test", "permission_test")
+	require.Error(t, c.SaveUploadedFile(f, dst, mode))
+}
+
+// TestSaveUploadedFileToExistingDir is a regression test for issue #4622.
+// SaveUploadedFile must not call os.Chmod on a directory that already exists,
+// because the process may not own it (e.g. /tmp on Linux/macOS), where chmod
+// fails with "operation not permitted". This asserts the behavioral contract
+// directly — a pre-existing directory's permissions are left unchanged — so it
+// catches the regression on every platform, including environments (root/CI,
+// user-owned $TMPDIR) where chmod on the temp dir would otherwise succeed.
+func TestSaveUploadedFileToExistingDir(t *testing.T) {
+	buf := new(bytes.Buffer)
+	mw := multipart.NewWriter(buf)
+	w, err := mw.CreateFormFile("file", "existing_dir_test")
+	require.NoError(t, err)
+	_, err = w.Write([]byte("existing_dir_test"))
+	require.NoError(t, err)
+	mw.Close()
+
+	c, _ := CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodPost, "/", buf)
+	c.Request.Header.Set("Content-Type", mw.FormDataContentType())
+	f, err := c.FormFile("file")
+	require.NoError(t, err)
+
+	// A pre-existing directory owned by this process, set to a known mode.
+	dir := t.TempDir()
+	require.NoError(t, os.Chmod(dir, 0o700))
+
+	// Pass a perm that differs from the directory's current mode. The fix must
+	// not apply it to the pre-existing directory; the old code chmod'd it
+	// unconditionally, which also failed outright on unowned dirs like /tmp.
+	dst := filepath.Join(dir, "existing_dir_test.txt")
+	require.NoError(t, c.SaveUploadedFile(f, dst, 0o755))
+
+	// The pre-existing directory's permissions must be unchanged.
+	info, err := os.Stat(dir)
+	require.NoError(t, err)
+	assert.Equal(t, os.FileMode(0o700), info.Mode().Perm(),
+		"permissions of a pre-existing directory must not be modified")
+
+	// The file must still be written with the correct content.
+	content, err := os.ReadFile(dst)
+	require.NoError(t, err)
+	assert.Equal(t, "existing_dir_test", string(content))
 }
 
 func TestContextReset(t *testing.T) {
@@ -689,6 +733,50 @@ func TestContextCopy(t *testing.T) {
 	assert.Equal(t, cp.fullPath, c.fullPath)
 }
 
+func TestContextCopyCopiesErrors(t *testing.T) {
+	c, _ := CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	_ = c.Error(errors.New("first error"))
+	_ = c.Error(errors.New("second error"))
+
+	cp := c.Copy()
+
+	// copied context has the same errors
+	assert.Len(t, cp.Errors, 2)
+	assert.Equal(t, c.Errors[0].Error(), cp.Errors[0].Error())
+	assert.Equal(t, c.Errors[1].Error(), cp.Errors[1].Error())
+
+	// mutations on the copy do not affect the original
+	_ = cp.Error(errors.New("third error"))
+	assert.Len(t, c.Errors, 2)
+	assert.Len(t, cp.Errors, 3)
+}
+
+func TestContextCopyCopiesAccepted(t *testing.T) {
+	c, _ := CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.SetAccepted("application/json", "text/html")
+
+	cp := c.Copy()
+
+	assert.Equal(t, c.Accepted, cp.Accepted)
+
+	// mutations on the copy do not affect the original
+	cp.SetAccepted("text/plain")
+	assert.Equal(t, []string{"application/json", "text/html"}, c.Accepted)
+	assert.Equal(t, []string{"text/plain"}, cp.Accepted)
+}
+
+func TestContextCopyNilErrorsAndAccepted(t *testing.T) {
+	c, _ := CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+
+	cp := c.Copy()
+
+	assert.Nil(t, cp.Errors)
+	assert.Nil(t, cp.Accepted)
+}
+
 func TestContextHandlerName(t *testing.T) {
 	c, _ := CreateTestContext(httptest.NewRecorder())
 	c.handlers = HandlersChain{func(c *Context) {}, handlerNameTest}
@@ -2962,6 +3050,65 @@ func TestWebsocketsRequired(t *testing.T) {
 	assert.False(t, c.IsWebsocket())
 }
 
+func TestContextScheme(t *testing.T) {
+	// TLS connection takes highest priority.
+	c, _ := CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.TLS = &tls.ConnectionState{}
+	assert.Equal(t, "https", c.Scheme())
+
+	// X-Forwarded-Proto header.
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.Header.Set("X-Forwarded-Proto", "https")
+	assert.Equal(t, "https", c.Scheme())
+
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.Header.Set("X-Forwarded-Proto", "http")
+	assert.Equal(t, "http", c.Scheme())
+
+	// X-Forwarded-Protocol header.
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.Header.Set("X-Forwarded-Protocol", "https")
+	assert.Equal(t, "https", c.Scheme())
+
+	// X-Forwarded-Ssl: on header.
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.Header.Set("X-Forwarded-Ssl", "on")
+	assert.Equal(t, "https", c.Scheme())
+
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.Header.Set("X-Forwarded-Ssl", "off")
+	assert.Equal(t, "http", c.Scheme())
+
+	// X-Url-Scheme header.
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.Header.Set("X-Url-Scheme", "https")
+	assert.Equal(t, "https", c.Scheme())
+
+	// Request.URL.Scheme fallback.
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "https://example.com/", nil)
+	assert.Equal(t, "https", c.Scheme())
+
+	// Default fallback: plain http.
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	assert.Equal(t, "http", c.Scheme())
+
+	// TLS takes priority over X-Forwarded-Proto.
+	c, _ = CreateTestContext(httptest.NewRecorder())
+	c.Request, _ = http.NewRequest(http.MethodGet, "/", nil)
+	c.Request.TLS = &tls.ConnectionState{}
+	c.Request.Header.Set("X-Forwarded-Proto", "http")
+	assert.Equal(t, "https", c.Scheme())
+}
+
 func TestGetRequestHeaderValue(t *testing.T) {
 	c, _ := CreateTestContext(httptest.NewRecorder())
 	c.Request, _ = http.NewRequest(http.MethodGet, "/chat", nil)

go.mod

@@ -12,11 +12,11 @@ require (
 	github.com/mattn/go-isatty v0.0.20
 	github.com/modern-go/reflect2 v1.0.2
 	github.com/pelletier/go-toml/v2 v2.2.4
-	github.com/quic-go/quic-go v0.59.0
+	github.com/quic-go/quic-go v0.60.0
 	github.com/stretchr/testify v1.11.1
 	github.com/ugorji/go/codec v1.3.1
 	go.mongodb.org/mongo-driver/v2 v2.5.0
-	golang.org/x/net v0.52.0
+	golang.org/x/net v0.55.0
 	google.golang.org/protobuf v1.36.11
 )
 
@@ -39,7 +39,7 @@ require (
 	github.com/twitchyliquid64/golang-asm v0.15.1 // indirect
 	go.uber.org/mock v0.6.0 // indirect
 	golang.org/x/arch v0.25.0 // indirect
-	golang.org/x/crypto v0.49.0 // indirect
-	golang.org/x/sys v0.42.0 // indirect
-	golang.org/x/text v0.35.0 // indirect
+	golang.org/x/crypto v0.51.0 // indirect
+	golang.org/x/sys v0.45.0 // indirect
+	golang.org/x/text v0.37.0 // indirect
 )

go.sum

@@ -50,10 +50,12 @@ github.com/pelletier/go-toml/v2 v2.2.4 h1:mye9XuhQ6gvn5h28+VilKrrPoQVanw5PMw/TB0
 github.com/pelletier/go-toml/v2 v2.2.4/go.mod h1:2gIqNv+qfxSVS7cM2xJQKtLSTLUE9V8t9Stt+h56mCY=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/quic-go/go-ossfuzz-seeds v0.1.0 h1:APacT+iIaNF6fd8AGEiN3bT/Jtkd2jz4v4TzM7MFjy0=
+github.com/quic-go/go-ossfuzz-seeds v0.1.0/go.mod h1:3IOHRbJIc+L6YKMwfDtJAM9Vj9k0YY4muhuyUYk5tbk=
 github.com/quic-go/qpack v0.6.0 h1:g7W+BMYynC1LbYLSqRt8PBg5Tgwxn214ZZR34VIOjz8=
 github.com/quic-go/qpack v0.6.0/go.mod h1:lUpLKChi8njB4ty2bFLX2x4gzDqXwUpaO1DP9qMDZII=
-github.com/quic-go/quic-go v0.59.0 h1:OLJkp1Mlm/aS7dpKgTc6cnpynnD2Xg7C1pwL6vy/SAw=
-github.com/quic-go/quic-go v0.59.0/go.mod h1:upnsH4Ju1YkqpLXC305eW3yDZ4NfnNbmQRCMWS58IKU=
+github.com/quic-go/quic-go v0.60.0 h1:xcQioE8OM66UQLeUMHltK1CCcOu3JbVB4JAQdDQSB+0=
+github.com/quic-go/quic-go v0.60.0/go.mod h1:wpKpjmPpftl30sL6pFh7REVpjbcCVy4zt2vDyK1TuJk=
 github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
 github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
@@ -77,15 +79,15 @@ go.uber.org/mock v0.6.0 h1:hyF9dfmbgIX5EfOdasqLsWD6xqpNZlXblLB/Dbnwv3Y=
 go.uber.org/mock v0.6.0/go.mod h1:KiVJ4BqZJaMj4svdfmHM0AUx4NJYO8ZNpPnZn1Z+BBU=
 golang.org/x/arch v0.25.0 h1:qnk6Ksugpi5Bz32947rkUgDt9/s5qvqDPl/gBKdMJLE=
 golang.org/x/arch v0.25.0/go.mod h1:0X+GdSIP+kL5wPmpK7sdkEVTt2XoYP0cSjQSbZBwOi8=
-golang.org/x/crypto v0.49.0 h1:+Ng2ULVvLHnJ/ZFEq4KdcDd/cfjrrjjNSXNzxg0Y4U4=
-golang.org/x/crypto v0.49.0/go.mod h1:ErX4dUh2UM+CFYiXZRTcMpEcN8b/1gxEuv3nODoYtCA=
-golang.org/x/net v0.52.0 h1:He/TN1l0e4mmR3QqHMT2Xab3Aj3L9qjbhRm78/6jrW0=
-golang.org/x/net v0.52.0/go.mod h1:R1MAz7uMZxVMualyPXb+VaqGSa3LIaUqk0eEt3w36Sw=
+golang.org/x/crypto v0.51.0 h1:IBPXwPfKxY7cWQZ38ZCIRPI50YLeevDLlLnyC5wRGTI=
+golang.org/x/crypto v0.51.0/go.mod h1:8AdwkbraGNABw2kOX6YFPs3WM22XqI4EXEd8g+x7Oc8=
+golang.org/x/net v0.55.0 h1:bcvxaJn3e1U6InsFWt1JUq1aSjnRxLzT2rtD2KfkDF8=
+golang.org/x/net v0.55.0/go.mod h1:L5U2KuzuOe1lY7Z+aWVIKK6qEeJXnXV9yzGA+WCHJww=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
-golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
-golang.org/x/text v0.35.0 h1:JOVx6vVDFokkpaq1AEptVzLTpDe9KGpj5tR4/X+ybL8=
-golang.org/x/text v0.35.0/go.mod h1:khi/HExzZJ2pGnjenulevKNX1W67CUy0AsXcNubPGCA=
+golang.org/x/sys v0.45.0 h1:dO4czNzziLiiXplLQgBCEpCvXQ3dnkn0SdaZSYdQ+FY=
+golang.org/x/sys v0.45.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
+golang.org/x/text v0.37.0 h1:Cqjiwd9eSg8e0QAkyCaQTNHFIIzWtidPahFWR83rTrc=
+golang.org/x/text v0.37.0/go.mod h1:a5sjxXGs9hsn/AJVwuElvCAo9v8QYLzvavO5z2PiM38=
 google.golang.org/protobuf v1.36.11 h1:fV6ZwhNocDyBLK0dj+fg8ektcVegBBuEolpbTQyBNVE=
 google.golang.org/protobuf v1.36.11/go.mod h1:HTf+CrKn2C3g5S8VImy6tdcUvCska2kB7j23XfzDpco=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=

recovery.go

@@ -106,7 +106,12 @@ func secureRequestDump(r *http.Request) string {
 	return strings.Join(lines, "\r\n")
 }
 
-func defaultHandleRecovery(c *Context, _ any) {
+func defaultHandleRecovery(c *Context, err any) {
+	e, ok := err.(error)
+	if !ok {
+		e = fmt.Errorf("%v", err)
+	}
+	c.Error(e) //nolint: errcheck
 	c.AbortWithStatus(http.StatusInternalServerError)
 }
 

recovery_test.go

@@ -5,6 +5,7 @@
 package gin
 
 import (
+	"errors"
 	"net"
 	"net/http"
 	"os"
@@ -152,6 +153,49 @@ func TestPanicWithAbortHandler(t *testing.T) {
 	assert.NotContains(t, out, "panic recovered")
 }
 
+func TestPanicInHandlerRecordsError(t *testing.T) {
+	tests := []struct {
+		name         string
+		recoveredErr any
+		expectedErr  string
+	}{
+		{
+			name:         "string panic",
+			recoveredErr: "Oops, Houston, we have a problem",
+			expectedErr:  "Oops, Houston, we have a problem",
+		},
+		{
+			name:         "error panic",
+			recoveredErr: errors.New("recovered error"),
+			expectedErr:  "recovered error",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			router := New()
+
+			var recoveredErrors errorMsgs
+			router.Use(func(c *Context) {
+				c.Next()
+				recoveredErrors = c.Errors
+			})
+			router.Use(RecoveryWithWriter(nil))
+			router.GET("/recovery", func(_ *Context) {
+				panic(tt.recoveredErr)
+			})
+
+			w := PerformRequest(router, http.MethodGet, "/recovery")
+
+			assert.Equal(t, http.StatusInternalServerError, w.Code)
+			if assert.Len(t, recoveredErrors, 1) {
+				assert.EqualError(t, recoveredErrors[0], tt.expectedErr)
+				assert.Equal(t, ErrorTypePrivate, recoveredErrors[0].Type)
+			}
+		})
+	}
+}
+
 func TestCustomRecoveryWithWriter(t *testing.T) {
 	errBuffer := new(strings.Builder)
 	buffer := new(strings.Builder)

response_writer.go

@@ -114,15 +114,22 @@ func (w *responseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
 	if w.size > 0 {
 		return nil, nil, errHijackAlreadyWritten
 	}
+	hijacker, ok := w.ResponseWriter.(http.Hijacker)
+	if !ok {
+		return nil, nil, http.ErrNotSupported
+	}
 	if w.size < 0 {
 		w.size = 0
 	}
-	return w.ResponseWriter.(http.Hijacker).Hijack()
+	return hijacker.Hijack()
 }
 
 // CloseNotify implements the http.CloseNotifier interface.
 func (w *responseWriter) CloseNotify() <-chan bool {
-	return w.ResponseWriter.(http.CloseNotifier).CloseNotify()
+	if cn, ok := w.ResponseWriter.(http.CloseNotifier); ok {
+		return cn.CloseNotify()
+	}
+	return nil
 }
 
 // Flush implements the http.Flusher interface.

response_writer_test.go

@@ -15,10 +15,33 @@ import (
 	"github.com/stretchr/testify/require"
 )
 
-// TODO
-// func (w *responseWriter) Hijack() (net.Conn, *bufio.ReadWriter, error) {
-// func (w *responseWriter) CloseNotify() <-chan bool {
-// func (w *responseWriter) Flush() {
+// TestResponseWriterFlushWithFlusher verifies Flush() calls the underlying Flusher.
+func TestResponseWriterFlushWithFlusher(t *testing.T) {
+	testWriter := httptest.NewRecorder()
+	writer := &responseWriter{ResponseWriter: testWriter}
+	writer.Flush()
+	assert.True(t, testWriter.Flushed)
+}
+
+// TestResponseWriterFlushWithNonFlusher verifies Flush() is a no-op
+// when the underlying ResponseWriter does not implement http.Flusher.
+// Guards against the panic reported in https://github.com/gin-gonic/gin/issues/4460
+func TestResponseWriterFlushWithNonFlusher(t *testing.T) {
+	nonFlusher := &nonFlusherWriter{header: http.Header{}}
+	writer := &responseWriter{ResponseWriter: nonFlusher}
+	require.NotPanics(t, func() {
+		writer.Flush()
+	})
+}
+
+// nonFlusherWriter is a minimal http.ResponseWriter that does NOT implement http.Flusher.
+type nonFlusherWriter struct {
+	header http.Header
+}
+
+func (w *nonFlusherWriter) Header() http.Header         { return w.header }
+func (w *nonFlusherWriter) Write(b []byte) (int, error) { return len(b), nil }
+func (w *nonFlusherWriter) WriteHeader(code int)        {}
 
 var (
 	_ ResponseWriter      = &responseWriter{}
@@ -113,15 +136,18 @@ func TestResponseWriterHijack(t *testing.T) {
 	writer.reset(testWriter)
 	w := ResponseWriter(writer)
 
-	assert.Panics(t, func() {
-		_, _, err := w.Hijack()
-		require.NoError(t, err)
-	})
-	assert.True(t, w.Written())
+	// httptest.ResponseRecorder doesn't implement http.Hijacker; return
+	// http.ErrNotSupported instead of panicking (#4638). On unsupported the
+	// writer state stays untouched so the handler can still emit a normal
+	// HTTP response as a fallback.
+	conn, buf, err := w.Hijack()
+	assert.Nil(t, conn)
+	assert.Nil(t, buf)
+	require.ErrorIs(t, err, http.ErrNotSupported)
+	assert.False(t, w.Written())
 
-	assert.Panics(t, func() {
-		w.CloseNotify()
-	})
+	// CloseNotify on a non-CloseNotifier returns nil instead of panicking.
+	assert.Nil(t, w.CloseNotify())
 
 	w.Flush()
 }