fix(middleware): keep gzip match to EqualFold only

Drop TrimSpace so the change is strictly RFC 9110 case-insensitivity
for content codings, per review discussion.

Author: sonnemusk

middleware/decompress.go

@@ -129,10 +129,10 @@ func (config DecompressConfig) ToMiddleware() (echo.MiddlewareFunc, error) {
 }
 
 
-// isGzipContentEncoding reports whether Content-Encoding is gzip (case-insensitive).
-// Surrounding whitespace is ignored so common proxy variations still match.
+// isGzipContentEncoding reports whether Content-Encoding is gzip.
+// Content codings are case-insensitive per RFC 9110 §8.4.1.
 func isGzipContentEncoding(v string) bool {
-	return strings.EqualFold(strings.TrimSpace(v), GZIPEncoding)
+	return strings.EqualFold(v, GZIPEncoding)
 }
 
 // limitedGzipReader wraps a gzip reader with size limiting to prevent zip bombs

middleware/decompress_test.go

@@ -513,7 +513,7 @@ func TestDecompressContentEncodingCaseInsensitive(t *testing.T) {
 	gz, err := gzipString(body)
 	assert.NoError(t, err)
 
-	for _, encoding := range []string{"GZIP", "Gzip", " gzip "} {
+	for _, encoding := range []string{"GZIP", "Gzip"} {
 		t.Run(encoding, func(t *testing.T) {
 			req := httptest.NewRequest(http.MethodPost, "/", bytes.NewReader(gz))
 			req.Header.Set(echo.HeaderContentEncoding, encoding)