fix(middleware): fix Accept-Encoding matching in compress middleware

middleware/compress.go

@@ -9,6 +9,7 @@ import (
 	"io"
 	"net"
 	"net/http"
+	"strconv"
 	"strings"
 	"sync"
 )
@@ -239,9 +240,21 @@ func (c *Compressor) selectEncoder(h http.Header, w io.Writer) (io.Writer, strin
 
 func matchAcceptEncoding(accepted []string, encoding string) bool {
 	for _, v := range accepted {
-		if strings.Contains(v, encoding) {
-			return true
+		name, params, _ := strings.Cut(strings.TrimSpace(v), ";")
+		if !strings.EqualFold(strings.TrimSpace(name), encoding) {
+			continue
 		}
+		for _, param := range strings.Split(params, ";") {
+			key, value, ok := strings.Cut(strings.TrimSpace(param), "=")
+			if !ok || !strings.EqualFold(strings.TrimSpace(key), "q") {
+				continue
+			}
+			quality, err := strconv.ParseFloat(strings.TrimSpace(value), 64)
+			if err == nil && quality <= 0 {
+				return false
+			}
+		}
+		return true
 	}
 	return false
 }

middleware/compress_test.go

@@ -92,6 +92,18 @@ func TestCompressor(t *testing.T) {
 			acceptedEncodings: []string{"nop, gzip, deflate"},
 			expectedEncoding:  "nop",
 		},
+		{
+			name:              "gzip rejected with q=0 returns no encoding",
+			path:              "/gethtml",
+			acceptedEncodings: []string{"gzip;q=0"},
+			expectedEncoding:  "",
+		},
+		{
+			name:              "gzip rejected with q=0 falls back to deflate",
+			path:              "/gethtml",
+			acceptedEncodings: []string{"gzip;q=0", "deflate"},
+			expectedEncoding:  "deflate",
+		},
 	}
 
 	for _, tc := range tests {
@@ -169,6 +181,122 @@ func TestCompressorWildcards(t *testing.T) {
 	}
 }
 
+func TestMatchAcceptEncoding(t *testing.T) {
+	tests := []struct {
+		name     string
+		accepted []string
+		encoding string
+		want     bool
+	}{
+		{
+			name:     "exact match",
+			accepted: []string{"gzip"},
+			encoding: "gzip",
+			want:     true,
+		},
+		{
+			name:     "no match",
+			accepted: []string{"deflate"},
+			encoding: "gzip",
+			want:     false,
+		},
+		{
+			name:     "empty list",
+			accepted: []string{""},
+			encoding: "gzip",
+			want:     false,
+		},
+		{
+			name:     "leading space",
+			accepted: []string{" gzip"},
+			encoding: "gzip",
+			want:     true,
+		},
+		{
+			name:     "trailing space",
+			accepted: []string{"gzip "},
+			encoding: "gzip",
+			want:     true,
+		},
+		{
+			name:     "mixed case encoding",
+			accepted: []string{"GZip"},
+			encoding: "gzip",
+			want:     true,
+		},
+		{
+			name:     "br should not match b",
+			accepted: []string{"br"},
+			encoding: "b",
+			want:     false,
+		},
+		{
+			name:     "gzip should not match zip",
+			accepted: []string{"gzip"},
+			encoding: "zip",
+			want:     false,
+		},
+		{
+			name:     "q=0 rejected",
+			accepted: []string{"gzip;q=0"},
+			encoding: "gzip",
+			want:     false,
+		},
+		{
+			name:     "q=0.0 rejected",
+			accepted: []string{"gzip;q=0.0"},
+			encoding: "gzip",
+			want:     false,
+		},
+		{
+			name:     "q=0 with space",
+			accepted: []string{"gzip; q=0"},
+			encoding: "gzip",
+			want:     false,
+		},
+		{
+			name:     "mixed case q=0 rejected",
+			accepted: []string{"gzip; Q=0"},
+			encoding: "gzip",
+			want:     false,
+		},
+		{
+			name:     "q=0.5 accepted",
+			accepted: []string{"gzip;q=0.5"},
+			encoding: "gzip",
+			want:     true,
+		},
+		{
+			name:     "q=1.0 accepted",
+			accepted: []string{"gzip;q=1.0"},
+			encoding: "gzip",
+			want:     true,
+		},
+		{
+			name:     "match on second element",
+			accepted: []string{"deflate", "gzip"},
+			encoding: "gzip",
+			want:     true,
+		},
+		{
+			name:     "q=0 on second element",
+			accepted: []string{"deflate", "gzip;q=0"},
+			encoding: "gzip",
+			want:     false,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := matchAcceptEncoding(tt.accepted, tt.encoding)
+			if got != tt.want {
+				t.Errorf("matchAcceptEncoding(%v, %q) = %v, want %v",
+					tt.accepted, tt.encoding, got, tt.want)
+			}
+		})
+	}
+}
+
 func testRequestWithAcceptedEncodings(t *testing.T, ts *httptest.Server, method, path string, encodings ...string) (*http.Response, string) {
 	req, err := http.NewRequest(method, ts.URL+path, nil)
 	if err != nil {