1 files changed, 72 insertions, 0 deletions
diff --git a/plugins/static/etag.go b/plugins/static/etag.go
new file mode 100644
index 00000000..5ee0d2f3
--- /dev/null
+++ b/plugins/static/etag.go
@@ -0,0 +1,72 @@
+package static
+
+import (
+	"hash/crc32"
+	"io"
+	"net/http"
+
+	"github.com/spiral/roadrunner/v2/utils"
+)
+
+const etag string = "Etag"
+
+// weak Etag prefix
+var weakPrefix = []byte(`W/`)
+
+// CRC32 table
+var crc32q = crc32.MakeTable(0x48D90782)
+
+// SetEtag sets etag for the file
+func SetEtag(weak bool, f http.File, name string, w http.ResponseWriter) {
+	// preallocate
+	calculatedEtag := make([]byte, 0, 64)
+
+	// write weak
+	if weak {
+		calculatedEtag = append(calculatedEtag, weakPrefix...)
+		calculatedEtag = append(calculatedEtag, '"')
+		calculatedEtag = appendUint(calculatedEtag, crc32.Checksum(utils.AsBytes(name), crc32q))
+		calculatedEtag = append(calculatedEtag, '"')
+
+		w.Header().Set(etag, utils.AsString(calculatedEtag))
+		return
+	}
+
+	// read the file content
+	body, err := io.ReadAll(f)
+	if err != nil {
+		return
+	}
+
+	// skip for 0 body
+	if len(body) == 0 {
+		return
+	}
+
+	calculatedEtag = append(calculatedEtag, '"')
+	calculatedEtag = appendUint(calculatedEtag, uint32(len(body)))
+	calculatedEtag = append(calculatedEtag, '-')
+	calculatedEtag = appendUint(calculatedEtag, crc32.Checksum(body, crc32q))
+	calculatedEtag = append(calculatedEtag, '"')
+
+	w.Header().Set(etag, utils.AsString(calculatedEtag))
+}
+
+// appendUint appends n to dst and returns the extended dst.
+func appendUint(dst []byte, n uint32) []byte {
+	var b [20]byte
+	buf := b[:]
+	i := len(buf)
+	var q uint32
+	for n >= 10 {
+		i--
+		q = n / 10
+		buf[i] = '0' + byte(n-q*10)
+		n = q
+	}
+	i--
+	buf[i] = '0' + byte(n)
+
+	dst = append(dst, buf[i:]...)
+	return dst
+}