feat: image variants engine

internal/domain/image/variantRequest.go

@@ -0,0 +1,54 @@
+package image
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"strings"
+)
+
+const etagDigestLength = 32
+
+type VariantRequestError struct {
+	cause  error
+	Detail string
+}
+
+func NewUnknownVariantError(name string) error {
+	return VariantRequestError{cause: ErrUnknownVariant, Detail: name}
+}
+
+func NewUnsupportedParameterError(parameter string) error {
+	return VariantRequestError{cause: ErrUnsupportedParameter, Detail: parameter}
+}
+
+func (e VariantRequestError) Error() string {
+	return e.cause.Error() + ": " + e.Detail
+}
+
+func (e VariantRequestError) Unwrap() error {
+	return e.cause
+}
+
+func VariantRequestDetail(err error) string {
+	var requestError VariantRequestError
+	if errors.As(err, &requestError) {
+		return requestError.Detail
+	}
+	return ""
+}
+
+func VariantETag(settings VariantSettings, sourceName string) string {
+	digest := sha256.Sum256([]byte(settings.Fingerprint() + "|" + sourceName))
+	return `"` + hex.EncodeToString(digest[:])[:etagDigestLength] + `"`
+}
+
+func ETagMatches(ifNoneMatch string, etag string) bool {
+	for _, candidate := range strings.Split(ifNoneMatch, ",") {
+		trimmed := strings.TrimPrefix(strings.TrimSpace(candidate), "W/")
+		if trimmed == "*" || trimmed == etag {
+			return true
+		}
+	}
+	return false
+}