feat(transcode): add a generic transcoding package for encoding/decoding/caching

server/ctrlsubsonic/httprange/httprange.go

@@ -0,0 +1,59 @@
+package httprange
+
+import (
+	"fmt"
+	"regexp"
+	"strconv"
+)
+
+type Unit string
+
+const (
+	UnitBytes Unit = "bytes"
+)
+
+//nolint:gochecknoglobals
+var (
+	reg   = regexp.MustCompile(`^(?P<unit>\w+)=(?P<start>(?:\d+)?)\s*-\s*(?P<end>(?:\d+)?)$`)
+	unit  = reg.SubexpIndex("unit")
+	start = reg.SubexpIndex("start")
+	end   = reg.SubexpIndex("end")
+)
+
+var (
+	ErrInvalidRange = fmt.Errorf("invalid range")
+	ErrUnknownUnit  = fmt.Errorf("unknown range")
+)
+
+type Range struct {
+	Start, End, Length int // bytes
+	Partial            bool
+}
+
+func Parse(in string, fullLength int) (Range, error) {
+	parts := reg.FindStringSubmatch(in)
+	if len(parts)-1 != reg.NumSubexp() {
+		return Range{0, fullLength - 1, fullLength, false}, nil
+	}
+
+	switch unit := parts[unit]; Unit(unit) {
+	case UnitBytes:
+	default:
+		return Range{}, fmt.Errorf("%q: %w", unit, ErrUnknownUnit)
+	}
+
+	start, _ := strconv.Atoi(parts[start])
+	end, _ := strconv.Atoi(parts[end])
+	length := fullLength
+	partial := false
+
+	switch {
+	case end > 0 && end < length:
+		length = end - start + 1
+		partial = true
+	case end == 0 && length > 0:
+		end = length - 1
+	}
+
+	return Range{start, end, length, partial}, nil
+}