1 files changed, 40 insertions, 0 deletions
diff --git a/format/sideband64k/append.go b/format/sideband64k/append.go
new file mode 100644
index 00000000..59dbdf43
--- /dev/null
+++ b/format/sideband64k/append.go
@@ -0,0 +1,40 @@
+package sideband64k
+
+import (
+	"fmt"
+
+	"codeberg.org/lindenii/furgit/format/pktline"
+)
+
+// AppendBand appends one side-band-64k data frame to dst.
+func AppendBand(dst []byte, band Band, payload []byte) ([]byte, error) {
+	if !validBand(band) {
+		return dst, fmt.Errorf("%w: %d", ErrInvalidBand, band)
+	}
+
+	maxData := effectiveMaxData(DataMax)
+	if len(payload) > maxData {
+		return dst, fmt.Errorf("%w: %d > %d", ErrTooLarge, len(payload), maxData)
+	}
+
+	framed := make([]byte, len(payload)+1)
+	framed[0] = byte(band)
+	copy(framed[1:], payload)
+
+	return pktline.AppendData(dst, framed)
+}
+
+// AppendData appends one band-1 data frame to dst.
+func AppendData(dst, payload []byte) ([]byte, error) {
+	return AppendBand(dst, BandData, payload)
+}
+
+// AppendProgress appends one band-2 progress frame to dst.
+func AppendProgress(dst, payload []byte) ([]byte, error) {
+	return AppendBand(dst, BandProgress, payload)
+}
+
+// AppendError appends one band-3 error frame to dst.
+func AppendError(dst, payload []byte) ([]byte, error) {
+	return AppendBand(dst, BandError, payload)
+}