objectheader: Add loose-object header parsing and emitting code

1 files changed, 40 insertions, 0 deletions

diff --git a/internal/objectheader/parse.go b/internal/objectheader/parse.go
new file mode 100644
index 00000000..c3d7d5dd
--- /dev/null
+++ b/internal/objectheader/parse.go
@@ -0,0 +1,40 @@
+package objectheader
+
+import (
+	"bytes"
+	"strconv"
+
+	"codeberg.org/lindenii/furgit/objecttype"
+)
+
+// Parse parses a canonical loose-object header ("type size\\x00").
+// It returns the parsed type, size, bytes consumed (including trailing NUL),
+// and whether parsing succeeded.
+func Parse(data []byte) (objecttype.Type, int64, int, bool) {
+	space := bytes.IndexByte(data, ' ')
+	if space <= 0 {
+		return objecttype.TypeInvalid, 0, 0, false
+	}
+
+	nulRel := bytes.IndexByte(data[space+1:], 0)
+	if nulRel < 0 {
+		return objecttype.TypeInvalid, 0, 0, false
+	}
+	nul := space + 1 + nulRel
+
+	ty, ok := objecttype.ParseName(string(data[:space]))
+	if !ok {
+		return objecttype.TypeInvalid, 0, 0, false
+	}
+
+	sizeBytes := data[space+1 : nul]
+	if len(sizeBytes) == 0 {
+		return objecttype.TypeInvalid, 0, 0, false
+	}
+	size, err := strconv.ParseInt(string(sizeBytes), 10, 64)
+	if err != nil || size < 0 {
+		return objecttype.TypeInvalid, 0, 0, false
+	}
+
+	return ty, size, nul + 1, true
+}