1 files changed, 44 insertions, 0 deletions
diff --git a/format/packfile/ingest/fill.go b/format/packfile/ingest/fill.go
new file mode 100644
index 00000000..eca4e4d6
--- /dev/null
+++ b/format/packfile/ingest/fill.go
@@ -0,0 +1,44 @@
+package ingest
+
+import (
+	"errors"
+	"fmt"
+	"io"
+)
+
+// fill ensures at least min unread bytes are available in receiver's buffer.
+func (scanner *streamScanner) fill(minLen int) error {
+	if minLen <= 0 {
+		return nil
+	}
+
+	if minLen > len(scanner.buf) {
+		return fmt.Errorf("packfile/ingest: fill(%d) exceeds scanner buffer", minLen)
+	}
+
+	for scanner.n-scanner.off < minLen {
+		err := scanner.flushConsumedPrefix()
+		if err != nil {
+			return err
+		}
+
+		readN, err := scanner.src.Read(scanner.buf[scanner.n:])
+		if readN > 0 {
+			scanner.n += readN
+		}
+
+		if err != nil {
+			if errors.Is(err, io.EOF) && scanner.n-scanner.off >= minLen {
+				return nil
+			}
+
+			return err
+		}
+
+		if readN == 0 {
+			return io.ErrNoProgress
+		}
+	}
+
+	return nil
+}