1 files changed, 145 insertions, 0 deletions
diff --git a/format/pktline/encoder.go b/format/pktline/encoder.go
new file mode 100644
index 00000000..b4c6dbf0
--- /dev/null
+++ b/format/pktline/encoder.go
@@ -0,0 +1,145 @@
+package pktline
+
+import (
+	"fmt"
+	"io"
+)
+
+// WriteFlusher is the output transport contract required by Encoder.
+//
+// Write emits framed bytes and Flush pushes buffered transport state.
+type WriteFlusher interface {
+	io.Writer
+	Flush() error
+}
+
+// Encoder writes pkt-line frames to a flush-capable output transport.
+//
+// It writes exactly one frame per method call and does not auto-chunk data.
+type Encoder struct {
+	w       WriteFlusher
+	maxData int
+}
+
+// NewEncoder creates an encoder over w.
+func NewEncoder(w WriteFlusher) *Encoder {
+	return &Encoder{
+		w:       w,
+		maxData: LargePacketDataMax,
+	}
+}
+
+// SetMaxData sets the maximum payload size accepted by WriteData.
+//
+// Non-positive n resets to LargePacketDataMax.
+func (e *Encoder) SetMaxData(n int) {
+	if n <= 0 {
+		e.maxData = LargePacketDataMax
+
+		return
+	}
+
+	e.maxData = n
+}
+
+func writeAll(w io.Writer, b []byte) error {
+	for len(b) > 0 {
+		n, err := w.Write(b)
+		if err != nil {
+			return err
+		}
+
+		if n <= 0 {
+			return io.ErrShortWrite
+		}
+
+		b = b[n:]
+	}
+
+	return nil
+}
+
+// WriteData writes one data frame.
+//
+// Empty payload is encoded as 0004.
+func (e *Encoder) WriteData(p []byte) error {
+	maxData := e.effectiveMaxData()
+	if len(p) > maxData {
+		return fmt.Errorf("%w: %d > %d", ErrTooLarge, len(p), maxData)
+	}
+
+	var hdr [4]byte
+
+	err := EncodeLengthHeader(&hdr, len(p)+4)
+	if err != nil {
+		return err
+	}
+
+	err = writeAll(e.w, hdr[:])
+	if err != nil {
+		return err
+	}
+
+	return writeAll(e.w, p)
+}
+
+// WriteString writes one data frame containing s and returns len(s) on success.
+func (e *Encoder) WriteString(s string) (int, error) {
+	err := e.WriteData([]byte(s))
+	if err != nil {
+		return 0, err
+	}
+
+	return len(s), nil
+}
+
+// WriteFlush writes control frame 0000 (flush-pkt).
+func (e *Encoder) WriteFlush() error {
+	return e.writeControl(0)
+}
+
+// WriteDelim writes control frame 0001 (delim-pkt).
+func (e *Encoder) WriteDelim() error {
+	return e.writeControl(1)
+}
+
+// WriteResponseEnd writes control frame 0002 (response-end-pkt).
+func (e *Encoder) WriteResponseEnd() error {
+	return e.writeControl(2)
+}
+
+// FlushIO flushes buffered output in the underlying transport.
+//
+// FlushIO does not emit any pkt-line control frame.
+func (e *Encoder) FlushIO() error {
+	return e.w.Flush()
+}
+
+// WriteFlushAndFlushIO writes a flush-pkt (0000) then flushes transport I/O.
+func (e *Encoder) WriteFlushAndFlushIO() error {
+	err := e.WriteFlush()
+	if err != nil {
+		return err
+	}
+
+	return e.FlushIO()
+}
+
+func (e *Encoder) writeControl(n int) error {
+	var hdr [4]byte
+
+	err := EncodeLengthHeader(&hdr, n)
+	if err != nil {
+		return err
+	}
+
+	return writeAll(e.w, hdr[:])
+}
+
+func (e *Encoder) effectiveMaxData() int {
+	if e.maxData <= 0 || e.maxData > LargePacketDataMax {
+		return LargePacketDataMax
+	}
+
+	return e.maxData
+}