mox!

message/writer.go

@@ -0,0 +1,55 @@
+package message
+
+import (
+	"io"
+)
+
+// Writer is a write-through helper, collecting properties about the written
+// message.
+type Writer struct {
+	Writer      io.Writer
+	HaveHeaders bool
+	Has8bit     bool // Whether a byte with the high/8bit has been read. So whether this is 8BITMIME instead of 7BIT.
+	Size        int64
+	tail        [3]byte // For detecting crlfcrlf.
+	// todo: should be parsing headers here, as we go
+}
+
+// Write implements io.Writer.
+func (w *Writer) Write(buf []byte) (int, error) {
+	if !w.HaveHeaders && len(buf) > 0 {
+		get := func(i int) byte {
+			if i < 0 {
+				return w.tail[3+i]
+			}
+			return buf[i]
+		}
+
+		for i, b := range buf {
+			if b == '\n' && get(i-3) == '\r' && get(i-2) == '\n' && get(i-1) == '\r' {
+				w.HaveHeaders = true
+				break
+			}
+		}
+
+		n := len(buf)
+		if n > 3 {
+			n = 3
+		}
+		copy(w.tail[:], w.tail[n:])
+		copy(w.tail[3-n:], buf[len(buf)-n:])
+	}
+	if !w.Has8bit {
+		for _, b := range buf {
+			if b&0x80 != 0 {
+				w.Has8bit = true
+				break
+			}
+		}
+	}
+	n, err := w.Writer.Write(buf)
+	if n > 0 {
+		w.Size += int64(n)
+	}
+	return n, err
+}