Use original header bytes instead of printing parsed forms.

cmd/addhashheader/addhashheader.go

@@ -1,6 +1,7 @@
 package main
 
 import (
+	"bytes"
 	"flag"
 	"fmt"
 	"io"
@@ -16,7 +17,8 @@ func main() {
 	flag.Parse()
 	defer glog.Flush()
 
-	msg, err := mail.ReadMessage(os.Stdin)
+	hdrBuf := new(bytes.Buffer)
+	msg, err := mail.ReadMessage(io.TeeReader(os.Stdin, hdrBuf))
 	if err != nil {
 		glog.Fatal(err)
 	}
@@ -25,12 +27,20 @@ func main() {
 	if err != nil {
 		glog.Fatal(err)
 	}
-	for k, vs := range msg.Header {
-		for _, v := range vs {
-			fmt.Printf("%s: %s\n", k, v)
+	// Find end of header in original byte stream.
+	n := bytes.Index(hdrBuf.Bytes(), []byte("\n\n"))
+	if n == -1 {
+		glog.Error("Couldn't find end of headers in hdrBuf")
+		// Copy the original message untouched.
+		io.Copy(os.Stdout, hdrBuf)
+		io.Copy(os.Stdout, os.Stdin)
+		return
 	}
-	}
-	fmt.Println("X-Xinu-Hash:", h)
-	fmt.Println()
+
+	// Copy the headers out untouched.
+	io.CopyN(os.Stdout, hdrBuf, int64(n))
+	// Insert our new header.
+	fmt.Printf("\nX-Xinu-Hash: %s\n\n", h)
+	// Copy the message body out untouched.
 	io.Copy(os.Stdout, msg.Body)
 }