From 95d79341bff3c66c6d32b373994d3a1be26295b9 Mon Sep 17 00:00:00 2001
From: René 'Necoro' Neumann <necoro@necoro.eu>
Date: Mon, 15 Feb 2021 01:28:07 +0100
Subject: Issue #46: Make the resulting email body not to include single \r or
 \n. This now pleases Cyrus IMAP.

---
 internal/feed/mail.go |  5 ++--
 pkg/util/fixWriter.go | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 66 insertions(+), 2 deletions(-)
 create mode 100644 pkg/util/fixWriter.go

diff --git a/internal/feed/mail.go b/internal/feed/mail.go
index 2dda3ca..0bc7d37 100644
--- a/internal/feed/mail.go
+++ b/internal/feed/mail.go
@@ -11,11 +11,11 @@ import (
 	"strings"
 	"time"
 
-	"github.com/jaytaylor/html2text"
 	"github.com/PuerkitoBio/goquery"
 	"github.com/emersion/go-message"
 	"github.com/emersion/go-message/mail"
 	"github.com/gabriel-vasile/mimetype"
+	"github.com/jaytaylor/html2text"
 	"golang.org/x/net/html"
 
 	"github.com/Necoro/feed2imap-go/internal/feed/template"
@@ -23,6 +23,7 @@ import (
 	"github.com/Necoro/feed2imap-go/internal/msg"
 	"github.com/Necoro/feed2imap-go/pkg/config"
 	"github.com/Necoro/feed2imap-go/pkg/log"
+	"github.com/Necoro/feed2imap-go/pkg/util"
 	"github.com/Necoro/feed2imap-go/pkg/version"
 )
 
@@ -97,7 +98,7 @@ func (item *item) writeContentPart(w *message.Writer, typ string, tpl template.T
 	}
 	defer partW.Close()
 
-	if err = tpl.Execute(w, item); err != nil {
+	if err = tpl.Execute(util.FixWriter(w), item); err != nil {
 		return fmt.Errorf("writing %s part: %w", typ, err)
 	}
 
diff --git a/pkg/util/fixWriter.go b/pkg/util/fixWriter.go
new file mode 100644
index 0000000..51637eb
--- /dev/null
+++ b/pkg/util/fixWriter.go
@@ -0,0 +1,63 @@
+package util
+
+import "io"
+
+type fixWriter struct {
+	w io.Writer
+}
+
+var lf = []byte{'\n'}
+var cr = []byte{'\r'}
+
+func (f fixWriter) Write(p []byte) (n int, err error) {
+	crFound := false
+	start := 0
+
+	write := func(str []byte) {
+		var j int
+		j, err = f.w.Write(str)
+		n = n + j
+	}
+
+	for idx, b := range p {
+		if crFound && b != '\n' {
+			// insert '\n'
+			if write(p[start:idx]); err != nil {
+				return
+			}
+			if write(lf); err != nil {
+				return
+			}
+
+			start = idx
+		} else if !crFound && b == '\n' {
+			// insert '\r'
+			if write(p[start:idx]); err != nil {
+				return
+			}
+			if write(cr); err != nil {
+				return
+			}
+
+			start = idx
+		}
+		crFound = b == '\r'
+	}
+
+	// write the remainder
+	if write(p[start:]); err != nil {
+		return
+	}
+
+	if crFound { // dangling \r
+		write(lf)
+	}
+
+	return
+}
+
+// Cyrus IMAP really cares about single \r and \n.
+// Implement this fixer to change them into \r\n.
+func FixWriter(w io.Writer) io.Writer {
+	return &fixWriter{w}
+}
-- 
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