From ffc086e75f6a9d8b4873a3c882fd5b301cd69914 Mon Sep 17 00:00:00 2001
From: Winni Neessen <wn@neessen.net>
Date: Thu, 8 Sep 2022 11:47:11 +0200
Subject: [PATCH] #42: Better test coverage for b64linebreaker.go. Also we
 return errors now

---
 b64linebreaker.go      | 18 +++++++++++++-----
 b64linebreaker_test.go | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/b64linebreaker.go b/b64linebreaker.go
index ff99696..ecad47d 100644
--- a/b64linebreaker.go
+++ b/b64linebreaker.go
@@ -4,7 +4,12 @@
 
 package mail
 
-import "io"
+import (
+	"fmt"
+	"io"
+)
+
+const ErrNoOutWriter = "no io.Writer set for Base64LineBreaker"
 
 // Base64LineBreaker is a io.WriteCloser that writes Base64 encoded data streams
 // with line breaks at a given line length
@@ -19,6 +24,9 @@ var nl = []byte(SingleNewLine)
 // Write writes the data stream and inserts a SingleNewLine when the maximum
 // line length is reached
 func (l *Base64LineBreaker) Write(b []byte) (n int, err error) {
+	if l.out == nil {
+		return 0, fmt.Errorf(ErrNoOutWriter)
+	}
 	if l.used+len(b) < MaxBodyLength {
 		copy(l.line[l.used:], b)
 		l.used += len(b)
@@ -27,19 +35,19 @@ func (l *Base64LineBreaker) Write(b []byte) (n int, err error) {
 
 	n, err = l.out.Write(l.line[0:l.used])
 	if err != nil {
-		return
+		return 0, err
 	}
 	excess := MaxBodyLength - l.used
 	l.used = 0
 
 	n, err = l.out.Write(b[0:excess])
 	if err != nil {
-		return
+		return 0, err
 	}
 
 	n, err = l.out.Write(nl)
 	if err != nil {
-		return
+		return 0, err
 	}
 
 	return l.Write(b[excess:])
@@ -51,7 +59,7 @@ func (l *Base64LineBreaker) Close() (err error) {
 	if l.used > 0 {
 		_, err = l.out.Write(l.line[0:l.used])
 		if err != nil {
-			return
+			return err
 		}
 		_, err = l.out.Write(nl)
 	}
diff --git a/b64linebreaker_test.go b/b64linebreaker_test.go
index 05c61c3..f2b3891 100644
--- a/b64linebreaker_test.go
+++ b/b64linebreaker_test.go
@@ -7,6 +7,7 @@ package mail
 import (
 	"bytes"
 	"encoding/base64"
+	"fmt"
 	"io"
 	"os"
 	"testing"
@@ -410,6 +411,31 @@ func TestBase64LineBreaker(t *testing.T) {
 	}
 }
 
+// TestBase64LineBreakerFailures tests the cases in which the Base64LineBreaker would fail
+func TestBase64LineBreakerFailures(t *testing.T) {
+	stt := []byte("short")
+	ltt := []byte(logoB64)
+
+	// No output writer defined
+	lb := Base64LineBreaker{}
+	if _, err := lb.Write(stt); err == nil {
+		t.Errorf("writing to Base64LineBreaker with no output io.Writer was supposed to failed, but didn't")
+	}
+	if err := lb.Close(); err != nil {
+		t.Errorf("failed to close Base64LineBreaker: %s", err)
+	}
+
+	// Closed output writer
+	wbuf := errorWriter{}
+	fb := Base64LineBreaker{out: wbuf}
+	if _, err := fb.Write(ltt); err == nil {
+		t.Errorf("writing to Base64LineBreaker with errorWriter was supposed to failed, but didn't")
+	}
+	if err := fb.Close(); err != nil {
+		t.Errorf("failed to close Base64LineBreaker: %s", err)
+	}
+}
+
 // removeNewLines removes any newline characters from the given data
 func removeNewLines(data []byte) []byte {
 	result := make([]byte, len(data))
@@ -425,3 +451,13 @@ func removeNewLines(data []byte) []byte {
 
 	return result[0:n]
 }
+
+type errorWriter struct{}
+
+func (e errorWriter) Write([]byte) (int, error) {
+	return 0, fmt.Errorf("supposed to always fail")
+}
+
+func (e errorWriter) Close() error {
+	return fmt.Errorf("supposed to always fail")
+}