Finalized the Reader type and removed the broken Read() method

msg.go

@@ -840,16 +840,6 @@ func (m *Msg) UpdateReader(r *Reader) {
 	r.err = err
 }
 
-// Read outputs the length of p into p to satisfy the io.Reader interface
-func (m *Msg) Read(p []byte) (int, error) {
-	wbuf := bytes.Buffer{}
-	_, err := m.WriteTo(&wbuf)
-	if err != nil {
-		return 0, fmt.Errorf("failed to write message to internal write buffer: %w", err)
-	}
-	return wbuf.Read(p)
-}
-
 // encodeString encodes a string based on the configured message encoder and the corresponding
 // charset for the Msg
 func (m *Msg) encodeString(s string) string {

msg_test.go

@@ -1718,72 +1718,6 @@ func TestMsg_multipleWrites(t *testing.T) {
 	}
 }
 
-// TestMsg_Read tests the Msg.Read method that implements the io.Reader interface
-func TestMsg_Read(t *testing.T) {
-	tests := []struct {
-		name string
-		plen int
-	}{
-		{"P length is bigger than the mail", 32000},
-		{"P length is smaller than the mail", 128},
-	}
-
-	m := NewMsg()
-	m.SetBodyString(TypeTextPlain, "TEST123")
-	wbuf := bytes.Buffer{}
-	_, err := m.Write(&wbuf)
-	if err != nil {
-		t.Errorf("failed to write message into temporary buffer: %s", err)
-	}
-	elen := wbuf.Len()
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			p := make([]byte, tt.plen)
-			n, err := m.Read(p)
-			if err != nil {
-				t.Errorf("failed to Read(): %s", err)
-			}
-			if n == 0 {
-				t.Errorf("failed to Read() - received 0 bytes of data")
-			}
-			if tt.plen >= elen && n != elen {
-				t.Errorf("failed to Read() - not all data received. Expected: %d, got: %d", elen, n)
-			}
-			if tt.plen < elen && n != tt.plen {
-				t.Errorf("failed to Read() - full length of p wasn't filled with data. Expected: %d, got: %d",
-					tt.plen, n)
-			}
-		})
-	}
-}
-
-// TestMsg_Read_ioCopy tests the Msg.Read method using io.Copy
-func TestMsg_Read_ioCopy(t *testing.T) {
-	wbuf1 := bytes.Buffer{}
-	wbuf2 := bytes.Buffer{}
-	m := NewMsg()
-	m.SetBodyString(TypeTextPlain, "TEST123")
-
-	// First we use WriteTo to have something to compare to
-	_, err := m.WriteTo(&wbuf1)
-	if err != nil {
-		t.Errorf("failed to write body to buffer: %s", err)
-	}
-
-	// Then we write to wbuf2 via io.Copy
-	n, err := io.Copy(&wbuf2, m)
-	if err != nil {
-		t.Errorf("failed to use io.Copy on Msg: %s", err)
-	}
-	if n != int64(wbuf1.Len()) {
-		t.Errorf("message length of WriteTo and io.Copy differ. Expected: %d, got: %d", wbuf1.Len(), n)
-	}
-	if wbuf1.String() != wbuf2.String() {
-		t.Errorf("message content of WriteTo and io.Copy differ")
-	}
-}
-
 // TestMsg_NewReader tests the Msg.NewReader method
 func TestMsg_NewReader(t *testing.T) {
 	m := NewMsg()
@@ -1792,14 +1726,8 @@ func TestMsg_NewReader(t *testing.T) {
 	if mr == nil {
 		t.Errorf("NewReader failed: Reader is nil")
 	}
-}
-
-// TestMsg_NewReader_broken tests the Msg.NewReader method error handling
-func TestMsg_NewReader_broken(t *testing.T) {
-	m := &Msg{}
-	mr := m.NewReader()
-	if mr == nil {
-		t.Errorf("NewReader failed: Reader is nil")
+	if mr.Error() != nil {
+		t.Errorf("NewReader failed: %s", mr.Error())
 	}
 }
 

reader.go

@@ -15,6 +15,11 @@ type Reader struct {
 	err error  // initalization error
 }
 
+// Error returns an error if the Reader err field is not nil
+func (r *Reader) Error() error {
+	return r.err
+}
+
 // Read reads the length of p of the Msg buffer to satisfy the io.Reader interface
 func (r *Reader) Read(p []byte) (n int, err error) {
 	if r.err != nil {

reader_test.go

@@ -0,0 +1,68 @@
+package mail
+
+import (
+	"bytes"
+	"fmt"
+	"testing"
+)
+
+// TestReader_Read tests the Reader.Read method that implements the io.Reader interface
+func TestReader_Read(t *testing.T) {
+	tests := []struct {
+		name string
+		plen int
+	}{
+		{"P length is bigger than the mail", 3200000},
+		{"P length is smaller than the mail", 128},
+	}
+
+	m := NewMsg()
+	m.SetBodyString(TypeTextPlain, "TEST123")
+	wbuf := bytes.Buffer{}
+	_, err := m.Write(&wbuf)
+	if err != nil {
+		t.Errorf("failed to write message into temporary buffer: %s", err)
+	}
+	elen := wbuf.Len()
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			p := make([]byte, tt.plen)
+			mr := m.NewReader()
+			n, err := mr.Read(p)
+			if err != nil {
+				t.Errorf("failed to Read(): %s", err)
+			}
+			if n == 0 {
+				t.Errorf("failed to Read() - received 0 bytes of data")
+			}
+			if tt.plen >= elen && n != elen {
+				t.Errorf("failed to Read() - not all data received. Expected: %d, got: %d", elen, n)
+			}
+			if tt.plen < elen && n != tt.plen {
+				t.Errorf("failed to Read() - full length of p wasn't filled with data. Expected: %d, got: %d",
+					tt.plen, n)
+			}
+		})
+	}
+}
+
+// TestReader_Read_error tests the Reader.Read method with an intentional error
+func TestReader_Read_error(t *testing.T) {
+	r := Reader{err: fmt.Errorf("FAILED")}
+	var p []byte
+	_, err := r.Read(p)
+	if err == nil {
+		t.Errorf("Reader was supposed to fail, but didn't")
+	}
+}
+
+// TestReader_Read_empty tests the Reader.Read method with an empty buffer
+func TestReader_Read_empty(t *testing.T) {
+	r := Reader{buf: []byte{}}
+	var p []byte
+	_, err := r.Read(p)
+	if err != nil {
+		t.Errorf("Reader failed: %s", err)
+	}
+}