Merge pull request #68 from wneessen/fix-io-reader

New Reader type

msg.go

@@ -181,6 +181,9 @@ func (m *Msg) Charset() string {
 
 // SetHeader sets a generic header field of the Msg
 func (m *Msg) SetHeader(h Header, v ...string) {
+	if m.genHeader == nil {
+		m.genHeader = make(map[Header][]string)
+	}
 	for i, hv := range v {
 		v[i] = m.encodeString(hv)
 	}
@@ -189,6 +192,9 @@ func (m *Msg) SetHeader(h Header, v ...string) {
 
 // SetAddrHeader sets an address related header field of the Msg
 func (m *Msg) SetAddrHeader(h AddrHeader, v ...string) error {
+	if m.addrHeader == nil {
+		m.addrHeader = make(map[AddrHeader][]*mail.Address)
+	}
 	var al []*mail.Address
 	for _, av := range v {
 		a, err := mail.ParseAddress(av)
@@ -807,14 +813,31 @@ func (m *Msg) WriteToSendmailWithContext(ctx context.Context, sp string, a ...st
 	return nil
 }
 
-// Read outputs the length of p into p to satisfy the io.Reader interface
-func (m *Msg) Read(p []byte) (int, error) {
+// NewReader returns a Reader type that satisfies the io.Reader interface.
+//
+// IMPORTANT: when creating a new Reader, the current state of the Msg is taken, as
+// basis for the Reader. If you perform changes on Msg after creating the Reader, these
+// changes will not be reflected in the Reader. You will have to use Msg.UpdateReader
+// first to update the Reader's buffer with the current Msg content
+func (m *Msg) NewReader() *Reader {
+	r := &Reader{}
 	wbuf := bytes.Buffer{}
-	_, err := m.WriteTo(&wbuf)
+	_, err := m.Write(&wbuf)
 	if err != nil {
-		return 0, fmt.Errorf("failed to write message to internal write buffer: %w", err)
+		r.err = fmt.Errorf("failed to write Msg to Reader buffer: %w", err)
 	}
-	return wbuf.Read(p)
+	r.buf = wbuf.Bytes()
+	return r
+}
+
+// UpdateReader will update a Reader with the content of the given Msg and reset the
+// Reader position to the start
+func (m *Msg) UpdateReader(r *Reader) {
+	wbuf := bytes.Buffer{}
+	_, err := m.Write(&wbuf)
+	r.Reset()
+	r.buf = wbuf.Bytes()
+	r.err = err
 }
 
 // encodeString encodes a string based on the configured message encoder and the corresponding

msg_test.go

@@ -1718,52 +1718,29 @@ 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},
-	}
-
+// TestMsg_NewReader tests the Msg.NewReader method
+func TestMsg_NewReader(t *testing.T) {
 	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)
+	mr := m.NewReader()
+	if mr == nil {
+		t.Errorf("NewReader failed: Reader is nil")
 	}
-	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)
-			}
-		})
+	if mr.Error() != nil {
+		t.Errorf("NewReader failed: %s", mr.Error())
 	}
 }
 
-// TestMsg_Read_ioCopy tests the Msg.Read method using io.Copy
-func TestMsg_Read_ioCopy(t *testing.T) {
+// TestMsg_NewReader_ioCopy tests the Msg.NewReader method using io.Copy
+func TestMsg_NewReader_ioCopy(t *testing.T) {
 	wbuf1 := bytes.Buffer{}
 	wbuf2 := bytes.Buffer{}
 	m := NewMsg()
 	m.SetBodyString(TypeTextPlain, "TEST123")
+	mr := m.NewReader()
+	if mr == nil {
+		t.Errorf("NewReader failed: Reader is nil")
+	}
 
 	// First we use WriteTo to have something to compare to
 	_, err := m.WriteTo(&wbuf1)
@@ -1772,9 +1749,9 @@ func TestMsg_Read_ioCopy(t *testing.T) {
 	}
 
 	// Then we write to wbuf2 via io.Copy
-	n, err := io.Copy(&wbuf2, m)
+	n, err := io.Copy(&wbuf2, mr)
 	if err != nil {
-		t.Errorf("failed to use io.Copy on Msg: %s", err)
+		t.Errorf("failed to use io.Copy on Reader: %s", err)
 	}
 	if n != int64(wbuf1.Len()) {
 		t.Errorf("message length of WriteTo and io.Copy differ. Expected: %d, got: %d", wbuf1.Len(), n)
@@ -1784,6 +1761,37 @@ func TestMsg_Read_ioCopy(t *testing.T) {
 	}
 }
 
+// TestMsg_UpdateReader tests the Msg.UpdateReader method
+func TestMsg_UpdateReader(t *testing.T) {
+	m := NewMsg()
+	m.Subject("Subject-Run 1")
+	mr := m.NewReader()
+	if mr == nil {
+		t.Errorf("NewReader failed: Reader is nil")
+	}
+	wbuf1 := bytes.Buffer{}
+	_, err := io.Copy(&wbuf1, mr)
+	if err != nil {
+		t.Errorf("io.Copy on Reader failed: %s", err)
+	}
+	if !strings.Contains(wbuf1.String(), "Subject: Subject-Run 1") {
+		t.Errorf("io.Copy on Reader failed. Expected to find %q but string in Subject was not found",
+			"Subject-Run 1")
+	}
+
+	m.Subject("Subject-Run 2")
+	m.UpdateReader(mr)
+	wbuf2 := bytes.Buffer{}
+	_, err = io.Copy(&wbuf2, mr)
+	if err != nil {
+		t.Errorf("2nd io.Copy on Reader failed: %s", err)
+	}
+	if !strings.Contains(wbuf2.String(), "Subject: Subject-Run 2") {
+		t.Errorf("io.Copy on Reader failed. Expected to find %q but string in Subject was not found",
+			"Subject-Run 2")
+	}
+}
+
 // TestMsg_SetBodyTextTemplate tests the Msg.SetBodyTextTemplate method
 func TestMsg_SetBodyTextTemplate(t *testing.T) {
 	tests := []struct {

reader.go

@@ -0,0 +1,48 @@
+// SPDX-FileCopyrightText: 2022 Winni Neessen <winni@neessen.dev>
+//
+// SPDX-License-Identifier: MIT
+
+package mail
+
+import (
+	"io"
+)
+
+// Reader is a type that implements the io.Reader interface for a Msg
+type Reader struct {
+	buf []byte // contents are the bytes buf[off : len(buf)]
+	off int    // read at &buf[off], write at &buf[len(buf)]
+	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 {
+		return 0, r.err
+	}
+	if r.empty() {
+		r.Reset()
+		if len(p) == 0 {
+			return 0, nil
+		}
+		return 0, io.EOF
+	}
+	n = copy(p, r.buf[r.off:])
+	r.off += n
+	return n, err
+}
+
+// Reset resets the Reader buffer to be empty, but it retains the underlying storage
+// for use by future writes.
+func (r *Reader) Reset() {
+	r.buf = r.buf[:0]
+	r.off = 0
+}
+
+// empty reports whether the unread portion of the Reader buffer is empty.
+func (r *Reader) empty() bool { return len(r.buf) <= r.off }

reader_test.go

@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: 2022 Winni Neessen <winni@neessen.dev>
+//
+// SPDX-License-Identifier: MIT
+
+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)
+	}
+}