go-mail/msgwriter.go

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// SPDX-FileCopyrightText: 2022-2023 The go-mail Authors
//
// SPDX-License-Identifier: MIT
package mail
import (
"bytes"
"encoding/base64"
"fmt"
"io"
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"mime"
"mime/multipart"
"mime/quotedprintable"
"net/textproto"
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"path/filepath"
"sort"
"strings"
)
// MaxHeaderLength defines the maximum line length for a mail header
// RFC 2047 suggests 76 characters
const MaxHeaderLength = 76
// MaxBodyLength defines the maximum line length for the mail body
// RFC 2047 suggests 76 characters
const MaxBodyLength = 76
// SingleNewLine represents a new line that can be used by the msgWriter to issue a carriage return
const SingleNewLine = "\r\n"
// DoubleNewLine represents a double new line that can be used by the msgWriter to
// indicate a new segement of the mail
const DoubleNewLine = "\r\n\r\n"
// msgWriter handles the I/O to the io.WriteCloser of the SMTP client
type msgWriter struct {
bytesWritten int64
charset Charset
depth int8
encoder mime.WordEncoder
err error
multiPartWriter [3]*multipart.Writer
partWriter io.Writer
writer io.Writer
}
// Write implements the io.Writer interface for msgWriter
func (mw *msgWriter) Write(payload []byte) (int, error) {
if mw.err != nil {
return 0, fmt.Errorf("failed to write due to previous error: %w", mw.err)
}
var n int
n, mw.err = mw.writer.Write(payload)
mw.bytesWritten += int64(n)
return n, mw.err
}
// writeMsg formats the message and sends it to its io.Writer
func (mw *msgWriter) writeMsg(msg *Msg) {
msg.addDefaultHeader()
msg.checkUserAgent()
mw.writeGenHeader(msg)
mw.writePreformattedGenHeader(msg)
// Set the FROM header (or envelope FROM if FROM is empty)
hasFrom := true
from, ok := msg.addrHeader[HeaderFrom]
if !ok || (len(from) == 0 || from == nil) {
from, ok = msg.addrHeader[HeaderEnvelopeFrom]
if !ok || (len(from) == 0 || from == nil) {
hasFrom = false
}
}
if hasFrom && (len(from) > 0 && from[0] != nil) {
mw.writeHeader(Header(HeaderFrom), from[0].String())
}
// Set the rest of the address headers
for _, to := range []AddrHeader{HeaderTo, HeaderCc} {
if addresses, ok := msg.addrHeader[to]; ok {
var val []string
for _, addr := range addresses {
val = append(val, addr.String())
}
mw.writeHeader(Header(to), val...)
}
}
if msg.hasMixed() {
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mw.startMP(MIMEMixed, msg.boundary)
mw.writeString(DoubleNewLine)
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}
if msg.hasRelated() {
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mw.startMP(MIMERelated, msg.boundary)
mw.writeString(DoubleNewLine)
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}
if msg.hasAlt() {
mw.startMP(MIMEAlternative, msg.boundary)
mw.writeString(DoubleNewLine)
}
if msg.hasPGPType() {
switch msg.pgptype {
case PGPEncrypt:
mw.startMP(`encrypted; protocol="application/pgp-encrypted"`,
msg.boundary)
case PGPSignature:
mw.startMP(`signed; protocol="application/pgp-signature";`,
msg.boundary)
default:
}
mw.writeString(DoubleNewLine)
}
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for _, part := range msg.parts {
if !part.isDeleted {
mw.writePart(part, msg.charset)
}
}
if msg.hasAlt() {
mw.stopMP()
}
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// Add embeds
mw.addFiles(msg.embeds, false)
if msg.hasRelated() {
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mw.stopMP()
}
// Add attachments
mw.addFiles(msg.attachments, true)
if msg.hasMixed() {
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mw.stopMP()
}
}
// writeGenHeader writes out all generic headers to the msgWriter
func (mw *msgWriter) writeGenHeader(msg *Msg) {
keys := make([]string, 0, len(msg.genHeader))
for key := range msg.genHeader {
keys = append(keys, string(key))
}
sort.Strings(keys)
for _, key := range keys {
mw.writeHeader(Header(key), msg.genHeader[Header(key)]...)
}
}
// writePreformatedHeader writes out all preformated generic headers to the msgWriter
func (mw *msgWriter) writePreformattedGenHeader(msg *Msg) {
for key, val := range msg.preformHeader {
mw.writeString(fmt.Sprintf("%s: %s%s", key, val, SingleNewLine))
}
}
// startMP writes a multipart beginning
func (mw *msgWriter) startMP(mimeType MIMEType, boundary string) {
multiPartWriter := multipart.NewWriter(mw)
if boundary != "" {
mw.err = multiPartWriter.SetBoundary(boundary)
}
contentType := fmt.Sprintf("multipart/%s;\r\n boundary=%s", mimeType,
multiPartWriter.Boundary())
mw.multiPartWriter[mw.depth] = multiPartWriter
if mw.depth == 0 {
mw.writeString(fmt.Sprintf("%s: %s", HeaderContentType, contentType))
}
if mw.depth > 0 {
mw.newPart(map[string][]string{"Content-Type": {contentType}})
}
mw.depth++
}
// stopMP closes the multipart
func (mw *msgWriter) stopMP() {
if mw.depth > 0 {
mw.err = mw.multiPartWriter[mw.depth-1].Close()
mw.depth--
}
}
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// addFiles adds the attachments/embeds file content to the mail body
func (mw *msgWriter) addFiles(files []*File, isAttachment bool) {
for _, file := range files {
encoding := EncodingB64
if _, ok := file.getHeader(HeaderContentType); !ok {
mimeType := mime.TypeByExtension(filepath.Ext(file.Name))
if mimeType == "" {
mimeType = "application/octet-stream"
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}
if file.ContentType != "" {
mimeType = string(file.ContentType)
}
file.setHeader(HeaderContentType, fmt.Sprintf(`%s; name="%s"`, mimeType,
mw.encoder.Encode(mw.charset.String(), file.Name)))
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}
if _, ok := file.getHeader(HeaderContentTransferEnc); !ok {
if file.Enc != "" {
encoding = file.Enc
}
file.setHeader(HeaderContentTransferEnc, string(encoding))
}
if file.Desc != "" {
if _, ok := file.getHeader(HeaderContentDescription); !ok {
file.setHeader(HeaderContentDescription, file.Desc)
}
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}
if _, ok := file.getHeader(HeaderContentDisposition); !ok {
disposition := "inline"
if isAttachment {
disposition = "attachment"
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}
file.setHeader(HeaderContentDisposition, fmt.Sprintf(`%s; filename="%s"`,
disposition, mw.encoder.Encode(mw.charset.String(), file.Name)))
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}
if !isAttachment {
if _, ok := file.getHeader(HeaderContentID); !ok {
file.setHeader(HeaderContentID, fmt.Sprintf("<%s>", file.Name))
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}
}
if mw.depth == 0 {
for header, val := range file.Header {
mw.writeHeader(Header(header), val...)
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}
mw.writeString(SingleNewLine)
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}
if mw.depth > 0 {
mw.newPart(file.Header)
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}
if mw.err == nil {
mw.writeBody(file.Writer, encoding)
}
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}
}
// newPart creates a new MIME multipart io.Writer and sets the partwriter to it
func (mw *msgWriter) newPart(header map[string][]string) {
mw.partWriter, mw.err = mw.multiPartWriter[mw.depth-1].CreatePart(header)
}
// writePart writes the corresponding part to the Msg body
func (mw *msgWriter) writePart(part *Part, charset Charset) {
partCharset := part.charset
if partCharset.String() == "" {
partCharset = charset
}
contentType := fmt.Sprintf("%s; charset=%s", part.contentType, partCharset)
contentTransferEnc := part.encoding.String()
if mw.depth == 0 {
mw.writeHeader(HeaderContentType, contentType)
mw.writeHeader(HeaderContentTransferEnc, contentTransferEnc)
mw.writeString(SingleNewLine)
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}
if mw.depth > 0 {
mimeHeader := textproto.MIMEHeader{}
if part.description != "" {
mimeHeader.Add(string(HeaderContentDescription), part.description)
}
mimeHeader.Add(string(HeaderContentType), contentType)
mimeHeader.Add(string(HeaderContentTransferEnc), contentTransferEnc)
mw.newPart(mimeHeader)
}
mw.writeBody(part.writeFunc, part.encoding)
}
// writeString writes a string into the msgWriter's io.Writer interface
func (mw *msgWriter) writeString(s string) {
if mw.err != nil {
return
}
var n int
n, mw.err = io.WriteString(mw.writer, s)
mw.bytesWritten += int64(n)
}
// writeHeader writes a header into the msgWriter's io.Writer
func (mw *msgWriter) writeHeader(key Header, values ...string) {
buffer := strings.Builder{}
charLength := MaxHeaderLength - 2
buffer.WriteString(string(key))
charLength -= len(key)
if len(values) == 0 {
buffer.WriteString(":\r\n")
return
}
buffer.WriteString(": ")
charLength -= 2
fullValueStr := strings.Join(values, ", ")
words := strings.Split(fullValueStr, " ")
for i, val := range words {
if charLength-len(val) <= 1 {
buffer.WriteString(fmt.Sprintf("%s ", SingleNewLine))
charLength = MaxHeaderLength - 3
}
buffer.WriteString(val)
if i < len(words)-1 {
buffer.WriteString(" ")
charLength -= 1
}
charLength -= len(val)
}
bufferString := buffer.String()
bufferString = strings.ReplaceAll(bufferString, fmt.Sprintf(" %s", SingleNewLine),
SingleNewLine)
mw.writeString(bufferString)
mw.writeString("\r\n")
}
// writeBody writes an io.Reader into an io.Writer using provided Encoding
func (mw *msgWriter) writeBody(writeFunc func(io.Writer) (int64, error), encoding Encoding) {
var writer io.Writer
var encodedWriter io.WriteCloser
var n int64
var err error
if mw.depth == 0 {
writer = mw.writer
}
if mw.depth > 0 {
writer = mw.partWriter
}
writeBuffer := bytes.Buffer{}
lineBreaker := Base64LineBreaker{}
lineBreaker.out = &writeBuffer
switch encoding {
case EncodingQP:
encodedWriter = quotedprintable.NewWriter(&writeBuffer)
case EncodingB64:
encodedWriter = base64.NewEncoder(base64.StdEncoding, &lineBreaker)
case NoEncoding:
_, err = writeFunc(&writeBuffer)
if err != nil {
mw.err = fmt.Errorf("bodyWriter function: %w", err)
}
n, err = io.Copy(writer, &writeBuffer)
if err != nil && mw.err == nil {
mw.err = fmt.Errorf("bodyWriter io.Copy: %w", err)
}
if mw.depth == 0 {
mw.bytesWritten += n
}
return
default:
encodedWriter = quotedprintable.NewWriter(writer)
}
_, err = writeFunc(encodedWriter)
if err != nil {
mw.err = fmt.Errorf("bodyWriter function: %w", err)
}
err = encodedWriter.Close()
if err != nil && mw.err == nil {
mw.err = fmt.Errorf("bodyWriter close encoded writer: %w", err)
}
err = lineBreaker.Close()
if err != nil && mw.err == nil {
mw.err = fmt.Errorf("bodyWriter close linebreaker: %w", err)
}
n, err = io.Copy(writer, &writeBuffer)
if err != nil && mw.err == nil {
mw.err = fmt.Errorf("bodyWriter io.Copy: %w", err)
}
// Since the part writer uses the WriteTo() method, we don't need to add the
// bytes twice
if mw.depth == 0 {
mw.bytesWritten += n
}
}