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eml.go
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eml.go
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// SPDX-FileCopyrightText: 2022-2023 The go-mail Authors
//
// SPDX-License-Identifier: MIT
package mail
import (
"bytes"
"encoding/base64"
"errors"
"fmt"
"io"
"mime"
"mime/multipart"
"mime/quotedprintable"
netmail "net/mail"
"os"
"strings"
)
// EMLToMsgFromString will parse a given EML string and returns a pre-filled Msg pointer
func EMLToMsgFromString(emlString string) (*Msg, error) {
eb := bytes.NewBufferString(emlString)
return EMLToMsgFromReader(eb)
}
// EMLToMsgFromReader will parse a reader that holds EML content and returns a pre-filled
// Msg pointer
func EMLToMsgFromReader(reader io.Reader) (*Msg, error) {
msg := &Msg{
addrHeader: make(map[AddrHeader][]*netmail.Address),
genHeader: make(map[Header][]string),
preformHeader: make(map[Header]string),
mimever: MIME10,
}
parsedMsg, bodybuf, err := readEMLFromReader(reader)
if err != nil || parsedMsg == nil {
return msg, fmt.Errorf("failed to parse EML from reader: %w", err)
}
if err := parseEML(parsedMsg, bodybuf, msg); err != nil {
return msg, fmt.Errorf("failed to parse EML contents: %w", err)
}
return msg, nil
}
// EMLToMsgFromFile will open and parse a .eml file at a provided file path and returns a
// pre-filled Msg pointer
func EMLToMsgFromFile(filePath string) (*Msg, error) {
msg := &Msg{
addrHeader: make(map[AddrHeader][]*netmail.Address),
genHeader: make(map[Header][]string),
preformHeader: make(map[Header]string),
mimever: MIME10,
}
parsedMsg, bodybuf, err := readEML(filePath)
if err != nil || parsedMsg == nil {
return msg, fmt.Errorf("failed to parse EML file: %w", err)
}
if err := parseEML(parsedMsg, bodybuf, msg); err != nil {
return msg, fmt.Errorf("failed to parse EML contents: %w", err)
}
return msg, nil
}
// parseEML parses the EML's headers and body and inserts the parsed values into the Msg
func parseEML(parsedMsg *netmail.Message, bodybuf *bytes.Buffer, msg *Msg) error {
if err := parseEMLHeaders(&parsedMsg.Header, msg); err != nil {
return fmt.Errorf("failed to parse EML headers: %w", err)
}
if err := parseEMLBodyParts(parsedMsg, bodybuf, msg); err != nil {
return fmt.Errorf("failed to parse EML body parts: %w", err)
}
return nil
}
// readEML opens an EML file and uses net/mail to parse the header and body
func readEML(filePath string) (*netmail.Message, *bytes.Buffer, error) {
fileHandle, err := os.Open(filePath)
if err != nil {
return nil, nil, fmt.Errorf("failed to open EML file: %w", err)
}
defer func() {
_ = fileHandle.Close()
}()
return readEMLFromReader(fileHandle)
}
// readEMLFromReader uses net/mail to parse the header and body from a given io.Reader
func readEMLFromReader(reader io.Reader) (*netmail.Message, *bytes.Buffer, error) {
parsedMsg, err := netmail.ReadMessage(reader)
if err != nil {
return parsedMsg, nil, fmt.Errorf("failed to parse EML: %w", err)
}
buf := bytes.Buffer{}
if _, err = buf.ReadFrom(parsedMsg.Body); err != nil {
return nil, nil, err
}
return parsedMsg, &buf, nil
}
// parseEMLHeaders will check the EML headers for the most common headers and set the
// according settings in the Msg
func parseEMLHeaders(mailHeader *netmail.Header, msg *Msg) error {
commonHeaders := []Header{
HeaderContentType, HeaderImportance, HeaderInReplyTo, HeaderListUnsubscribe,
HeaderListUnsubscribePost, HeaderMessageID, HeaderMIMEVersion, HeaderOrganization,
HeaderPrecedence, HeaderPriority, HeaderReferences, HeaderSubject, HeaderUserAgent,
HeaderXMailer, HeaderXMSMailPriority, HeaderXPriority,
}
// Extract content type, charset and encoding first
parseEMLEncoding(mailHeader, msg)
parseEMLContentTypeCharset(mailHeader, msg)
// Extract address headers
if value := mailHeader.Get(HeaderFrom.String()); value != "" {
if err := msg.From(value); err != nil {
return fmt.Errorf(`failed to parse %q header: %w`, HeaderFrom, err)
}
}
addrHeaders := map[AddrHeader]func(...string) error{
HeaderTo: msg.To,
HeaderCc: msg.Cc,
HeaderBcc: msg.Bcc,
}
for addrHeader, addrFunc := range addrHeaders {
if v := mailHeader.Get(addrHeader.String()); v != "" {
var addrStrings []string
parsedAddrs, err := netmail.ParseAddressList(v)
if err != nil {
return fmt.Errorf(`failed to parse address list: %w`, err)
}
for _, addr := range parsedAddrs {
addrStrings = append(addrStrings, addr.String())
}
if err = addrFunc(addrStrings...); err != nil {
return fmt.Errorf(`failed to parse %q header: %w`, addrHeader, err)
}
}
}
// Extract date from message
date, err := mailHeader.Date()
if err != nil {
switch {
case errors.Is(err, netmail.ErrHeaderNotPresent):
msg.SetDate()
default:
return fmt.Errorf("failed to parse EML date: %w", err)
}
}
if err == nil {
msg.SetDateWithValue(date)
}
// Extract common headers
for _, header := range commonHeaders {
if value := mailHeader.Get(header.String()); value != "" {
if strings.EqualFold(header.String(), HeaderContentType.String()) &&
strings.HasPrefix(value, TypeMultipartMixed.String()) {
continue
}
msg.SetGenHeader(header, value)
}
}
return nil
}
// parseEMLBodyParts parses the body of a EML based on the different content types and encodings
func parseEMLBodyParts(parsedMsg *netmail.Message, bodybuf *bytes.Buffer, msg *Msg) error {
// Extract the transfer encoding of the body
mediatype, params, err := mime.ParseMediaType(parsedMsg.Header.Get(HeaderContentType.String()))
if err != nil {
switch {
// If no Content-Type header is found, we assume that this is a plain text, 7bit, US-ASCII mail
case strings.EqualFold(err.Error(), "mime: no media type"):
mediatype = TypeTextPlain.String()
params = make(map[string]string)
params["charset"] = CharsetASCII.String()
default:
return fmt.Errorf("failed to extract content type: %w", err)
}
}
if value, ok := params["charset"]; ok {
msg.SetCharset(Charset(value))
}
switch {
case strings.EqualFold(mediatype, TypeTextPlain.String()),
strings.EqualFold(mediatype, TypeTextHTML.String()):
if err = parseEMLBodyPlain(mediatype, parsedMsg, bodybuf, msg); err != nil {
return fmt.Errorf("failed to parse plain body: %w", err)
}
case strings.EqualFold(mediatype, TypeMultipartAlternative.String()),
strings.EqualFold(mediatype, TypeMultipartMixed.String()),
strings.EqualFold(mediatype, TypeMultipartRelated.String()):
if err = parseEMLMultipart(params, bodybuf, msg); err != nil {
return fmt.Errorf("failed to parse multipart body: %w", err)
}
default:
return fmt.Errorf("failed to parse body, unknown content type: %s", mediatype)
}
return nil
}
// parseEMLBodyPlain parses the mail body of plain type mails
func parseEMLBodyPlain(mediatype string, parsedMsg *netmail.Message, bodybuf *bytes.Buffer, msg *Msg) error {
contentTransferEnc := parsedMsg.Header.Get(HeaderContentTransferEnc.String())
// According to RFC2045, if no Content-Transfer-Encoding is set, we can imply 7bit US-ASCII encoding
if contentTransferEnc == "" || strings.EqualFold(contentTransferEnc, EncodingUSASCII.String()) {
msg.SetEncoding(EncodingUSASCII)
msg.SetBodyString(ContentType(mediatype), bodybuf.String())
return nil
}
if strings.EqualFold(contentTransferEnc, NoEncoding.String()) {
msg.SetEncoding(NoEncoding)
msg.SetBodyString(ContentType(mediatype), bodybuf.String())
return nil
}
if strings.EqualFold(contentTransferEnc, EncodingQP.String()) {
msg.SetEncoding(EncodingQP)
qpReader := quotedprintable.NewReader(bodybuf)
qpBuffer := bytes.Buffer{}
if _, err := qpBuffer.ReadFrom(qpReader); err != nil {
return fmt.Errorf("failed to read quoted-printable body: %w", err)
}
msg.SetBodyString(ContentType(mediatype), qpBuffer.String())
return nil
}
if strings.EqualFold(contentTransferEnc, EncodingB64.String()) {
msg.SetEncoding(EncodingB64)
b64Decoder := base64.NewDecoder(base64.StdEncoding, bodybuf)
b64Buffer := bytes.Buffer{}
if _, err := b64Buffer.ReadFrom(b64Decoder); err != nil {
return fmt.Errorf("failed to read base64 body: %w", err)
}
msg.SetBodyString(ContentType(mediatype), b64Buffer.String())
return nil
}
return fmt.Errorf("unsupported Content-Transfer-Encoding")
}
// parseEMLMultipart parses a multipart body part of a EML
func parseEMLMultipart(params map[string]string, bodybuf *bytes.Buffer, msg *Msg) error {
boundary, ok := params["boundary"]
if !ok {
return fmt.Errorf("no boundary tag found in multipart body")
}
multipartReader := multipart.NewReader(bodybuf, boundary)
ReadNextPart:
multiPart, err := multipartReader.NextPart()
defer func() {
if multiPart != nil {
_ = multiPart.Close()
}
}()
if err != nil && !errors.Is(err, io.EOF) {
return fmt.Errorf("failed to get next part of multipart message: %w", err)
}
for err == nil {
// Multipart/related and Multipart/alternative parts need to be parsed seperately
if contentTypeSlice, ok := multiPart.Header[HeaderContentType.String()]; ok && len(contentTypeSlice) == 1 {
contentType, _ := parseMultiPartHeader(contentTypeSlice[0])
if strings.EqualFold(contentType, TypeMultipartRelated.String()) ||
strings.EqualFold(contentType, TypeMultipartAlternative.String()) {
relatedPart := &netmail.Message{
Header: netmail.Header(multiPart.Header),
Body: multiPart,
}
relatedBuf := &bytes.Buffer{}
if _, err = relatedBuf.ReadFrom(multiPart); err != nil {
return fmt.Errorf("failed to read related multipart message to buffer: %w", err)
}
if err := parseEMLBodyParts(relatedPart, relatedBuf, msg); err != nil {
return fmt.Errorf("failed to parse related multipart body: %w", err)
}
}
}
// Content-Disposition header means we have an attachment or embed
if contentDisposition, ok := multiPart.Header[HeaderContentDisposition.String()]; ok {
if err = parseEMLAttachmentEmbed(contentDisposition, multiPart, msg); err != nil {
return fmt.Errorf("failed to parse attachment/embed: %w", err)
}
goto ReadNextPart
}
multiPartData, mperr := io.ReadAll(multiPart)
if mperr != nil {
_ = multiPart.Close()
return fmt.Errorf("failed to read multipart: %w", err)
}
multiPartContentType, ok := multiPart.Header[HeaderContentType.String()]
if !ok {
return fmt.Errorf("failed to get content-type from part")
}
contentType, optional := parseMultiPartHeader(multiPartContentType[0])
if strings.EqualFold(contentType, TypeMultipartRelated.String()) {
goto ReadNextPart
}
part := msg.newPart(ContentType(contentType))
if charset, ok := optional["charset"]; ok {
part.SetCharset(Charset(charset))
}
mutliPartTransferEnc, ok := multiPart.Header[HeaderContentTransferEnc.String()]
if !ok {
// If CTE is empty we can assume that it's a quoted-printable CTE since the
// GO stdlib multipart packages deletes that header
// See: https://cs.opensource.google/go/go/+/refs/tags/go1.22.0:src/mime/multipart/multipart.go;l=161
mutliPartTransferEnc = []string{EncodingQP.String()}
}
switch {
case strings.EqualFold(mutliPartTransferEnc[0], EncodingUSASCII.String()):
part.SetEncoding(EncodingUSASCII)
part.SetContent(string(multiPartData))
case strings.EqualFold(mutliPartTransferEnc[0], NoEncoding.String()):
part.SetEncoding(NoEncoding)
part.SetContent(string(multiPartData))
case strings.EqualFold(mutliPartTransferEnc[0], EncodingB64.String()):
part.SetEncoding(EncodingB64)
if err = handleEMLMultiPartBase64Encoding(multiPartData, part); err != nil {
return fmt.Errorf("failed to handle multipart base64 transfer-encoding: %w", err)
}
case strings.EqualFold(mutliPartTransferEnc[0], EncodingQP.String()):
part.SetEncoding(EncodingQP)
part.SetContent(string(multiPartData))
default:
return fmt.Errorf("unsupported Content-Transfer-Encoding: %s", mutliPartTransferEnc[0])
}
msg.parts = append(msg.parts, part)
multiPart, err = multipartReader.NextPart()
}
if !errors.Is(err, io.EOF) {
return fmt.Errorf("failed to read multipart: %w", err)
}
return nil
}
// parseEMLEncoding parses and determines the encoding of the message
func parseEMLEncoding(mailHeader *netmail.Header, msg *Msg) {
if value := mailHeader.Get(HeaderContentTransferEnc.String()); value != "" {
switch {
case strings.EqualFold(value, EncodingQP.String()):
msg.SetEncoding(EncodingQP)
case strings.EqualFold(value, EncodingB64.String()):
msg.SetEncoding(EncodingB64)
default:
msg.SetEncoding(NoEncoding)
}
}
}
// parseEMLContentTypeCharset parses and determines the charset and content type of the message
func parseEMLContentTypeCharset(mailHeader *netmail.Header, msg *Msg) {
if value := mailHeader.Get(HeaderContentType.String()); value != "" {
contentType, optional := parseMultiPartHeader(value)
if charset, ok := optional["charset"]; ok {
msg.SetCharset(Charset(charset))
}
msg.setEncoder()
if contentType != "" && !strings.EqualFold(contentType, TypeMultipartMixed.String()) {
msg.SetGenHeader(HeaderContentType, contentType)
}
}
}
// handleEMLMultiPartBase64Encoding sets the content body of a base64 encoded Part
func handleEMLMultiPartBase64Encoding(multiPartData []byte, part *Part) error {
part.SetEncoding(EncodingB64)
content, err := base64.StdEncoding.DecodeString(string(multiPartData))
if err != nil {
return fmt.Errorf("failed to decode base64 part: %w", err)
}
part.SetContent(string(content))
return nil
}
// parseMultiPartHeader parses a multipart header and returns the value and optional parts as
// separate map
func parseMultiPartHeader(multiPartHeader string) (header string, optional map[string]string) {
optional = make(map[string]string)
headerSplit := strings.SplitN(multiPartHeader, ";", 2)
header = headerSplit[0]
if len(headerSplit) == 2 {
optString := strings.TrimLeft(headerSplit[1], " ")
optSplit := strings.SplitN(optString, "=", 2)
if len(optSplit) == 2 {
optional[optSplit[0]] = optSplit[1]
}
}
return
}
// parseEMLAttachmentEmbed parses a multipart that is an attachment or embed
func parseEMLAttachmentEmbed(contentDisposition []string, multiPart *multipart.Part, msg *Msg) error {
cdType, optional := parseMultiPartHeader(contentDisposition[0])
filename := "generic.attachment"
if name, ok := optional["filename"]; ok {
filename = name[1 : len(name)-1]
}
var dataReader io.Reader
dataReader = multiPart
contentTransferEnc, _ := parseMultiPartHeader(multiPart.Header.Get(HeaderContentTransferEnc.String()))
b64Decoder := base64.NewDecoder(base64.StdEncoding, multiPart)
if strings.EqualFold(contentTransferEnc, EncodingB64.String()) {
dataReader = b64Decoder
}
switch strings.ToLower(cdType) {
case "attachment":
if err := msg.AttachReader(filename, dataReader); err != nil {
return fmt.Errorf("failed to attach multipart body: %w", err)
}
case "inline":
if contentID, _ := parseMultiPartHeader(multiPart.Header.Get(HeaderContentID.String())); contentID != "" {
if err := msg.EmbedReader(filename, dataReader, WithFileContentID(contentID)); err != nil {
return fmt.Errorf("failed to embed multipart body: %w", err)
}
return nil
}
if err := msg.EmbedReader(filename, dataReader); err != nil {
return fmt.Errorf("failed to embed multipart body: %w", err)
}
}
return nil
}