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header.go
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package enmime
import (
"bufio"
"bytes"
"errors"
"fmt"
"io"
"mime"
"net/textproto"
"strings"
)
const (
// Standard MIME content dispositions
cdAttachment = "attachment"
cdInline = "inline"
// Standard MIME content types
ctAppOctetStream = "application/octet-stream"
ctMultipartAltern = "multipart/alternative"
ctMultipartPrefix = "multipart/"
ctTextPlain = "text/plain"
ctTextHTML = "text/html"
// Standard MIME header names
hnContentDisposition = "Content-Disposition"
hnContentEncoding = "Content-Transfer-Encoding"
hnContentType = "Content-Type"
// Standard MIME header parameters
hpBoundary = "boundary"
hpCharset = "charset"
hpFile = "file"
hpFilename = "filename"
hpName = "name"
)
var errEmptyHeaderBlock = errors.New("empty header block")
// AddressHeaders is the set of SMTP headers that contain email addresses, used by
// Envelope.AddressList(). Key characters must be all lowercase.
var AddressHeaders = map[string]bool{
"bcc": true,
"cc": true,
"delivered-to": true,
"from": true,
"reply-to": true,
"to": true,
"sender": true,
"resent-bcc": true,
"resent-cc": true,
"resent-from": true,
"resent-reply-to": true,
"resent-to": true,
"resent-sender": true,
}
func debug(format string, args ...interface{}) {
if false {
fmt.Printf(format, args...)
fmt.Println()
}
}
// Terminology from RFC 2047:
// encoded-word: the entire =?charset?encoding?encoded-text?= string
// charset: the character set portion of the encoded word
// encoding: the character encoding type used for the encoded-text
// encoded-text: the text we are decoding
// readHeader reads a block of SMTP or MIME headers and returns a textproto.MIMEHeader.
// Header parse warnings & errors will be added to p.Errors, io errors will be returned directly.
func readHeader(r *bufio.Reader, p *Part) (textproto.MIMEHeader, error) {
// buf holds the massaged output for textproto.Reader.ReadMIMEHeader()
buf := &bytes.Buffer{}
tp := textproto.NewReader(r)
firstHeader := true
for {
// Pull out each line of the headers as a temporary slice s
s, err := tp.ReadLineBytes()
if err != nil {
if err == io.ErrUnexpectedEOF && buf.Len() == 0 {
return nil, errEmptyHeaderBlock
} else if err == io.EOF {
buf.Write([]byte{'\r', '\n'})
break
}
return nil, err
}
firstColon := bytes.IndexByte(s, ':')
firstSpace := bytes.IndexAny(s, " \t\n\r")
if firstSpace == 0 {
// Starts with space: continuation
buf.WriteByte(' ')
buf.Write(textproto.TrimBytes(s))
continue
}
if firstColon == 0 {
// Can't parse line starting with colon: skip
p.addError(errorMalformedHeader, "Header line %q started with a colon", s)
continue
}
if firstColon > 0 {
// Contains a colon, treat as a new header line
if !firstHeader {
// New Header line, end the previous
buf.Write([]byte{'\r', '\n'})
}
s = textproto.TrimBytes(s)
buf.Write(s)
firstHeader = false
} else {
// No colon: potential non-indented continuation
if len(s) > 0 {
// Attempt to detect and repair a non-indented continuation of previous line
buf.WriteByte(' ')
buf.Write(s)
p.addWarning(errorMalformedHeader, "Continued line %q was not indented", s)
} else {
// Empty line, finish header parsing
buf.Write([]byte{'\r', '\n'})
break
}
}
}
buf.Write([]byte{'\r', '\n'})
tr := textproto.NewReader(bufio.NewReader(buf))
header, err := tr.ReadMIMEHeader()
return header, err
}
// decodeHeader decodes a single line (per RFC 2047) using Golang's mime.WordDecoder
func decodeHeader(input string) string {
if !strings.Contains(input, "=?") {
// Don't scan if there is nothing to do here
return input
}
dec := new(mime.WordDecoder)
dec.CharsetReader = newCharsetReader
header, err := dec.DecodeHeader(input)
if err != nil {
return input
}
return header
}
// decodeToUTF8Base64Header decodes a MIME header per RFC 2047, reencoding to =?utf-8b?
func decodeToUTF8Base64Header(input string) string {
if !strings.Contains(input, "=?") {
// Don't scan if there is nothing to do here
return input
}
debug("input = %q", input)
tokens := strings.FieldsFunc(input, isWhiteSpaceRune)
output := make([]string, len(tokens), len(tokens))
for i, token := range tokens {
if len(token) > 4 && strings.Contains(token, "=?") {
// Stash parenthesis, they should not be encoded
prefix := ""
suffix := ""
if token[0] == '(' {
prefix = "("
token = token[1:]
}
if token[len(token)-1] == ')' {
suffix = ")"
token = token[:len(token)-1]
}
// Base64 encode token
output[i] = prefix + mime.BEncoding.Encode("UTF-8", decodeHeader(token)) + suffix
} else {
output[i] = token
}
debug("%v %q %q", i, token, output[i])
}
// Return space separated tokens
return strings.Join(output, " ")
}
// Detects a RFC-822 linear-white-space, passed to strings.FieldsFunc
func isWhiteSpaceRune(r rune) bool {
switch r {
case ' ':
return true
case '\t':
return true
case '\r':
return true
case '\n':
return true
default:
return false
}
}