// Copyright 2010 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
//
/*
Package multipart implements MIME multipart parsing, as defined in RFC
2046.
The implementation is sufficient for HTTP (RFC 2388) and the multipart
bodies generated by popular browsers.
*/
package multipart
import (
"bufio"
"bytes"
"fmt"
"io"
"io/ioutil"
"mime"
"mime/quotedprintable"
"net/textproto"
"strings"
)
var emptyParams = make(map[string]string)
// This constant needs to be at least 76 for this package to work correctly.
// This is because \r\n--separator_of_len_70- would fill the buffer and it
// wouldn't be safe to consume a single byte from it.
const peekBufferSize = 4096
// A Part represents a single part in a multipart body.
type Part struct {
// The headers of the body, if any, with the keys canonicalized
// in the same fashion that the Go http.Request headers are.
// For example, "foo-bar" changes case to "Foo-Bar"
//
// As a special case, if the "Content-Transfer-Encoding" header
// has a value of "quoted-printable", that header is instead
// hidden from this map and the body is transparently decoded
// during Read calls.
Header textproto.MIMEHeader
mr *Reader
disposition string
dispositionParams map[string]string
// r is either a reader directly reading from mr, or it's a
// wrapper around such a reader, decoding the
// Content-Transfer-Encoding
r io.Reader
n int // known data bytes waiting in mr.bufReader
total int64 // total data bytes read already
err error // error to return when n == 0
readErr error // read error observed from mr.bufReader
}
// FormName returns the name parameter if p has a Content-Disposition
// of type "form-data". Otherwise it returns the empty string.
func (p *Part) FormName() string {
// See https://tools.ietf.org/html/rfc2183 section 2 for EBNF
// of Content-Disposition value format.
if p.dispositionParams == nil {
p.parseContentDisposition()
}
if p.disposition != "form-data" {
return ""
}
return p.dispositionParams["name"]
}
// FileName returns the filename parameter of the Part's
// Content-Disposition header.
func (p *Part) FileName() string {
if p.dispositionParams == nil {
p.parseContentDisposition()
}
return p.dispositionParams["filename"]
}
func (p *Part) parseContentDisposition() {
v := p.Header.Get("Content-Disposition")
var err error
p.disposition, p.dispositionParams, err = mime.ParseMediaType(v)
if err != nil {
p.dispositionParams = emptyParams
}
}
// NewReader creates a new multipart Reader reading from r using the
// given MIME boundary.
//
// The boundary is usually obtained from the "boundary" parameter of
// the message's "Content-Type" header. Use mime.ParseMediaType to
// parse such headers.
func NewReader(r io.Reader, boundary string) *Reader {
b := []byte("\r\n--" + boundary + "--")
return &Reader{
bufReader: bufio.NewReaderSize(&stickyErrorReader{r: r}, peekBufferSize),
nl: b[:2],
nlDashBoundary: b[:len(b)-2],
dashBoundaryDash: b[2:],
dashBoundary: b[2 : len(b)-2],
}
}
// stickyErrorReader is an io.Reader which never calls Read on its
// underlying Reader once an error has been seen. (the io.Reader
// interface's contract promises nothing about the return values of
// Read calls after an error, yet this package does do multiple Reads
// after error)
type stickyErrorReader struct {
r io.Reader
err error
}
func (r *stickyErrorReader) Read(p []byte) (n int, _ error) {
if r.err != nil {
return 0, r.err
}
n, r.err = r.r.Read(p)
return n, r.err
}
func newPart(mr *Reader) (*Part, error) {
bp := &Part{
Header: make(map[string][]string),
mr: mr,
}
if err := bp.populateHeaders(); err != nil {
return nil, err
}
bp.r = partReader{bp}
const cte = "Content-Transfer-Encoding"
if strings.EqualFold(bp.Header.Get(cte), "quoted-printable") {
bp.Header.Del(cte)
bp.r = quotedprintable.NewReader(bp.r)
}
return bp, nil
}
func (bp *Part) populateHeaders() error {
r := textproto.NewReader(bp.mr.bufReader)
header, err := r.ReadMIMEHeader()
if err == nil {
bp.Header = header
}
return err
}
// Read reads the body of a part, after its headers and before the
// next part (if any) begins.
func (p *Part) Read(d []byte) (n int, err error) {
return p.r.Read(d)
}
// partReader implements io.Reader by reading raw bytes directly from the
// wrapped *Part, without doing any Transfer-Encoding decoding.
type partReader struct {
p *Part
}
func (pr partReader) Read(d []byte) (int, error) {
p := pr.p
br := p.mr.bufReader
// Read into buffer until we identify some data to return,
// or we find a reason to stop (boundary or read error).
for p.n == 0 && p.err == nil {
peek, _ := br.Peek(br.Buffered())
p.n, p.err = scanUntilBoundary(peek, p.mr.dashBoundary, p.mr.nlDashBoundary, p.total, p.readErr)
if p.n == 0 && p.err == nil {
// Force buffered I/O to read more into buffer.
_, p.readErr = br.Peek(len(peek) + 1)
if p.readErr == io.EOF {
p.readErr = io.ErrUnexpectedEOF
}
}
}
// Read out from "data to return" part of buffer.
if p.n == 0 {
return 0, p.err
}
n := len(d)
if n > p.n {
n = p.n
}
n, _ = br.Read(d[:n])
p.total += int64(n)
p.n -= n
if p.n == 0 {
return n, p.err
}
return n, nil
}
// scanUntilBoundary scans buf to identify how much of it can be safely
// returned as part of the Part body.
// dashBoundary is "--boundary".
// nlDashBoundary is "\r\n--boundary" or "\n--boundary", depending on what mode we are in.
// The comments below (and the name) assume "\n--boundary", but either is accepted.
// total is the number of bytes read out so far. If total == 0, then a leading "--boundary" is recognized.
// readErr is the read error, if any, that followed reading the bytes in buf.
// scanUntilBoundary returns the number of data bytes from buf that can be
// returned as part of the Part body and also the error to return (if any)
// once those data bytes are done.
func scanUntilBoundary(buf, dashBoundary, nlDashBoundary []byte, total int64, readErr error) (int, error) {
if total == 0 {
// At beginning of body, allow dashBoundary.
if bytes.HasPrefix(buf, dashBoundary) {
switch matchAfterPrefix(buf, dashBoundary, readErr) {
case -1:
return len(dashBoundary), nil
case 0:
return 0, nil
case +1:
return 0, io.EOF
}
}
if bytes.HasPrefix(dashBoundary, buf) {
return 0, readErr
}
}
// Search for "\n--boundary".
if i := bytes.Index(buf, nlDashBoundary); i >= 0 {
switch matchAfterPrefix(buf[i:], nlDashBoundary, readErr) {
case -1:
return i + len(nlDashBoundary), nil
case 0:
return i, nil
case +1:
return i, io.EOF
}
}
if bytes.HasPrefix(nlDashBoundary, buf) {
return 0, readErr
}
// Otherwise, anything up to the final \n is not part of the boundary
// and so must be part of the body.
// Also if the section from the final \n onward is not a prefix of the boundary,
// it too must be part of the body.
i := bytes.LastIndexByte(buf, nlDashBoundary[0])
if i >= 0 && bytes.HasPrefix(nlDashBoundary, buf[i:]) {
return i, nil
}
return len(buf), readErr
}
// matchAfterPrefix checks whether buf should be considered to match the boundary.
// The prefix is "--boundary" or "\r\n--boundary" or "\n--boundary",
// and the caller has verified already that bytes.HasPrefix(buf, prefix) is true.
//
// matchAfterPrefix returns +1 if the buffer does match the boundary,
// meaning the prefix is followed by a dash, space, tab, cr, nl, or end of input.
// It returns -1 if the buffer definitely does NOT match the boundary,
// meaning the prefix is followed by some other character.
// For example, "--foobar" does not match "--foo".
// It returns 0 more input needs to be read to make the decision,
// meaning that len(buf) == len(prefix) and readErr == nil.
func matchAfterPrefix(buf, prefix []byte, readErr error) int {
if len(buf) == len(prefix) {
if readErr != nil {
return +1
}
return 0
}
c := buf[len(prefix)]
if c == ' ' || c == '\t' || c == '\r' || c == '\n' || c == '-' {
return +1
}
return -1
}
func (p *Part) Close() error {
io.Copy(ioutil.Discard, p)
return nil
}
// Reader is an iterator over parts in a MIME multipart body.
// Reader's underlying parser consumes its input as needed. Seeking
// isn't supported.
type Reader struct {
bufReader *bufio.Reader
currentPart *Part
partsRead int
nl []byte // "\r\n" or "\n" (set after seeing first boundary line)
nlDashBoundary []byte // nl + "--boundary"
dashBoundaryDash []byte // "--boundary--"
dashBoundary []byte // "--boundary"
}
// NextPart returns the next part in the multipart or an error.
// When there are no more parts, the error io.EOF is returned.
func (r *Reader) NextPart() (*Part, error) {
if r.currentPart != nil {
r.currentPart.Close()
}
if string(r.dashBoundary) == "--" {
return nil, fmt.Errorf("multipart: boundary is empty")
}
expectNewPart := false
for {
line, err := r.bufReader.ReadSlice('\n')
if err == io.EOF && r.isFinalBoundary(line) {
// If the buffer ends in "--boundary--" without the
// trailing "\r\n", ReadSlice will return an error
// (since it's missing the '\n'), but this is a valid
// multipart EOF so we need to return io.EOF instead of
// a fmt-wrapped one.
return nil, io.EOF
}
if err != nil {
return nil, fmt.Errorf("multipart: NextPart: %v", err)
}
if r.isBoundaryDelimiterLine(line) {
r.partsRead++
bp, err := newPart(r)
if err != nil {
return nil, err
}
r.currentPart = bp
return bp, nil
}
if r.isFinalBoundary(line) {
// Expected EOF
return nil, io.EOF
}
if expectNewPart {
return nil, fmt.Errorf("multipart: expecting a new Part; got line %q", string(line))
}
if r.partsRead == 0 {
// skip line
continue
}
// Consume the "\n" or "\r\n" separator between the
// body of the previous part and the boundary line we
// now expect will follow. (either a new part or the
// end boundary)
if bytes.Equal(line, r.nl) {
expectNewPart = true
continue
}
return nil, fmt.Errorf("multipart: unexpected line in Next(): %q", line)
}
}
// isFinalBoundary reports whether line is the final boundary line
// indicating that all parts are over.
// It matches `^--boundary--[ \t]*(\r\n)?$`
func (mr *Reader) isFinalBoundary(line []byte) bool {
if !bytes.HasPrefix(line, mr.dashBoundaryDash) {
return false
}
rest := line[len(mr.dashBoundaryDash):]
rest = skipLWSPChar(rest)
return len(rest) == 0 || bytes.Equal(rest, mr.nl)
}
func (mr *Reader) isBoundaryDelimiterLine(line []byte) (ret bool) {
// https://tools.ietf.org/html/rfc2046#section-5.1
// The boundary delimiter line is then defined as a line
// consisting entirely of two hyphen characters ("-",
// decimal value 45) followed by the boundary parameter
// value from the Content-Type header field, optional linear
// whitespace, and a terminating CRLF.
if !bytes.HasPrefix(line, mr.dashBoundary) {
return false
}
rest := line[len(mr.dashBoundary):]
rest = skipLWSPChar(rest)
// On the first part, see our lines are ending in \n instead of \r\n
// and switch into that mode if so. This is a violation of the spec,
// but occurs in practice.
if mr.partsRead == 0 && len(rest) == 1 && rest[0] == '\n' {
mr.nl = mr.nl[1:]
mr.nlDashBoundary = mr.nlDashBoundary[1:]
}
return bytes.Equal(rest, mr.nl)
}
// skipLWSPChar returns b with leading spaces and tabs removed.
// RFC 822 defines:
// LWSP-char = SPACE / HTAB
func skipLWSPChar(b []byte) []byte {
for len(b) > 0 && (b[0] == ' ' || b[0] == '\t') {
b = b[1:]
}
return b
}
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