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