Source file src/pkg/mime/multipart/multipart.go

     1	// Copyright 2010 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	//
     5	
     6	/*
     7	Package multipart implements MIME multipart parsing, as defined in RFC
     8	2046.
     9	
    10	The implementation is sufficient for HTTP (RFC 2388) and the multipart
    11	bodies generated by popular browsers.
    12	*/
    13	package multipart
    14	
    15	import (
    16		"bufio"
    17		"bytes"
    18		"fmt"
    19		"io"
    20		"io/ioutil"
    21		"mime"
    22		"net/textproto"
    23	)
    24	
    25	var emptyParams = make(map[string]string)
    26	
    27	// A Part represents a single part in a multipart body.
    28	type Part struct {
    29		// The headers of the body, if any, with the keys canonicalized
    30		// in the same fashion that the Go http.Request headers are.
    31		// For example, "foo-bar" changes case to "Foo-Bar"
    32		//
    33		// As a special case, if the "Content-Transfer-Encoding" header
    34		// has a value of "quoted-printable", that header is instead
    35		// hidden from this map and the body is transparently decoded
    36		// during Read calls.
    37		Header textproto.MIMEHeader
    38	
    39		buffer    *bytes.Buffer
    40		mr        *Reader
    41		bytesRead int
    42	
    43		disposition       string
    44		dispositionParams map[string]string
    45	
    46		// r is either a reader directly reading from mr, or it's a
    47		// wrapper around such a reader, decoding the
    48		// Content-Transfer-Encoding
    49		r io.Reader
    50	}
    51	
    52	// FormName returns the name parameter if p has a Content-Disposition
    53	// of type "form-data".  Otherwise it returns the empty string.
    54	func (p *Part) FormName() string {
    55		// See http://tools.ietf.org/html/rfc2183 section 2 for EBNF
    56		// of Content-Disposition value format.
    57		if p.dispositionParams == nil {
    58			p.parseContentDisposition()
    59		}
    60		if p.disposition != "form-data" {
    61			return ""
    62		}
    63		return p.dispositionParams["name"]
    64	}
    65	
    66	// FileName returns the filename parameter of the Part's
    67	// Content-Disposition header.
    68	func (p *Part) FileName() string {
    69		if p.dispositionParams == nil {
    70			p.parseContentDisposition()
    71		}
    72		return p.dispositionParams["filename"]
    73	}
    74	
    75	func (p *Part) parseContentDisposition() {
    76		v := p.Header.Get("Content-Disposition")
    77		var err error
    78		p.disposition, p.dispositionParams, err = mime.ParseMediaType(v)
    79		if err != nil {
    80			p.dispositionParams = emptyParams
    81		}
    82	}
    83	
    84	// NewReader creates a new multipart Reader reading from reader using the
    85	// given MIME boundary.
    86	func NewReader(reader io.Reader, boundary string) *Reader {
    87		b := []byte("\r\n--" + boundary + "--")
    88		return &Reader{
    89			bufReader: bufio.NewReader(reader),
    90	
    91			nl:               b[:2],
    92			nlDashBoundary:   b[:len(b)-2],
    93			dashBoundaryDash: b[2:],
    94			dashBoundary:     b[2 : len(b)-2],
    95		}
    96	}
    97	
    98	func newPart(mr *Reader) (*Part, error) {
    99		bp := &Part{
   100			Header: make(map[string][]string),
   101			mr:     mr,
   102			buffer: new(bytes.Buffer),
   103		}
   104		if err := bp.populateHeaders(); err != nil {
   105			return nil, err
   106		}
   107		bp.r = partReader{bp}
   108		const cte = "Content-Transfer-Encoding"
   109		if bp.Header.Get(cte) == "quoted-printable" {
   110			bp.Header.Del(cte)
   111			bp.r = newQuotedPrintableReader(bp.r)
   112		}
   113		return bp, nil
   114	}
   115	
   116	func (bp *Part) populateHeaders() error {
   117		r := textproto.NewReader(bp.mr.bufReader)
   118		header, err := r.ReadMIMEHeader()
   119		if err == nil {
   120			bp.Header = header
   121		}
   122		return err
   123	}
   124	
   125	// Read reads the body of a part, after its headers and before the
   126	// next part (if any) begins.
   127	func (p *Part) Read(d []byte) (n int, err error) {
   128		return p.r.Read(d)
   129	}
   130	
   131	// partReader implements io.Reader by reading raw bytes directly from the
   132	// wrapped *Part, without doing any Transfer-Encoding decoding.
   133	type partReader struct {
   134		p *Part
   135	}
   136	
   137	func (pr partReader) Read(d []byte) (n int, err error) {
   138		p := pr.p
   139		defer func() {
   140			p.bytesRead += n
   141		}()
   142		if p.buffer.Len() >= len(d) {
   143			// Internal buffer of unconsumed data is large enough for
   144			// the read request.  No need to parse more at the moment.
   145			return p.buffer.Read(d)
   146		}
   147		peek, err := p.mr.bufReader.Peek(4096) // TODO(bradfitz): add buffer size accessor
   148	
   149		// Look for an immediate empty part without a leading \r\n
   150		// before the boundary separator.  Some MIME code makes empty
   151		// parts like this. Most browsers, however, write the \r\n
   152		// before the subsequent boundary even for empty parts and
   153		// won't hit this path.
   154		if p.bytesRead == 0 && p.mr.peekBufferIsEmptyPart(peek) {
   155			return 0, io.EOF
   156		}
   157		unexpectedEOF := err == io.EOF
   158		if err != nil && !unexpectedEOF {
   159			return 0, fmt.Errorf("multipart: Part Read: %v", err)
   160		}
   161		if peek == nil {
   162			panic("nil peek buf")
   163		}
   164	
   165		// Search the peek buffer for "\r\n--boundary". If found,
   166		// consume everything up to the boundary. If not, consume only
   167		// as much of the peek buffer as cannot hold the boundary
   168		// string.
   169		nCopy := 0
   170		foundBoundary := false
   171		if idx := bytes.Index(peek, p.mr.nlDashBoundary); idx != -1 {
   172			nCopy = idx
   173			foundBoundary = true
   174		} else if safeCount := len(peek) - len(p.mr.nlDashBoundary); safeCount > 0 {
   175			nCopy = safeCount
   176		} else if unexpectedEOF {
   177			// If we've run out of peek buffer and the boundary
   178			// wasn't found (and can't possibly fit), we must have
   179			// hit the end of the file unexpectedly.
   180			return 0, io.ErrUnexpectedEOF
   181		}
   182		if nCopy > 0 {
   183			if _, err := io.CopyN(p.buffer, p.mr.bufReader, int64(nCopy)); err != nil {
   184				return 0, err
   185			}
   186		}
   187		n, err = p.buffer.Read(d)
   188		if err == io.EOF && !foundBoundary {
   189			// If the boundary hasn't been reached there's more to
   190			// read, so don't pass through an EOF from the buffer
   191			err = nil
   192		}
   193		return
   194	}
   195	
   196	func (p *Part) Close() error {
   197		io.Copy(ioutil.Discard, p)
   198		return nil
   199	}
   200	
   201	// Reader is an iterator over parts in a MIME multipart body.
   202	// Reader's underlying parser consumes its input as needed.  Seeking
   203	// isn't supported.
   204	type Reader struct {
   205		bufReader *bufio.Reader
   206	
   207		currentPart *Part
   208		partsRead   int
   209	
   210		nl               []byte // "\r\n" or "\n" (set after seeing first boundary line)
   211		nlDashBoundary   []byte // nl + "--boundary"
   212		dashBoundaryDash []byte // "--boundary--"
   213		dashBoundary     []byte // "--boundary"
   214	}
   215	
   216	// NextPart returns the next part in the multipart or an error.
   217	// When there are no more parts, the error io.EOF is returned.
   218	func (r *Reader) NextPart() (*Part, error) {
   219		if r.currentPart != nil {
   220			r.currentPart.Close()
   221		}
   222	
   223		expectNewPart := false
   224		for {
   225			line, err := r.bufReader.ReadSlice('\n')
   226			if err == io.EOF && r.isFinalBoundary(line) {
   227				// If the buffer ends in "--boundary--" without the
   228				// trailing "\r\n", ReadSlice will return an error
   229				// (since it's missing the '\n'), but this is a valid
   230				// multipart EOF so we need to return io.EOF instead of
   231				// a fmt-wrapped one.
   232				return nil, io.EOF
   233			}
   234			if err != nil {
   235				return nil, fmt.Errorf("multipart: NextPart: %v", err)
   236			}
   237	
   238			if r.isBoundaryDelimiterLine(line) {
   239				r.partsRead++
   240				bp, err := newPart(r)
   241				if err != nil {
   242					return nil, err
   243				}
   244				r.currentPart = bp
   245				return bp, nil
   246			}
   247	
   248			if r.isFinalBoundary(line) {
   249				// Expected EOF
   250				return nil, io.EOF
   251			}
   252	
   253			if expectNewPart {
   254				return nil, fmt.Errorf("multipart: expecting a new Part; got line %q", string(line))
   255			}
   256	
   257			if r.partsRead == 0 {
   258				// skip line
   259				continue
   260			}
   261	
   262			// Consume the "\n" or "\r\n" separator between the
   263			// body of the previous part and the boundary line we
   264			// now expect will follow. (either a new part or the
   265			// end boundary)
   266			if bytes.Equal(line, r.nl) {
   267				expectNewPart = true
   268				continue
   269			}
   270	
   271			return nil, fmt.Errorf("multipart: unexpected line in Next(): %q", line)
   272		}
   273	}
   274	
   275	// isFinalBoundary returns whether line is the final boundary line
   276	// indicating that all parts are over.
   277	// It matches `^--boundary--[ \t]*(\r\n)?$`
   278	func (mr *Reader) isFinalBoundary(line []byte) bool {
   279		if !bytes.HasPrefix(line, mr.dashBoundaryDash) {
   280			return false
   281		}
   282		rest := line[len(mr.dashBoundaryDash):]
   283		rest = skipLWSPChar(rest)
   284		return len(rest) == 0 || bytes.Equal(rest, mr.nl)
   285	}
   286	
   287	func (mr *Reader) isBoundaryDelimiterLine(line []byte) (ret bool) {
   288		// http://tools.ietf.org/html/rfc2046#section-5.1
   289		//   The boundary delimiter line is then defined as a line
   290		//   consisting entirely of two hyphen characters ("-",
   291		//   decimal value 45) followed by the boundary parameter
   292		//   value from the Content-Type header field, optional linear
   293		//   whitespace, and a terminating CRLF.
   294		if !bytes.HasPrefix(line, mr.dashBoundary) {
   295			return false
   296		}
   297		rest := line[len(mr.dashBoundary):]
   298		rest = skipLWSPChar(rest)
   299	
   300		// On the first part, see our lines are ending in \n instead of \r\n
   301		// and switch into that mode if so.  This is a violation of the spec,
   302		// but occurs in practice.
   303		if mr.partsRead == 0 && len(rest) == 1 && rest[0] == '\n' {
   304			mr.nl = mr.nl[1:]
   305			mr.nlDashBoundary = mr.nlDashBoundary[1:]
   306		}
   307		return bytes.Equal(rest, mr.nl)
   308	}
   309	
   310	// peekBufferIsEmptyPart returns whether the provided peek-ahead
   311	// buffer represents an empty part.  This is only called if we've not
   312	// already read any bytes in this part and checks for the case of MIME
   313	// software not writing the \r\n on empty parts. Some does, some
   314	// doesn't.
   315	//
   316	// This checks that what follows the "--boundary" is actually the end
   317	// ("--boundary--" with optional whitespace) or optional whitespace
   318	// and then a newline, so we don't catch "--boundaryFAKE", in which
   319	// case the whole line is part of the data.
   320	func (mr *Reader) peekBufferIsEmptyPart(peek []byte) bool {
   321		// End of parts case.
   322		// Test whether peek matches `^--boundary--[ \t]*(?:\r\n|$)`
   323		if bytes.HasPrefix(peek, mr.dashBoundaryDash) {
   324			rest := peek[len(mr.dashBoundaryDash):]
   325			rest = skipLWSPChar(rest)
   326			return bytes.HasPrefix(rest, mr.nl) || len(rest) == 0
   327		}
   328		if !bytes.HasPrefix(peek, mr.dashBoundary) {
   329			return false
   330		}
   331		// Test whether rest matches `^[ \t]*\r\n`)
   332		rest := peek[len(mr.dashBoundary):]
   333		rest = skipLWSPChar(rest)
   334		return bytes.HasPrefix(rest, mr.nl)
   335	}
   336	
   337	// skipLWSPChar returns b with leading spaces and tabs removed.
   338	// RFC 822 defines:
   339	//    LWSP-char = SPACE / HTAB
   340	func skipLWSPChar(b []byte) []byte {
   341		for len(b) > 0 && (b[0] == ' ' || b[0] == '\t') {
   342			b = b[1:]
   343		}
   344		return b
   345	}

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