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Source file src/mime/multipart/multipart.go

Documentation: mime/multipart

     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  	"mime/quotedprintable"
    23  	"net/textproto"
    24  )
    25  
    26  var emptyParams = make(map[string]string)
    27  
    28  // This constant needs to be at least 76 for this package to work correctly.
    29  // This is because \r\n--separator_of_len_70- would fill the buffer and it
    30  // wouldn't be safe to consume a single byte from it.
    31  const peekBufferSize = 4096
    32  
    33  // A Part represents a single part in a multipart body.
    34  type Part struct {
    35  	// The headers of the body, if any, with the keys canonicalized
    36  	// in the same fashion that the Go http.Request headers are.
    37  	// For example, "foo-bar" changes case to "Foo-Bar"
    38  	//
    39  	// As a special case, if the "Content-Transfer-Encoding" header
    40  	// has a value of "quoted-printable", that header is instead
    41  	// hidden from this map and the body is transparently decoded
    42  	// during Read calls.
    43  	Header textproto.MIMEHeader
    44  
    45  	mr *Reader
    46  
    47  	disposition       string
    48  	dispositionParams map[string]string
    49  
    50  	// r is either a reader directly reading from mr, or it's a
    51  	// wrapper around such a reader, decoding the
    52  	// Content-Transfer-Encoding
    53  	r io.Reader
    54  
    55  	n       int   // known data bytes waiting in mr.bufReader
    56  	total   int64 // total data bytes read already
    57  	err     error // error to return when n == 0
    58  	readErr error // read error observed from mr.bufReader
    59  }
    60  
    61  // FormName returns the name parameter if p has a Content-Disposition
    62  // of type "form-data".  Otherwise it returns the empty string.
    63  func (p *Part) FormName() string {
    64  	// See https://tools.ietf.org/html/rfc2183 section 2 for EBNF
    65  	// of Content-Disposition value format.
    66  	if p.dispositionParams == nil {
    67  		p.parseContentDisposition()
    68  	}
    69  	if p.disposition != "form-data" {
    70  		return ""
    71  	}
    72  	return p.dispositionParams["name"]
    73  }
    74  
    75  // FileName returns the filename parameter of the Part's
    76  // Content-Disposition header.
    77  func (p *Part) FileName() string {
    78  	if p.dispositionParams == nil {
    79  		p.parseContentDisposition()
    80  	}
    81  	return p.dispositionParams["filename"]
    82  }
    83  
    84  func (p *Part) parseContentDisposition() {
    85  	v := p.Header.Get("Content-Disposition")
    86  	var err error
    87  	p.disposition, p.dispositionParams, err = mime.ParseMediaType(v)
    88  	if err != nil {
    89  		p.dispositionParams = emptyParams
    90  	}
    91  }
    92  
    93  // NewReader creates a new multipart Reader reading from r using the
    94  // given MIME boundary.
    95  //
    96  // The boundary is usually obtained from the "boundary" parameter of
    97  // the message's "Content-Type" header. Use mime.ParseMediaType to
    98  // parse such headers.
    99  func NewReader(r io.Reader, boundary string) *Reader {
   100  	b := []byte("\r\n--" + boundary + "--")
   101  	return &Reader{
   102  		bufReader:        bufio.NewReaderSize(&stickyErrorReader{r: r}, peekBufferSize),
   103  		nl:               b[:2],
   104  		nlDashBoundary:   b[:len(b)-2],
   105  		dashBoundaryDash: b[2:],
   106  		dashBoundary:     b[2 : len(b)-2],
   107  	}
   108  }
   109  
   110  // stickyErrorReader is an io.Reader which never calls Read on its
   111  // underlying Reader once an error has been seen. (the io.Reader
   112  // interface's contract promises nothing about the return values of
   113  // Read calls after an error, yet this package does do multiple Reads
   114  // after error)
   115  type stickyErrorReader struct {
   116  	r   io.Reader
   117  	err error
   118  }
   119  
   120  func (r *stickyErrorReader) Read(p []byte) (n int, _ error) {
   121  	if r.err != nil {
   122  		return 0, r.err
   123  	}
   124  	n, r.err = r.r.Read(p)
   125  	return n, r.err
   126  }
   127  
   128  func newPart(mr *Reader) (*Part, error) {
   129  	bp := &Part{
   130  		Header: make(map[string][]string),
   131  		mr:     mr,
   132  	}
   133  	if err := bp.populateHeaders(); err != nil {
   134  		return nil, err
   135  	}
   136  	bp.r = partReader{bp}
   137  	const cte = "Content-Transfer-Encoding"
   138  	if bp.Header.Get(cte) == "quoted-printable" {
   139  		bp.Header.Del(cte)
   140  		bp.r = quotedprintable.NewReader(bp.r)
   141  	}
   142  	return bp, nil
   143  }
   144  
   145  func (bp *Part) populateHeaders() error {
   146  	r := textproto.NewReader(bp.mr.bufReader)
   147  	header, err := r.ReadMIMEHeader()
   148  	if err == nil {
   149  		bp.Header = header
   150  	}
   151  	return err
   152  }
   153  
   154  // Read reads the body of a part, after its headers and before the
   155  // next part (if any) begins.
   156  func (p *Part) Read(d []byte) (n int, err error) {
   157  	return p.r.Read(d)
   158  }
   159  
   160  // partReader implements io.Reader by reading raw bytes directly from the
   161  // wrapped *Part, without doing any Transfer-Encoding decoding.
   162  type partReader struct {
   163  	p *Part
   164  }
   165  
   166  func (pr partReader) Read(d []byte) (int, error) {
   167  	p := pr.p
   168  	br := p.mr.bufReader
   169  
   170  	// Read into buffer until we identify some data to return,
   171  	// or we find a reason to stop (boundary or read error).
   172  	for p.n == 0 && p.err == nil {
   173  		peek, _ := br.Peek(br.Buffered())
   174  		p.n, p.err = scanUntilBoundary(peek, p.mr.dashBoundary, p.mr.nlDashBoundary, p.total, p.readErr)
   175  		if p.n == 0 && p.err == nil {
   176  			// Force buffered I/O to read more into buffer.
   177  			_, p.readErr = br.Peek(len(peek) + 1)
   178  			if p.readErr == io.EOF {
   179  				p.readErr = io.ErrUnexpectedEOF
   180  			}
   181  		}
   182  	}
   183  
   184  	// Read out from "data to return" part of buffer.
   185  	if p.n == 0 {
   186  		return 0, p.err
   187  	}
   188  	n := len(d)
   189  	if n > p.n {
   190  		n = p.n
   191  	}
   192  	n, _ = br.Read(d[:n])
   193  	p.total += int64(n)
   194  	p.n -= n
   195  	if p.n == 0 {
   196  		return n, p.err
   197  	}
   198  	return n, nil
   199  }
   200  
   201  // scanUntilBoundary scans buf to identify how much of it can be safely
   202  // returned as part of the Part body.
   203  // dashBoundary is "--boundary".
   204  // nlDashBoundary is "\r\n--boundary" or "\n--boundary", depending on what mode we are in.
   205  // The comments below (and the name) assume "\n--boundary", but either is accepted.
   206  // total is the number of bytes read out so far. If total == 0, then a leading "--boundary" is recognized.
   207  // readErr is the read error, if any, that followed reading the bytes in buf.
   208  // scanUntilBoundary returns the number of data bytes from buf that can be
   209  // returned as part of the Part body and also the error to return (if any)
   210  // once those data bytes are done.
   211  func scanUntilBoundary(buf, dashBoundary, nlDashBoundary []byte, total int64, readErr error) (int, error) {
   212  	if total == 0 {
   213  		// At beginning of body, allow dashBoundary.
   214  		if bytes.HasPrefix(buf, dashBoundary) {
   215  			switch matchAfterPrefix(buf, dashBoundary, readErr) {
   216  			case -1:
   217  				return len(dashBoundary), nil
   218  			case 0:
   219  				return 0, nil
   220  			case +1:
   221  				return 0, io.EOF
   222  			}
   223  		}
   224  		if bytes.HasPrefix(dashBoundary, buf) {
   225  			return 0, readErr
   226  		}
   227  	}
   228  
   229  	// Search for "\n--boundary".
   230  	if i := bytes.Index(buf, nlDashBoundary); i >= 0 {
   231  		switch matchAfterPrefix(buf[i:], nlDashBoundary, readErr) {
   232  		case -1:
   233  			return i + len(nlDashBoundary), nil
   234  		case 0:
   235  			return i, nil
   236  		case +1:
   237  			return i, io.EOF
   238  		}
   239  	}
   240  	if bytes.HasPrefix(nlDashBoundary, buf) {
   241  		return 0, readErr
   242  	}
   243  
   244  	// Otherwise, anything up to the final \n is not part of the boundary
   245  	// and so must be part of the body.
   246  	// Also if the section from the final \n onward is not a prefix of the boundary,
   247  	// it too must be part of the body.
   248  	i := bytes.LastIndexByte(buf, nlDashBoundary[0])
   249  	if i >= 0 && bytes.HasPrefix(nlDashBoundary, buf[i:]) {
   250  		return i, nil
   251  	}
   252  	return len(buf), readErr
   253  }
   254  
   255  // matchAfterPrefix checks whether buf should be considered to match the boundary.
   256  // The prefix is "--boundary" or "\r\n--boundary" or "\n--boundary",
   257  // and the caller has verified already that bytes.HasPrefix(buf, prefix) is true.
   258  //
   259  // matchAfterPrefix returns +1 if the buffer does match the boundary,
   260  // meaning the prefix is followed by a dash, space, tab, cr, nl, or end of input.
   261  // It returns -1 if the buffer definitely does NOT match the boundary,
   262  // meaning the prefix is followed by some other character.
   263  // For example, "--foobar" does not match "--foo".
   264  // It returns 0 more input needs to be read to make the decision,
   265  // meaning that len(buf) == len(prefix) and readErr == nil.
   266  func matchAfterPrefix(buf, prefix []byte, readErr error) int {
   267  	if len(buf) == len(prefix) {
   268  		if readErr != nil {
   269  			return +1
   270  		}
   271  		return 0
   272  	}
   273  	c := buf[len(prefix)]
   274  	if c == ' ' || c == '\t' || c == '\r' || c == '\n' || c == '-' {
   275  		return +1
   276  	}
   277  	return -1
   278  }
   279  
   280  func (p *Part) Close() error {
   281  	io.Copy(ioutil.Discard, p)
   282  	return nil
   283  }
   284  
   285  // Reader is an iterator over parts in a MIME multipart body.
   286  // Reader's underlying parser consumes its input as needed. Seeking
   287  // isn't supported.
   288  type Reader struct {
   289  	bufReader *bufio.Reader
   290  
   291  	currentPart *Part
   292  	partsRead   int
   293  
   294  	nl               []byte // "\r\n" or "\n" (set after seeing first boundary line)
   295  	nlDashBoundary   []byte // nl + "--boundary"
   296  	dashBoundaryDash []byte // "--boundary--"
   297  	dashBoundary     []byte // "--boundary"
   298  }
   299  
   300  // NextPart returns the next part in the multipart or an error.
   301  // When there are no more parts, the error io.EOF is returned.
   302  func (r *Reader) NextPart() (*Part, error) {
   303  	if r.currentPart != nil {
   304  		r.currentPart.Close()
   305  	}
   306  	if string(r.dashBoundary) == "--" {
   307  		return nil, fmt.Errorf("multipart: boundary is empty")
   308  	}
   309  	expectNewPart := false
   310  	for {
   311  		line, err := r.bufReader.ReadSlice('\n')
   312  
   313  		if err == io.EOF && r.isFinalBoundary(line) {
   314  			// If the buffer ends in "--boundary--" without the
   315  			// trailing "\r\n", ReadSlice will return an error
   316  			// (since it's missing the '\n'), but this is a valid
   317  			// multipart EOF so we need to return io.EOF instead of
   318  			// a fmt-wrapped one.
   319  			return nil, io.EOF
   320  		}
   321  		if err != nil {
   322  			return nil, fmt.Errorf("multipart: NextPart: %v", err)
   323  		}
   324  
   325  		if r.isBoundaryDelimiterLine(line) {
   326  			r.partsRead++
   327  			bp, err := newPart(r)
   328  			if err != nil {
   329  				return nil, err
   330  			}
   331  			r.currentPart = bp
   332  			return bp, nil
   333  		}
   334  
   335  		if r.isFinalBoundary(line) {
   336  			// Expected EOF
   337  			return nil, io.EOF
   338  		}
   339  
   340  		if expectNewPart {
   341  			return nil, fmt.Errorf("multipart: expecting a new Part; got line %q", string(line))
   342  		}
   343  
   344  		if r.partsRead == 0 {
   345  			// skip line
   346  			continue
   347  		}
   348  
   349  		// Consume the "\n" or "\r\n" separator between the
   350  		// body of the previous part and the boundary line we
   351  		// now expect will follow. (either a new part or the
   352  		// end boundary)
   353  		if bytes.Equal(line, r.nl) {
   354  			expectNewPart = true
   355  			continue
   356  		}
   357  
   358  		return nil, fmt.Errorf("multipart: unexpected line in Next(): %q", line)
   359  	}
   360  }
   361  
   362  // isFinalBoundary reports whether line is the final boundary line
   363  // indicating that all parts are over.
   364  // It matches `^--boundary--[ \t]*(\r\n)?$`
   365  func (mr *Reader) isFinalBoundary(line []byte) bool {
   366  	if !bytes.HasPrefix(line, mr.dashBoundaryDash) {
   367  		return false
   368  	}
   369  	rest := line[len(mr.dashBoundaryDash):]
   370  	rest = skipLWSPChar(rest)
   371  	return len(rest) == 0 || bytes.Equal(rest, mr.nl)
   372  }
   373  
   374  func (mr *Reader) isBoundaryDelimiterLine(line []byte) (ret bool) {
   375  	// https://tools.ietf.org/html/rfc2046#section-5.1
   376  	//   The boundary delimiter line is then defined as a line
   377  	//   consisting entirely of two hyphen characters ("-",
   378  	//   decimal value 45) followed by the boundary parameter
   379  	//   value from the Content-Type header field, optional linear
   380  	//   whitespace, and a terminating CRLF.
   381  	if !bytes.HasPrefix(line, mr.dashBoundary) {
   382  		return false
   383  	}
   384  	rest := line[len(mr.dashBoundary):]
   385  	rest = skipLWSPChar(rest)
   386  
   387  	// On the first part, see our lines are ending in \n instead of \r\n
   388  	// and switch into that mode if so. This is a violation of the spec,
   389  	// but occurs in practice.
   390  	if mr.partsRead == 0 && len(rest) == 1 && rest[0] == '\n' {
   391  		mr.nl = mr.nl[1:]
   392  		mr.nlDashBoundary = mr.nlDashBoundary[1:]
   393  	}
   394  	return bytes.Equal(rest, mr.nl)
   395  }
   396  
   397  // skipLWSPChar returns b with leading spaces and tabs removed.
   398  // RFC 822 defines:
   399  //    LWSP-char = SPACE / HTAB
   400  func skipLWSPChar(b []byte) []byte {
   401  	for len(b) > 0 && (b[0] == ' ' || b[0] == '\t') {
   402  		b = b[1:]
   403  	}
   404  	return b
   405  }
   406  

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