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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  	"strings"
    25  )
    26  
    27  var emptyParams = make(map[string]string)
    28  
    29  // This constant needs to be at least 76 for this package to work correctly.
    30  // This is because \r\n--separator_of_len_70- would fill the buffer and it
    31  // wouldn't be safe to consume a single byte from it.
    32  const peekBufferSize = 4096
    33  
    34  // A Part represents a single part in a multipart body.
    35  type Part struct {
    36  	// The headers of the body, if any, with the keys canonicalized
    37  	// in the same fashion that the Go http.Request headers are.
    38  	// For example, "foo-bar" changes case to "Foo-Bar"
    39  	//
    40  	// As a special case, if the "Content-Transfer-Encoding" header
    41  	// has a value of "quoted-printable", that header is instead
    42  	// hidden from this map and the body is transparently decoded
    43  	// during Read calls.
    44  	Header textproto.MIMEHeader
    45  
    46  	mr *Reader
    47  
    48  	disposition       string
    49  	dispositionParams map[string]string
    50  
    51  	// r is either a reader directly reading from mr, or it's a
    52  	// wrapper around such a reader, decoding the
    53  	// Content-Transfer-Encoding
    54  	r io.Reader
    55  
    56  	n       int   // known data bytes waiting in mr.bufReader
    57  	total   int64 // total data bytes read already
    58  	err     error // error to return when n == 0
    59  	readErr error // read error observed from mr.bufReader
    60  }
    61  
    62  // FormName returns the name parameter if p has a Content-Disposition
    63  // of type "form-data".  Otherwise it returns the empty string.
    64  func (p *Part) FormName() string {
    65  	// See https://tools.ietf.org/html/rfc2183 section 2 for EBNF
    66  	// of Content-Disposition value format.
    67  	if p.dispositionParams == nil {
    68  		p.parseContentDisposition()
    69  	}
    70  	if p.disposition != "form-data" {
    71  		return ""
    72  	}
    73  	return p.dispositionParams["name"]
    74  }
    75  
    76  // FileName returns the filename parameter of the Part's
    77  // Content-Disposition header.
    78  func (p *Part) FileName() string {
    79  	if p.dispositionParams == nil {
    80  		p.parseContentDisposition()
    81  	}
    82  	return p.dispositionParams["filename"]
    83  }
    84  
    85  func (p *Part) parseContentDisposition() {
    86  	v := p.Header.Get("Content-Disposition")
    87  	var err error
    88  	p.disposition, p.dispositionParams, err = mime.ParseMediaType(v)
    89  	if err != nil {
    90  		p.dispositionParams = emptyParams
    91  	}
    92  }
    93  
    94  // NewReader creates a new multipart Reader reading from r using the
    95  // given MIME boundary.
    96  //
    97  // The boundary is usually obtained from the "boundary" parameter of
    98  // the message's "Content-Type" header. Use mime.ParseMediaType to
    99  // parse such headers.
   100  func NewReader(r io.Reader, boundary string) *Reader {
   101  	b := []byte("\r\n--" + boundary + "--")
   102  	return &Reader{
   103  		bufReader:        bufio.NewReaderSize(&stickyErrorReader{r: r}, peekBufferSize),
   104  		nl:               b[:2],
   105  		nlDashBoundary:   b[:len(b)-2],
   106  		dashBoundaryDash: b[2:],
   107  		dashBoundary:     b[2 : len(b)-2],
   108  	}
   109  }
   110  
   111  // stickyErrorReader is an io.Reader which never calls Read on its
   112  // underlying Reader once an error has been seen. (the io.Reader
   113  // interface's contract promises nothing about the return values of
   114  // Read calls after an error, yet this package does do multiple Reads
   115  // after error)
   116  type stickyErrorReader struct {
   117  	r   io.Reader
   118  	err error
   119  }
   120  
   121  func (r *stickyErrorReader) Read(p []byte) (n int, _ error) {
   122  	if r.err != nil {
   123  		return 0, r.err
   124  	}
   125  	n, r.err = r.r.Read(p)
   126  	return n, r.err
   127  }
   128  
   129  func newPart(mr *Reader) (*Part, error) {
   130  	bp := &Part{
   131  		Header: make(map[string][]string),
   132  		mr:     mr,
   133  	}
   134  	if err := bp.populateHeaders(); err != nil {
   135  		return nil, err
   136  	}
   137  	bp.r = partReader{bp}
   138  	const cte = "Content-Transfer-Encoding"
   139  	if strings.EqualFold(bp.Header.Get(cte), "quoted-printable") {
   140  		bp.Header.Del(cte)
   141  		bp.r = quotedprintable.NewReader(bp.r)
   142  	}
   143  	return bp, nil
   144  }
   145  
   146  func (bp *Part) populateHeaders() error {
   147  	r := textproto.NewReader(bp.mr.bufReader)
   148  	header, err := r.ReadMIMEHeader()
   149  	if err == nil {
   150  		bp.Header = header
   151  	}
   152  	return err
   153  }
   154  
   155  // Read reads the body of a part, after its headers and before the
   156  // next part (if any) begins.
   157  func (p *Part) Read(d []byte) (n int, err error) {
   158  	return p.r.Read(d)
   159  }
   160  
   161  // partReader implements io.Reader by reading raw bytes directly from the
   162  // wrapped *Part, without doing any Transfer-Encoding decoding.
   163  type partReader struct {
   164  	p *Part
   165  }
   166  
   167  func (pr partReader) Read(d []byte) (int, error) {
   168  	p := pr.p
   169  	br := p.mr.bufReader
   170  
   171  	// Read into buffer until we identify some data to return,
   172  	// or we find a reason to stop (boundary or read error).
   173  	for p.n == 0 && p.err == nil {
   174  		peek, _ := br.Peek(br.Buffered())
   175  		p.n, p.err = scanUntilBoundary(peek, p.mr.dashBoundary, p.mr.nlDashBoundary, p.total, p.readErr)
   176  		if p.n == 0 && p.err == nil {
   177  			// Force buffered I/O to read more into buffer.
   178  			_, p.readErr = br.Peek(len(peek) + 1)
   179  			if p.readErr == io.EOF {
   180  				p.readErr = io.ErrUnexpectedEOF
   181  			}
   182  		}
   183  	}
   184  
   185  	// Read out from "data to return" part of buffer.
   186  	if p.n == 0 {
   187  		return 0, p.err
   188  	}
   189  	n := len(d)
   190  	if n > p.n {
   191  		n = p.n
   192  	}
   193  	n, _ = br.Read(d[:n])
   194  	p.total += int64(n)
   195  	p.n -= n
   196  	if p.n == 0 {
   197  		return n, p.err
   198  	}
   199  	return n, nil
   200  }
   201  
   202  // scanUntilBoundary scans buf to identify how much of it can be safely
   203  // returned as part of the Part body.
   204  // dashBoundary is "--boundary".
   205  // nlDashBoundary is "\r\n--boundary" or "\n--boundary", depending on what mode we are in.
   206  // The comments below (and the name) assume "\n--boundary", but either is accepted.
   207  // total is the number of bytes read out so far. If total == 0, then a leading "--boundary" is recognized.
   208  // readErr is the read error, if any, that followed reading the bytes in buf.
   209  // scanUntilBoundary returns the number of data bytes from buf that can be
   210  // returned as part of the Part body and also the error to return (if any)
   211  // once those data bytes are done.
   212  func scanUntilBoundary(buf, dashBoundary, nlDashBoundary []byte, total int64, readErr error) (int, error) {
   213  	if total == 0 {
   214  		// At beginning of body, allow dashBoundary.
   215  		if bytes.HasPrefix(buf, dashBoundary) {
   216  			switch matchAfterPrefix(buf, dashBoundary, readErr) {
   217  			case -1:
   218  				return len(dashBoundary), nil
   219  			case 0:
   220  				return 0, nil
   221  			case +1:
   222  				return 0, io.EOF
   223  			}
   224  		}
   225  		if bytes.HasPrefix(dashBoundary, buf) {
   226  			return 0, readErr
   227  		}
   228  	}
   229  
   230  	// Search for "\n--boundary".
   231  	if i := bytes.Index(buf, nlDashBoundary); i >= 0 {
   232  		switch matchAfterPrefix(buf[i:], nlDashBoundary, readErr) {
   233  		case -1:
   234  			return i + len(nlDashBoundary), nil
   235  		case 0:
   236  			return i, nil
   237  		case +1:
   238  			return i, io.EOF
   239  		}
   240  	}
   241  	if bytes.HasPrefix(nlDashBoundary, buf) {
   242  		return 0, readErr
   243  	}
   244  
   245  	// Otherwise, anything up to the final \n is not part of the boundary
   246  	// and so must be part of the body.
   247  	// Also if the section from the final \n onward is not a prefix of the boundary,
   248  	// it too must be part of the body.
   249  	i := bytes.LastIndexByte(buf, nlDashBoundary[0])
   250  	if i >= 0 && bytes.HasPrefix(nlDashBoundary, buf[i:]) {
   251  		return i, nil
   252  	}
   253  	return len(buf), readErr
   254  }
   255  
   256  // matchAfterPrefix checks whether buf should be considered to match the boundary.
   257  // The prefix is "--boundary" or "\r\n--boundary" or "\n--boundary",
   258  // and the caller has verified already that bytes.HasPrefix(buf, prefix) is true.
   259  //
   260  // matchAfterPrefix returns +1 if the buffer does match the boundary,
   261  // meaning the prefix is followed by a dash, space, tab, cr, nl, or end of input.
   262  // It returns -1 if the buffer definitely does NOT match the boundary,
   263  // meaning the prefix is followed by some other character.
   264  // For example, "--foobar" does not match "--foo".
   265  // It returns 0 more input needs to be read to make the decision,
   266  // meaning that len(buf) == len(prefix) and readErr == nil.
   267  func matchAfterPrefix(buf, prefix []byte, readErr error) int {
   268  	if len(buf) == len(prefix) {
   269  		if readErr != nil {
   270  			return +1
   271  		}
   272  		return 0
   273  	}
   274  	c := buf[len(prefix)]
   275  	if c == ' ' || c == '\t' || c == '\r' || c == '\n' || c == '-' {
   276  		return +1
   277  	}
   278  	return -1
   279  }
   280  
   281  func (p *Part) Close() error {
   282  	io.Copy(ioutil.Discard, p)
   283  	return nil
   284  }
   285  
   286  // Reader is an iterator over parts in a MIME multipart body.
   287  // Reader's underlying parser consumes its input as needed. Seeking
   288  // isn't supported.
   289  type Reader struct {
   290  	bufReader *bufio.Reader
   291  
   292  	currentPart *Part
   293  	partsRead   int
   294  
   295  	nl               []byte // "\r\n" or "\n" (set after seeing first boundary line)
   296  	nlDashBoundary   []byte // nl + "--boundary"
   297  	dashBoundaryDash []byte // "--boundary--"
   298  	dashBoundary     []byte // "--boundary"
   299  }
   300  
   301  // NextPart returns the next part in the multipart or an error.
   302  // When there are no more parts, the error io.EOF is returned.
   303  func (r *Reader) NextPart() (*Part, error) {
   304  	if r.currentPart != nil {
   305  		r.currentPart.Close()
   306  	}
   307  	if string(r.dashBoundary) == "--" {
   308  		return nil, fmt.Errorf("multipart: boundary is empty")
   309  	}
   310  	expectNewPart := false
   311  	for {
   312  		line, err := r.bufReader.ReadSlice('\n')
   313  
   314  		if err == io.EOF && r.isFinalBoundary(line) {
   315  			// If the buffer ends in "--boundary--" without the
   316  			// trailing "\r\n", ReadSlice will return an error
   317  			// (since it's missing the '\n'), but this is a valid
   318  			// multipart EOF so we need to return io.EOF instead of
   319  			// a fmt-wrapped one.
   320  			return nil, io.EOF
   321  		}
   322  		if err != nil {
   323  			return nil, fmt.Errorf("multipart: NextPart: %v", err)
   324  		}
   325  
   326  		if r.isBoundaryDelimiterLine(line) {
   327  			r.partsRead++
   328  			bp, err := newPart(r)
   329  			if err != nil {
   330  				return nil, err
   331  			}
   332  			r.currentPart = bp
   333  			return bp, nil
   334  		}
   335  
   336  		if r.isFinalBoundary(line) {
   337  			// Expected EOF
   338  			return nil, io.EOF
   339  		}
   340  
   341  		if expectNewPart {
   342  			return nil, fmt.Errorf("multipart: expecting a new Part; got line %q", string(line))
   343  		}
   344  
   345  		if r.partsRead == 0 {
   346  			// skip line
   347  			continue
   348  		}
   349  
   350  		// Consume the "\n" or "\r\n" separator between the
   351  		// body of the previous part and the boundary line we
   352  		// now expect will follow. (either a new part or the
   353  		// end boundary)
   354  		if bytes.Equal(line, r.nl) {
   355  			expectNewPart = true
   356  			continue
   357  		}
   358  
   359  		return nil, fmt.Errorf("multipart: unexpected line in Next(): %q", line)
   360  	}
   361  }
   362  
   363  // isFinalBoundary reports whether line is the final boundary line
   364  // indicating that all parts are over.
   365  // It matches `^--boundary--[ \t]*(\r\n)?$`
   366  func (mr *Reader) isFinalBoundary(line []byte) bool {
   367  	if !bytes.HasPrefix(line, mr.dashBoundaryDash) {
   368  		return false
   369  	}
   370  	rest := line[len(mr.dashBoundaryDash):]
   371  	rest = skipLWSPChar(rest)
   372  	return len(rest) == 0 || bytes.Equal(rest, mr.nl)
   373  }
   374  
   375  func (mr *Reader) isBoundaryDelimiterLine(line []byte) (ret bool) {
   376  	// https://tools.ietf.org/html/rfc2046#section-5.1
   377  	//   The boundary delimiter line is then defined as a line
   378  	//   consisting entirely of two hyphen characters ("-",
   379  	//   decimal value 45) followed by the boundary parameter
   380  	//   value from the Content-Type header field, optional linear
   381  	//   whitespace, and a terminating CRLF.
   382  	if !bytes.HasPrefix(line, mr.dashBoundary) {
   383  		return false
   384  	}
   385  	rest := line[len(mr.dashBoundary):]
   386  	rest = skipLWSPChar(rest)
   387  
   388  	// On the first part, see our lines are ending in \n instead of \r\n
   389  	// and switch into that mode if so. This is a violation of the spec,
   390  	// but occurs in practice.
   391  	if mr.partsRead == 0 && len(rest) == 1 && rest[0] == '\n' {
   392  		mr.nl = mr.nl[1:]
   393  		mr.nlDashBoundary = mr.nlDashBoundary[1:]
   394  	}
   395  	return bytes.Equal(rest, mr.nl)
   396  }
   397  
   398  // skipLWSPChar returns b with leading spaces and tabs removed.
   399  // RFC 822 defines:
   400  //    LWSP-char = SPACE / HTAB
   401  func skipLWSPChar(b []byte) []byte {
   402  	for len(b) > 0 && (b[0] == ' ' || b[0] == '\t') {
   403  		b = b[1:]
   404  	}
   405  	return b
   406  }
   407  

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