writer.go

Documentation: mime/multipart

     1  // Copyright 2011 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  package multipart
     6  
     7  import (
     8  	"bytes"
     9  	"crypto/rand"
    10  	"errors"
    11  	"fmt"
    12  	"io"
    13  	"net/textproto"
    14  	"sort"
    15  	"strings"
    16  )
    17  
    18  // A Writer generates multipart messages.
    19  type Writer struct {
    20  	w        io.Writer
    21  	boundary string
    22  	lastpart *part
    23  }
    24  
    25  // NewWriter returns a new multipart Writer with a random boundary,
    26  // writing to w.
    27  func NewWriter(w io.Writer) *Writer {
    28  	return &Writer{
    29  		w:        w,
    30  		boundary: randomBoundary(),
    31  	}
    32  }
    33  
    34  // Boundary returns the Writer's boundary.
    35  func (w *Writer) Boundary() string {
    36  	return w.boundary
    37  }
    38  
    39  // SetBoundary overrides the Writer's default randomly-generated
    40  // boundary separator with an explicit value.
    41  //
    42  // SetBoundary must be called before any parts are created, may only
    43  // contain certain ASCII characters, and must be non-empty and
    44  // at most 70 bytes long.
    45  func (w *Writer) SetBoundary(boundary string) error {
    46  	if w.lastpart != nil {
    47  		return errors.New("mime: SetBoundary called after write")
    48  	}
    49  	// rfc2046#section-5.1.1
    50  	if len(boundary) < 1 || len(boundary) > 70 {
    51  		return errors.New("mime: invalid boundary length")
    52  	}
    53  	end := len(boundary) - 1
    54  	for i, b := range boundary {
    55  		if 'A' <= b && b <= 'Z' || 'a' <= b && b <= 'z' || '0' <= b && b <= '9' {
    56  			continue
    57  		}
    58  		switch b {
    59  		case '\'', '(', ')', '+', '_', ',', '-', '.', '/', ':', '=', '?':
    60  			continue
    61  		case ' ':
    62  			if i != end {
    63  				continue
    64  			}
    65  		}
    66  		return errors.New("mime: invalid boundary character")
    67  	}
    68  	w.boundary = boundary
    69  	return nil
    70  }
    71  
    72  // FormDataContentType returns the Content-Type for an HTTP
    73  // multipart/form-data with this Writer's Boundary.
    74  func (w *Writer) FormDataContentType() string {
    75  	return "multipart/form-data; boundary=" + w.boundary
    76  }
    77  
    78  func randomBoundary() string {
    79  	var buf [30]byte
    80  	_, err := io.ReadFull(rand.Reader, buf[:])
    81  	if err != nil {
    82  		panic(err)
    83  	}
    84  	return fmt.Sprintf("%x", buf[:])
    85  }
    86  
    87  // CreatePart creates a new multipart section with the provided
    88  // header. The body of the part should be written to the returned
    89  // Writer. After calling CreatePart, any previous part may no longer
    90  // be written to.
    91  func (w *Writer) CreatePart(header textproto.MIMEHeader) (io.Writer, error) {
    92  	if w.lastpart != nil {
    93  		if err := w.lastpart.close(); err != nil {
    94  			return nil, err
    95  		}
    96  	}
    97  	var b bytes.Buffer
    98  	if w.lastpart != nil {
    99  		fmt.Fprintf(&b, "\r\n--%s\r\n", w.boundary)
   100  	} else {
   101  		fmt.Fprintf(&b, "--%s\r\n", w.boundary)
   102  	}
   103  
   104  	keys := make([]string, 0, len(header))
   105  	for k := range header {
   106  		keys = append(keys, k)
   107  	}
   108  	sort.Strings(keys)
   109  	for _, k := range keys {
   110  		for _, v := range header[k] {
   111  			fmt.Fprintf(&b, "%s: %s\r\n", k, v)
   112  		}
   113  	}
   114  	fmt.Fprintf(&b, "\r\n")
   115  	_, err := io.Copy(w.w, &b)
   116  	if err != nil {
   117  		return nil, err
   118  	}
   119  	p := &part{
   120  		mw: w,
   121  	}
   122  	w.lastpart = p
   123  	return p, nil
   124  }
   125  
   126  var quoteEscaper = strings.NewReplacer("\\", "\\\\", `"`, "\\\"")
   127  
   128  func escapeQuotes(s string) string {
   129  	return quoteEscaper.Replace(s)
   130  }
   131  
   132  // CreateFormFile is a convenience wrapper around CreatePart. It creates
   133  // a new form-data header with the provided field name and file name.
   134  func (w *Writer) CreateFormFile(fieldname, filename string) (io.Writer, error) {
   135  	h := make(textproto.MIMEHeader)
   136  	h.Set("Content-Disposition",
   137  		fmt.Sprintf(`form-data; name="%s"; filename="%s"`,
   138  			escapeQuotes(fieldname), escapeQuotes(filename)))
   139  	h.Set("Content-Type", "application/octet-stream")
   140  	return w.CreatePart(h)
   141  }
   142  
   143  // CreateFormField calls CreatePart with a header using the
   144  // given field name.
   145  func (w *Writer) CreateFormField(fieldname string) (io.Writer, error) {
   146  	h := make(textproto.MIMEHeader)
   147  	h.Set("Content-Disposition",
   148  		fmt.Sprintf(`form-data; name="%s"`, escapeQuotes(fieldname)))
   149  	return w.CreatePart(h)
   150  }
   151  
   152  // WriteField calls CreateFormField and then writes the given value.
   153  func (w *Writer) WriteField(fieldname, value string) error {
   154  	p, err := w.CreateFormField(fieldname)
   155  	if err != nil {
   156  		return err
   157  	}
   158  	_, err = p.Write([]byte(value))
   159  	return err
   160  }
   161  
   162  // Close finishes the multipart message and writes the trailing
   163  // boundary end line to the output.
   164  func (w *Writer) Close() error {
   165  	if w.lastpart != nil {
   166  		if err := w.lastpart.close(); err != nil {
   167  			return err
   168  		}
   169  		w.lastpart = nil
   170  	}
   171  	_, err := fmt.Fprintf(w.w, "\r\n--%s--\r\n", w.boundary)
   172  	return err
   173  }
   174  
   175  type part struct {
   176  	mw     *Writer
   177  	closed bool
   178  	we     error // last error that occurred writing
   179  }
   180  
   181  func (p *part) close() error {
   182  	p.closed = true
   183  	return p.we
   184  }
   185  
   186  func (p *part) Write(d []byte) (n int, err error) {
   187  	if p.closed {
   188  		return 0, errors.New("multipart: can't write to finished part")
   189  	}
   190  	n, err = p.mw.w.Write(d)
   191  	if err != nil {
   192  		p.we = err
   193  	}
   194  	return
   195  }
   196
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