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// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package multipart
import (
"bytes"
"crypto/rand"
"errors"
"fmt"
"io"
"net/textproto"
"strings"
)
// A Writer generates multipart messages.
type Writer struct {
w io.Writer
boundary string
lastpart *part
}
// NewWriter returns a new multipart Writer with a random boundary,
// writing to w.
func NewWriter(w io.Writer) *Writer {
return &Writer{
w: w,
boundary: randomBoundary(),
}
}
// Boundary returns the Writer's boundary.
func (w *Writer) Boundary() string {
return w.boundary
}
// SetBoundary overrides the Writer's default randomly-generated
// boundary separator with an explicit value.
//
// SetBoundary must be called before any parts are created, may only
// contain certain ASCII characters, and must be 1-69 bytes long.
func (w *Writer) SetBoundary(boundary string) error {
if w.lastpart != nil {
return errors.New("mime: SetBoundary called after write")
}
// rfc2046#section-5.1.1
if len(boundary) < 1 || len(boundary) > 69 {
return errors.New("mime: invalid boundary length")
}
for _, b := range boundary {
if 'A' <= b && b <= 'Z' || 'a' <= b && b <= 'z' || '0' <= b && b <= '9' {
continue
}
switch b {
case '\'', '(', ')', '+', '_', ',', '-', '.', '/', ':', '=', '?':
continue
}
return errors.New("mime: invalid boundary character")
}
w.boundary = boundary
return nil
}
// FormDataContentType returns the Content-Type for an HTTP
// multipart/form-data with this Writer's Boundary.
func (w *Writer) FormDataContentType() string {
return "multipart/form-data; boundary=" + w.boundary
}
func randomBoundary() string {
var buf [30]byte
_, err := io.ReadFull(rand.Reader, buf[:])
if err != nil {
panic(err)
}
return fmt.Sprintf("%x", buf[:])
}
// CreatePart creates a new multipart section with the provided
// header. The body of the part should be written to the returned
// Writer. After calling CreatePart, any previous part may no longer
// be written to.
func (w *Writer) CreatePart(header textproto.MIMEHeader) (io.Writer, error) {
if w.lastpart != nil {
if err := w.lastpart.close(); err != nil {
return nil, err
}
}
var b bytes.Buffer
if w.lastpart != nil {
fmt.Fprintf(&b, "\r\n--%s\r\n", w.boundary)
} else {
fmt.Fprintf(&b, "--%s\r\n", w.boundary)
}
// TODO(bradfitz): move this to textproto.MimeHeader.Write(w), have it sort
// and clean, like http.Header.Write(w) does.
for k, vv := range header {
for _, v := range vv {
fmt.Fprintf(&b, "%s: %s\r\n", k, v)
}
}
fmt.Fprintf(&b, "\r\n")
_, err := io.Copy(w.w, &b)
if err != nil {
return nil, err
}
p := &part{
mw: w,
}
w.lastpart = p
return p, nil
}
var quoteEscaper = strings.NewReplacer("\\", "\\\\", `"`, "\\\"")
func escapeQuotes(s string) string {
return quoteEscaper.Replace(s)
}
// CreateFormFile is a convenience wrapper around CreatePart. It creates
// a new form-data header with the provided field name and file name.
func (w *Writer) CreateFormFile(fieldname, filename string) (io.Writer, error) {
h := make(textproto.MIMEHeader)
h.Set("Content-Disposition",
fmt.Sprintf(`form-data; name="%s"; filename="%s"`,
escapeQuotes(fieldname), escapeQuotes(filename)))
h.Set("Content-Type", "application/octet-stream")
return w.CreatePart(h)
}
// CreateFormField calls CreatePart with a header using the
// given field name.
func (w *Writer) CreateFormField(fieldname string) (io.Writer, error) {
h := make(textproto.MIMEHeader)
h.Set("Content-Disposition",
fmt.Sprintf(`form-data; name="%s"`, escapeQuotes(fieldname)))
return w.CreatePart(h)
}
// WriteField calls CreateFormField and then writes the given value.
func (w *Writer) WriteField(fieldname, value string) error {
p, err := w.CreateFormField(fieldname)
if err != nil {
return err
}
_, err = p.Write([]byte(value))
return err
}
// Close finishes the multipart message and writes the trailing
// boundary end line to the output.
func (w *Writer) Close() error {
if w.lastpart != nil {
if err := w.lastpart.close(); err != nil {
return err
}
w.lastpart = nil
}
_, err := fmt.Fprintf(w.w, "\r\n--%s--\r\n", w.boundary)
return err
}
type part struct {
mw *Writer
closed bool
we error // last error that occurred writing
}
func (p *part) close() error {
p.closed = true
return p.we
}
func (p *part) Write(d []byte) (n int, err error) {
if p.closed {
return 0, errors.New("multipart: can't write to finished part")
}
n, err = p.mw.w.Write(d)
if err != nil {
p.we = err
}
return
}
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