formdata.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  	"errors"
    10  	"io"
    11  	"io/ioutil"
    12  	"net/textproto"
    13  	"os"
    14  )
    15  
    16  // ErrMessageTooLarge is returned by ReadForm if the message form
    17  // data is too large to be processed.
    18  var ErrMessageTooLarge = errors.New("multipart: message too large")
    19  
    20  // TODO(adg,bradfitz): find a way to unify the DoS-prevention strategy here
    21  // with that of the http package's ParseForm.
    22  
    23  // ReadForm parses an entire multipart message whose parts have
    24  // a Content-Disposition of "form-data".
    25  // It stores up to maxMemory bytes + 10MB (reserved for non-file parts)
    26  // in memory. File parts which can't be stored in memory will be stored on
    27  // disk in temporary files.
    28  // It returns ErrMessageTooLarge if all non-file parts can't be stored in
    29  // memory.
    30  func (r *Reader) ReadForm(maxMemory int64) (*Form, error) {
    31  	return r.readForm(maxMemory)
    32  }
    33  
    34  func (r *Reader) readForm(maxMemory int64) (_ *Form, err error) {
    35  	form := &Form{make(map[string][]string), make(map[string][]*FileHeader)}
    36  	defer func() {
    37  		if err != nil {
    38  			form.RemoveAll()
    39  		}
    40  	}()
    41  
    42  	// Reserve an additional 10 MB for non-file parts.
    43  	maxValueBytes := maxMemory + int64(10<<20)
    44  	for {
    45  		p, err := r.NextPart()
    46  		if err == io.EOF {
    47  			break
    48  		}
    49  		if err != nil {
    50  			return nil, err
    51  		}
    52  
    53  		name := p.FormName()
    54  		if name == "" {
    55  			continue
    56  		}
    57  		filename := p.FileName()
    58  
    59  		var b bytes.Buffer
    60  
    61  		_, hasContentTypeHeader := p.Header["Content-Type"]
    62  		if !hasContentTypeHeader && filename == "" {
    63  			// value, store as string in memory
    64  			n, err := io.CopyN(&b, p, maxValueBytes+1)
    65  			if err != nil && err != io.EOF {
    66  				return nil, err
    67  			}
    68  			maxValueBytes -= n
    69  			if maxValueBytes < 0 {
    70  				return nil, ErrMessageTooLarge
    71  			}
    72  			form.Value[name] = append(form.Value[name], b.String())
    73  			continue
    74  		}
    75  
    76  		// file, store in memory or on disk
    77  		fh := &FileHeader{
    78  			Filename: filename,
    79  			Header:   p.Header,
    80  		}
    81  		n, err := io.CopyN(&b, p, maxMemory+1)
    82  		if err != nil && err != io.EOF {
    83  			return nil, err
    84  		}
    85  		if n > maxMemory {
    86  			// too big, write to disk and flush buffer
    87  			file, err := ioutil.TempFile("", "multipart-")
    88  			if err != nil {
    89  				return nil, err
    90  			}
    91  			size, err := io.Copy(file, io.MultiReader(&b, p))
    92  			if cerr := file.Close(); err == nil {
    93  				err = cerr
    94  			}
    95  			if err != nil {
    96  				os.Remove(file.Name())
    97  				return nil, err
    98  			}
    99  			fh.tmpfile = file.Name()
   100  			fh.Size = size
   101  		} else {
   102  			fh.content = b.Bytes()
   103  			fh.Size = int64(len(fh.content))
   104  			maxMemory -= n
   105  			maxValueBytes -= n
   106  		}
   107  		form.File[name] = append(form.File[name], fh)
   108  	}
   109  
   110  	return form, nil
   111  }
   112  
   113  // Form is a parsed multipart form.
   114  // Its File parts are stored either in memory or on disk,
   115  // and are accessible via the *FileHeader's Open method.
   116  // Its Value parts are stored as strings.
   117  // Both are keyed by field name.
   118  type Form struct {
   119  	Value map[string][]string
   120  	File  map[string][]*FileHeader
   121  }
   122  
   123  // RemoveAll removes any temporary files associated with a Form.
   124  func (f *Form) RemoveAll() error {
   125  	var err error
   126  	for _, fhs := range f.File {
   127  		for _, fh := range fhs {
   128  			if fh.tmpfile != "" {
   129  				e := os.Remove(fh.tmpfile)
   130  				if e != nil && err == nil {
   131  					err = e
   132  				}
   133  			}
   134  		}
   135  	}
   136  	return err
   137  }
   138  
   139  // A FileHeader describes a file part of a multipart request.
   140  type FileHeader struct {
   141  	Filename string
   142  	Header   textproto.MIMEHeader
   143  	Size     int64
   144  
   145  	content []byte
   146  	tmpfile string
   147  }
   148  
   149  // Open opens and returns the FileHeader's associated File.
   150  func (fh *FileHeader) Open() (File, error) {
   151  	if b := fh.content; b != nil {
   152  		r := io.NewSectionReader(bytes.NewReader(b), 0, int64(len(b)))
   153  		return sectionReadCloser{r}, nil
   154  	}
   155  	return os.Open(fh.tmpfile)
   156  }
   157  
   158  // File is an interface to access the file part of a multipart message.
   159  // Its contents may be either stored in memory or on disk.
   160  // If stored on disk, the File's underlying concrete type will be an *os.File.
   161  type File interface {
   162  	io.Reader
   163  	io.ReaderAt
   164  	io.Seeker
   165  	io.Closer
   166  }
   167  
   168  // helper types to turn a []byte into a File
   169  
   170  type sectionReadCloser struct {
   171  	*io.SectionReader
   172  }
   173  
   174  func (rc sectionReadCloser) Close() error {
   175  	return nil
   176  }
   177
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