mime/multipart: add ReadForm and associated types

R=brad_danga_com, rsc, dfc, r, dchest, bradfitz
CC=golang-dev
https://golang.org/cl/4439075

src/pkg/mime/multipart/Makefile

@@ -6,6 +6,7 @@ include ../../../Make.inc
 
 TARG=mime/multipart
 GOFILES=\
+	formdata.go\
 	multipart.go\
 
 include ../../../Make.pkg

src/pkg/mime/multipart/formdata.go

+// 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"
+	"io"
+	"io/ioutil"
+	"net/textproto"
+	"os"
+)
+
+// TODO(adg,bradfitz): find a way to unify the DoS-prevention strategy here
+// with that of the http package's ParseForm.
+
+// ReadForm parses an entire multipart message whose parts have
+// a Content-Disposition of "form-data".
+// It stores up to maxMemory bytes of the file parts in memory
+// and the remainder on disk in temporary files.
+func (r *multiReader) ReadForm(maxMemory int64) (f *Form, err os.Error) {
+	form := &Form{make(map[string][]string), make(map[string][]*FileHeader)}
+	defer func() {
+		if err != nil {
+			form.RemoveAll()
+		}
+	}()
+
+	maxValueBytes := int64(10 << 20) // 10 MB is a lot of text.
+	for {
+		p, err := r.NextPart()
+		if err != nil {
+			return nil, err
+		}
+		if p == nil {
+			break
+		}
+
+		name := p.FormName()
+		if name == "" {
+			continue
+		}
+		var filename string
+		if p.dispositionParams != nil {
+			filename = p.dispositionParams["filename"]
+		}
+
+		var b bytes.Buffer
+
+		if filename == "" {
+			// value, store as string in memory
+			n, err := io.Copyn(&b, p, maxValueBytes)
+			if err != nil && err != os.EOF {
+				return nil, err
+			}
+			maxValueBytes -= n
+			if maxValueBytes == 0 {
+				return nil, os.NewError("multipart: message too large")
+			}
+			form.Value[name] = append(form.Value[name], b.String())
+			continue
+		}
+
+		// file, store in memory or on disk
+		fh := &FileHeader{
+			Filename: filename,
+			Header:   p.Header,
+		}
+		n, err := io.Copyn(&b, p, maxMemory+1)
+		if err != nil && err != os.EOF {
+			return nil, err
+		}
+		if n > maxMemory {
+			// too big, write to disk and flush buffer
+			file, err := ioutil.TempFile("", "multipart-")
+			if err != nil {
+				return nil, err
+			}
+			defer file.Close()
+			_, err = io.Copy(file, io.MultiReader(&b, p))
+			if err != nil {
+				os.Remove(file.Name())
+				return nil, err
+			}
+			fh.tmpfile = file.Name()
+		} else {
+			fh.content = b.Bytes()
+			maxMemory -= n
+		}
+		form.File[name] = append(form.File[name], fh)
+	}
+
+	return form, nil
+}
+
+// Form is a parsed multipart form.
+// Its File parts are stored either in memory or on disk,
+// and are accessible via the *FileHeader's Open method.
+// Its Value parts are stored as strings.
+// Both are keyed by field name.
+type Form struct {
+	Value map[string][]string
+	File  map[string][]*FileHeader
+}
+
+// RemoveAll removes any temporary files associated with a Form.
+func (f *Form) RemoveAll() os.Error {
+	var err os.Error
+	for _, fhs := range f.File {
+		for _, fh := range fhs {
+			if fh.tmpfile != "" {
+				e := os.Remove(fh.tmpfile)
+				if e != nil && err == nil {
+					err = e
+				}
+			}
+		}
+	}
+	return err
+}
+
+// A FileHeader describes a file part of a multipart request.
+type FileHeader struct {
+	Filename string
+	Header   textproto.MIMEHeader
+
+	content []byte
+	tmpfile string
+}
+
+// Open opens and returns the FileHeader's associated File.
+func (fh *FileHeader) Open() (File, os.Error) {
+	if b := fh.content; b != nil {
+		r := io.NewSectionReader(sliceReaderAt(b), 0, int64(len(b)))
+		return sectionReadCloser{r}, nil
+	}
+	return os.Open(fh.tmpfile)
+}
+
+// File is an interface to access the file part of a multipart message.
+// Its contents may be either stored in memory or on disk.
+// If stored on disk, the File's underlying concrete type will be an *os.File.
+type File interface {
+	io.Reader
+	io.ReaderAt
+	io.Seeker
+	io.Closer
+}
+
+// helper types to turn a []byte into a File
+
+type sectionReadCloser struct {
+	*io.SectionReader
+}
+
+func (rc sectionReadCloser) Close() os.Error {
+	return nil
+}
+
+type sliceReaderAt []byte
+
+func (r sliceReaderAt) ReadAt(b []byte, off int64) (int, os.Error) {
+	if int(off) >= len(r) || off < 0 {
+		return 0, os.EINVAL
+	}
+	n := copy(b, r[int(off):])
+	return n, nil
+}

src/pkg/mime/multipart/formdata_test.go

+// 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"
+	"io"
+	"os"
+	"regexp"
+	"testing"
+)
+
+func TestReadForm(t *testing.T) {
+	testBody := regexp.MustCompile("\n").ReplaceAllString(message, "\r\n")
+	b := bytes.NewBufferString(testBody)
+	r := NewReader(b, boundary)
+	f, err := r.ReadForm(25)
+	if err != nil {
+		t.Fatal("ReadForm:", err)
+	}
+	defer f.RemoveAll()
+	if g, e := f.Value["texta"][0], textaValue; g != e {
+		t.Errorf("texta value = %q, want %q", g, e)
+	}
+	if g, e := f.Value["textb"][0], textbValue; g != e {
+		t.Errorf("texta value = %q, want %q", g, e)
+	}
+	fd := testFile(t, f.File["filea"][0], "filea.txt", fileaContents)
+	if _, ok := fd.(*os.File); ok {
+		t.Error("file is *os.File, should not be")
+	}
+	fd = testFile(t, f.File["fileb"][0], "fileb.txt", filebContents)
+	if _, ok := fd.(*os.File); !ok {
+		t.Error("file has unexpected underlying type %T", fd)
+	}
+}
+
+func testFile(t *testing.T, fh *FileHeader, efn, econtent string) File {
+	if fh.Filename != efn {
+		t.Errorf("filename = %q, want %q", fh.Filename, efn)
+	}
+	f, err := fh.Open()
+	if err != nil {
+		t.Fatal("opening file:", err)
+	}
+	b := new(bytes.Buffer)
+	_, err = io.Copy(b, f)
+	if err != nil {
+		t.Fatal("copying contents:", err)
+	}
+	if g := b.String(); g != econtent {
+		t.Errorf("contents = %q, want %q", g, econtent)
+	}
+	return f
+}
+
+const (
+	fileaContents = "This is a test file."
+	filebContents = "Another test file."
+	textaValue    = "foo"
+	textbValue    = "bar"
+	boundary      = `MyBoundary`
+)
+
+const message = `
+--MyBoundary
+Content-Disposition: form-data; name="filea"; filename="filea.txt"
+Content-Type: text/plain
+
+` + fileaContents + `
+--MyBoundary
+Content-Disposition: form-data; name="fileb"; filename="fileb.txt"
+Content-Type: text/plain
+
+` + filebContents + `
+--MyBoundary
+Content-Disposition: form-data; name="texta"
+
+` + textaValue + `
+--MyBoundary
+Content-Disposition: form-data; name="textb"
+
+` + textbValue + `
+--MyBoundary--
+`

src/pkg/mime/multipart/multipart.go

@@ -35,6 +35,12 @@ type Reader interface {
 	// reports errors, or on truncated or otherwise malformed
 	// input.
 	NextPart() (*Part, os.Error)
+
+	// ReadForm parses an entire multipart message whose parts have
+	// a Content-Disposition of "form-data".
+	// It stores up to maxMemory bytes of the file parts in memory
+	// and the remainder on disk in temporary files.
+	ReadForm(maxMemory int64) (*Form, os.Error)
 }
 
 // A Part represents a single part in a multipart body.
@@ -46,6 +52,8 @@ type Part struct {
 
 	buffer *bytes.Buffer
 	mr     *multiReader
+
+	dispositionParams map[string]string
 }
 
 // FormName returns the name parameter if p has a Content-Disposition
@@ -53,15 +61,19 @@ type Part struct {
 func (p *Part) FormName() string {
 	// See http://tools.ietf.org/html/rfc2183 section 2 for EBNF
 	// of Content-Disposition value format.
+	if p.dispositionParams != nil {
+		return p.dispositionParams["name"]
+	}
 	v := p.Header.Get("Content-Disposition")
 	if v == "" {
 		return ""
 	}
-	d, params := mime.ParseMediaType(v)
-	if d != "form-data" {
+	if d, params := mime.ParseMediaType(v); d != "form-data" {
 		return ""
+	} else {
+		p.dispositionParams = params
 	}
-	return params["name"]
+	return p.dispositionParams["name"]
 }
 
 // NewReader creates a new multipart Reader reading from r using the