mime/multipart: add a multipart Writer

Fixes #1823

R=golang-dev, adg, robert.hencke
CC=golang-dev
https://golang.org/cl/4530054

src/pkg/mime/multipart/Makefile

@@ -8,5 +8,6 @@ TARG=mime/multipart
 GOFILES=\
 	formdata.go\
 	multipart.go\
+	writer.go\
 
 include ../../../Make.pkg

src/pkg/mime/multipart/writer.go

@@ -0,0 +1,160 @@
+// 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"
+	"fmt"
+	"io"
+	"net/textproto"
+	"os"
+	"rand"
+	"strings"
+)
+
+// Writer is used to generate multipart messages.
+type Writer struct {
+	// Boundary is the random boundary string between
+	// parts. NewWriter will generate this but it must
+	// not be changed after a part has been created.
+	// Setting this to an invalid value will generate
+	// malformed messages.
+	Boundary string
+
+	w        io.Writer
+	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(),
+	}
+}
+
+// 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
+}
+
+const randChars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+
+func randomBoundary() string {
+	var buf [60]byte
+	for i := range buf {
+		buf[i] = randChars[rand.Intn(len(randChars))]
+	}
+	return string(buf[:])
+}
+
+// CreatePart creates a new multipart section with the provided
+// header. The previous part, if still open, is closed. The body of
+// the part should be written to the returned WriteCloser. Closing the
+// returned WriteCloser after writing is optional.
+func (w *Writer) CreatePart(header textproto.MIMEHeader) (io.WriteCloser, os.Error) {
+	if w.lastpart != nil {
+		if err := w.lastpart.Close(); err != nil {
+			return nil, err
+		}
+	}
+	var b bytes.Buffer
+	fmt.Fprintf(&b, "\r\n--%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
+}
+
+func escapeQuotes(s string) string {
+	s = strings.Replace(s, "\\", "\\\\", -1)
+	s = strings.Replace(s, "\"", "\\\"", -1)
+	return 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.WriteCloser, os.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 is a convenience wrapper around CreatePart. It creates
+// a new form-data header with the provided field name.
+func (w *Writer) CreateFormField(fieldname string) (io.WriteCloser, os.Error) {
+	h := make(textproto.MIMEHeader)
+	h.Set("Content-Disposition",
+		fmt.Sprintf(`form-data; name="%s"`, escapeQuotes(fieldname)))
+	return w.CreatePart(h)
+}
+
+// WriteField is a convenience wrapper around CreateFormField. It creates and
+// writes a part with the provided name and value.
+func (w *Writer) WriteField(fieldname, value string) os.Error {
+	p, err := w.CreateFormField(fieldname)
+	if err != nil {
+		return err
+	}
+	_, err = p.Write([]byte(value))
+	if err != nil {
+		return err
+	}
+	return p.Close()
+}
+
+// Close finishes the multipart message. It closes the previous part,
+// if still open, and writes the trailing boundary end line to the
+// output.
+func (w *Writer) Close() os.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     os.Error // last error that occurred writing
+}
+
+func (p *part) Close() os.Error {
+	p.closed = true
+	return p.we
+}
+
+func (p *part) Write(d []byte) (n int, err os.Error) {
+	if p.closed {
+		return 0, os.NewError("multipart: Write after Close")
+	}
+	n, err = p.mw.w.Write(d)
+	if err != nil {
+		p.we = err
+	}
+	return
+}

src/pkg/mime/multipart/writer_test.go

@@ -0,0 +1,71 @@
+// 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/ioutil"
+	"testing"
+)
+
+func TestWriter(t *testing.T) {
+	fileContents := []byte("my file contents")
+
+	var b bytes.Buffer
+	w := NewWriter(&b)
+	{
+		part, err := w.CreateFormFile("myfile", "my-file.txt")
+		if err != nil {
+			t.Fatalf("CreateFormFile: %v", err)
+		}
+		part.Write(fileContents)
+		err = w.WriteField("key", "val")
+		if err != nil {
+			t.Fatalf("CreateFormFieldValue: %v", err)
+		}
+		part.Write([]byte("val"))
+		err = w.Close()
+		if err != nil {
+			t.Fatalf("Close: %v", err)
+		}
+	}
+
+	r := NewReader(&b, w.Boundary)
+
+	part, err := r.NextPart()
+	if err != nil {
+		t.Fatalf("part 1: %v", err)
+	}
+	if g, e := part.FormName(), "myfile"; g != e {
+		t.Errorf("part 1: want form name %q, got %q", e, g)
+	}
+	slurp, err := ioutil.ReadAll(part)
+	if err != nil {
+		t.Fatalf("part 1: ReadAll: %v", err)
+	}
+	if e, g := string(fileContents), string(slurp); e != g {
+		t.Errorf("part 1: want contents %q, got %q", e, g)
+	}
+
+	part, err = r.NextPart()
+	if err != nil {
+		t.Fatalf("part 2: %v", err)
+	}
+	if g, e := part.FormName(), "key"; g != e {
+		t.Errorf("part 2: want form name %q, got %q", e, g)
+	}
+	slurp, err = ioutil.ReadAll(part)
+	if err != nil {
+		t.Fatalf("part 2: ReadAll: %v", err)
+	}
+	if e, g := "val", string(slurp); e != g {
+		t.Errorf("part 2: want contents %q, got %q", e, g)
+	}
+
+	part, err = r.NextPart()
+	if part != nil || err == nil {
+		t.Fatalf("expected end of parts; got %v, %v", part, err)
+	}
+}