multipart: return an error on Reader EOF, not (nil, nil)

R=rsc, adg
CC=golang-dev
https://golang.org/cl/4430074

src/pkg/mime/multipart/formdata.go

@@ -30,12 +30,12 @@ func (r *multiReader) ReadForm(maxMemory int64) (f *Form, err os.Error) {
 	maxValueBytes := int64(10 << 20) // 10 MB is a lot of text.
 	for {
 		p, err := r.NextPart()
+		if err == os.EOF {
+			break
+		}
 		if err != nil {
 			return nil, err
 		}
-		if p == nil {
-			break
-		}
 
 		name := p.FormName()
 		if name == "" {

src/pkg/mime/multipart/multipart.go

@@ -30,10 +30,8 @@ var headerRegexp *regexp.Regexp = regexp.MustCompile("^([a-zA-Z0-9\\-]+): *([^\r
 // Reader's underlying parser consumes its input as needed.  Seeking
 // isn't supported.
 type Reader interface {
-	// NextPart returns the next part in the multipart, or (nil,
-	// nil) on EOF.  An error is returned if the underlying reader
-	// reports errors, or on truncated or otherwise malformed
-	// input.
+	// NextPart returns the next part in the multipart or an error.
+	// When there are no more parts, the error os.EOF is returned.
 	NextPart() (*Part, os.Error)
 
 	// ReadForm parses an entire multipart message whose parts have
@@ -207,9 +205,8 @@ func (mr *multiReader) NextPart() (*Part, os.Error) {
 		}
 
 		if hasPrefixThenNewline(line, mr.dashBoundaryDash) {
-			// Expected EOF (no error)
-			// TODO(bradfitz): should return an os.EOF error here, not using nil for errors
-			return nil, nil
+			// Expected EOF
+			return nil, os.EOF
 		}
 
 		if expectNewPart {

src/pkg/mime/multipart/multipart_test.go

@@ -201,8 +201,8 @@ func testMultipart(t *testing.T, r io.Reader) {
 	if part != nil {
 		t.Error("Didn't expect a fifth part.")
 	}
-	if err != nil {
-		t.Errorf("Unexpected error getting fifth part: %v", err)
+	if err != os.EOF {
+		t.Errorf("On  fifth part expected os.EOF; got %v", err)
 	}
 }
 
@@ -246,8 +246,8 @@ func TestVariousTextLineEndings(t *testing.T) {
 		if part != nil {
 			t.Errorf("Unexpected part in test %d", testNum)
 		}
-		if err != nil {
-			t.Errorf("Unexpected error in test %d: %v", testNum, err)
+		if err != os.EOF {
+			t.Errorf("On test %d expected os.EOF; got %v", testNum, err)
 		}
 
 	}