mime/multipart: handle ReadForm(math.MaxInt64) better

Returning an error about integer overflow is needlessly pedantic.
The meaning of ReadForm(MaxInt64) is easily understood
(accept a lot of data) and can be implemented.

Fixes #40430.

Change-Id: I8a522033dd9a2f9ad31dd2ad82cf08d553736ab9
Reviewed-on: https://go-review.googlesource.com/c/go/+/275112
Trust: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 11 insertions, 11 deletions

diff --git a/src/mime/multipart/formdata.go b/src/mime/multipart/formdata.go
index 4eb3101294..9c42ea8c02 100644
--- a/src/mime/multipart/formdata.go
+++ b/src/mime/multipart/formdata.go
@@ -7,9 +7,9 @@ package multipart
 import (
 	"bytes"
 	"errors"
-	"fmt"
 	"io"
 	"io/ioutil"
+	"math"
 	"net/textproto"
 	"os"
 )
@@ -43,7 +43,11 @@ func (r *Reader) readForm(maxMemory int64) (_ *Form, err error) {
 	// Reserve an additional 10 MB for non-file parts.
 	maxValueBytes := maxMemory + int64(10<<20)
 	if maxValueBytes <= 0 {
-		return nil, fmt.Errorf("multipart: integer overflow from maxMemory(%d) + 10MiB for non-file parts", maxMemory)
+		if maxMemory < 0 {
+			maxValueBytes = 0
+		} else {
+			maxValueBytes = math.MaxInt64
+		}
 	}
 	for {
 		p, err := r.NextPart()
diff --git a/src/mime/multipart/formdata_test.go b/src/mime/multipart/formdata_test.go
index 7112e0d372..e3a3a3eae8 100644
--- a/src/mime/multipart/formdata_test.go
+++ b/src/mime/multipart/formdata_test.go
@@ -53,20 +53,16 @@ func TestReadFormWithNamelessFile(t *testing.T) {
 	}
 }
 
-// Issue 40430: Ensure that we report integer overflows in additions of maxMemory,
-// instead of silently and subtly failing without indication.
+// Issue 40430: Handle ReadForm(math.MaxInt64)
 func TestReadFormMaxMemoryOverflow(t *testing.T) {
 	b := strings.NewReader(strings.ReplaceAll(messageWithTextContentType, "\n", "\r\n"))
 	r := NewReader(b, boundary)
 	f, err := r.ReadForm(math.MaxInt64)
-	if err == nil {
-		t.Fatal("Unexpected a non-nil error")
-	}
-	if f != nil {
-		t.Fatalf("Unexpected returned a non-nil form: %v\n", f)
+	if err != nil {
+		t.Fatalf("ReadForm(MaxInt64): %v", err)
 	}
-	if g, w := err.Error(), "integer overflow from maxMemory"; !strings.Contains(g, w) {
-		t.Errorf(`Error mismatch\n%q\ndid not contain\n%q`, g, w)
+	if f == nil {
+		t.Fatal("ReadForm(MaxInt64): missing form")
 	}
 }