net/http: send Content-Range if no byte range overlaps

RFC 7233, section 4.4 says:
>>>
For byte ranges, failing to overlap the current extent means that the
first-byte-pos of all of the byte-range-spec values were greater than the
current length of the selected representation.  When this status code is
generated in response to a byte-range request, the sender SHOULD generate a
Content-Range header field specifying the current length of the selected
representation
<<<

Thus, we should send the Content-Range only if none of the ranges
overlap.

Fixes #15798.

Change-Id: Ic9a3e1b3a8730398b4bdff877a8f2fd2e30149e3
Reviewed-on: https://go-review.googlesource.com/24212
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/net/http/fs.go

@@ -140,6 +140,10 @@ func ServeContent(w ResponseWriter, req *Request, name string, modtime time.Time
 // users.
 var errSeeker = errors.New("seeker can't seek")
 
+// errNoOverlap is returned by serveContent's parseRange if first-byte-pos of
+// all of the byte-range-spec values is greater than the content size.
+var errNoOverlap = errors.New("invalid range: failed to overlap")
+
 // if name is empty, filename is unknown. (used for mime type, before sniffing)
 // if modtime.IsZero(), modtime is unknown.
 // content must be seeked to the beginning of the file.
@@ -189,6 +193,9 @@ func serveContent(w ResponseWriter, r *Request, name string, modtime time.Time,
 	if size >= 0 {
 		ranges, err := parseRange(rangeReq, size)
 		if err != nil {
+			if err == errNoOverlap {
+				w.Header().Set("Content-Range", fmt.Sprintf("bytes */%d", size))
+			}
 			Error(w, err.Error(), StatusRequestedRangeNotSatisfiable)
 			return
 		}
@@ -543,6 +550,7 @@ func (r httpRange) mimeHeader(contentType string, size int64) textproto.MIMEHead
 }
 
 // parseRange parses a Range header string as per RFC 2616.
+// errNoOverlap is returned if none of the ranges overlap.
 func parseRange(s string, size int64) ([]httpRange, error) {
 	if s == "" {
 		return nil, nil // header not present
@@ -552,6 +560,7 @@ func parseRange(s string, size int64) ([]httpRange, error) {
 		return nil, errors.New("invalid range")
 	}
 	var ranges []httpRange
+	noOverlap := false
 	for _, ra := range strings.Split(s[len(b):], ",") {
 		ra = strings.TrimSpace(ra)
 		if ra == "" {
@@ -577,9 +586,15 @@ func parseRange(s string, size int64) ([]httpRange, error) {
 			r.length = size - r.start
 		} else {
 			i, err := strconv.ParseInt(start, 10, 64)
-			if err != nil || i >= size || i < 0 {
+			if err != nil || i < 0 {
 				return nil, errors.New("invalid range")
 			}
+			if i >= size {
+				// If the range begins after the size of the content,
+				// then it does not overlap.
+				noOverlap = true
+				continue
+			}
 			r.start = i
 			if end == "" {
 				// If no end is specified, range extends to end of the file.
@@ -597,6 +612,10 @@ func parseRange(s string, size int64) ([]httpRange, error) {
 		}
 		ranges = append(ranges, r)
 	}
+	if noOverlap && len(ranges) == 0 {
+		// The specified ranges did not overlap with the content.
+		return nil, errNoOverlap
+	}
 	return ranges, nil
 }
 

src/net/http/fs_test.go

@@ -765,6 +765,7 @@ func TestServeContent(t *testing.T) {
 		reqHeader        map[string]string
 		wantLastMod      string
 		wantContentType  string
+		wantContentRange string
 		wantStatus       int
 	}
 	htmlModTime := mustStat(t, "testdata/index.html").ModTime()
@@ -822,6 +823,17 @@ func TestServeContent(t *testing.T) {
 			},
 			wantStatus:       StatusPartialContent,
 			wantContentType:  "text/css; charset=utf-8",
+			wantContentRange: "bytes 0-4/8",
+		},
+		"range_no_overlap": {
+			file:      "testdata/style.css",
+			serveETag: `"A"`,
+			reqHeader: map[string]string{
+				"Range": "bytes=10-20",
+			},
+			wantStatus:       StatusRequestedRangeNotSatisfiable,
+			wantContentType:  "text/plain; charset=utf-8",
+			wantContentRange: "bytes */8",
 		},
 		// An If-Range resource for entity "A", but entity "B" is now current.
 		// The Range request should be ignored.
@@ -844,6 +856,7 @@ func TestServeContent(t *testing.T) {
 			},
 			wantStatus:       StatusPartialContent,
 			wantContentType:  "text/css; charset=utf-8",
+			wantContentRange: "bytes 0-4/8",
 			wantLastMod:      "Wed, 25 Jun 2014 17:12:18 GMT",
 		},
 		"range_with_modtime_nanos": {
@@ -855,6 +868,7 @@ func TestServeContent(t *testing.T) {
 			},
 			wantStatus:       StatusPartialContent,
 			wantContentType:  "text/css; charset=utf-8",
+			wantContentRange: "bytes 0-4/8",
 			wantLastMod:      "Wed, 25 Jun 2014 17:12:18 GMT",
 		},
 		"unix_zero_modtime": {
@@ -903,6 +917,9 @@ func TestServeContent(t *testing.T) {
 		if g, e := res.Header.Get("Content-Type"), tt.wantContentType; g != e {
 			t.Errorf("test %q: content-type = %q, want %q", testName, g, e)
 		}
+		if g, e := res.Header.Get("Content-Range"), tt.wantContentRange; g != e {
+			t.Errorf("test %q: content-range = %q, want %q", testName, g, e)
+		}
 		if g, e := res.Header.Get("Last-Modified"), tt.wantLastMod; g != e {
 			t.Errorf("test %q: last-modified = %q, want %q", testName, g, e)
 		}

src/net/http/range_test.go

@@ -38,7 +38,7 @@ var ParseRangeTests = []struct {
 	{"bytes=0-", 10, []httpRange{{0, 10}}},
 	{"bytes=5-", 10, []httpRange{{5, 5}}},
 	{"bytes=0-20", 10, []httpRange{{0, 10}}},
-	{"bytes=15-,0-5", 10, nil},
+	{"bytes=15-,0-5", 10, []httpRange{{0, 6}}},
 	{"bytes=1-2,5-", 10, []httpRange{{1, 2}, {5, 5}}},
 	{"bytes=-2 , 7-", 11, []httpRange{{9, 2}, {7, 4}}},
 	{"bytes=0-0 ,2-2, 7-", 11, []httpRange{{0, 1}, {2, 1}, {7, 4}}},