net/http: check If-Range header when request method is HEAD

When If-Range does not match and the requested resource is
available, server should return a "200 OK" response to client.
Currently server returns "200 OK" when the request method is
GET, but "206 Partial Content" when method is HEAD.
This change fixed this inconsistency.

Change-Id: I5ad979919f4f089baba54a4445b70ca38471a906
Reviewed-on: https://go-review.googlesource.com/54110
Run-TryBot: Tom Bergan <tombergan@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tom Bergan <tombergan@google.com>

src/net/http/fs.go

@@ -445,7 +445,7 @@ func checkIfModifiedSince(r *Request, modtime time.Time) condResult {
 }
 
 func checkIfRange(w ResponseWriter, r *Request, modtime time.Time) condResult {
-	if r.Method != "GET" {
+	if r.Method != "GET" && r.Method != "HEAD" {
 		return condNone
 	}
 	ir := r.Header.get("If-Range")

src/net/http/fs_test.go

@@ -895,6 +895,17 @@ func TestServeContent(t *testing.T) {
 			wantContentRange: "bytes 0-4/8",
 			wantLastMod:      "Wed, 25 Jun 2014 17:12:18 GMT",
 		},
+		"range_with_modtime_mismatch": {
+			file:    "testdata/style.css",
+			modtime: time.Date(2014, 6, 25, 17, 12, 18, 0 /* nanos */, time.UTC),
+			reqHeader: map[string]string{
+				"Range":    "bytes=0-4",
+				"If-Range": "Wed, 25 Jun 2014 17:12:19 GMT",
+			},
+			wantStatus:      StatusOK,
+			wantContentType: "text/css; charset=utf-8",
+			wantLastMod:     "Wed, 25 Jun 2014 17:12:18 GMT",
+		},
 		"range_with_modtime_nanos": {
 			file:    "testdata/style.css",
 			modtime: time.Date(2014, 6, 25, 17, 12, 18, 123 /* nanos */, time.UTC),
@@ -982,40 +993,46 @@ func TestServeContent(t *testing.T) {
 		} else {
 			content = tt.content
 		}
+		for _, method := range []string{"GET", "HEAD"} {
+			//restore content in case it is consumed by previous method
+			if content, ok := content.(*strings.Reader); ok {
+				content.Seek(io.SeekStart, 0)
+			}
 
-		servec <- serveParam{
-			name:        filepath.Base(tt.file),
-			content:     content,
-			modtime:     tt.modtime,
-			etag:        tt.serveETag,
-			contentType: tt.serveContentType,
-		}
-		req, err := NewRequest("GET", ts.URL, nil)
-		if err != nil {
-			t.Fatal(err)
-		}
-		for k, v := range tt.reqHeader {
-			req.Header.Set(k, v)
-		}
+			servec <- serveParam{
+				name:        filepath.Base(tt.file),
+				content:     content,
+				modtime:     tt.modtime,
+				etag:        tt.serveETag,
+				contentType: tt.serveContentType,
+			}
+			req, err := NewRequest(method, ts.URL, nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			for k, v := range tt.reqHeader {
+				req.Header.Set(k, v)
+			}
 
-		c := ts.Client()
-		res, err := c.Do(req)
-		if err != nil {
-			t.Fatal(err)
-		}
-		io.Copy(ioutil.Discard, res.Body)
-		res.Body.Close()
-		if res.StatusCode != tt.wantStatus {
-			t.Errorf("test %q: status = %d; want %d", testName, res.StatusCode, tt.wantStatus)
-		}
-		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)
+			c := ts.Client()
+			res, err := c.Do(req)
+			if err != nil {
+				t.Fatal(err)
+			}
+			io.Copy(ioutil.Discard, res.Body)
+			res.Body.Close()
+			if res.StatusCode != tt.wantStatus {
+				t.Errorf("test %q using %q: got status = %d; want %d", testName, method, res.StatusCode, tt.wantStatus)
+			}
+			if g, e := res.Header.Get("Content-Type"), tt.wantContentType; g != e {
+				t.Errorf("test %q using %q: got content-type = %q, want %q", testName, method, g, e)
+			}
+			if g, e := res.Header.Get("Content-Range"), tt.wantContentRange; g != e {
+				t.Errorf("test %q using %q: got content-range = %q, want %q", testName, method, g, e)
+			}
+			if g, e := res.Header.Get("Last-Modified"), tt.wantLastMod; g != e {
+				t.Errorf("test %q using %q: got last-modified = %q, want %q", testName, method, g, e)
+			}
 		}
 	}
 }