limit bytes passed to http.DetectContentType (#10348)

client/allocdir/alloc_dir.go

@@ -426,9 +426,9 @@ func detectContentType(fileInfo os.FileInfo, path string) string {
 		// We ignore errors because this is optional information
 		if err == nil {
 			fileBytes := make([]byte, 512)
-			_, err := f.Read(fileBytes)
+			n, err := f.Read(fileBytes)
 			if err == nil {
-				contentType = http.DetectContentType(fileBytes)
+				contentType = http.DetectContentType(fileBytes[:n])
 			}
 			f.Close()
 		}

client/allocdir/alloc_dir_test.go

@@ -493,6 +493,7 @@ func TestAllocDir_DetectContentType(t *testing.T) {
 		"input/test.json": "application/json",
 		"input/test.txt":  "text/plain; charset=utf-8",
 		"input/test.go":   "text/plain; charset=utf-8",
+		"input/test.hcl":  "text/plain; charset=utf-8",
 	}
 	for _, file := range testFiles {
 		fileInfo, err := os.Stat(file)

client/allocdir/input/test.hcl

@@ -0,0 +1,3 @@
+test "test" {
+  test = "test"
+}