[ChromeDriver] Confirm brackets found before substr

Some code paths do not set the status message for UnexpectedAlertOpen
errors. When these are encountered, the code crashes when the { or }
are not found. This CL checks for that state and prevents the crash.

Fixed: chromedriver:3073
Change-Id: I9cc1cf4f1988af1300f9363add90a1217f0cb26c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1877136Reviewed-by: John Chen <johnchen@chromium.org>
Commit-Queue: Tricia Crichton <triciac@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709051}

chrome/test/chromedriver/server/http_handler.cc

@@ -1249,11 +1249,15 @@ HttpHandler::PrepareStandardResponse(
     // error UnexpectedAlertOpen should contain 'data.text' with alert text
     if (status.code() == kUnexpectedAlertOpen) {
       const std::string& message = status.message();
-      unsigned first = message.find("{");
-      unsigned last = message.find_last_of("}");
-      std::string alertText = message.substr(first, last-first);
-      alertText = alertText.substr(alertText.find(":") + 2);
-      inner_params->SetString("data.text", alertText);
+      auto first = message.find("{");
+      auto last = message.find_last_of("}");
+      if (first == std::string::npos || last == std::string::npos) {
+        inner_params->SetString("data.text", "");
+      } else {
+        std::string alertText = message.substr(first, last - first);
+        alertText = alertText.substr(alertText.find(":") + 2);
+        inner_params->SetString("data.text", alertText);
+      }
     }
     body_params.SetDictionary("value", std::move(inner_params));
   } else {

chrome/test/chromedriver/server/http_handler.h

@@ -85,6 +85,7 @@ class HttpHandler {
   FRIEND_TEST_ALL_PREFIXES(HttpHandlerTest, HandleInvalidPost);
   FRIEND_TEST_ALL_PREFIXES(HttpHandlerTest, HandleUnimplementedCommand);
   FRIEND_TEST_ALL_PREFIXES(HttpHandlerTest, HandleCommand);
+  FRIEND_TEST_ALL_PREFIXES(HttpHandlerTest, StandardResponse_ErrorNoMessage);
   typedef std::vector<CommandMapping> CommandMap;
 
   Command WrapToCommand(const char* name,

chrome/test/chromedriver/server/http_handler_unittest.cc

@@ -126,6 +126,13 @@ TEST(HttpHandlerTest, HandleCommand) {
   ASSERT_EQ(json, response.body());
 }
 
+TEST(HttpHandlerTest, StandardResponse_ErrorNoMessage) {
+  HttpHandler handler("/");
+  Status status = Status(kUnexpectedAlertOpen);
+  ASSERT_NO_FATAL_FAILURE(handler.PrepareStandardResponse(
+      "not used", status, std::make_unique<base::Value>(), "1234"));
+}
+
 TEST(MatchesCommandTest, DiffMethod) {
   CommandMapping command(kPost, "path", base::Bind(&DummyCommand, Status(kOk)));
   std::string session_id;