[PDF Ink Signatures] Move and refactor PrepareReplyMessage()

Move PrepareReplyMessage() to a util file so that it can be used in
other files in future CLs (see https://crrev.com/c/5941005).

Remove a redundant param for setting the reply type. This can already be
retrieved from the `message` param.

Add CHECKs before accessing pointers.

Bug: 373672165
Change-Id: I88aaef1bdf2cde42309b6a4e4a06046fb3e790df
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5941004
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Andy Phan <andyphan@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1370814}

pdf/BUILD.gn

@@ -92,6 +92,8 @@ if (enable_pdf) {
       "draw_utils/shadow.h",
       "input_utils.cc",
       "input_utils.h",
+      "message_util.cc",
+      "message_util.h",
       "metrics_handler.cc",
       "metrics_handler.h",
       "page_orientation.cc",
@@ -411,6 +413,7 @@ if (enable_pdf) {
       "document_layout_unittest.cc",
       "draw_utils/coordinates_unittest.cc",
       "input_utils_unittest.cc",
+      "message_util_unittest.cc",
       "page_orientation_unittest.cc",
       "paint_manager_unittest.cc",
       "parsed_params_unittest.cc",

pdf/message_util.cc

@@ -0,0 +1,26 @@
+// Copyright 2024 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "pdf/message_util.h"
+
+#include <string>
+
+#include "base/values.h"
+
+namespace chrome_pdf {
+
+base::Value::Dict PrepareReplyMessage(const base::Value::Dict& message) {
+  const std::string* original_type = message.FindString("type");
+  CHECK(original_type);
+
+  const std::string* message_id = message.FindString("messageId");
+  CHECK(message_id);
+
+  base::Value::Dict reply;
+  reply.Set("type", *original_type + "Reply");
+  reply.Set("messageId", *message_id);
+  return reply;
+}
+
+}  // namespace chrome_pdf

pdf/message_util.h

@@ -0,0 +1,20 @@
+// Copyright 2024 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef PDF_MESSAGE_UTIL_H_
+#define PDF_MESSAGE_UTIL_H_
+
+#include "base/values.h"
+
+namespace chrome_pdf {
+
+// Prepares messages from the plugin that reply to messages from the embedder.
+// If the "type" value of `message` is "foo", then the reply "type" will be
+// "fooReply". The `message` from the embedder must have a "messageId" value
+// that will be copied to the reply message.
+base::Value::Dict PrepareReplyMessage(const base::Value::Dict& message);
+
+}  // namespace chrome_pdf
+
+#endif  // PDF_MESSAGE_UTIL_H_

pdf/message_util_unittest.cc

@@ -0,0 +1,29 @@
+// Copyright 2024 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "pdf/message_util.h"
+
+#include "base/test/values_test_util.h"
+#include "base/values.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace chrome_pdf {
+
+TEST(PrepareReplyMessageTest, BasicReply) {
+  base::Value::Dict message;
+  message.Set("type", "typeBasic");
+  message.Set("messageId", "messageIdBasic");
+
+  base::Value::Dict reply = PrepareReplyMessage(message);
+
+  const std::string* reply_type = reply.FindString("type");
+  ASSERT_TRUE(reply_type);
+  EXPECT_EQ("typeBasicReply", *reply_type);
+
+  const std::string* reply_message_id = reply.FindString("messageId");
+  ASSERT_TRUE(reply_message_id);
+  EXPECT_EQ("messageIdBasic", *reply_message_id);
+}
+
+}  // namespace chrome_pdf

pdf/pdf_view_web_plugin.cc

@@ -58,6 +58,7 @@
 #include "pdf/document_layout.h"
 #include "pdf/loader/result_codes.h"
 #include "pdf/loader/url_loader.h"
+#include "pdf/message_util.h"
 #include "pdf/metrics_handler.h"
 #include "pdf/mojom/pdf.mojom.h"
 #include "pdf/paint_manager.h"
@@ -255,20 +256,6 @@ bool IsPreviewingPDF(int print_preview_page_count) {
   return print_preview_page_count == 0;
 }
 
-// Prepares messages from the plugin that reply to messages from the embedder.
-// If the "type" value of `message` is "foo", then the `reply_type` must be
-// "fooReply". The `message` from the embedder must have a "messageId" value
-// that will be copied to the reply message.
-base::Value::Dict PrepareReplyMessage(std::string_view reply_type,
-                                      const base::Value::Dict& message) {
-  DCHECK_EQ(reply_type, *message.FindString("type") + "Reply");
-
-  base::Value::Dict reply;
-  reply.Set("type", reply_type);
-  reply.Set("messageId", *message.FindString("messageId"));
-  return reply;
-}
-
 bool IsSaveDataSizeValid(size_t size) {
   return size > 0 && size <= PdfViewWebPlugin::kMaximumSavedFileSize;
 }
@@ -1460,8 +1447,7 @@ void PdfViewWebPlugin::HandleGetNamedDestinationMessage(
                               ? base::checked_cast<int>(named_destination->page)
                               : -1;
 
-  base::Value::Dict reply =
-      PrepareReplyMessage("getNamedDestinationReply", message);
+  base::Value::Dict reply = PrepareReplyMessage(message);
   reply.Set("pageNumber", page_number);
 
   if (named_destination.has_value() && !named_destination->view.empty()) {
@@ -1483,8 +1469,7 @@ void PdfViewWebPlugin::HandleGetNamedDestinationMessage(
 void PdfViewWebPlugin::HandleGetPageBoundingBoxMessage(
     const base::Value::Dict& message) {
   const int page_index = message.FindInt("page").value();
-  base::Value::Dict reply =
-      PrepareReplyMessage("getPageBoundingBoxReply", message);
+  base::Value::Dict reply = PrepareReplyMessage(message);
 
   PDFiumPage* page = engine_->GetPage(page_index);
   CHECK(page);
@@ -1514,8 +1499,7 @@ void PdfViewWebPlugin::HandleGetSelectedTextMessage(
   std::string selected_text;
   base::RemoveChars(engine_->GetSelectedText(), "\r", &selected_text);
 
-  base::Value::Dict reply =
-      PrepareReplyMessage("getSelectedTextReply", message);
+  base::Value::Dict reply = PrepareReplyMessage(message);
   reply.Set("selectedText", selected_text);
   client_->PostMessage(std::move(reply));
 }
@@ -1523,7 +1507,7 @@ void PdfViewWebPlugin::HandleGetSelectedTextMessage(
 void PdfViewWebPlugin::HandleGetThumbnailMessage(
     const base::Value::Dict& message) {
   const int page_index = message.FindInt("pageIndex").value();
-  base::Value::Dict reply = PrepareReplyMessage("getThumbnailReply", message);
+  base::Value::Dict reply = PrepareReplyMessage(message);
 
   engine_->RequestThumbnail(
       page_index, device_scale_,
@@ -1561,7 +1545,7 @@ void PdfViewWebPlugin::HandleSaveAttachmentMessage(
   base::Value data_to_save(
       IsSaveDataSizeValid(data.size()) ? data : std::vector<uint8_t>());
 
-  base::Value::Dict reply = PrepareReplyMessage("saveAttachmentReply", message);
+  base::Value::Dict reply = PrepareReplyMessage(message);
   reply.Set("dataToSave", std::move(data_to_save));
   client_->PostMessage(std::move(reply));
 }