[FS] Go through file system abstraction for truncating files.

The save file dialog needs to truncate any files that are opened. Before
this was using base::File directly. This CL routes truncating through
the file system backends to facilitate supporting non-local files.

Bug: 1093653
Change-Id: I51c2cf8a776de70375e57be7a8a5d02641226bfa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2392414
Commit-Queue: Marijn Kruisselbrink <mek@chromium.org>
Reviewed-by: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805501}

content/browser/native_file_system/native_file_system_manager_impl.cc

@@ -117,10 +117,50 @@ void ShowFilePickerOnUIThread(const url::Origin& requesting_origin,
                                    std::move(fullscreen_block));
 }
 
-bool CreateOrTruncateFile(const base::FilePath& path) {
-  int creation_flags = base::File::FLAG_CREATE_ALWAYS | base::File::FLAG_WRITE;
-  base::File file(path, creation_flags);
-  return file.IsValid();
+// Called after creating a file that was picked by a save file picker. If
+// creation succeeded (or the file already existed) this will attempt to
+// truncate the file to zero bytes, and call `callback` on `reply_runner`
+// with the result of this operation.
+void DidCreateFileToTruncate(
+    storage::FileSystemURL url,
+    base::OnceCallback<void(bool)> callback,
+    scoped_refptr<base::SequencedTaskRunner> reply_runner,
+    storage::FileSystemOperationRunner* operation_runner,
+    base::File::Error result) {
+  if (result != base::File::FILE_OK) {
+    // Failed to create the file, don't even try to truncate it.
+    reply_runner->PostTask(FROM_HERE,
+                           base::BindOnce(std::move(callback), false));
+    return;
+  }
+  operation_runner->Truncate(
+      url, /*length=*/0,
+      base::BindOnce(
+          [](base::OnceCallback<void(bool)> callback,
+             scoped_refptr<base::SequencedTaskRunner> reply_runner,
+             base::File::Error result) {
+            reply_runner->PostTask(
+                FROM_HERE, base::BindOnce(std::move(callback),
+                                          result == base::File::FILE_OK));
+          },
+          std::move(callback), std::move(reply_runner)));
+}
+
+// Creates and truncates the file at `url`. Calls `callback` on `reply_runner`
+// with true if this succeeded, or false if either creation or truncation
+// failed.
+void CreateAndTruncateFile(
+    storage::FileSystemURL url,
+    base::OnceCallback<void(bool)> callback,
+    scoped_refptr<base::SequencedTaskRunner> reply_runner,
+    storage::FileSystemOperationRunner* operation_runner) {
+  // Binding operation_runner as a raw pointer is safe, since the callback is
+  // invoked by the operation runner, and thus won't be invoked if the operation
+  // runner has been destroyed.
+  operation_runner->CreateFile(
+      url, /*exclusive=*/false,
+      base::BindOnce(&DidCreateFileToTruncate, url, std::move(callback),
+                     std::move(reply_runner), operation_runner));
 }
 
 bool IsValidTransferToken(NativeFileSystemTransferTokenImpl* token,
@@ -845,12 +885,19 @@ void NativeFileSystemManagerImpl::DidVerifySensitiveDirectoryAccess(
   if (options.type() == blink::mojom::ChooseFileSystemEntryType::kSaveFile) {
     DCHECK_EQ(entries.size(), 1u);
     // Create file if it doesn't yet exist, and truncate file if it does exist.
-    base::ThreadPool::PostTaskAndReplyWithResult(
-        FROM_HERE, {base::TaskPriority::USER_BLOCKING, base::MayBlock()},
-        base::BindOnce(&CreateOrTruncateFile, entries.front()),
+    FileSystemURLAndFSHandle url =
+        CreateFileSystemURLFromPath(binding_context.origin, entries.front());
+
+    auto fs_url = url.url;
+    operation_runner().PostTaskWithThisObject(
+        FROM_HERE,
         base::BindOnce(
-            &NativeFileSystemManagerImpl::DidCreateOrTruncateSaveFile, this,
-            binding_context, entries.front(), std::move(callback)));
+            &CreateAndTruncateFile, fs_url,
+            base::BindOnce(
+                &NativeFileSystemManagerImpl::DidCreateAndTruncateSaveFile,
+                this, binding_context, entries.front(), std::move(url),
+                std::move(callback)),
+            base::SequencedTaskRunnerHandle::Get()));
     return;
   }
 
@@ -864,14 +911,18 @@ void NativeFileSystemManagerImpl::DidVerifySensitiveDirectoryAccess(
                           std::move(result_entries));
 }
 
-void NativeFileSystemManagerImpl::DidCreateOrTruncateSaveFile(
+void NativeFileSystemManagerImpl::DidCreateAndTruncateSaveFile(
     const BindingContext& binding_context,
     const base::FilePath& path,
+    FileSystemURLAndFSHandle url,
     ChooseEntriesCallback callback,
     bool success) {
   DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   std::vector<blink::mojom::NativeFileSystemEntryPtr> result_entries;
   if (!success) {
+    // TODO(https://crbug.com/1124871): Failure to create or truncate the file
+    // should probably not just result in a generic error, but instead inform
+    // the user of the problem?
     std::move(callback).Run(
         native_file_system_error::FromStatus(
             blink::mojom::NativeFileSystemStatus::kOperationFailed,
@@ -879,8 +930,16 @@ void NativeFileSystemManagerImpl::DidCreateOrTruncateSaveFile(
         std::move(result_entries));
     return;
   }
-  result_entries.push_back(
-      CreateFileEntryFromPath(binding_context, path, UserAction::kSave));
+
+  SharedHandleState shared_handle_state = GetSharedHandleStateForPath(
+      path, binding_context.origin, std::move(url.file_system),
+      HandleType::kFile, NativeFileSystemPermissionContext::UserAction::kSave);
+
+  result_entries.push_back(blink::mojom::NativeFileSystemEntry::New(
+      blink::mojom::NativeFileSystemHandle::NewFile(
+          CreateFileHandle(binding_context, url.url, shared_handle_state)),
+      url.base_name));
+
   std::move(callback).Run(native_file_system_error::Ok(),
                           std::move(result_entries));
 }

content/browser/native_file_system/native_file_system_manager_impl.h

@@ -248,10 +248,11 @@ class CONTENT_EXPORT NativeFileSystemManagerImpl
       ChooseEntriesCallback callback,
       std::vector<base::FilePath> entries,
       NativeFileSystemPermissionContext::SensitiveDirectoryResult result);
-  void DidCreateOrTruncateSaveFile(const BindingContext& binding_context,
-                                   const base::FilePath& path,
-                                   ChooseEntriesCallback callback,
-                                   bool success);
+  void DidCreateAndTruncateSaveFile(const BindingContext& binding_context,
+                                    const base::FilePath& path,
+                                    FileSystemURLAndFSHandle url,
+                                    ChooseEntriesCallback callback,
+                                    bool success);
   void DidChooseDirectory(
       const BindingContext& binding_context,
       const base::FilePath& path,