ShellUtil: Add generic methods to add/delete Windows file associations.

chrome/browser/file_associations_win.cc

Index: chrome/browser/file_associations_win.cc
diff --git a/chrome/browser/file_associations_win.cc b/chrome/browser/file_associations_win.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d2a6f4574b4fa7c7e3f9b9718c966110a95ab31c
--- /dev/null
+++ b/chrome/browser/file_associations_win.cc
@@ -0,0 +1,196 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/file_associations_win.h"
+
+#include <vector>
+
+#include <shlobj.h>
+
+#include "base/command_line.h"
+#include "base/files/file_path.h"
+#include "base/logging.h"
+#include "base/strings/string16.h"
+#include "base/strings/string_util.h"
+#include "base/strings/utf_string_conversions.h"
+#include "base/win/registry.h"
+
+namespace {
+
+// Key relative to HKEY_CURRENT_USER that provides a user-writable alias for
+// HKEY_CLASSES_ROOT.
+const wchar_t kRegClassesRootAlias[] = L"Software\\Classes";
+const wchar_t kRegDefaultIcon[] = L"\\DefaultIcon";
+const wchar_t kRegShellOpen[] = L"\\shell\\open\\command";
+const wchar_t kRegOpenWithProgids[] = L"\\OpenWithProgids";
+
+// Writes a value to the Windows registry under HKEY_CURRENT_USER, creating the
+// key if it does not already exist. If |value_name| is the empty string, writes
+// to the default value for the given key. If |keep_existing| is true, will not
+// overwrite an existing value. If an error occurs, logs an error and returns
+// false.
+bool WriteCurrentUserRegistryValue(const base::string16& key_name,
+                                   const base::string16& value_name,
+                                   const base::string16& value_data,
+                                   bool keep_existing) {
+  base::win::RegKey key;
+  if (key.Create(HKEY_CURRENT_USER, key_name.c_str(), KEY_ALL_ACCESS) !=
+      ERROR_SUCCESS) {
+    LOG(ERROR) << "Could not create HKEY_CURRENT_USER\\" << key_name;

[jackhou1, 2014/08/19 08:16:54]

I think in general logging that will not be seen is discouraged. Maybe make
these DLOGs.

[Matt Giuca, 2014/08/19 08:24:48]

Hmm OK. Well the problem is that these errors are likely to be caused by
transient problems like registry being unavailable for some reason. So I think
we do want it to be logged somewhere, but it shouldn't crash the program or
interrupt the user.

What is the reason for DLOG instead of LOG? It just means if it's happening to a
user they'll be less likely to be able to diagnose it.

+    return false;
+  }
+  if (keep_existing && key.HasValue(NULL))
+    return true;
+  if (key.WriteValue(value_name.empty() ? NULL : value_name.c_str(),
+                     value_data.c_str()) != ERROR_SUCCESS) {
+    LOG(ERROR) << "Could not write HKEY_CURRENT_USER\\" << key_name << "."
+               << (value_name.empty() ? L"(Default)" : value_name);
+    return false;
+  }
+  return true;
+}
+
+// Writes a value to the Windows registry, overwriting any existing data.
+bool WriteCurrentUserRegistryValue(const base::string16& key_name,
+                                   const base::string16& value_name,
+                                   const base::string16& value_data) {
+  return WriteCurrentUserRegistryValue(key_name, value_name, value_data, false);
+}
+
+// Class helper for AddWindowsFileAssociations. Objects of this class live only
+// during the AddWindowsFileAssociations operation.
+class FileAssociator {
+ public:
+  FileAssociator(const base::string16& progid);
+
+  // Creates the registry key for the file association class. This is the key
+  // that supplies information about the class (such as its name and command
+  // line), and is referenced by all file extensions sharing the association.
+  bool RegisterClass(const base::string16& file_type_name,
+                     const base::FilePath& icon_path,
+                     const base::CommandLine& command_line);
+
+  // Deletes the registry key for the file association class.
+  bool DeleteClass();
+
+  // Adds a file extension as a supported type of this class. |ext| is the file
+  // extension (without a leading '.').
+  bool AssociateExtension(const base::string16& ext);
+
+ private:
+  // The class name for this association.
+  base::string16 progid_;
+};
+
+FileAssociator::FileAssociator(const base::string16& progid) : progid_(progid) {
+}
+
+bool FileAssociator::RegisterClass(const base::string16& file_type_name,
+                                   const base::FilePath& icon_path,
+                                   const base::CommandLine& command_line) {
+  // Open or create a key HKEY_CLASSES_ROOT\PROGID.
+  base::string16 class_key_name = kRegClassesRootAlias;
+  class_key_name += L"\\";
+  class_key_name += progid_;
+
+  // Set the file type's user-visible name.
+  if (!WriteCurrentUserRegistryValue(class_key_name, L"", file_type_name))
+    return false;
+
+  // Set the file type's icon.
+  if (!WriteCurrentUserRegistryValue(
+          class_key_name + kRegDefaultIcon, L"", icon_path.value() + L",0")) {
+    return false;
+  }
+
+  // Set the command line to execute for the "open" verb.
+  if (!WriteCurrentUserRegistryValue(class_key_name + kRegShellOpen,
+                                     L"",
+                                     command_line.GetCommandLineString())) {
+    return false;
+  }
+
+  return true;
+}
+
+bool FileAssociator::DeleteClass() {
+  // Delete the key HKEY_CLASSES_ROOT\PROGID.
+  base::win::RegKey key;
+  if (key.Open(HKEY_CURRENT_USER, kRegClassesRootAlias, KEY_ALL_ACCESS) !=
+      ERROR_SUCCESS) {
+    LOG(ERROR) << "Could not open HKEY_CURRENT_USER\\" << kRegClassesRootAlias;
+    return false;
+  }
+
+  if (key.DeleteKey(progid_.c_str()) != ERROR_SUCCESS) {
+    LOG(ERROR) << "Could not delete HKEY_CURRENT_USER\\" << kRegClassesRootAlias
+               << "\\" << progid_;
+    return false;
+  }
+
+  return true;
+}
+
+bool FileAssociator::AssociateExtension(const base::string16& ext) {
+  // Open or create a key HKEY_CLASSES_ROOT\.EXT.
+  base::string16 ext_key_name = kRegClassesRootAlias;
+  ext_key_name += L"\\.";
+  ext_key_name += ext;
+
+  // Under OpenWithProgids, create an empty value with this class's name.
+  if (!WriteCurrentUserRegistryValue(
+          ext_key_name + kRegOpenWithProgids, progid_, L"")) {
+    return false;
+  }
+
+  // If the extension key has no default value (the default class for this
+  // file type) is blank, register this application as the default handler.
+  // Otherwise, leave the existing default as-is.
+  return WriteCurrentUserRegistryValue(ext_key_name, L"", progid_, true);
+}
+
+}  // namespace
+
+bool AddWindowsFileAssociations(const std::string& progid,
+                                const base::CommandLine& command_line,
+                                const std::string& file_type_name,
+                                const base::FilePath& icon_path,
+                                const std::set<std::string>& file_extensions) {
+  FileAssociator associator(base::UTF8ToUTF16(progid));
+
+  // Create a class for this app.
+  if (!associator.RegisterClass(
+          base::UTF8ToUTF16(file_type_name), icon_path, command_line)) {
+    return false;
+  }
+
+  // Associate each extension that the app can handle with the class.
+  for (std::set<std::string>::const_iterator it = file_extensions.begin();
+       it != file_extensions.end();
+       ++it) {
+    if (!associator.AssociateExtension(base::UTF8ToUTF16(*it)))
+      return false;
+  }
+
+  // Success. Tell Windows Explorer to update its cache.
+  SHChangeNotify(
+      SHCNE_ASSOCCHANGED, SHCNF_IDLIST | SHCNF_FLUSHNOWAIT, NULL, NULL);
+  return true;
+}
+
+bool DeleteWindowsFileAssociations(const std::string& progid) {

[jackhou1, 2014/08/19 08:16:54]

Is there a way to delete the entries added by AssociateExtension? If not, would
that be a problem?

[Matt Giuca, 2014/08/19 08:24:48]

We could, but it would mean either:
a) Taking a list of extensions. Then we would have to make sure that the list of
extensions we give during delete is different to the list we give during add
(which it might not be, if for example the app changes or our internal list of
extensions corresponding to a mime type changes), or
b) Iterate over all extensions registered and find the ones mentioning our
progid. (Seems unscalable.)

This makes me think about an interesting problem: say an app changes its
manifest and removes an extension from file handlers. Should we go in and delete
that extension's association (without deleting the progid)? Sounds hard... (but
a challenge for another CL.)

[jackhou1, 2014/08/19 08:40:03]

What if we add a value to the progid key that contains the list of extensions?
When updating, if this changes, we make the necessary additions/deletions.

[Matt Giuca, 2014/08/22 03:48:58]

Yeah that sounds reasonable. But I'd like to do it in a follow-up CL; it's a
good separate chunk of functionality and it's non-trivial (updating and deleting
should both be modified to respect this list).

I *could* use SupportedTypes -- Windows already provides a mechanism for
applications to list all of the extensions they support in a big list in the
registry:
http://msdn.microsoft.com/en-us/library/windows/desktop/ee872121.aspx
but I tried to use it and it didn't seem to have any effect. Still, it can't
hurt to use this for our record-keeping instead of inventing a new key.

+  FileAssociator associator(base::UTF8ToUTF16(progid));
+
+  // Delete the class for this app.
+  associator.DeleteClass();
+
+  // Note: there is no need to remove the association from the extension to the
+  // class, as Windows will ignore it. See:
+  // http://msdn.microsoft.com/en-us/library/windows/desktop/cc144148.aspx
+
+  // Success. Tell Windows Explorer to update its cache.
+  SHChangeNotify(
+      SHCNE_ASSOCCHANGED, SHCNF_IDLIST | SHCNF_FLUSHNOWAIT, NULL, NULL);
+  return true;
+}