Bug 1811830 - Add a preference to force downloading of attachments. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D187285

modules/libpref/init/StaticPrefList.yaml

@@ -1362,6 +1362,12 @@
   value: false
   mirror: always
 
+# See bug 1811830
+- name: browser.download.force_save_internally_handled_attachments
+  type: bool
+  value: false
+  mirror: always
+
 - name: browser.download.sanitize_non_media_extensions
   type: bool
   value: true

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -1273,6 +1273,7 @@ nsExternalAppHandler::nsExternalAppHandler(
       mWindowContext(aWindowContext),
       mSuggestedFileName(aSuggestedFileName),
       mForceSave(aForceSave),
+      mForceSaveInternallyHandled(false),
       mCanceled(false),
       mStopRequestIssued(false),
       mIsFileChannel(false),
@@ -1740,6 +1741,16 @@ NS_IMETHODIMP nsExternalAppHandler::OnStartRequest(nsIRequest* request) {
   bool shouldAutomaticallyHandleInternally =
       action == nsIMIMEInfo::handleInternally;
 
+  if (aChannel) {
+    uint32_t disposition = -1;
+    aChannel->GetContentDisposition(&disposition);
+    mForceSaveInternallyHandled =
+        shouldAutomaticallyHandleInternally &&
+        disposition == nsIChannel::DISPOSITION_ATTACHMENT &&
+        mozilla::StaticPrefs::
+            browser_download_force_save_internally_handled_attachments();
+  }
+
   // If we're not asking, check we actually know what to do:
   if (!alwaysAsk) {
     alwaysAsk = action != nsIMIMEInfo::saveToDisk &&
@@ -1777,7 +1788,7 @@ NS_IMETHODIMP nsExternalAppHandler::OnStartRequest(nsIRequest* request) {
 
   // if we were told that we _must_ save to disk without asking, all the stuff
   // before this is irrelevant; override it
-  if (mForceSave) {
+  if (mForceSave || mForceSaveInternallyHandled) {
     alwaysAsk = false;
     action = nsIMIMEInfo::saveToDisk;
     shouldAutomaticallyHandleInternally = false;
@@ -2449,7 +2460,7 @@ void nsExternalAppHandler::RequestSaveDestination(
 NS_IMETHODIMP nsExternalAppHandler::PromptForSaveDestination() {
   if (mCanceled) return NS_OK;
 
-  if (mForceSave) {
+  if (mForceSave || mForceSaveInternallyHandled) {
     mMimeInfo->SetPreferredAction(nsIMIMEInfo::saveToDisk);
   }
 

uriloader/exthandler/nsExternalHelperAppService.h

@@ -362,6 +362,12 @@ class nsExternalAppHandler final : public nsIStreamListener,
    */
   bool mForceSave;
 
+  /**
+   * If set, any internally handled type that has a disposition of
+     nsIChannel::DISPOSITION_ATTACHMENT will be saved to disk.
+   */
+  bool mForceSaveInternallyHandled;
+
   /**
    * The canceled flag is set if the user canceled the launching of this
    * application before we finished saving the data to a temp file.