rssguard/resources/docs/Message-filters.md

Message filtering

RSS Guard supports automagic message filtering. The filtering system is automatically triggered when new messages for each feed are downloaded. User can write scripts which perform filtering decisions. JavaScript with ECMA standard is supported.

Message downloading/filtering workflow

foreach (feed in feeds_to_update) do
  messages = download_messages(feed)
  filtered_messages = filter_messages(messages)
  save_messages_to_database(filtered_messages)

As you can see, RSS Guard processes all feeds scheduled for message downloading one by one; downloading new messages, feeding them to filtering system and then saving all approved messages to RSS Guard's database.

Writing message filter

Message filter consists of arbitrary JavaScript code which must provide function with prototype

function filterMessage() { }

This function must be fast and must return values which belong to enumeration FilteringAction from this file. You can you use either direct numerical value of each enumerant, for example 2 or you can use self-descriptive enumerant name, for example MessageObject.Ignore. There are also names MSG_ACCEPT and MSG_IGNORE as aliases for MessageObject.Accept and MessageObject.Ignore.

Each message is accessible in your script via global variable named msg of type MessageObject, see this file for the declaration. Some properties are writable, allowing you to change contents of the message before it is written to DB. You can mark message important, parse its description or perhaps change author name or even assign some label to it!!!

You can use special placeholders within message filter.

RSS Guard also offers list of labels assigned to each message. You can therefore do actions in your filtering script based on which labels are assigned to the message. The property is called assignedLabels and is array of Label objects. If you change assigned labels to the message, then the change will be eventually synchronized back to server if respective plugin supports it.

Passed message also offers special function

MessageObject.isDuplicateWithAttribute(DuplicationAttributeCheck)

which allows you to perform runtime check for existence of the message in RSS Guard's database. The parameter is integer value from enumeration DuplicationAttributeCheck from this file and specifies how exactly you want to determine if given message is "duplicate". Again, you can use direct integer values or enumerant names.

For example if you want to check if there is already another message with same author in database, then you call msg.isDuplicateWithAttribute(MessageObject.SameAuthor). Enumeration even supports "flags" approach, thus you can combine multiple checks via bitwise OR operation in single call, for example like this: msg.isDuplicateWithAttribute(MessageObject.SameAuthor | MessageObject.SameUrl).

API reference

Here is the reference of methods and properties of some types available in your filtering scipts.

MessageObject class

Property/method	Description
Array<Label> assignedLabels	READ-ONLY List of labels assigned to the message.
Array<Label> availableLabels	READ-ONLY List of labels which are currently available and can be assigned to the message. Available in RSS Guard 3.8.1+.
String feedCustomId	READ-ONLY Service-specific ID of the feed which this message belongs to.
Number accountId	READ-ONLY RSS Guard's ID of the account activated in the program. This property is highly advanced and you probably do not need to use it at all.
String title	Title of the message.
String url	URL of the message.
String author	Author of the message.
String contents	Contents of the message.
Number score	Arbitrary number in range <0.0, 100.0>. You can use this number to sort messages in a custom fashion as this attribute also has its own column in messages list.
Date created	Date/time of the message.
Boolean isRead	Is message read?
Boolean isImportant	Is message important?
Boolean isDeleted	Is message placed in recycle bin? Available in RSS Guard 3.8.4+.
Boolean isDuplicateWithAttribute(DuplicationAttributeCheck)	Allows you to test if this particular message is already stored in RSS Guard's DB.
Boolean assignLabel(String)	Assigns label to this message. The passed String value is the customId property of Label type. See its API reference for relevant info. Available in RSS Guard 3.8.1+.
Boolean deassignLabel(String)	Removes label from this message. The passed String value is the customId property of Label type. See its API reference for relevant info. Available in RSS Guard 3.8.1+.
Boolean alreadyStoredInDb	READ-ONLY Returns true if this message is already stored in DB. This function is the way to check if the filter is being run automatically for newly downloaded messages or manually for already existing messages.

Label class

Property/method	Description
String title	READ-ONLY Label title.
String customId	READ-ONLY Service-specific ID of this label. This ID is used as unique identifier for the label and is particularly useful if you want to (de)assign label to/from message.
color color	READ-ONLY Label color. Note that type color has its documentation here.

FilteringAction enum

Enumerant name	Integer value	Description
Accept	1	Message is accepted and will be added to DB or updated in DB.
Ignore	2	Message is ignored and will be NOT added to DB or updated in DB, but is not purged from DB if already exists.
Purge	4	Existing message is purged from the DB completely.

Note that MessageObject attributes which can be synchronized back to service are synchronized even if you return Purge or Ignore. In other words: even if you filter ignores the message you can still tweak its properties which will get synchronized back to your server.

DuplicationAttributeCheck enum

Enumerant name	Integer value	Description
SameTitle	1	Check if message has same title as some another messages.
SameUrl	2	Check if message has same URL as some another messages.
SameAuthor	4	Check if message has same author as some another messages.
SameDateCreated	8	Check if message has same date of creation as some another messages.
AllFeedsSameAccount	16	Perform the check across all feeds from your account, not just "current" feed.

Examples

Accept only messages from "Bob" while also marking them important.

function filterMessage() {
  if (msg.author == "Bob") {
    msg.isImportant = true;
    return MessageObject.Accept;
  }
  else {
    return MessageObject.Ignore;
  }
}

Replace all dogs with cats!

function filterMessage() {
  msg.title = msg.title.replace("dogs", "cats");
  return MessageObject.Accept;
}

Write details of available labels and assign the first label to the message.

function filterMessage() {
  console.log('Number of assigned labels ' + msg.assignedLabels.length);
  console.log('Number of available labels ' + msg.availableLabels.length);

  var i;
  for (i = 0; i < msg.availableLabels.length; i++) {
    var lbl = msg.availableLabels[i];

    console.log('Available label:');
    console.log('  Title: \'' + lbl.title + '\' ID: \'' + lbl.customId + '\'');
  }

  if (msg.availableLabels.length > 0) {
    console.log('Assigning first label to message...');
    msg.assignLabel(msg.availableLabels[0].customId);

    console.log('Number of assigned labels ' + msg.assignedLabels.length);
  }

  console.log();
  return MessageObject.Accept;
}

Make sure that your receive only one message with particular URL and all other messages with same URL are subsequently ignored.

function filterMessage() {
  if (msg.isDuplicateWithAttribute(MessageObject.SameUrl)) {
    return MessageObject.Ignore;
  }
  else {
    return MessageObject.Accept;
  }
}

Remove "ads" from messages received from Inoreader. Method simply removes div which contains the advertisement.

function filterMessage() {
  msg.contents = msg.contents.replace(/<div>\s*Ads[\S\s]+Remove<\/a>[\S\s]+adv\/www\/delivery[\S\s]+?<\/div>/im, '');

  return MessageObject.Accept;
}

Message filters dialog

The dialog is accessible from menu Messages -> Message filters and is the central place for message filters management within RSS Guard. It allows you to:

• add or remove message filters,
• assign filter to whatever feeds (across all accounts) you want,
• rename filters and write their JavaScript-based scripts,
• reformat source code of script with clang-format tool (which is preinstalled on Windows version of RSS Guard),
• debug your script against sample MessageObject instance,
• debug your script agains list of real messages of some feed (available in RSS Guard 3.8.4+),
• execute message filters manually against feeds (available in RSS Guard 3.8.4+).

Performance

Note that evaluations of JavaScript expressions are NOT that fast. They are much slower than native C++ code, but well-optimized scripts usually take only several milliseconds to finish for each message.