factor search tokenization out into a function

This ensures that the tokenization algorithm will remain in sync between
querying, indexing, and deindexing. The existing code had slightly
different behavior for querying, because it did not discard words with
>50 bytes. This was inconsequential, because >50 byte tokens are never
present in the index.

Signed-off-by: strawberry <strawberry@puppygock.gay>

src/service/rooms/search/data.rs

@@ -10,20 +10,26 @@ pub trait Data: Send + Sync {
 	fn search_pdus<'a>(&'a self, room_id: &RoomId, search_string: &str) -> SearchPdusResult<'a>;
 }
 
+/// Splits a string into tokens used as keys in the search inverted index
+///
+/// This may be used to tokenize both message bodies (for indexing) or search
+/// queries (for querying).
+fn tokenize(body: &str) -> impl Iterator<Item = String> + '_ {
+	body.split_terminator(|c: char| !c.is_alphanumeric())
+		.filter(|s| !s.is_empty())
+		.filter(|word| word.len() <= 50)
+		.map(str::to_lowercase)
+}
+
 impl Data for KeyValueDatabase {
 	fn index_pdu(&self, shortroomid: u64, pdu_id: &[u8], message_body: &str) -> Result<()> {
-		let mut batch = message_body
-			.split_terminator(|c: char| !c.is_alphanumeric())
-			.filter(|s| !s.is_empty())
-			.filter(|word| word.len() <= 50)
-			.map(str::to_lowercase)
-			.map(|word| {
-				let mut key = shortroomid.to_be_bytes().to_vec();
-				key.extend_from_slice(word.as_bytes());
-				key.push(0xFF);
-				key.extend_from_slice(pdu_id); // TODO: currently we save the room id a second time here
-				(key, Vec::new())
-			});
+		let mut batch = tokenize(message_body).map(|word| {
+			let mut key = shortroomid.to_be_bytes().to_vec();
+			key.extend_from_slice(word.as_bytes());
+			key.push(0xFF);
+			key.extend_from_slice(pdu_id); // TODO: currently we save the room id a second time here
+			(key, Vec::new())
+		});
 
 		self.tokenids.insert_batch(&mut batch)
 	}
@@ -37,11 +43,7 @@ fn search_pdus<'a>(&'a self, room_id: &RoomId, search_string: &str) -> SearchPdu
 			.to_be_bytes()
 			.to_vec();
 
-		let words: Vec<_> = search_string
-			.split_terminator(|c: char| !c.is_alphanumeric())
-			.filter(|s| !s.is_empty())
-			.map(str::to_lowercase)
-			.collect();
+		let words: Vec<_> = tokenize(search_string).collect();
 
 		let iterators = words.clone().into_iter().map(move |word| {
 			let mut prefix2 = prefix.clone();