From 36a3f3e60a3e34de8df3546e31443dcbe4e84dc9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Se=C3=A1n=20de=20B=C3=BArca?= <leftmostcat@gmail.com>
Date: Thu, 14 Sep 2023 12:04:11 -0700
Subject: [PATCH] Avoid infinite loop with invalid YEARLY recurrence rule.

---
 lib/ical/recur_iterator.js  | 31 +++++++++++++++++++++++++------
 test/recur_iterator_test.js | 19 +++++++++++++------
 test/recur_test.js          | 20 ++++++++++----------
 3 files changed, 48 insertions(+), 22 deletions(-)

diff --git a/lib/ical/recur_iterator.js b/lib/ical/recur_iterator.js
index a6e4b21e..9406e3d4 100644
--- a/lib/ical/recur_iterator.js
+++ b/lib/ical/recur_iterator.js
@@ -179,7 +179,14 @@ class RecurIterator {
     this.initialized = options.initialized || false;
 
     if (!this.initialized) {
-      this.init();
+      try {
+        this.init();
+      } catch (e) {
+        // Init may error if there are no possible recurrence instances from the
+        // rule, but we don't want to bubble this error up. Instead, we create
+        // an empty iterator.
+        this.completed = true;
+      }
     }
   }
 
@@ -251,7 +258,17 @@ class RecurIterator {
     }
 
     if (this.rule.freq == "YEARLY") {
-      for (;;) {
+      // Some yearly recurrence rules may be specific enough to not actually
+      // occur on a yearly basis, e.g. the 29th day of February or the fifth
+      // Monday of a given month. The standard isn't clear on the intended
+      // behavior in these cases, but `libical` at least will iterate until it
+      // finds a matching year.
+      // CAREFUL: Some rules may specify an occurrence that can never happen,
+      // e.g. the first Monday of April so long as it falls on the 15th
+      // through the 21st. Detecting these is non-trivial, so ensure that we
+      // stop iterating at some point.
+      const untilYear = this.rule.until ? this.rule.until.year : 20000;
+      while (this.last.year <= untilYear) {
         this.expand_year_days(this.last.year);
         if (this.days.length > 0) {
           break;
@@ -259,6 +276,10 @@ class RecurIterator {
         this.increment_year(this.rule.interval);
       }
 
+      if (this.days.length == 0) {
+        throw new Error("No possible occurrences");
+      }
+
       this._nextByYearDay();
     }
 
@@ -346,11 +367,10 @@ class RecurIterator {
 
     if ((this.rule.count && this.occurrence_number >= this.rule.count) ||
         (this.rule.until && this.last.compare(this.rule.until) > 0)) {
-
-      //XXX: right now this is just a flag and has no impact
-      //     we can simplify the above case to check for completed later.
       this.completed = true;
+    }
 
+    if (this.completed) {
       return null;
     }
 
@@ -360,7 +380,6 @@ class RecurIterator {
       return this.last;
     }
 
-
     let valid;
     do {
       valid = 1;
diff --git a/test/recur_iterator_test.js b/test/recur_iterator_test.js
index 4ed19ce0..ee2fa938 100644
--- a/test/recur_iterator_test.js
+++ b/test/recur_iterator_test.js
@@ -143,13 +143,13 @@ suite('recur_iterator', function() {
 
       let start = ICAL.Time.fromString(options.dtStart);
       let recur = ICAL.Recur.fromString(ruleString);
-      if (options.throws) {
-        assert.throws(function() {
-          recur.iterator(start);
-        });
+
+      let iterator = recur.iterator(start);
+
+      if (options.noInstance) {
+        assert.equal(iterator.next(), null);
         return;
       }
-      let iterator = recur.iterator(start);
 
       let inc = 0;
       let dates = [];
@@ -688,7 +688,7 @@ suite('recur_iterator', function() {
       // Invalid rule. There's never a 31st of Feburary, check that this fails.
       testRRULE('FREQ=MONTHLY;INTERVAL=12;BYMONTHDAY=31', {
         dtStart: '2022-02-01T08:00:00',
-        throws: true,
+        noInstance: true,
       });
 
       // monthly + by month
@@ -963,6 +963,13 @@ suite('recur_iterator', function() {
         ]
       });
 
+      // Invalid recurrence rule. The first Monday can never fall later than the
+      // 7th.
+      testRRULE('FREQ=YEARLY;BYMONTHDAY=15,16,17,18,19,20,21;BYDAY=1MO', {
+        dtStart: '2015-01-01T08:00:00',
+        noInstance: true,
+      });
+
       // Tycho brahe days - yearly, byYearDay with negative offsets
       testRRULE('FREQ=YEARLY;BYYEARDAY=1,2,4,6,11,12,20,42,48,49,-306,-303,' +
                 '-293,-292,-266,-259,-258,-239,-228,-209,-168,-164,-134,-133,' +
diff --git a/test/recur_test.js b/test/recur_test.js
index a511cecb..2511d7c4 100644
--- a/test/recur_test.js
+++ b/test/recur_test.js
@@ -26,7 +26,7 @@ suite('recur', function() {
       });
     }
 
-    function checkThrow(data, expectedMessage, dtstart, stack) {
+    function checkNoInstance(data, expectedMessage, dtstart, stack) {
       test(expectedMessage, function() {
         let recur = new ICAL.Recur(data);
         if (dtstart) {
@@ -34,48 +34,48 @@ suite('recur', function() {
         } else {
           dtstart = ICAL.Time.epochTime.clone();
         }
-        assert.throws(function() {
-          recur.iterator(dtstart);
-        }, expectedMessage);
+
+        const iter = recur.iterator(dtstart);
+        assert.equal(iter.next(), null);
       });
     }
 
-    checkThrow({
+    checkNoInstance({
       parts: {
         BYYEARDAY: [3, 4, 5],
         BYMONTH: [2]
       }
     }, 'Invalid BYYEARDAY rule');
 
-    checkThrow({
+    checkNoInstance({
       parts: {
         BYWEEKNO: [3],
         BYMONTHDAY: [2]
       }
    }, 'BYWEEKNO does not fit to BYMONTHDAY');
 
-    checkThrow({
+    checkNoInstance({
       freq: 'MONTHLY',
       parts: {
         BYWEEKNO: [30]
       }
     }, 'For MONTHLY recurrences neither BYYEARDAY nor BYWEEKNO may appear');
 
-    checkThrow({
+    checkNoInstance({
       freq: 'WEEKLY',
       parts: {
         BYMONTHDAY: [20]
       }
     }, 'For WEEKLY recurrences neither BYMONTHDAY nor BYYEARDAY may appear');
 
-    checkThrow({
+    checkNoInstance({
       freq: 'DAILY',
       parts: {
         BYYEARDAY: [200]
       }
     }, 'BYYEARDAY may only appear in YEARLY rules');
 
-    checkThrow({
+    checkNoInstance({
       freq: 'MONTHLY',
       parts: {
         BYDAY: ['-6TH']