Limit history to 500 lines by default and add limitHistory() method

Author: clue

README.md

@@ -346,6 +346,29 @@ $list = $readline->listHistory();
 assert(count($list) === 0);
 ```
 
+The `limitHistory(?int $limit): Readline` method can be used to
+set a limit of history lines to keep in memory.
+By default, only the last 500 lines will be kept in memory and everything else
+will be discarded.
+You can use an integer value to limit this to the given number of entries or
+use `null` for an unlimited number (not recommended, because everything is
+kept in RAM).
+If you set the limit to `0` (int zero), the history will effectively be
+disabled, as no lines can be added to or returned from the history list.
+If you're building a CLI application, you may also want to use something like
+this to obey the `HISTSIZE` environment variable:
+
+```php
+$limit = getenv('HISTSIZE');
+if ($limit === '' || $limit < 0) {
+    // empty string or negative value means unlimited
+    $readline->limitHistory(null);
+} elseif ($limit !== false) {
+    // apply any other value if given
+    $readline->limitHistory($limit);
+}
+```
+
 There is no such thing as a `readHistory()` or `writeHistory()` method
 because filesystem operations are inherently blocking and thus beyond the scope
 of this library.

examples/periodic.php

@@ -11,6 +11,16 @@
 
 $readline->setPrompt('> ');
 
+// limit history to HISTSIZE env
+$limit = getenv('HISTSIZE');
+if ($limit === '' || $limit < 0) {
+    // empty string or negative value means unlimited
+    $readline->limitHistory(null);
+} elseif ($limit !== false) {
+    // apply any other value if given
+    $readline->limitHistory($limit);
+}
+
 // add all lines from input to history
 $readline->on('data', function ($line) use ($readline) {
     $all = $readline->listHistory();

src/Readline.php

@@ -27,6 +27,7 @@ class Readline extends EventEmitter implements ReadableStreamInterface
     private $historyLines = array();
     private $historyPosition = null;
     private $historyUnsaved = null;
+    private $historyLimit = 500;
 
     public function __construct(ReadableStreamInterface $input, WritableStreamInterface $output)
     {
@@ -323,6 +324,10 @@ public function addHistory($line)
     {
         $this->historyLines []= $line;
 
+        if ($this->historyLimit !== null) {
+            $this->historyLines = array_slice($this->historyLines, -$this->historyLimit, $this->historyLimit);
+        }
+
         return $this;
     }
 
@@ -354,6 +359,23 @@ public function listHistory()
         return $this->historyLines;
     }
 
+    /**
+     * Limits the history to a maximum of N entries and truncates the current history list accordingly
+     *
+     * @param int|null $limit
+     * @return self
+     */
+    public function limitHistory($limit)
+    {
+        $this->historyLimit = $limit === null ? null : (int)$limit;
+
+        if ($this->historyLimit !== null) {
+            $this->historyLines = array_slice($this->historyLines, -$this->historyLimit, $this->historyLimit);
+        }
+
+        return $this;
+    }
+
     /**
      * set autocompletion handler to use (or none)
      *

tests/ReadlineTest.php

@@ -777,4 +777,66 @@ public function testHistoryClearWhileCyclingRestoresOriginalInput()
 
         $this->assertEquals('hello', $this->readline->getInput());
     }
+
+    public function testHistoryLimitReturnsSelf()
+    {
+        $this->assertSame($this->readline, $this->readline->limitHistory(100));
+    }
+
+    public function testHistoryLimitTruncatesCurrentListToLimit()
+    {
+        $this->readline->addHistory('a');
+        $this->readline->addHistory('b');
+        $this->readline->addHistory('c');
+
+        $this->readline->limitHistory(2);
+
+        $this->assertCount(2, $this->readline->listHistory());
+        $this->assertEquals(array('b', 'c'), $this->readline->listHistory());
+    }
+
+    public function testHistoryLimitToZeroEmptiesCurrentList()
+    {
+        $this->readline->addHistory('a');
+        $this->readline->addHistory('b');
+        $this->readline->addHistory('c');
+
+        $this->readline->limitHistory(0);
+
+        $this->assertCount(0, $this->readline->listHistory());
+    }
+
+    public function testHistoryLimitTruncatesAddingBeyondLimit()
+    {
+        $this->readline->limitHistory(2);
+
+        $this->readline->addHistory('a');
+        $this->readline->addHistory('b');
+        $this->readline->addHistory('c');
+
+        $this->assertCount(2, $this->readline->listHistory());
+        $this->assertEquals(array('b', 'c'), $this->readline->listHistory());
+    }
+
+    public function testHistoryLimitZeroAlwaysReturnsEmpty()
+    {
+        $this->readline->limitHistory(0);
+
+        $this->readline->addHistory('a');
+        $this->readline->addHistory('b');
+        $this->readline->addHistory('c');
+
+        $this->assertCount(0, $this->readline->listHistory());
+    }
+
+    public function testHistoryLimitUnlimitedDoesNotTruncate()
+    {
+        $this->readline->limitHistory(null);
+
+        for ($i = 0; $i < 1000; ++$i) {
+            $this->readline->addHistory('line' . $i);
+        }
+
+        $this->assertCount(1000, $this->readline->listHistory());
+    }
 }