added FileSystem::readLines() [Closes #220]

src/Utils/FileSystem.php

@@ -176,6 +176,37 @@ public static function read(string $file): string
 	}
 
 
+	/**
+	 * Reads the file content line by line. Because it reads continuously as we iterate over the lines,
+	 * it is possible to read files larger than the available memory.
+	 * @return \Generator<int, string>
+	 * @throws Nette\IOException  on error occurred
+	 */
+	public static function readLines(string $file, bool $stripNewLines = true): \Generator
+	{
+		return (function ($f) use ($file, $stripNewLines) {
+			$counter = 0;
+			do {
+				$line = Callback::invokeSafe('fgets', [$f], fn($error) => throw new Nette\IOException(sprintf(
+					"Unable to read file '%s'. %s",
+					self::normalizePath($file),
+					$error,
+				)));
+				if ($line === false) {
+					fclose($f);
+					break;
+				}
+				if ($stripNewLines) {
+					$line = rtrim($line, "\r\n");
+				}
+
+				yield $counter++ => $line;
+
+			} while (true);
+		})(static::open($file, 'r'));
+	}
+
+
 	/**
 	 * Writes the string to a file.
 	 * @throws Nette\IOException  on error occurred

tests/Utils/FileSystem.readLines.phpt

@@ -0,0 +1,32 @@
+<?php
+
+/**
+ * Test: Nette\Utils\FileSystem readLines()
+ */
+
+declare(strict_types=1);
+
+use Nette\Utils\FileSystem;
+use Tester\Assert;
+
+require __DIR__ . '/../bootstrap.php';
+
+
+test('readLines', function () {
+	FileSystem::write(getTempDir() . '/2/file', "\r\nHello\nWorld");
+
+	$lines = FileSystem::readLines(getTempDir() . '/2/file');
+	Assert::type(Generator::class, $lines);
+	Assert::same(['', 'Hello', 'World'], iterator_to_array($lines));
+
+	$lines = FileSystem::readLines(getTempDir() . '/2/file', stripNewLines: false);
+	Assert::type(Generator::class, $lines);
+	Assert::same(["\r\n", "Hello\n", 'World'], iterator_to_array($lines));
+});
+
+
+Assert::exception(
+	fn() => FileSystem::readLines('missing'),
+	Nette\IOException::class,
+	"Unable to open file 'missing'.%A%",
+);