fix: performance when processing remote CSV files

src/adapter/etl-adapter-csv/src/Flow/ETL/Adapter/CSV/functions.php

@@ -37,7 +37,7 @@ function from_csv(
     ?string $separator = null,
     ?string $enclosure = null,
     ?string $escape = null,
-    int $characters_read_in_line = 1000,
+    int $characters_read_in_line = 10 * 1024 * 1024,
     ?Schema $schema = null,
 ): CSVExtractor {
     $loader = (new CSVExtractor(is_string($path) ? path_real($path) : $path))

src/adapter/etl-adapter-csv/tests/Flow/ETL/Adapter/CSV/Tests/Double/LengthCapturingSourceStream.php

@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Flow\ETL\Adapter\CSV\Tests\Double;
+
+use Flow\Filesystem\Path;
+use Flow\Filesystem\SourceStream;
+use Generator;
+
+use function explode;
+use function strlen;
+use function substr;
+
+final class LengthCapturingSourceStream implements SourceStream
+{
+    /**
+     * @var array<null|int> the length argument captured on each readLines() call
+     */
+    public array $capturedLengths = [];
+
+    public function __construct(
+        private readonly string $contents,
+        private readonly Path $path,
+    ) {}
+
+    public function close(): void {}
+
+    public function content(): string
+    {
+        return $this->contents;
+    }
+
+    public function isOpen(): bool
+    {
+        return true;
+    }
+
+    public function iterate(int $length = 1): Generator
+    {
+        for ($i = 0; $i < strlen($this->contents); $i += $length) {
+            yield substr($this->contents, $i, $length);
+        }
+    }
+
+    public function path(): Path
+    {
+        return $this->path;
+    }
+
+    public function read(int $length, int $offset): string
+    {
+        return substr($this->contents, $offset, $length);
+    }
+
+    public function readLines(string $separator = "\n", ?int $length = null): Generator
+    {
+        $this->capturedLengths[] = $length;
+
+        foreach (explode($separator, $this->contents) as $line) {
+            yield $line;
+        }
+    }
+
+    public function size(): int
+    {
+        return strlen($this->contents);
+    }
+}

src/adapter/etl-adapter-csv/tests/Flow/ETL/Adapter/CSV/Tests/Unit/CSVLineReaderTest.php

@@ -5,11 +5,33 @@
 namespace Flow\ETL\Adapter\CSV\Tests\Unit;
 
 use Flow\ETL\Adapter\CSV\CSVLineReader;
+use Flow\ETL\Adapter\CSV\Tests\Double\LengthCapturingSourceStream;
 use Flow\Filesystem\Stream\MemorySourceStream;
+use PHPUnit\Framework\Attributes\TestWith;
 use PHPUnit\Framework\TestCase;
 
+use function Flow\Filesystem\DSL\path;
+
 final class CSVLineReaderTest extends TestCase
 {
+    public function test_characters_read_in_line_is_passed_through_to_the_stream(): void
+    {
+        $stream = new LengthCapturingSourceStream("id,name\n1,foo", path('s3://bucket/users.csv'));
+
+        iterator_to_array((new CSVLineReader('"', 4096))->readLines($stream));
+
+        static::assertSame([4096], $stream->capturedLengths);
+    }
+
+    public function test_null_characters_read_in_line_lets_the_stream_choose_its_default(): void
+    {
+        $stream = new LengthCapturingSourceStream("id,name\n1,foo", path('s3://bucket/users.csv'));
+
+        iterator_to_array((new CSVLineReader('"'))->readLines($stream));
+
+        static::assertSame([null], $stream->capturedLengths);
+    }
+
     public function test_detection_of_multiline_quotes(): void
     {
         $simpleContent = "field1,field2\nvalue1,value2";