PHP Networking, Regex & Parallel Execution

cURL & HTTP Requests

Basic Request

$ch = curl_init('https://api.example.com/data');
curl_setopt_array($ch, [
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_HTTPHEADER     => ['Accept: application/json', 'Authorization: Bearer ' . $token],
    CURLOPT_TIMEOUT        => 30,
    CURLOPT_CONNECTTIMEOUT => 5,
    CURLOPT_SSL_VERIFYPEER => true,   // NEVER disable in production
    CURLOPT_SSL_VERIFYHOST => 2,
]);
$response = curl_exec($ch);
if ($response === false) {
    throw new RuntimeException(curl_error($ch), curl_errno($ch));
}
$status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
// curl_close() optional in PHP 8+ (garbage collected)

POST / PUT / JSON

curl_setopt_array($ch, [
    CURLOPT_POST       => true,
    CURLOPT_POSTFIELDS => json_encode($data),
    CURLOPT_HTTPHEADER => ['Content-Type: application/json'],
]);

// Custom method (PUT, PATCH, DELETE)
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, 'PUT');

Multi-cURL (Parallel Requests)

$mh = curl_multi_init();
$handles = [];

foreach ($urls as $key => $url) {
    $ch = curl_init($url);
    curl_setopt_array($ch, [
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_TIMEOUT        => 10,
    ]);
    curl_multi_add_handle($mh, $ch);
    $handles[$key] = $ch;
}

// Run all in parallel
do {
    $status = curl_multi_exec($mh, $running);
    if ($running) { curl_multi_select($mh); } // block until I/O ready
} while ($running > 0);

// Collect results
$results = [];
foreach ($handles as $key => $ch) {
    $results[$key] = curl_multi_getcontent($ch);
    curl_multi_remove_handle($mh, $ch);
}
curl_multi_close($mh);

cURL Reference

Option	Purpose
CURLOPT_RETURNTRANSFER	Return body as string (not print)
CURLOPT_TIMEOUT	Total operation timeout (seconds)
CURLOPT_CONNECTTIMEOUT	Connection phase timeout
CURLOPT_FOLLOWLOCATION	Auto-follow redirects
CURLOPT_MAXREDIRS	Max redirects to follow
CURLOPT_USERPWD	Basic auth "user:pass"
CURLOPT_ACCEPT_ENCODING	Enable gzip/deflate (auto-decompressed)
CURLOPT_SSL_VERIFYPEER	Verify server certificate (default true)
CURLOPT_SSL_VERIFYHOST	Verify hostname in cert (use 2)
CURLOPT_HTTPHEADER	Custom request headers array
CURLOPT_POSTFIELDS	POST data (string or array)
CurlHandle (PHP 8.0+)	Opaque final class, replaces resource type

Rule	Detail
Always set timeouts	Prevent hanging on slow servers
Never disable SSL verification	Except in dev/test
Use === for curl_exec() check	Returns false on failure, not falsy
HTTP 4xx/5xx is not curl failure	Check CURLINFO_HTTP_CODE separately
Multi-curl for parallel	Much faster than sequential for multiple URLs

Regular Expressions (PCRE)

Key Functions

// Match — returns 1 (match), 0 (no match), false (error)
preg_match('/^[a-z]+$/i', $input, $matches);

// Match all — returns count of matches
preg_match_all('/\d+/', $text, $matches);

// Replace — string or callback
$clean = preg_replace('/\s+/', ' ', $text);
$result = preg_replace_callback('/\{(\w+)\}/', fn($m) => $vars[$m[1]] ?? '', $template);

// Split
$parts = preg_split('/[\s,]+/', $csv);

// Always check for errors
if (preg_last_error() !== PREG_NO_ERROR) {
    throw new RuntimeException(preg_last_error_msg());
}

Modifiers

Modifier	Effect
i	Case-insensitive
m	^/$ match line boundaries (not just string start/end)
s	. matches newlines
x	Ignore whitespace + # comments in pattern
u	UTF-8 mode — required for multibyte strings
U	Invert greediness (all quantifiers ungreedy by default)
n	Only named groups (?<name>) capture (PHP 8.2+)
D	$ matches only absolute end, not before final \n
A	Anchor to string start

Named Captures & Assertions

// Named captures — cleaner than $matches[1]
preg_match('/(?<year>\d{4})-(?<month>\d{2})-(?<day>\d{2})/', $date, $m);
echo $m['year']; // "2024"

// Lookahead/lookbehind (zero-width assertions)
'/(?<=\$)\d+/'      // Positive lookbehind: digits after $
'/\d+(?= USD)/'     // Positive lookahead: digits before " USD"
'/foo(?!bar)/'      // Negative lookahead: "foo" not followed by "bar"

ReDoS Prevention & Performance

Rule	Detail
Avoid nested quantifiers	(a+)*, (a*)+ cause exponential backtracking
Use atomic groups (?>...)	Prevent backtracking into group
Character classes over alternation	[aeiou] faster than (a|e|i|o|u)
Anchor patterns	^pattern / \Apattern fastest
Check preg_last_error()	Detect PREG_BACKTRACK_LIMIT_ERROR
pcre.backtrack_limit	Default 1M — may hit on large subjects
Lookbehind must be fixed-length	Variable-length lookbehind not supported

Parallel & Async Patterns

Process Control (pcntl)

$pid = pcntl_fork();
if ($pid === -1) {
    throw new RuntimeException('Fork failed');
} elseif ($pid > 0) {
    // Parent — wait for child to prevent zombies
    pcntl_wait($status);
} else {
    // Child (pid === 0)
    doWork();
    exit(0);
}

Non-Blocking I/O with stream_select

stream_set_blocking($stream, false);
$read = [$stream1, $stream2, $stream3];
$write = $except = [];
// Block up to 200ms waiting for any stream to be ready
if (stream_select($read, $write, $except, 0, 200000) > 0) {
    foreach ($read as $ready) {
        $data = fread($ready, 8192);
    }
}

parallel Extension (Modern Async)

$runtime = new parallel\Runtime();
$futures = [];
foreach ($tasks as $i => $task) {
    $futures[$i] = $runtime->run(fn() => processTask($task), [$task]);
}
// Collect results (blocks if not ready)
foreach ($futures as $i => $future) {
    $results[$i] = $future->value();
}
$runtime->close();

Comparison

Approach	Best for	Notes
curl_multi_*	Parallel HTTP requests	Built-in, no extensions needed
pcntl_fork()	CPU-bound parallel work	Unix only, not thread-safe
stream_select()	High-concurrency I/O	Event loop pattern, thousands of connections
parallel extension	General async tasks	Requires ZTS PHP, message-passing model
Fibers (8.1+)	Cooperative concurrency	Single-thread, no true parallelism

Rule	Detail
pcntl_fork() workers	Match CPU count (2-4)
stream_select() timeout	Min 200ms to avoid CPU spin