PHP getprotobynumber Function
last modified April 4, 2025
The PHP getprotobynumber function looks up protocol names by number.
It's useful for network programming and protocol analysis.
Basic Definition
getprotobynumber returns the protocol name associated with a number.
It checks the system's protocol database (/etc/protocols on Unix-like systems).
Syntax: getprotobynumber(int $number): string|false.
Returns protocol name or false if not found. Requires network support.
Basic Protocol Lookup
This example demonstrates looking up a protocol name by its standard number.
<?php
declare(strict_types=1);
$protocolNumber = 6;
$protocolName = getprotobynumber($protocolNumber);
if ($protocolName !== false) {
echo "Protocol number $protocolNumber is $protocolName";
} else {
echo "Protocol number $protocolNumber not found";
}
This looks up protocol number 6, which is TCP. The function returns the name if found in the system's protocol database.
Checking Common Protocols
This example checks several common protocol numbers and displays their names.
<?php
declare(strict_types=1);
$protocols = [
1 => "ICMP",
6 => "TCP",
17 => "UDP",
58 => "ICMPv6"
];
foreach ($protocols as $number => $expected) {
$name = getprotobynumber($number);
echo "$number: " . ($name === $expected ? "OK" : "Mismatch") . "\n";
}
This verifies standard protocol numbers against expected names. It's useful for validating system protocol database contents.
Handling Unknown Protocols
This example shows how to handle cases where a protocol number isn't recognized.
<?php
declare(strict_types=1);
$unknownNumber = 255;
$protocolName = getprotobynumber($unknownNumber);
if ($protocolName === false) {
echo "Protocol number $unknownNumber is unknown";
} else {
echo "Protocol number $unknownNumber is $protocolName";
}
The function returns false for unknown protocol numbers. This example demonstrates proper error handling for such cases.
Protocol Analysis Function
This shows a complete function for analyzing protocol numbers in network data.
<?php
declare(strict_types=1);
function analyzeProtocol(int $number): string {
$name = getprotobynumber($number);
if ($name === false) {
return "Unknown protocol ($number)";
}
return "$name ($number)";
}
echo analyzeProtocol(17); // UDP
echo "\n";
echo analyzeProtocol(99); // Unknown
This function provides a standardized way to display protocol information. It handles both known and unknown protocol numbers gracefully.
Building a Protocol Reference
This example builds a reference table of protocol numbers and names.
<?php
declare(strict_types=1);
$protocolNumbers = range(0, 30);
echo "Protocol Number Reference:\n";
foreach ($protocolNumbers as $number) {
$name = getprotobynumber($number);
echo sprintf("%3d: %s\n", $number, $name ?? "Not assigned");
}
This generates a reference table for protocol numbers 0 through 30. It shows how to systematically examine protocol number assignments.
Best Practices
- Error Handling: Always check for false return values
- Caching: Cache results if repeatedly looking up same numbers
- Validation: Validate protocol numbers before lookup
- Documentation: Refer to IANA protocol number assignments
Source
PHP getprotobynumber Documentation
This tutorial covered the PHP getprotobynumber function with practical
examples for protocol number lookups in network programming.