Added printer enumeration

examples/printers.php

@@ -0,0 +1,12 @@
+<?php
+
+require_once __DIR__."/../vendor/autoload.php";
+
+use NoccyLabs\Lpr\PrinterList;
+
+$printers = new PrinterList();
+
+foreach ($printers as $printer=>$meta) {
+    printf("%s\n%s\n\n", $printer, json_encode($meta,JSON_PRETTY_PRINT));
+}
+

src/PrinterList.php

@@ -0,0 +1,49 @@
+<?php
+
+namespace NoccyLabs\Lpr;
+
+use ArrayIterator;
+
+class PrinterList implements \IteratorAggregate
+{
+    const PRINTCAP_FILE = "/etc/printcap";
+
+    /** @var array */
+    private static $printers = [];
+
+    private static function update()
+    {
+        self::$printers = [];
+        if (file_exists(self::PRINTCAP_FILE) && is_readable(self::PRINTCAP_FILE)) {
+            $printcap = file(self::PRINTCAP_FILE, FILE_SKIP_EMPTY_LINES|FILE_IGNORE_NEW_LINES);
+            foreach ($printcap as $line) {
+                if (empty($line) || (strpos(trim($line),"#") === 0)) continue;
+                if (strpos($line, "|") === false) continue;
+                list ($name, $info) = explode("|", $line, 2);
+                $meta = explode(":", $info);
+                $props = [
+                    'name' => $name,
+                    'description' => array_shift($meta),
+                ];
+                foreach ($meta as $prop) {
+                    if (strpos($prop, "=") === false) continue;
+                    list($key,$value) = explode("=",$prop,2);
+                    $props[$key] = $value;
+                }
+                self::$printers[$name] = $props;
+            }
+        }
+    }
+
+    public function getIterator()
+    {
+        if (empty(self::$printers)) self::update();
+        return new ArrayIterator(self::$printers);
+    }
+
+    public function getPrinterNames()
+    {
+        if (empty(self::$printers)) self::update();
+        return array_keys(self::$printers);
+    }
+}