Added support for searching for arp entry

doc/API/API-Docs.md

@@ -49,6 +49,8 @@
     - [`bills`](#api-bills)
         - [`list_bills`](#api-route-22)
         - [`get_bill`](#api-route-23)
+    - [`resources`](#api-resources)
+        - [`list_arp`](#api-resources-list_arp)
 Describes the API structure.
 
 # <a name="api-structure">`Structure`</a> [`top`](#top)
@@ -1403,3 +1405,37 @@ Output:
 }
 ```
 
+### <a name="api-resources-list_arp">Function: `list_arp`</a> [`top`](#top)
+
+Retrieve a specific ARP entry or all ARP enties for a device
+
+Route: /api/v0/resources/ip/arp/:ip
+
+ - ip is the specific IP you would like to query, if this is all then you need to pass ?device=_hostname_ (or device id)
+
+Input:
+
+ - device if you specify all for the IP then you need to populate this with the hostname or id of the device.
+
+Example:
+```curl
+curl -H 'X-Auth-Token: YOURAPITOKENHERE' https://librenms.org/api/v0/resources/ip/arp/1.1.1.1
+curl -H 'X-Auth-Token: YOURAPITOKENHERE' https://librenms.org/api/v0/resources/ip/arp/1.1.1.1?device=localhost
+```
+
+Output:
+```text
+{
+    "status": "ok",
+    "err-msg": "",
+    "count": 1,
+    "arp": [
+        {
+            "port_id": "229",
+            "mac_address": "da160e5c2002",
+            "ipv4_address": "1.1.1.1",
+            "context_name": ""
+        }
+    ]
+}
+```

html/api_v0.php

@@ -141,6 +141,19 @@ $app->group(
                     }
                 );
 		// End Routing
+                // Resources section
+                $app->group(
+                    '/resources',
+                    function () use ($app) {
+                        $app->group(
+                            '/ip',
+                            function () use ($app) {
+                                $app->get('/arp/:ip', 'authToken', 'list_arp')->name('list_arp');
+                            }
+                        );
+                    }
+                );
+                // End Resources
             }
         );
         $app->get('/v0', 'authToken', 'show_endpoints');

html/includes/api_functions.inc.php

@@ -1323,3 +1323,37 @@ function list_ipsec() {
     $app->response->headers->set('Content-Type', 'application/json');
     echo _json_encode($output);
 }
+
+function list_arp() {
+    $app      = \Slim\Slim::getInstance();
+    $router   = $app->router()->getCurrentRoute()->getParams();
+    $status   = 'error';
+    $code     = 404;
+    $message  = '';
+    $ip       = $router['ip'];
+    if (empty($ip)) {
+        $message = "No valid IP provided";
+    }
+    else {
+        $code = 200;
+        $status = 'ok';
+        if ($ip === "all") {
+            $hostname =  mres($_GET['device']);
+            $device_id = ctype_digit($hostname) ? $hostname : getidbyname($hostname);
+            $arp = dbFetchRows("SELECT `ipv4_mac`.* FROM `ipv4_mac` LEFT JOIN `ports` ON `ipv4_mac`.`port_id` = `ports`.`port_id` WHERE `ports`.`device_id` = ?", array($device_id));
+        }
+        else {
+            $arp = dbFetchRows("SELECT * FROM `ipv4_mac` WHERE `ipv4_address`=?", array($ip));
+        }
+        $total  = count($arp);
+    }
+    $output  = array(
+        'status'  => $status,
+        'err-msg' => $message,
+        'count'   => $total,
+        'arp'  => $arp,
+    );
+    $app->response->setStatus($code);
+    $app->response->headers->set('Content-Type', 'application/json');
+    echo _json_encode($output);
+}