When attempting to create pad, bail if a 4xx response is returned

This technique prevents infinite loops when an unexpected result is returned
by requests to Etherpad Lite, such as for an overlong request URI.

See #23

includes/class-participad-client.php

@@ -54,10 +54,14 @@ protected function call( $function, array $arguments = array() ) {
 			throw $e;
 		}
 
+		if ( 200 !== $request['response']['code'] ) {
+			throw new UnexpectedValueException( "Unknown error: " . $request['response']['code'] );
+		}
+
 		$result = json_decode( $request['body'] );
 
 		if ( $result === null ) {
-			throw new UnexpectedValueException("JSON response could not be decoded");
+			throw new UnexpectedValueException( "JSON response could not be decoded" );
 		}
 
 		return $this->handleResult($result);

includes/class-participad-post.php

@@ -115,7 +115,24 @@ public static function create_ep_post( $wp_post_id, $ep_post_group_id ) {
 				$ep_post         = participad_client()->createGroupPad( $ep_post_group_id, $ep_post_id, $wp_post_content );
 				$pad_created     = true;
 			} catch ( Exception $e ) {
-				$ep_post_id      = self::generate_random_name();
+
+				$error_message = $e->getMessage();
+				$error_code = substr( $error_message, strrpos( $error_message, ':' ) + 2 );
+
+				switch ( $error_code ) {
+
+					// Request URI too long
+					// @see https://github.com/boonebgorges/participad/issues/23
+					case '414' :
+						return new WP_Error( 'create_ep_post', __( 'Could not create the Etherpad Lite post', 'participad' ) );
+						break;
+
+					// Assume that there's a conflict, and try again
+					default :
+						$ep_post_id = self::generate_random_name();
+						break;
+
+				}
 			}
 		}