From 52345eaf5c857cb7d3e84a2051fec756bb6888cc Mon Sep 17 00:00:00 2001
From: Eduardo Nunes <esnunes@gmail.com>
Date: Tue, 21 Jul 2015 11:25:51 -0300
Subject: [PATCH] fixed issue regarding concurrent requests to dns

---
 lib/index.js | 358 ++++++++++++++++++++++++++++++---------------------
 1 file changed, 212 insertions(+), 146 deletions(-)

diff --git a/lib/index.js b/lib/index.js
index eb34309..33a20f9 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -7,6 +7,12 @@
 var CacheObject = require('./cache.js'),
     dns = require('dns');
 
+/*
+ * Stores the list of callbacks waiting for a dns call.
+ */
+var callbackList = {};
+
+
 /*
  * Make a deep copy of the supplied object. This function reliably copies only
  * what is valid for a JSON object, array, or other element.
@@ -49,7 +55,7 @@ var EnhanceDns = function (conf) {
             //cache already exists, means this code has already execute ie method are already overwritten
             return dns;
         }
-        
+
         // original function storage
         var backup_object = {
                 lookup : dns.lookup,
@@ -65,7 +71,7 @@ var EnhanceDns = function (conf) {
             },
             // cache storage instance
             cache = conf.cache ? new conf.cache(conf) : new CacheObject(conf);
-        
+
         // insert cache object to the instance
         dns.internalCache = cache;
 
@@ -94,23 +100,29 @@ var EnhanceDns = function (conf) {
                 }
             }
 
-            cache.get('lookup_' + domain + '_' + family, function (error, record) {
-                if (record) {
-                    callback(error, record.address, record.family);
-                } else {
-                    backup_object.lookup(domain, family, function (err, address, family_r) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('lookup_' + domain + '_' + family, {
-                                'address' : address,
-                                'family' : family_r
-                            }, function () {
-                                callback(err, address, family_r);
-                            });
-                        }
-                    });
-                }
+            var key = 'lookup_' + domain + '_' + family;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, record.address, record.family); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.lookup(domain, family, function (err, address, family_r) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('lookup_' + domain + '_' + family, {
+                            'address' : address,
+                            'family' : family_r
+                        }, function () {
+                            list.forEach(function (cb) { cb(err, address, family_r); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
@@ -126,172 +138,226 @@ var EnhanceDns = function (conf) {
                 callback_new = type;
             }
 
-            cache.get('resolve_' + domain + '_' + type_new, function (error, record) {
-                if (record) {
-                    callback_new(error, deepCopy(record), true);
-                } else {
-                    backup_object.resolve(domain, type_new, function (err, addresses) {
-                        if (err) {
-                            callback_new(err);
-                        } else {
-                            cache.set('resolve_' + domain + '_' + type_new, addresses, function () {
-                                callback_new(err, deepCopy(addresses), false);
-                            });
-                        }
-                    });
-                }
+            var key = 'resolve_' + domain + '_' + type_new;
+            cache.get(key, function (error, record) {
+                if (record) { return callback_new(error, deepCopy(record), true); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback_new);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolve(domain, type_new, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolve_' + domain + '_' + type_new, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses), false); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.resolve4 method
         dns.resolve4 = function (domain, callback) {
-            cache.get('resolve4_' + domain, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.resolve4(domain, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('resolve4_' + domain, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'resolve4_' + domain;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolve4(domain, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolve4_' + domain, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.resolve6 method
         dns.resolve6 = function (domain, callback) {
-            cache.get('resolve6_' + domain, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.resolve6(domain, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('resolve6_' + domain, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'resolve6_' + domain;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolve6(domain, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolve6_' + domain, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.resolveMx method
         dns.resolveMx = function (domain, callback) {
-            cache.get('resolveMx_' + domain, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.resolveMx(domain, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('resolveMx_' + domain, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'resolveMx_' + domain;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolveMx(domain, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolveMx_' + domain, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.resolveTxt method
         dns.resolveTxt = function (domain, callback) {
-            cache.get('resolveTxt_' + domain, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.resolveTxt(domain, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('resolveTxt_' + domain, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'resolveTxt_' + domain;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolveTxt(domain, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolveTxt_' + domain, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.resolveSrv method
         dns.resolveSrv = function (domain, callback) {
-            cache.get('resolveSrv_' + domain, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.resolveSrv(domain, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('resolveSrv_' + domain, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'resolveSrv_' + domain;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolveSrv(domain, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolveSrv_' + domain, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.resolveNs method
         dns.resolveNs = function (domain, callback) {
-            cache.get('resolveNs_' + domain, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.resolveNs(domain, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('resolveNs_' + domain, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'resolveNs_' + domain;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolveNs(domain, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolveNs_' + domain, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.resolveCname method
         dns.resolveCname = function (domain, callback) {
-            cache.get('resolveCname_' + domain, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.resolveCname(domain, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('resolveCname_' + domain, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'resolveCname_' + domain;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.resolveCname(domain, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('resolveCname_' + domain, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
 
         // override dns.reverse method
         dns.reverse = function (ip, callback) {
-            cache.get('reverse_' + ip, function (error, record) {
-                if (record) {
-                    callback(error, deepCopy(record));
-                } else {
-                    backup_object.reverse(ip, function (err, addresses) {
-                        if (err) {
-                            callback(err);
-                        } else {
-                            cache.set('reverse_' + ip, addresses, function () {
-                                callback(err, deepCopy(addresses));
-                            });
-                        }
-                    });
-                }
+            var key = 'reverse_' + ip;
+            cache.get(key, function (error, record) {
+                if (record) { return callback(error, deepCopy(record)); }
+
+                var list = callbackList[key] = callbackList[key] || [];
+                list.push(callback);
+
+                if (list.length > 1) { return; }
+
+                backup_object.reverse(ip, function (err, addresses) {
+                    if (err) {
+                        list.forEach(function (cb) { cb(err); });
+                        delete callbackList[key];
+                    } else {
+                        cache.set('reverse_' + ip, addresses, function () {
+                            list.forEach(function (cb) { cb(err, deepCopy(addresses)); });
+                            delete callbackList[key];
+                        });
+                    }
+                });
             });
         };
         return dns;
@@ -299,4 +365,4 @@ var EnhanceDns = function (conf) {
 
 module.exports = function(conf) {
     return new EnhanceDns(conf);
-};
\ No newline at end of file
+};