Attempt evalsha before eval

Fix #253

Signed-off-by: DTrejo <david.trejo@voxer.com>

index.js

@@ -5,6 +5,7 @@ var net = require("net"),
     Queue = require("./lib/queue"),
     to_array = require("./lib/to_array"),
     events = require("events"),
+    crypto = require("crypto"),
     parsers = [], commands,
     connection_id = 0,
     default_port = 6379,
@@ -1059,6 +1060,36 @@ RedisClient.prototype.MULTI = function (args) {
     return new Multi(this, args);
 };
 
+
+// stash original eval method
+var eval = RedisClient.prototype.eval;
+// hook eval with an attempt to evalsha for cached scripts
+RedisClient.prototype.eval =
+RedisClient.prototype.EVAL = function () {
+    var self = this,
+        args = to_array(arguments),
+        callback;
+
+    if (typeof args[args.length - 1] === "function") {
+        callback = args.pop();
+    }
+
+    // replace script source with sha value
+    var source = args[0];
+    args[0] = crypto.createHash("sha1").update(source).digest("hex");
+
+    self.evalsha(args, function (err, reply) {
+        if (err && /NOSCRIPT/.test(err.message)) {
+            args[0] = source;
+            eval.call(self, args, callback);
+
+        } else if (callback) {
+            callback(err, reply);
+        }
+    });
+};
+
+
 exports.createClient = function (port_arg, host_arg, options) {
     var port = port_arg || default_port,
         host = host_arg || default_host,