Added direct support for domains.

There are three pieces to this support, all of them small, and none of
them with large overhead:

  1. When sending a command, ensure that any callback is bound to the
     current domain, if one is present.
  2. Also add the RedisClient to the current domain so that error
     events bubble properly.
  3. In try_callback, when a domain is in play, instead of throwing
     on the next tick, emit the error on the domain. The parser can
     still finish processing the response and the error ends up in
     the correct place.

index.js

@@ -573,15 +573,20 @@ RedisClient.prototype.return_error = function (err) {
 };
 
 // if a callback throws an exception, re-throw it on a new stack so the parser can keep going.
+// if a domain is active, emit the error on the domain, which will serve the same function.
 // put this try/catch in its own function because V8 doesn't optimize this well yet.
 function try_callback(callback, reply) {
     try {
         callback(null, reply);
     } catch (err) {
+        if (process.domain) {
+            process.domain.emit('error', err);
+        } else {
             process.nextTick(function () {
                 throw err;
             });
         }
+    }
 }
 
 // hgetall converts its replies to an Object.  If the reply is empty, null is returned.
@@ -750,6 +755,12 @@ RedisClient.prototype.send_command = function (command, args, callback) {
         throw new Error("send_command: second argument must be an array");
     }
 
+    if (callback && process.domain) {
+        callback = process.domain.bind(callback);
+        // ensure that any unhandled error events emitted by the client are scoped to the correct domain
+        process.domain.add(this);
+    }
+
     // if the last argument is an array and command is sadd or srem, expand it out:
     //     client.sadd(arg1, [arg2, arg3, arg4], cb);
     //  converts to:

test.js

@@ -1950,6 +1950,30 @@ tests.SLOWLOG = function () {
     });
 }
 
+tests.DOMAIN = function () {
+    var name = "DOMAIN";
+
+    var domain;
+    try {
+        domain = require('domain').create();
+    } catch (err) {
+        console.log("Skipping " + name + " because this version of node doesn't have domains.");
+        next(name);
+    }
+
+    if (domain) {
+        domain.run(function () {
+            client.set('domain', 'value', function (err, res) {
+                assert.ok(process.domain);
+                var notFound = res.not.existing.thing; // ohhh nooooo
+            });
+        });
+
+        // this is the expected and desired behavior
+        domain.on('error', function (err) { next(name); });
+    }
+};
+
 // TODO - need a better way to test auth, maybe auto-config a local Redis server or something.
 // Yes, this is the real password.  Please be nice, thanks.
 tests.auth = function () {