Hello!
I am pretty new to nodejs and I'm writing a client api module that will
provide CRUD operations by calling json-rpc methods on an outside server.
The server provides it's currently running version via a json-rpc request
and based on that the client api may or may not have additional
functionality.
My question is more of a design question than anything else. I'm not sure
the best way to get the server's version and cache it within an
asynchronous environment. I am currently using the http module to make the
requests and the q module to use promises. Below is some pseudo code to
illustrate basically what I have.
function Client(url, opts) {
> var info = {
> 'url': url,
> 'server_version': null
> };
> };
>
Client.prototype.server_version = function (cb) {
> if (!this.info.server_version){
> this.request("info").then(function(result) {
> this.info.server_version = result.version;
> }).nodeify(cb);
> } else {
> cb(this.info.server_version);
> };
> };
>
Client.prototype.read = function(params, cb) {
> this.server_version(function(err, result) {
> if (result > [3, 3, 0]) {
> ...
> };
> else {
> ...
> }
> });
> return this.request(params).nodeify(cb);
> };
>
Client.prototype.request = function(method) {
> defer = Q.defer();
> ...
> return defer.promise;
> };
I guess my question is this the "right" way to deal with figuring out the
server version to make logical decisions at various points in the code? I
see a few issues with the way I am currently doing it, if the
server_version is requested multiple times before it's been cached there
will be unnecessary additional calls made to the server. It would be nice
to have a better way to attach callbacks to the original promise that's
made when the first request is sent out. Also using always using a
callback and nested functions to check the server version feels a bit
inelegant. I'm not sure if this is the way it needs to be done. Is this a
situation where I would want to use yield? If so do I need to run the
unstable 11.* version of Node to take advantage of that?
I apologize in advance if this question is vague. I am trying to
understand how to do something asynchronous that I would normally do
synchronously, ie: halting code flow the first time a call to check the
server_version is made and being able to reference
"this.info.server_version" afterwards versus always having to use a
callback to do the check.
Any and all advice is much appreciated.
Best,
Tony
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