Connecting to users local machine from my WebApp

I have a Web App that i have deve开发者_运维技巧loped I am looking to develop a plugin for this app so that i can pull information from the users accounts package such as sage or quickbooks(offline version). Ideally I would like to do this without them having to have a static ip etc.

Unfortunately this is way over my head I currently have no idea on how to do this.

Please can some one guide me in the right direction I will probably use json data between the webapp and the client service that I will make and im fine with that part its just the initial connection that I am confused about.

Any help would be really really appreciated I hope this makes sense.

Thanks

Ash

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The way the Shopify Quickbooks integration (Quickify) works is by setting up a tiny local server that listens on a high port number and is able to play with the local filesystem. The web app part of the solution sends JSON back to it.