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Update porting_to_new_environment.md

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This MetamaskInpageProvider file was moved out into its own repo, this updates the link to point to that repo.
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Brian R. Bondy 2019-04-08 15:43:34 -04:00 committed by GitHub
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docs/porting_to_new_environment.md
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@ -10,7 +10,7 @@ The `metamask-background` describes the file at `app/scripts/background.js`, whi
When a new site is visited, the WebExtension creates a new `ContentScript` in that page's context, which can be seen at `app/scripts/contentscript.js`. This script represents a per-page setup process, which creates the per-page `web3` api, connects it to the background script via the Port API (wrapped in a [stream abstraction](https://github.com/substack/stream-handbook)), and injected into the DOM before anything loads.
The most confusing part about porting MetaMask to a new platform is the way we provide the Web3 API over a series of streams between contexts. Once you understand how we create the [InpageProvider](../app/scripts/lib/inpage-provider.js) in the [inpage.js script](../app/scripts/inpage.js), you will be able to understand how the [port-stream](../app/scripts/lib/port-stream.js) is just a thin wrapper around the [postMessage API](https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage), and a similar stream API can be wrapped around any communication channel to communicate with the `MetaMaskController` via its `setupUntrustedCommunication(stream, domain)` method.
The most confusing part about porting MetaMask to a new platform is the way we provide the Web3 API over a series of streams between contexts. Once you understand how we create the [MetamaskInpageProvider](https://github.com/MetaMask/metamask-inpage-provider/blob/master/index.js) in the [inpage.js script](../app/scripts/inpage.js), you will be able to understand how the [port-stream](../app/scripts/lib/port-stream.js) is just a thin wrapper around the [postMessage API](https://developer.mozilla.org/en-US/docs/Web/API/Window/postMessage), and a similar stream API can be wrapped around any communication channel to communicate with the `MetaMaskController` via its `setupUntrustedCommunication(stream, domain)` method.
### The MetaMask Controller
@ -89,7 +89,7 @@ MetaMask has two kinds of [duplex stream APIs](https://github.com/substack/strea
If you are making a MetaMask-powered browser for a new platform, one of the trickiest tasks will be injecting the Web3 API into websites that are visited. On WebExtensions, we actually have to pipe data through a total of three JS contexts just to let sites talk to our background process (site -> contentscript -> background).
To see how we do that, you can refer to the [inpage script](https://github.com/MetaMask/metamask-extension/blob/master/app/scripts/inpage.js) that we inject into every website. There you can see it creates a multiplex stream to the background, and uses it to initialize what we call the [inpage-provider](https://github.com/MetaMask/metamask-extension/blob/master/app/scripts/lib/inpage-provider.js), which you can see stubs a few methods out, but mostly just passes calls to `sendAsync` through the stream it's passed! That's really all the magic that's needed to create a web3-like API in a remote context, once you have a stream to MetaMask available.
To see how we do that, you can refer to the [inpage script](https://github.com/MetaMask/metamask-extension/blob/master/app/scripts/inpage.js) that we inject into every website. There you can see it creates a multiplex stream to the background, and uses it to initialize what we call the [MetamaskInpageProvider](https://github.com/MetaMask/metamask-inpage-provider/blob/master/index.js), which you can see stubs a few methods out, but mostly just passes calls to `sendAsync` through the stream it's passed! That's really all the magic that's needed to create a web3-like API in a remote context, once you have a stream to MetaMask available.
In `inpage.js` you can see we create a `PortStream`, that's just a class we use to wrap WebExtension ports as streams, so we can reuse our favorite stream abstraction over the more irregular API surface of the WebExtension. In a new platform, you will probably need to construct this stream differently. The key is that you need to construct a stream that talks from the site context to the background. Once you have that set up, it works like magic!