100 lines
3.9 KiB
Markdown
100 lines
3.9 KiB
Markdown
# jail [](https://godoc.org/github.com/status-im/status-go/geth/jail)
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jail - jailed environment for executing JS code.
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Download:
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```shell
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go get github.com/status-im/status-go/geth/jail
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```
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* * *
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jail - jailed environment for executing JS code.
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Package jail implements "jailed" environment for executing arbitrary
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JavaScript code using Otto JS interpreter (https://github.com/robertkrimen/otto).
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Jail create multiple Cells, one cell per status client chat. Each cell runs own
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Otto virtual machine and lives forever, but that may change in the future.
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```
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+----------------------------------------------+
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| Jail |
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+----------------------------------------------+
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+---------+ +---------+ +---------+ +---------+
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| Cell | | Cell | | Cell | | Cell |
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|ChatID 1 | |ChatID 2 | |ChatID 3 | |ChatID N |
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|+-------+| |+-------+| |+-------+| |+-------+|
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||Otto VM|| ||Otto VM|| ||Otto VM|| ||Otto VM||
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|+-------+| |+-------+| |+-------+| |+-------+|
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|| Loop || || Loop || || Loop || || Loop ||
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++-------++ ++-------++ ++-------++ ++-------++
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```
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## Cells
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Each Cell object embeds *VM from 'jail/vm' for concurrency safe wrapper around
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*otto.VM functions. This is important when dealing with setTimeout and Fetch API
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functions (see below).
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## Get and Set
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(*VM).Get/Set functions provide transparent and concurrently safe wrappers for
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Otto VM Get and Set functions respectively. See Otto documentation for usage examples:
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https://godoc.org/github.com/robertkrimen/otto
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## Call and Run
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(*VM).Call/Run functions allows executing arbitrary JS in the cell. They're also
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wrappers around Otto VM functions of the same name. `Run` accepts raw JS strings for execution while `Call` takes a JS function name (defined in VM) and parameters.
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## Timeouts and intervals support
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Default Otto VM interpreter doesn't support setTimeout() / setInterval() JS functions,
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because they're not part of ECMA-262 spec, but properties of the window object in browser.
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We add support for them using own implementation of Event Loop, heavily based on [ottoext package](https://github.com/deoxxa/ottoext). See loop/fetch/promise packages under [jail/internal/](https://github.com/status-im/status-go/tree/develop/geth/jail/internal).
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Each cell starts a new loop in a separate goroutine, registers functions for setTimeout / setInterval calls and associate them with this loop. All JS code executed as callback to setTimeout/setInterval will be handled by this loop.
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For example, following code:
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```
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cell.Run(`setTimeout(function(){ value = "42" }, 2000);`)
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```
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will execute setTimeout and return immediately, but callback function will
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be executed after 2 seconds in the loop that was started upon current cell.
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In order to capture response one may use following approach:
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```
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err = cell.Set("__captureResponse", func(val string) otto.Value {
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fmt.Println("Captured response from callback:", val)
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return otto.UndefinedValue()
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})
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cell.Run(`setTimeout(function(){ __captureResponse("OK") }, 2000);`)
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```
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## Fetch support
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Fetch API is implemented in a similar way using the same loop. When Cell is created, corresponding handlers are registered within VM and associated event loop.
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Due to asynchronous nature of Fetch API, the following code will return immediately:
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```
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cell.Run(`fetch('http://example.com/').then(function(data) { ... })`)
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```
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and callback function in a promise will be executed in a event loop in the background. Thus, it's user responsibility to register a corresponding callback function before:
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```
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cell.Set("__captureSuccess", func(res otto.Value) { ... })
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cell.Run(`fetch('http://example.com').then(function(r) {
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return r.text()
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}).then(function(data) {
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// user code
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__captureSuccess(data)
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}))
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```
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* * *
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Automatically generated by [autoreadme](https://github.com/jimmyfrasche/autoreadme) on 2018.02.08
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