103 lines
3.8 KiB
Markdown
103 lines
3.8 KiB
Markdown
# Package Jail
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[](https://godoc.org/github.com/status-im/status-go/geth/jail)
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--
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import "github.com/status-im/status-go/geth/jail"
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Package jail implements "jailed" enviroment for executing arbitrary JavaScript
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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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| 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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### 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
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examples: 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 arount Otto VM functions of the same name. Run accepts raw JS strings
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for execution, 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
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functions, because they're not part of ECMA-262 spec, but properties of the
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window object in browser. We add support for them using own implementation of
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Event Loop, heavily based on http://github.com/status-im/ottoext package. See
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loop/fetch/promise packages under `jail/internal/`.
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Each cell starts a new loop in a separate goroutine, registers functions for
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setTimeout/setInterval calls and associate them with this loop. All JS code
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executed as callback to setTimeout/setInterval will be handled by this loop.
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For example, following code:
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cell.Run(`setTimeout(function(){ value = "42" }, 2000);`)
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will execute setTimeout and return immidiately, but callback function will be
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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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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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### Fetch support
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Fetch API is implemented in a similar way using the same loop. When Cell is
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created, corresponding handlers are registered within VM and associated event
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loop.
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Due to asynchronous nature of Fetch API, the following code will return
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immediately:
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cell.Run(`fetch('http://example.com/').then(function(data) { ... })`)
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and callback function in a promise will be executed in a event loop in the
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background. Thus, it's user responsibility to register a corresponding callback
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function before:
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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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### Package documentation
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See: [](https://godoc.org/github.com/status-im/status-go/geth/jail) |