68 lines
1.6 KiB
Markdown
68 lines
1.6 KiB
Markdown
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# Middlewares
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Dispatcher provides basic middleware functionality. It is not as extensible
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as middlewares in frameworks likes [Telegraf](https://github.com/telegraf/telegraf),
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and that is by design, since we already have filters and propagation using which
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you can achieve pretty much the same.
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Middlewares are only called for parsed updates.
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## Middleware types
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Dispatcher supports 2 middlewares: pre-update and post-update.
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### Pre-update
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**Pre-update** middleware is called right before an update is going
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to be dispatched, and can be used to skip that update altogether.
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```ts
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dp.onPreUpdate((upd) => {
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// randomly skip 10% of updates
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if (Math.random() < 0.1)
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return PropagationAction.Stop
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})
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```
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### Post-update
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**Post-update** middleware is called after an update was processed
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by the dispatcher. Whether the update was handled is also provided here:
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```ts
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dp.onPostUpdate((handled, upd) => {
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if (handled) {
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console.log(`handled ${upd.name}`)
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}
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})
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```
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## Additional context
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You can add some additional context in the pre-update middleware,
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and that context will also be available in post-update middleware
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and error handler:
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```ts
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interface TimerContext {
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start: number
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}
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dp.onPreUpdate<TimerContext>((upd) => {
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upd.start = Date.now()
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})
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dp.onPostUpdate<TimerContext>((handled, upd) => {
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if (handled) {
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console.log(`handled ${upd.name} in ${Date.now() - upd.start} ms`)
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}
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})
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dp.onError<TimerContext>((err, upd) => {
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console.log(`error for ${upd.name} after ${Date.now() - upd.start} ms`)
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})
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```
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Note that *currently* you can't access that context from handlers or filters
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(see [mtcute#4](https://github.com/mtcute/mtcute/issues/4)).
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