74 lines
2.1 KiB
Markdown
74 lines
2.1 KiB
Markdown
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order: 12
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-->
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# RunTx recovery middleware
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`BaseApp.runTx()` function handles Golang panics that might occur during transactions execution, for example, keeper has faced an invalid state and paniced.
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Depending on the panic type different handler is used, for instance the default one prints an error log message.
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Recovery middleware is used to add custom panic recovery for Cosmos SDK application developers.
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More context could be found in the corresponding [ADR-022](../architecture/adr-022-custom-panic-handling.md).
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Implementation could be found in the [recovery.go](../../baseapp/recovery.go) file.
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## Interface
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```go
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type RecoveryHandler func(recoveryObj interface{}) error
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```
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`recoveryObj` is a return value for `recover()` function from the `buildin` Golang package.
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**Contract:**
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- RecoveryHandler returns `nil` if `recoveryObj` wasn't handled and should be passed to the next recovery middleware;
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- RecoveryHandler returns a non-nil `error` if `recoveryObj` was handled;
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## Custom RecoveryHandler register
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`BaseApp.AddRunTxRecoveryHandler(handlers ...RecoveryHandler)`
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BaseApp method adds recovery middleware to the default recovery chain.
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## Example
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Lets assume we want to emit the "Consensus failure" chain state if some particular error occurred.
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We have a module keeper that panics:
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```go
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func (k FooKeeper) Do(obj interface{}) {
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if obj == nil {
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// that shouldn't happen, we need to crash the app
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err := sdkErrors.Wrap(fooTypes.InternalError, "obj is nil")
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panic(err)
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}
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}
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```
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By default that panic would be recovered and an error message will be printed to log. To override that behaviour we should register a custom RecoveryHandler:
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```go
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// Cosmos SDK application constructor
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customHandler := func(recoveryObj interface{}) error {
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err, ok := recoveryObj.(error)
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if !ok {
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return nil
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}
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if fooTypes.InternalError.Is(err) {
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panic(fmt.Errorf("FooKeeper did panic with error: %w", err))
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}
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return nil
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}
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baseApp := baseapp.NewBaseApp(...)
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baseApp.AddRunTxRecoveryHandler(customHandler)
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```
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## Next {hide}
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Learn about the [IBC](./../ibc/README.md) protocol {hide}
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