RunTx recovery middleware

BaseApp.runTx() function handles Go panics that might occur during transactions execution, for example, keeper has faced an invalid state and panicked. Depending on the panic type different handler is used, for instance the default one prints an error log message. Recovery middleware is used to add custom panic recovery for Cosmos SDK application developers.

More context can found in the corresponding ADR-022 and the implementation in recovery.go.

Interface

baseapp/recovery.go

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See full example on GitHub

recoveryObj is a return value for recover() function from the buildin Go package.

Contract:

• RecoveryHandler returns nil if recoveryObj wasn't handled and should be passed to the next recovery middleware;
• RecoveryHandler returns a non-nil error if recoveryObj was handled;

Custom RecoveryHandler register

baseapp/baseapp.go

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See full example on GitHub

BaseApp method adds recovery middleware to the default recovery chain.

Example

Let's assume we want to emit the "Consensus failure" chain state if some particular error occurred.

We have a module keeper that panics:

func (k FooKeeper) Do(obj interface{}) {
    if obj == nil {
        // that shouldn't happen, we need to crash the app
        err := errorsmod.Wrap(fooTypes.InternalError, "obj is nil")
        panic(err)
    }
}

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:

// Cosmos SDK application constructor
customHandler := func(recoveryObj interface{}) error {
    err, ok := recoveryObj.(error)
    if !ok {
        return nil
    }

    if fooTypes.InternalError.Is(err) {
        panic(fmt.Errorf("FooKeeper did panic with error: %w", err))
    }

    return nil
}

baseApp := baseapp.NewBaseApp(...)
baseApp.AddRunTxRecoveryHandler(customHandler)