API Reference

Package: `@tetherto/wdk-failover-provider`

Class: `FailoverProvider\<T\>`

FailoverProvider\<T\> collects provider candidates of one shared shape and returns a proxied T that retries failed calls against the next provider.

Constructor

Use the constructor to set retry behavior before you add provider candidates:

Create A FailoverProvider Factory

new FailoverProvider({
  retries,        // optional, defaults to 3
  shouldRetryOn   // optional, defaults to (error) => error instanceof Error
})

retries (number, optional): Number of additional attempts after the first failure. Total attempts are 1 + retries.
shouldRetryOn ((error: Error) =\> boolean, optional): Predicate that decides whether the proxy should switch to the next provider after a failure.

Methods

Method	Description	Returns
`addProvider(provider)`	Register one provider candidate and return the same factory so you can chain more candidates.	`FailoverProvider\<T\>`
`initialize()`	Return a proxied provider of type `T` that reads from the active provider and retries failed calls against the next provider.	`T`

`addProvider(provider)`

Register a provider candidate. Every candidate should satisfy the same T shape because initialize() returns one proxied T.

const factory = new FailoverProvider({ retries: 1 })

factory.addProvider({
  name: 'primary',
  async getBlockNumber () {
    return 21345678
  }
})

`initialize()`

Create the failover-enabled proxy after you have added at least one provider. The runtime throws if the factory is still empty.

Initialize The Failover Proxy

const provider = new FailoverProvider({ retries: 1 })
  .addProvider(primary)
  .addProvider(secondary)
  .initialize()

const blockNumber = await provider.getBlockNumber()

`FailoverProviderConfig`

The package exports the FailoverProviderConfig type through its top-level type surface.

Field	Description
`retries?`	Additional retry attempts after the first failure. Defaults to `3`.
`shouldRetryOn?`	Retry predicate for thrown errors and rejected promises. Defaults to retrying any `Error` instance.

Runtime behavior

initialize() returns a JavaScript Proxy over the first added provider.
Non-function properties are forwarded from the currently active provider.
If a property getter throws and shouldRetryOn(error) returns true, the runtime advances to the next provider before retrying the property access.
If a synchronous method throws and shouldRetryOn(error) returns true, the runtime advances to the next provider and retries the method call.
If an asynchronous method rejects and shouldRetryOn(error) returns true, the runtime advances to the next provider and retries the method call.
Provider switching is round-robin. If the active provider already changed while another call was failing, the runtime keeps the newer active provider instead of advancing twice.

Example

This example shows a transient failure on the first provider and a successful retry on the second provider:

Retry Across Two Providers

import FailoverProvider from '@tetherto/wdk-failover-provider'

const primary = {
  async getBlockNumber () {
    throw new Error('temporary upstream outage')
  }
}

const secondary = {
  async getBlockNumber () {
    return 21345678
  }
}

const provider = new FailoverProvider({
  retries: 1,
  shouldRetryOn: (error) => error.message.includes('temporary')
})
  .addProvider(primary)
  .addProvider(secondary)
  .initialize()

const blockNumber = await provider.getBlockNumber()