# BlockSourceError Errors thrown by [`BlockSource`](/documentation/BitcoinKernel/BlockSource) conformers. ``` enum BlockSourceError ``` ## Overview Covers the five common failure modes of fetching blockchain data from a remote source: malformed responses, missing data, unsupported operations, rate-limiting, and transport-layer failures. Designed so that a single `catch let error as BlockSourceError` in calling code is sufficient to handle every source-side failure category. Inside [`BlockchainSync`](/documentation/BitcoinKernel/BlockchainSync), any `BlockSourceError` thrown from a conformer is re-surfaced to the caller as a terminal [`BlockchainSync.Update.State.failed(_:)`](/documentation/BitcoinKernel/BlockchainSync/Update/State-swift.enum/failed(_:)) update carrying the error’s localized description — the sequence itself does not throw.