github.com/decred/dcrd/mempool (go): Package mempool provides a policy-enforced pool of unmined Decred transactions.  A key responsibility of the Decred network is mining transactions – regular transactions and stake transactions – into blocks.  In order to facilitate this, the mining process relies on having a readily-available source of transactions to include in a block that is being solved.  At a high level, this package satisfies that requirement by providing an in-memory pool of fully validated transactions that can also optionally be further filtered based upon a configurable policy.  The Policy configuration options has flags that control whether or not "standard" transactions and old votes are accepted into the mempool. In essence, a "standard" transaction is one that satisfies a fairly strict set of requirements that are largely intended to help provide fair use of the system to all users.  It is important to note that what is considered to be a "standard" transaction changes over time as policy and consensus rules evolve. For some insight, at the time of this writing, an example of _some_ of the criteria that are required for a transaction to be considered standard are that it is of the most-recently supported version, finalized, does not exceed a specific size, and only consists of specific script forms.  Since this package does not deal with other Decred specifics such as network communication and transaction relay, it returns a list of transactions that were accepted which gives the caller a high level of flexibility in how they want to proceed.  Typically, this will involve things such as relaying the transactions to other peers on the network and notifying the mining process that new transactions are available.  This package has intentionally been designed so it can be used as a standalone package for any projects needing the ability create an in-memory pool of Decred transactions that are not only valid by consensus rules, but also adhere to a configurable policy  ## Feature Overview  The following is a quick overview of the major features.  It is not intended to be an exhaustive list.  - Maintain a pool of fully validated transactions  - Stake transaction support (ticket purchases, votes and revocations)  - Orphan transaction support (transactions that spend from unknown outputs)  - Configurable transaction acceptance policy  - Additional metadata tracking for each transaction  - Manual control of transaction removal  Errors returned by this package are either the raw errors provided by underlying calls or of type mempool.RuleError.  Since there are two classes of rules (mempool acceptance rules and blockchain (consensus) acceptance rules), the mempool.RuleError type contains a single Err field which will, in turn, either be a mempool.TxRuleError or a blockchain.RuleError.  The first indicates a violation of mempool acceptance rules while the latter indicates a violation of consensus acceptance rules.  This allows the caller to easily differentiate between unexpected errors, such as database errors, versus errors due to rule violations through type assertions.  In addition, callers can programmatically determine the specific rule violation by type asserting the Err field to one of the aforementioned types and examining their underlying ErrorCode field.
Keywords: blockchain|cryptocurrency|dcrd|decred|decred-daemon|decred-nodes|go|golang|p2p|peer-to-peer