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# Gossamer `cmd` Package | ||
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This package encapsulates the entry point to Gossamer - it uses the popular | ||
[`cli` package from `urfave`](https://github.com/urfave/cli/blob/master/docs/v1/manual.md) to expose a command-line | ||
interface (CLI). The Gossamer CLI accepts several subcommands, each of which is associated with an "action"; these | ||
subcommands and their corresponding actions are defined in [`main.go`](main.go). When the Gossamer CLI is executed | ||
without a subcommand, the `gossamerAction` is invoked. What follows is a list of the Gossamer subcommands, as well as an | ||
overview of some of the flags/parameters they accept. The flags/parameters that the Gossamer CLI supports are defined in | ||
[`flags.go`](flags.go). For an exhaustive reference of the Gossamer CLI capabilities, follow | ||
[the installation instructions](../../README.md#installation) and execute `./bin/gossamer --help`. | ||
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- `gossamerAction` - This the default Gossamer execution action - it will launch a Gossamer blockchain client. The | ||
details of how Gossamer orchestrates a blockchain client are [described below](#client-components). | ||
- `chain` - specifies the [chain configuration](../../chain) that the | ||
[Gossamer host node](https://chainsafe.github.io/gossamer/getting-started/overview/host-architecture/) should load | ||
- `log` - supports levels `crit` (silent) to `trce` (detailed), default is `info` | ||
- `name` - node name, as it will appear in, e.g., [telemetry](https://telemetry.polkadot.io/) | ||
- `account` - The `account` subcommand provides the user with capabilities related to generating and using `ed25519`, | ||
`secp256k1`, and `sr25519` [account keys](https://wiki.polkadot.network/docs/learn-keys), and managing the keys | ||
present in the [Gossamer keystore](#keystore). The action for this subcommand is defined in [account.go](account.go); | ||
it is an interface to the capabilities defined in the [`crypto`](../../lib/crypto) and | ||
[`keystore`](../../lib/keystore) packages. This subcommand provides capabilities that are similar to | ||
[Parity's Subkey utility](https://docs.substrate.io/v3/tools/subkey). | ||
- `generate` - creates a new key pair; specify `--ed25519`, `secp256k1`, or `--sr25519` (default) | ||
- `list` - lists the keys in the Gossamer keystore | ||
- `password` - allows the user to provide a password for encrypting a generated key, or unlocking the Gossamer | ||
keystore | ||
- `import-runtime` - This subcommand takes a [Wasm runtime binary](https://wiki.polkadot.network/docs/learn-wasm) and | ||
uses it to generate a [genesis](https://wiki.polkadot.network/docs/glossary#genesis) configuration file; it does not | ||
require any flags, but expects the path to a Wasm file to be provided as a command-line parameter (example: | ||
`./bin/gossamer import-runtime runtime.wasm > genesis.json`). | ||
- `build-spec` - This subcommand allows the user to "compile" a human-readable Gossamer genesis configuration file into | ||
a format that the Gossamer node can consume. If the `--genesis` parameter is not provided, the generated genesis | ||
configuration will represent the Gossamer default configuration. | ||
- `genesis` - path to the human-readable configuration file that should be compiled into a format that Gossamer can | ||
consume | ||
- `import-state` - The `import-state` subcommand allows a user to seed [Gossamer storage](../../dot/state) with | ||
key-value pairs in the form of a JSON file. The input for this subcommand can be retrieved from | ||
[the state_getPairs RPC endpoint](https://github.com/w3f/PSPs/blob/master/PSPs/drafts/psp-6.md#1114-state_getpairs). | ||
- `first-slot` - the first [BABE](https://wiki.polkadot.network/docs/learn-consensus#block-production-babe) slot, | ||
which is the timestamp of the first block divided by the slot duration | ||
- `header` - path to a JSON file that describes the block header corresponding to the given state | ||
- `state` - path to a JSON file that contains the key-value pairs with which to seed Gossamer storage | ||
- `init` - This subcommand accepts a genesis configuration file and uses it to initialise the Gossamer node and its | ||
state. | ||
- `genesis` - path to the "compiled" genesis configuration file that should be used to initialise the Gossamer node | ||
and its state | ||
- `export` - The `export` subcommand transforms a genesis configuration and Gossamer state into a TOML configuration | ||
file. | ||
- `config` - path to a TOML configuration file (e.g. [Polkadot](../../chain/polkadot/config.toml)) | ||
- `basepath` - path to the Gossamer data directory that defines the state to export | ||
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## Client Components | ||
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In its default method of execution, Gossamer orchestrates a number of modular services that run | ||
[concurrently as goroutines](https://www.golang-book.com/books/intro/10) and work together to implement the protocols of | ||
a blockchain network. Alongside these services, Gossamer manages [a keystore](#keystore), [a runtime](#runtime), and | ||
[a telemetry service](#telemetry), all of which are described in greater detail below. The entry point to the Gossamer | ||
blockchain client capabilities is the `gossamerAction` function that is defined in [main.go](main.go), which in turn | ||
invokes the `NewNode` function in [dot/node.go](../../dot/node.go). `NewNode` calls into functions that are defined in | ||
[dot/services.go](../../dot/services.go) and starts the services that power a Gossamer node. What follows is a list that | ||
describes the services and capabilities that inform a Gossamer blockchain client: | ||
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- State - This service is a wrapper around an instance of [`chaindb`](https://github.com/ChainSafe/chaindb), a key-value | ||
database that is built on top of [BadgerDB](https://github.com/dgraph-io/badger) from [Dgraph](https://dgraph.io/). | ||
The state service provides storage capabilities for the other Gossamer services - each service is assigned a prefix | ||
that is added to its storage keys. The state service is defined in [dot/state/service.go](../../dot/state/service.go). | ||
- Network - The network service, which is defined in [dot/network/service.go](../../dot/network/service.go), is built on | ||
top of [the Go implementation](https://github.com/libp2p/go-libp2p) of [the `libp2p` protocol](https://libp2p.io/). | ||
This service manages a `libp2p` "host", a peer-to-peer networking term for a network participant that is providing | ||
both client _and_ server capabilities to a peer-to-peer network. Gossamer's network service manages the discovery of | ||
other hosts as well as the connections with these hosts that allow Gossamer to communicate with its network peers. | ||
- Digest Handler - The digest handler ([dot/digest/digest.go](../../dot/digest/digest.go)) manages the verification of | ||
the [cryptographic digests](https://docs.substrate.io/v3/getting-started/glossary/#digest) that are present in block | ||
headers. | ||
- Consensus - The BABE and GRANDPA services work together to provide Gossamer with its | ||
[hybrid consensus](https://wiki.polkadot.network/docs/learn-consensus#hybrid-consensus) capabilities. The term "hybrid | ||
consensus" refers to the fact that block _production_ is decoupled from block _finalisation_. Block production is | ||
handled by the BABE service, which is defined in [lib/babe/babe.go](../../lib/babe/babe.go); block finalisation is | ||
handled by the GRANDPA service, which is defined in [lib/grandpa/grandpa.go](../../lib/grandpa/grandpa.go). | ||
- Sync - This service is concerned with keeping Gossamer in sync with a blockchain - it implements a "bootstrap" mode, | ||
to download and verify blocks that are part of an existing chain's history, and a "tip-syncing" mode that manages the | ||
multiple candidate forks that may exist at the head of a live chain. The sync service makes use of | ||
[a block verification utility](../../lib/babe/verify.go) that implements BABE logic and is used by Gossamer to verify | ||
blocks that were produced by other other nodes in the network. The sync service is defined | ||
[dot/sync/syncer.go](../../dot/sync/syncer.go). | ||
- RPC - This service, which is defined in [dot/rpc/service.go](../../dot/rpc/service.go), exposes a JSON-RPC interface | ||
that is used by client applications like [Polkadot JS Apps UI](https://polkadot.js.org/apps/). The RPC interface is | ||
used to interact with Gossamer to perform tasks such as key management, as well as for interacting with the "inner" | ||
runtime by querying storage and submitting transactions. | ||
- System - The system service is defined in [dot/system/service.go](../../dot/system/service.go) and exposes metadata | ||
about the Gossamer system, such as the names and versions of the protocols that it implements. | ||
- Core - As its name implies, the core service ([dot/core/service.go](../../dot/core/service.go)) encapsulates a range | ||
of capabilities that are central to the functioning of a Gossamer node. In general, the core service is a type of | ||
dispatcher that coordinates interactions between services, e.g. writing blocks to the database, reloading | ||
[the runtime](#runtime) when its definition is updated, etc. | ||
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### Keystore | ||
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The Gossamer keystore is used for managing the public/private cryptographic key pairs that are used for participating in | ||
a blockchain network. Public keys are used to identify network participants; network participants use their private keys | ||
to sign messages in order to authorise privileged actions. In addition to informing the Gossamer blockchain client | ||
capabilities, the Gossamer keystore is accessible by way of the `account` subcommand. The Gossamer keystore manages a | ||
number of key types, some of which are listed below: | ||
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- `babe` - This key is used for signing messages related to the BABE block production algorithm. | ||
- `gran` - The GRANDPA key is used for participating in GRANDPA block finalisation. | ||
- `imon` - The name of this key is a reference to "ImOnline", which is an | ||
[online message](https://wiki.polkadot.network/docs/glossary#online-message) that Gossamer nodes use to report | ||
liveliness. | ||
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### Runtime | ||
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In addition to the above-described services, Gossamer hosts a Wasm execution environment that is used to manage an | ||
upgradeable blockchain runtime. The runtime must be implemented in Wasm, and must expose an interface that is specified | ||
in [lib/runtime/interface.go](../../lib/runtime/interface.go). The runtime defines the blockchain's state transition | ||
function, and the various Gossamer services consume this capability in order to author blocks, as well as to verify | ||
blocks that were authored by network peers. | ||
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### Metrics & Telemetry | ||
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Gossamer publishes telemetry data and also includes an embedded Prometheus server that reports metrics. The metrics | ||
capabilities are defined in the [dot/metrics](../../dot/metrics) package and build on | ||
[the metrics library that is included with Go Ethereum](https://github.com/ethereum/go-ethereum/blob/master/metrics/README.md). | ||
The Gossamer telemetry server publishes telemetry data that is compatible with | ||
[Polkadot Telemetry](https://github.com/paritytech/substrate-telemetry) and | ||
[its helpful UI](https://telemetry.polkadot.io/). |