chainlib 0.5.4

Generic blockchain access library and tooling

chainlib

Overview

Chainlib is an attempt at employing a universal interface to manipulate and access blockchains regardless of underlying architecture.

It makes the following assumptions:

• A block MUST have a interpretable serializable format, and contains zero of more transactions

• A transaction MUST have a interpretable serializable format

• A transaction MUST have a nonce associated with a sender address. This uniquely identifies the transaction on the network.

• A transaction MUST have a fee bid to get the transaction executed on the network (a network that does not care about bids can just ignore this property).

• A transaction signature MAY be locked to a particular chain identifier

• The sender key of a transaction MAY be recovered by the signature of the transaction

Chainlib is specifically designed for building command line interface tools. It provides templates for handling configuration, argument parsing and environment variable processing to build RPC connections to chain nodes for network queries and signing operations.

Command line interface provisions

The base CLI provisions of chainlib simplifies the generation of a some base object instances by command line arguments, environment variables and configuration schemas.

To use CLI provisions, chainlib.cli should be imported. This automatically imports the following submodules:

arg
Define and/or select command-line arguments

config
Process configuration from command-line arguments and environment variables

rpc
Create RPC connection from configuration

wallet
Create wallet from configuration

Any chain implementation building on chainlib should extend one or more of the classes in these modules as needed, for example order to add more configuration directives or command line argument flags.

Arguments

chainlib defines a set of arguments that are common concepts for interfacing with blockchain RPCs. Which arguments to use for a specific instantiation can be defined using flags or symbols that define groups of flags.

This functionality is provided by the chainlib.cli.args.ArgumentParser class. It is a thin wrapper around the standard library argparser.ArgumentParser class, only adding a method to add arguments to the instance based on the aforementioned flags.

Following is a description of all pre-defined arguments that are available with chainlib.

-c, –config

Override configuration directives by reading ini-files in the given directory.

Only configuration directives defined in the schema may be overridden. See chainlib-config.

–env-prefix

Prepend the given string to configuration directives when overriding by environment variables

Normally, if a configuration directive FOO_BAR exists, the environment variable FOO_BAR will override its value. If --env-prefix BAZ is passed, the environment variable BAZ_FOO_BAR will be used instead to override the configuration directive FOO_BAR. The environment variable FOO_BAR will in this case not be used.

–height

Query the chain RPC for results at a specific block height.

Applies to read operations only.

-i, –chain-spec

Chain specification string for the blockchain connection.

This informs the implementing code about the architecture and deployment of the blockchain network. It can also be relevant when creating signatures for the network (e.g. the EIP155 signature scheme for EVM).

–fee-limit

Use the exact given fee multiplier to calculate the final bid to get transaction executed on the network.

How the fee semantics are employed depend on the chain implementation, but the final resulting bid must always be the product of price * limit.

If not defined, the multiplier will be retrieved using the fees provider defined by the implementation.

–fee-price

Use the exact given fee price as factor to calculate bid to get transaction executed on the network.

How the fee semantics are employed depend on the chain implementation, but the final resulting bid must always be the product of price * limit.

If not defined, the current recommended price will be retrieved from the fees provider defined by the implementation.

-n, –namespace

Append the given namespace to implicit configuration override paths.

For example, if linux xdg-basedir path is used, a namespace argument of foo in implementation domain bar will result in the configuration override path $HOME/.config/bar/foo.

–nonce

Start at the exact given nonce for the query.

If not defined, the next nonce will be retrieved from the nonce provider defined by the implementation.

-p, –provider

URL of the chain RPC provider.

-s, –send

CLI tools building on chainlib should never submit to the network by default. Instead, resulting transactions ready for network submission should be output to terminal.

If the implementation wishes to allow the user to directly send to the network, the -s flag must be used for this purpose.

–seq

By default, a random RPC id will be generated for every RPC call.

However, some RPCs will only allow sequential serial numbers to be used as RPC ids, in which case this flag should be used.

–raw

Generate output suitable for passing to another command (e.g. UNIX pipes).

–rpc-auth

Tells the implementer which RPC authentication scheme to use (e.g. "basic" for http basic).

–rpc-credentials

Tells the implemented wich RPC authentication credentials to use for selected rpc authentication scheme (e.g. "foo:bar" for user foo pass bar in scheme "basic" a.k.a. http basic).

Credentials may for example also be a single value, like a private key, depending on the scheme and implementation.

–rpc-dialect

Tells the implementer to optimize query, result and error reporting for the specific chain RPC backend dialect.

-u, –unsafe

Allow arguments with blockchain addresses that are not checksum protected.

-v, -vv

Defines logging verbosity.

Specifically, -v will set loglevel to INFO, wheres -vv will set loglevel to DEBUG.

Default loglevel is up to the implementer, but it is advisable to keep it at WARNING.

-w, -ww

Toggles blocking in relation to chain RPC calls.

If -w is set, the implementer should only block to obtain the result of the last, and as few as possible preceding RPC transactions.

If -ww is set, the implementer should block to retrieve the results of all of the preceding RPC transactions.

If the implementation consists of a single transaction, the effect of -w and -ww will always be the same. Nonetheless, the implementation will be forced to provide both arguments.

If neither flag is set, the typical consequence is that the network transaction hash of the last transaction will be returned.

-y, –key-file

Read private key from the given key file.

Rendering configurations

Configurations in chainlib are processed, rendered and interfaced using the confini python package.

In short, confini extends the functionality of Python’s standard library configparser package to allow merging of directives by parsing multiple ini-files from multiple directories.

Furthermore, it employs this same multi-file approach when defining a configuration schema, aswell as defining source to override the values defined in the schema.

See https://gitlab.com/nolash/python-confini for further details on confini.

Configuration schema in chainlib

The chainlib configuration schema is, along with the provided command line arguments and environment variables, designed to cover the settings necessary for most normal chain RPC operations.

Configuration mapping

Below follows a mapping of configuration directives to command line arguments and environment variables.

Note that any configuration directives prefixed by "_" are not defined in the configuration schema, and are not overrideable by environment variables. These are values typically are only valid within the context of a single execution of the implemented tool.

arg	config	env
—	—	CONFINI_DIR [^1]
-c. –config [^2]	—	—
-i, –chain-spec	CHAIN_SPEC	CHAIN_SPEC
–height	_HEIGHT	—
–fee-limit	_FEE_LIMIT	—
–fee-price	_FEE_PRICE	—
-n, –namespace	CONFIG_USER_NAMESPACE	CONFIG_USER_NAMESPACE
–nonce	_NONCE	—
-p, –rpc-provider	RPC_HTTP_PROVIDER	RPC_HTTP_PROVIDER
-a, -recipient	_RECIPIENT	—
-e, –executable-address	_EXEC_ADDRESS	—
–rpc-auth	RPC_AUTH	RPC_AUTH
—	RPC_PROVIDER	RPC_PROVIDER [^3]
—	RPC_SCHEME	RPC_SCHEME [^4]
–rpc-credentials	RPC_CREDENTIALS	RPC_CREDENTIALS
–rpc-dialect	RPC_DIALECT	RPC_DIALECT
-s, –send	_RPC_SEND	—
–seq	_SEQ	—
-u, –unsafe	_UNSAFE	—
-w	_WAIT	—
-ww	_WAIT_ALL	—
-y, –key-file	WALLET_KEY_FILE	WALLET_KEY_FILE
— [^5]	WALLET_PASSPHRASE	WALLET_PASSPHRASE

Currently chainlib only supports HTTP(S) when building RPC connections from command line arguments and configuration.

Base library contents

Pluggable method interface

The base chainlib blockchain interface is defined by the chainlib.interface.ChainInterface class. All of the methods in this class are unimplemented. Together they make up the methods necessary to interface with any blockchain RPC.

It is up to the implemenenter to choose which of the methods that are needed in any particular context. The implementer would then connect the method symbols with actual code.

Most methods in this class will return objects that can be passed to an RPC connection that fits the block context.

The available methods are:

block_latest
Retrieve the latest block from the network

block_by_hash
Retrieve the block corresponding to the given block hash

block_by_number
Retrieve the block corresponding to the given block number

block_from_src
Render a chainlib.block.Block derivative object from an architecture-dependent block representation source

block_to_src
Render an architecture dependent transaction representation from the given Block object

tx_by_hash
Retrieve the transaction corresponding to the given transaction hash

tx_by_block
Retrieve the transaction corresponding to the given block hash and transaction index

tx_receipt
Retrieve the details of a confirmed transaction

tx_raw
Generate an RPC query from raw transaction wire data

tx_pack
Generate raw transaction wire data from an architecture dependent transaction representation

tx_unpack
Generate architecture dependent transaction representation from raw transaction wire data

tx_from_src
Render a chainlib.tx.Tx derivative object from an architecture-dependent tx representation source

tx_to_src
Render an architecture dependent transaction representation from the given Tx object

address_safe
Generate a checksum-safe network address

address_normal
Generate an unambiguous network address

src_normalize
Generate an unambiguous dictionary from the given dictionary. For example, this can mean generating camel-case key equivalents for snake-case values.

The RPC interface

chainlib.connection currently has support for HTTP(S) and UNIX socket RPC connections. Both rely on the Python standard library only (urllib and socket).

It provides a thread-safe connection factory mechanism where connection constructor and location pairs are associated with string labels.

There is also explicit builtin support for the JSONRPC RPC protocol, which allows for a pluggable error translater that can be customized to every RPC "dialect" that needs to be supported (examples are "geth" and "openethereum" dialects of the Ethereum node fauna). Classes to handle JSONRPC results, requests and errors are defined in the chainlib.jsonrpc module.

Blocks and transactions

Common block and transaction concepts are represented by the chainlib.block.Block and chainlib.tx.Tx objects. These are very minimal base-classes that need to be extended for every blockchain implementation that is to be supported.

When building transactions, implementations of the chainlib.sign.Signer, chainlib.nonce.NonceOracle and chainlib.fee.FeeOracle interfaces will provide the transaction factory object of the implementation with signatures, transaction nonces and transaction fee details respectively.

Other code features

This section lists features that are considered outside the core of the chainlib package

RPC authenticator

If you are relying on an RPC provider instead of running your own node (although, you know you should run your own node, right?), then RPC authentication may be relevant.

chainlib.auth provides two authentication mechanisms for HTTP:

BasicAuth
The HTTP basic Authorization scheme

CustomHeaderTokenAuth
Define an arbitrary header name and value

Fee price aggregator

The chainlib.stat.ChainStat class provides a simple implementation of a running average aggregator for network fee prices. This can be used to generate more precise fee price heuristics that in turn can be fed to a Fee Oracle.

[^1]: The CONFINI_DIR environment variable defines an explicit configuration schema path.

[^2]: The -c flag defines an explicit configuration override path.

[^3]: RPC_PROVIDER will always be set to the same value as RPC_HTTP_PROVIDER by default.

[^4]: The RPC_SCHEME configuration directive is always set to ’http’ by default.

[^5]: This flag is not provided because it is simply not safe to define passphrases as an argument on the command line.