Stacks 2.0

Reference implementation of the Stacks blockchain in Rust.

Stacks 2.0 is a layer-1 blockchain that connects to Bitcoin for security and enables decentralized apps and predictable smart contracts. Stacks 2.0 implements Proof of Transfer (PoX) mining that anchors to Bitcoin security. Leader election happens at the Bitcoin blockchain and Stacks (STX) miners write new blocks on the separate Stacks blockchain. With PoX there is no need to modify Bitcoin to enable smart contracts and apps around it. See this page for more details and resources.

Repository

Blockstack Topic/Tech	Where to learn more more
Stacks 2.0	master branch
Stacks 1.0	legacy branch
Use the package	our core docs
Develop a Blockstack App	our developer docs
Use a Blockstack App	our browser docs
Blockstack PBC the company	our website

Release Schedule and Hotfixes

Normal releases in this repository that add features such as improved RPC endpoints, improved boot-up time, new event observer fields or event types, etc., are released on a monthly schedule. The currently staged changes for such releases are in the develop branch. It is generally safe to run a stacks-node from that branch, though it has received less rigorous testing than release tags. If bugs are found in the develop branch, please do report them as issues on this repository.

For fixes that impact the correct functioning or liveness of the network, hotfixes may be issued. These are patches to the main branch which are backported to the develop branch after merging. These hotfixes are categorized by priority according to the following rubric:

• High Priority. Any fix for an issue that could deny service to the network as a whole, e.g., an issue where a particular kind of invalid transaction would cause nodes to stop processing requests or shut down unintentionally. Any fix for an issue that could cause honest miners to produce invalid blocks.
• Medium Priority. Any fix for an issue that could cause miners to waste funds.
• Low Priority. Any fix for an issue that could deny service to individual nodes.

Versioning

This repository uses a 5 part version number.

X.Y.Z.A.n

X = 2 and does not change in practice unless there’s another Stacks 2.0 type event
Y increments on consensus-breaking changes
Z increments on non-consensus-breaking changes that require a fresh chainstate (akin to semantic MAJOR)
A increments on non-consensus-breaking changes that do not require a fresh chainstate, but introduce new features (akin to semantic MINOR)
n increments on patches and hot-fixes (akin to semantic PATCH)

For example, a node operator running version 2.0.10.0.0 would not need to wipe and refresh their chainstate to upgrade to 2.0.10.1.0 or 2.0.10.0.1. However, upgrading to 2.0.11.0.0 would require a new chainstate.

Roadmap

• SIP 001: Burn Election
• SIP 002: Clarity, a language for predictable smart contracts
• SIP 003: Peer Network
• SIP 004: Cryptographic Committment to Materialized Views
• SIP 005: Blocks, Transactions, and Accounts
• SIP 006: Clarity Execution Cost Assessment
• SIP 007: Stacking Consensus
• SIP 008: Clarity Parsing and Analysis Cost Assessment

Stacks improvement proposals (SIPs) are aimed at describing the implementation of the Stacks blockchain, as well as proposing improvements. They should contain concise technical specifications of features or standards and the rationale behind it. SIPs are intended to be the primary medium for proposing new features, for collecting community input on a system-wide issue, and for documenting design decisions.

See SIP 000 for more details.

The SIPs are now located in the stacksgov/sips repository as part of the Stacks Community Governance organization.

Testnet versions

• Krypton is a Stacks 2 testnet with a fixed, two-minute block time, called regtest. Regtest is generally unstable for regular use, and is reset often. See the regtest documentation for more information on using regtest.

• Xenon is the Stacks 2 public testnet, which runs PoX against the Bitcoin testnet. It is the full implementation of the Stacks 2 blockchain, and should be considered a stable testnet for developing Clarity smart contracts. See the testnet documentation for more information on the public testnet.

• Mainnet is the fully functional Stacks 2 blockchain, see the Stacks overview for information on running a Stacks node, mining, stacking, and writing Clarity smart contracts.

Getting started

Download and build stacks-blockchain

The first step is to ensure that you have Rust and the support software installed.

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

For building on Windows, follow the rustup installer instructions at https://rustup.rs/

From there, you can clone this repository:

git clone --depth=1 https://github.com/blockstack/stacks-blockchain.git

cd stacks-blockchain

Then build the project:

cargo build

Run the tests:

cargo test testnet  -- --test-threads=1

Encode and sign transactions

Here, we have generated a keypair that will be used for signing the upcoming transactions:

cargo run --bin blockstack-cli generate-sk --testnet

# Output
# {
#  secretKey: "b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001",
#  publicKey: "02781d2d3a545afdb7f6013a8241b9e400475397516a0d0f76863c6742210539b5",
#  stacksAddress: "ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH"
# }

This keypair is already registered in the testnet-follower-conf.toml file, so it can be used as presented here.

We will interact with the following simple contract kv-store. In our examples, we will assume this contract is saved to ./kv-store.clar:

(define-map store { key: (string-ascii 32) } { value: (string-ascii 32) })

(define-public (get-value (key (string-ascii 32)))
    (match (map-get? store { key: key })
        entry (ok (get value entry))
        (err 0)))

(define-public (set-value (key (string-ascii 32)) (value (string-ascii 32)))
    (begin
        (map-set store { key: key } { value: value })
        (ok true)))

We want to publish this contract on chain, then issue some transactions that interact with it by setting some keys and getting some values, so we can observe read and writes.

Our first step is to generate and sign, using your private key, the transaction that will publish the contract kv-store. To do that, we will use the subcommand:

cargo run --bin blockstack-cli publish --help

With the following arguments:

cargo run --bin blockstack-cli publish b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 515 0 kv-store ./kv-store.clar --testnet

The 515 is the transaction fee, denominated in microSTX. Right now, the testnet requires one microSTX per byte minimum, and this transaction should be less than 515 bytes. The third argument 0 is a nonce, that must be increased monotonically with each new transaction.

This command will output the binary format of the transaction. In our case, we want to pipe this output and dump it to a file that will be used later in this tutorial.

cargo run --bin blockstack-cli publish b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 515 0 kv-store ./kv-store.clar --testnet | xxd -r -p > tx1.bin

Run the testnet

You can observe the state machine in action locally by running:

cargo stacks-node start --config=./testnet/stacks-node/conf/testnet-follower-conf.toml

testnet-follower-conf.toml is a configuration file that you can use for setting genesis balances or configuring Event observers. You can grant an address an initial account balance by adding the following entries:

[[ustx_balance]]
address = "ST2VHM28V9E5QCRD6C73215KAPSBKQGPWTEE5CMQT"
amount = 100000000

The address field is the Stacks testnet address, and the amount field is the number of microSTX to grant to it in the genesis block. The addresses of the private keys used in the tutorial below are already added.

Publish your contract

Assuming that the testnet is running, we can publish our kv-store contract.

In another terminal (or file explorer), you can move the tx1.bin generated earlier, to the mempool:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx1.bin http://localhost:20443/v2/transactions

In the terminal window running the testnet, you can observe the state machine's reactions.

Reading from / Writing to the contract

Now that our contract has been published on chain, let's try to submit some read / write transactions. We will start by trying to read the value associated with the key foo.

To do that, we will use the subcommand:

cargo run --bin blockstack-cli contract-call --help

With the following arguments:

cargo run --bin blockstack-cli contract-call b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 500 1 ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH kv-store get-value -e \"foo\" --testnet | xxd -r -p > tx2.bin

contract-call generates and signs a contract-call transaction.

We can submit the transaction by moving it to the mempool path:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx2.bin http://localhost:20443/v2/transactions

Similarly, we can generate a transaction that would be setting the key foo to the value bar:

cargo run --bin blockstack-cli contract-call b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 500 2 ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH kv-store set-value -e \"foo\" -e \"bar\" --testnet | xxd -r -p > tx3.bin

And submit it by moving it to the mempool path:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx3.bin http://localhost:20443/v2/transactions

Finally, we can issue a third transaction, reading the key foo again, for ensuring that the previous transaction has successfully updated the state machine:

cargo run --bin blockstack-cli contract-call b8d99fd45da58038d630d9855d3ca2466e8e0f89d3894c4724f0efc9ff4b51f001 500 3 ST2ZRX0K27GW0SP3GJCEMHD95TQGJMKB7G9Y0X1MH kv-store get-value -e \"foo\" --testnet | xxd -r -p > tx4.bin

And submit this last transaction by moving it to the mempool path:

curl -X POST -H "Content-Type: application/octet-stream" --data-binary @./tx4.bin http://localhost:20443/v2/transactions

Congratulations, you can now write your own smart contracts with Clarity.

Platform support

Officially supported platforms: Linux 64-bit, MacOS 64-bit, Windows 64-bit.

Platforms with second-tier status (builds are provided but not tested): MacOS Apple Silicon (ARM64), Linux ARMv7, Linux ARM64.

For help cross-compiling on memory-constrained devices, please see the community supported documentation here: Cross Compiling.

Community

Beyond this Github project, Blockstack maintains a public forum and an opened Discord channel. In addition, the project maintains a mailing list which sends out community announcements.

The greater Blockstack community regularly hosts in-person meetups. The project's YouTube channel includes videos from some of these meetups, as well as video tutorials to help new users get started and help developers wrap their heads around the system's design.

Further Reading

You can learn more by visiting the Blockstack Website and checking out the documentation:

• Blockstack docs

You can also read the technical papers:

• "PoX: Proof of Transfer Mining with Bitcoin", May 2020
• "Stacks 2.0: Apps and Smart Contracts for Bitcoin", Dec 2020

If you have high-level questions about Blockstack, try searching our forum and start a new question if your question is not answered there.

Contributing

Tests and Coverage

PRs must include test coverage. However, if your PR includes large tests or tests which cannot run in parallel (which is the default operation of the cargo test command), these tests should be decorated with #[ignore]. If you add #[ignore] tests, you should add your branch to the filters for the all_tests job in our circle.yml (or if you are working on net code or marf code, your branch should be named such that it matches the existing filters there).

A test should be marked #[ignore] if:

1. It does not always pass cargo test in a vanilla environment (i.e., it does not need to run with --test-threads 1).
2. Or, it runs for over a minute via a normal cargo test execution (the cargo test command will warn if this is not the case).

Formatting

This repository uses the default rustfmt formatting style. PRs will be checked against rustfmt and will fail if not properly formatted.

You can check the formatting locally via:

cargo fmt --all -- --check

You can automatically reformat your commit via:

cargo fmt --all

Mining

Stacks tokens (STX) are mined by transferring BTC via PoX. To run as a miner, you should make sure to add the following config fields to your config file:

[node]
# Run as a miner
miner = True
# Bitcoin private key to spend
seed = "YOUR PRIVATE KEY"
# How long to wait for microblocks to arrive before mining a block to confirm them (in milliseconds)
wait_time_for_microblocks = 10000
# Run as a mock-miner, to test mining without spending BTC. Needs miner=True.
#mock_mining = True

[miner]
# Smallest allowed tx fee, in microSTX
min_tx_fee = 100
# Time to spend on the first attempt to make a block, in milliseconds.
# This can be small, so your node gets a block-commit into the Bitcoin mempool early.
first_attempt_time_ms = 1000
# Time to spend on subsequent attempts to make a block, in milliseconds.
# This can be bigger -- new block-commits will be RBF'ed.
subsequent_attempt_time_ms = 60000
# Time to spend mining a microblock, in milliseconds.
microblock_attempt_time_ms = 30000

You can verify that your node is operating as a miner by checking its log output to verify that it was able to find its Bitcoin UTXOs:

$ head -n 100 /path/to/your/node/logs | grep -i utxo
INFO [1630127492.031042] [testnet/stacks-node/src/run_loop/neon.rs:146] [main] Miner node: checking UTXOs at address: <redacted>
INFO [1630127492.062652] [testnet/stacks-node/src/run_loop/neon.rs:164] [main] UTXOs found - will run as a Miner node

Configuring Cost and Fee Estimation

Fee and cost estimators can be configure via the config section [fee_estimation]:

[fee_estimation]
cost_estimator = naive_pessimistic
fee_estimator = fuzzed_weighted_median_fee_rate
fee_rate_fuzzer_fraction = 0.1
fee_rate_window_size = 5
cost_metric = proportion_dot_product
log_error = true
enabled = true

Fee and cost estimators observe transactions on the network and use the observed costs of those transactions to build estimates for viable fee rates and expected execution costs for transactions. Estimators and metrics can be selected using the configuration fields above, though the default values are the only options currently. log_error controls whether or not the INFO logger will display information about the cost estimator accuracy as new costs are observed. Setting enabled = false turns off the cost estimators. Cost estimators are not consensus-critical components, but rather can be used by miners to rank transactions in the mempool or client to determine appropriate fee rates for transactions before broadcasting them.

The fuzzed_weighted_median_fee_rate uses a median estimate from a window of the fees paid in the last fee_rate_window_size blocks. Estimates are then randomly "fuzzed" using uniform random fuzz of size up to fee_rate_fuzzer_fraction of the base estimate.

Non-Consensus Breaking Release Process

For non-consensus breaking releases, this project uses the following release process:

1. The release must be timed so that it does not interfere with a prepare phase. The timing of the next Stacking cycle can be found here. A release to mainnet should happen at least 24 hours before the start of a new cycle, to avoid interfering with the prepare phase. So, start by being aware of when the release can happen.

2. Before creating the release, the release manager must determine the version number for this release. The factors that determine the version number are discussed in Versioning. We assume, in this section, that the change is not consensus-breaking. So, the release manager must first determine whether there are any "non-consensus-breaking changes that require a fresh chainstate". This means, in other words, that the database schema has changed, but an automatic migration was not implemented. Then, the release manager should determine whether this is a feature release, as opposed to a hot fix or a patch. Given the answers to these questions, the version number can be computed.

3. The release manager enumerates the PRs or issues that would block the release. A label should be applied to each such issue/PR as 2.0.x.y.z-blocker. The release manager should ping these issue/PR owners for updates on whether or not those issues/PRs have any blockers or are waiting on feedback.

4. The release manager should open a develop -> master PR. This can be done before all the blocker PRs have merged, as it is helpful for the manager and others to see the staged changes.

5. The release manager must update the CHANGELOG.md file with summaries what was Added, Changed, and Fixed. The pull requests merged into develop can be found here. Note, however, that GitHub apparently does not allow sorting by merge time, so, when sorting by some proxy criterion, some care should be used to understand which PR's were merged after the last develop -> master release PR. This CHANGELOG.md should also be used as the description of the develop -> master so that it acts as release notes when the branch is tagged.

6. Once the blocker PRs have merged, the release manager will create a new tag by manually triggering the stacks-blockchain Github Actions workflow against the develop branch, inputting the release candidate tag, 2.0.x.y.z-rc0, in the Action's input textbox.

7. Once the release candidate has been built, and docker images, etc. are available, the release manager will notify various ecosystem participants to test the release candidate on various staging infrastructure:

   1. Stacks Foundation staging environments.
   2. Hiro PBC testnet network.
   3. Hiro PBC mainnet mock miner.

   The release candidate should be announced in the #stacks-core-devs channel in the Stacks Discord. For coordinating rollouts on specific infrastructure, the release manager should contact the above participants directly either through e-mail or Discord DM. The release manager should also confirm that the built release on the Github releases page is marked as Pre-Release.

8. The release manager will test that the release candidate successfully syncs with the current chain from genesis both in testnet and mainnet. This requires starting the release candidate with an empty chainstate and confirming that it synchronizes with the current chain tip.

9. If bugs or issues emerge from the rollout on staging infrastructure, the release will be delayed until those regressions are resolved. As regressions are resolved, additional release candidates should be tagged. The release manager is responsible for updating the develop -> master PR with information about the discovered issues, even if other community members and developers may be addressing the discovered issues.

10. Once the final release candidate has rolled out successfully without issue on the above staging infrastructure, the release manager tags 2 additional stacks-blockchain team members to review the develop -> master PR. If there is a merge conflict in this PR, this is the protocol: open a branch off of develop, merge master into that branch, and then open a PR from this side branch to develop. The merge conflicts will be resolved.

11. Once reviewed and approved, the release manager merges the PR, and tags the release via the stacks-blockchain Github action by clicking "Run workflow" and providing the release version as the tag (e.g., 2.0.11.1.0) This creates a release and release images. Once the release has been created, the release manager should update the Github release text with the CHANGELOG.md "top-matter" for the release.

Copyright and License

The code and documentation copyright are attributed to blockstack.org for the year of 2020.

This code is released under the GPL v3 license, and the docs are released under the Creative Commons license.