Getting started with Mavkit¶

This short tutorial illustrates the use of the various Mavkit binaries as well as some concepts about the network.

The Binaries¶

After a successful compilation, you should have the following binaries:

mavkit-node: the Mavkit daemon itself (see Node);
mavkit-client: a command-line client and basic wallet (see Client);
mavkit-admin-client: administration tool for the node (see Admin Client);
mavkit-{baker,accuser}-*: daemons to bake and accuse on the Mavryk network (see How to run Mavkit);
mavkit-signer: a client to remotely sign operations or blocks (see Signer);
mavkit-smart-rollup-node: executable for using and running a smart rollup node as Layer 2 (see Smart rollup node);
mavkit-smart-rollup-wasm-debugger: debugger for smart rollup kernels (see Smart rollup node)
mavkit-proxy-server: a readonly frontend to mavkit-node designed to lower the load of full nodes (see Proxy server)
mavkit-codec: a utility for documenting the data encodings and for performing data encoding/decoding (see Codec)
mavkit-protocol-compiler: a domain-specific compiler for Mavryk protocols (see Protocol compiler)
mavkit-snoop: a tool for modeling the performance of any piece of OCaml code, based on benchmarking (see Benchmarking with Snoop)

The daemons other than the node are suffixed with the name of the protocol they are bound to. More precisely, the suffix consists of the first 8 characters of the protocol hash; except for protocol Alpha, for which the suffix is simply -alpha. For instance, mavkit-baker-PtAtLas is the baker for the Atlas protocol, and mavkit-baker-alpha is the baker of the development protocol. The mavkit-node daemon is not suffixed by any protocol name, because it is independent of the economic protocol. See also the Node’s Protocol section below.

Read the Manual¶

All the Mavkit binaries provide the --help option to display information about their usage, including the available options and the possible parameters.

Additionally, most of the above binaries (i.e., all but the node, the validator, and the compiler) provide a textual manual that can be obtained with the command man, whose verbosity can be increased with -v, for example:

mavkit-client man -v 3

It is also possible to get information on a specific command in the manual with man <command>:

mavkit-client man set

To see the usage of one specific command, you may also type the command without arguments, which displays its possible completions and options:

mavkit-client transfer

Warning

Beware that the commands available on the client depend on the specific protocol run by the node. For instance, transfer is not available when the node runs the genesis protocol, which may happen for a few minutes when launching a node for the first time, or when the client is not connected to a node. In the last case, the above command generates a warning followed by an error:

Warning:
  Failed to acquire the protocol version from the node
  [...]
Error:
  Unrecognized command.
  Try using the man command to get more information.
Usage:
  [...]

To make the client command behave as for a protocol other than that used by the node (or even when not connected to a node), use the option --protocol (or -p), e.g.:

mavkit-client --protocol ProtoALphaAL man transfer

Note that you can get the list of protocols known to the client with:

mavkit-client list understood protocols

The full command line documentation of the Mavkit binaries supporting the man command is also available online: Command Line Interface.

Node¶

The node is the main actor of the Mavryk blockchain and it has two main functions: running the gossip network and updating the context. The gossip network is where all Mavryk nodes exchange blocks and operations with each other (see Admin Client to monitor p2p connections). Using this peer-to-peer network, an operation originated by a user can hop several times through other nodes until it finds its way into a block baked by a baker. Using the blocks it receives on the gossip network the node also keeps up to date the current context, that is the full state of the blockchain shared by all peers. Approximately every 15 seconds a new block is created and, when the node receives it, it applies each operation in the block to its current context and computes a new context. The last block received on a chain is also called the head of that chain. Each new head is then advertised by the node to its peers, disseminating this information to build a consensus across the network.

Other than passively observing the network, your node can also inject its own new operations when instructed by the mavkit-client and even send new blocks when guided by the mavkit-baker-*. The node has also a view of the multiple chains that may exist concurrently and selects the best one based on its fitness (see The consensus algorithm).

Note

The mavkit-node uses (unless the option --singleprocess is given) an auxiliary daemon in order to validate, apply and compute the resulting context of blocks, in parallel to its main process. Thus, an mavkit-validator process can appear while monitoring the active processes of the machine.

Warning

To ensure the best conditions to run a node, we recommend users to use NTP to avoid clock drift. Clock drift may result in not being able to get recent blocks in case of negative lag time, and in not being able to inject new blocks in case of positive lag time.

Node Identity¶

First, we need to generate a new identity for the node to connect to the network:

mavkit-node identity generate

Note

If the node prompts you to install the Zcash parameter file, follow the corresponding instructions.

The identity comprises a pair of cryptographic keys that nodes use to encrypt messages sent to each other, and an antispam proof-of-work stamp proving that enough computing power has been dedicated to creating this identity. Note that this is merely a network identity and it is not related in any way to a Mavryk address on the blockchain.

If you wish to run your node on a test network, now is also a good time to configure your node for it (see Connecting to a Network).

Node Synchronization¶

Whenever a node starts, it tries to retrieve the most current head of the chain from its peers. This can be a long process if there are many blocks to retrieve (e.g. when a node is launched for the first time or has been out of sync for a while), or on a slow network connection. The mechanism of Snapshots can help in reducing the synchronization time.

Once the synchronization is complete, the node is said to be bootstrapped. Some operations require the node to be bootstrapped.

Node’s Protocol¶

A Mavryk node can switch from one protocol to another during its execution. This typically happens during the synchronization phase when a node launches for the first time. The node starts with the genesis protocol and then goes through all previous protocols until it finally switches to the current protocol.

Throughout the documentation, “Alpha” refers to the protocol in the src/proto_alpha directory of the master branch, that is, a protocol under development, which serves as a basis to propose replacements for the currently active protocol. The Alpha protocol is used by default in sandbox mode and in the various test suites.

Storage¶

All blockchain data is stored by the node under a data directory, which by default is $HOME/.mavryk-node/.

If for some reason your node is misbehaving or there has been an upgrade of the network, it is safe to remove this directory, it just means that your node will take some time to resync the chain.

If removing this directory, please note that if it took you a long time to compute your node identity, keep the identity.json file and instead only remove its child store, context and protocol (if any) sub-directories.

If you are also running a baker, make sure that it is configured to access the data directory of the node (see how to run a baker).

RPC Interface¶

The only programming interface to the node is through JSON RPC calls and it is disabled by default. More detailed documentation can be found in the RPC index. The RPC interface must be enabled for the clients to communicate with the node but it should not be publicly accessible on the internet. With the following command, it is available uniquely on the localhost address of your machine, on the default port 8732.

mavkit-node run --rpc-addr 127.0.0.1

Node configuration¶

Many options of the node can be configured when running the node:

RPC parameters (e.g. the port number for listening to RPC requests using option --rpc-addr)
The directory where the node stores local data (using option --data-dir)
Network parameters (e.g. the network to connect to, using option --network, the number of connections to peers, using option --connections)
Validator and mempool parameters
Logging options.

The list of configurable options can be obtained using the following command:

mavkit-node run --help

You can read more about the node configuration and its private mode.

Besides listening to requests from the client, the node listens to connections from peers, by default on port 9732 (this can be changed using option --net-addr), so it’s advisable to open incoming connections to that port.

Summing up¶

Putting together all the above instructions, you may want to run a node as follows:

# Download a snapshot for your target network, e.g. <test-net>:
wget <snapshot-url> -O <snapshot-file>
# Configure the node for running on <test-net>:
mavkit-node config init --data-dir ~/.mavryk-node-<test-net> --network <test-net>
# Import the snapshot into the node data directory:
mavkit-node snapshot import --data-dir ~/.mavryk-node-<test-net> --block <block-hash> <snapshot-file>
# Run the node:
mavkit-node run --data-dir ~/.mavryk-node-<test-net> --rpc-addr 127.0.0.1

Client¶

Mavkit client can be used to interact with the node, it can query its status or ask the node to perform some actions.

Note

The rest of this page assumes that you have launched a local node, as explained in the previous section. But it is useful to know that the client can be configured to interact with a public node instead, either using the configuration file or by supplying option -E <node-url> with a public RPC node.

After starting your local node you can check if it has finished synchronizing (see Synchronisation heuristic) using:

mavkit-client bootstrapped

This call will hang and return only when the node is synchronized (recall that this is much faster when starting a node from a snapshot). Once the above command returns, we can check what is the current timestamp of the head of the chain (time is in UTC so it may differ from your local time):

mavkit-client get timestamp

You can also use the above command before the node is bootstrapped, from another terminal. However, recall that the commands available on the client depend on the specific protocol run by the node. For instance, get timestamp isn’t available when the node runs the genesis protocol, which may happen for a few minutes when launching a node for the first time.

The behaviour of the client can be customized using various mechanisms, including command-line options, a configuration file, and environment variables. For details, refer to Setting up the client.

A Simple Wallet¶

The client is also a basic wallet. We can, for example, generate a new pair of keys, which can be used locally with the alias alice:

$ mavkit-client gen keys alice

To check the account (also called a contract) for Alice has been created:

$ mavkit-client list known contracts

You will notice that the client data directory (by default, ~/.mavryk-client) has been populated with 3 files public_key_hashs, public_keys and secret_keys. The content of each file is in JSON and keeps the mapping between aliases (e.g., alice) and the kind of keys indicated by the name of each file. Secret keys should be stored on disk encrypted with a password except when using a hardware wallet (see Ledger support). An additional file contracts contains the addresses of smart contracts, which have the form KT1….

Notice that by default, the keys were stored unencrypted, which is fine in our test example. In more realistic scenarios, you should supply the option --encrypted when generating a new account:

$ mavkit-client gen keys bob --encrypted

Mavryk supports four different ECC (Elliptic-Curve Cryptography) schemes: Ed25519, secp256k1 (the one used in Bitcoin), P-256 (also called secp256r1), and BLS (variant MinPk, for aggregated signatures). The secp256k1 and P256 curves have been added for interoperability with Bitcoin and Hardware Security Modules (HSMs) mostly. Unless your use case requires those, you should probably use Ed25519. We use a verified library for Ed25519, and it is generally recommended over other curves by the crypto community, for performance and security reasons.

Make sure to make a back-up of the client data directory and that the password protecting your secret keys is properly managed (if you stored them encrypted).

For more advanced key management we offer ledger support and a remote signer.

Get Free Test Tokens¶

To test the networks and help users get familiar with the system, on test networks you can obtain free tokens from a faucet. Transfer some to Alice’s address.

Transfers and Receipts¶

To fund our newly created account for Bob, we need to transfer some mav using the transfer operation. Every operation returns a receipt that recapitulates all the effects of the operation on the blockchain. A useful option for any operation is --dry-run, which instructs the client to simulate the operation without actually sending it to the network, so that we can inspect its receipt.

Let’s try:

mavkit-client transfer 1 from alice to bob --dry-run

Fatal error:
  The operation will burn 0.257 mav which is higher than the configured burn cap (0 mav).
   Use `--burn-cap 0.257` to emit this operation.

The client asks the node to validate the operation (without sending it) and obtains an error. The reason is that when we fund a new address we are also storing it on the blockchain. Any storage on chain has a cost associated to it which should be accounted for either by paying a fee to a baker or by destroying (burning) some mav. This is particularly important to protect the system from spam. Because storing an address requires burning 0.257 mav and the client has a default of 0, we need to explicitly set a cap on the amount that we allow to burn:

mavkit-client transfer 1 from alice to bob --dry-run --burn-cap 0.257

This should do it and you should see a rather long receipt being produced, here’s an excerpt:

...
Simulation result:
  Manager signed operations:
    From: mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe
    Fee to the baker: ṁ0.001259
    ...
    Balance updates:
      mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe ............ -ṁ0.001259
      fees(mv1CQJA6XDWcpVgVbxgSCTa69AW1y8iHbLx5,72) ... +ṁ0.001259
    Revelation of manager public key:
      Contract: mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe
      Key: edpkuK4o4ZGyNHKrQqAox7hELeKEceg5isH18CCYUaQ3tF7xZ8HW3X
      ...
  Manager signed operations:
    From: mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe
    Fee to the baker: ṁ0.001179
    ...
    Balance updates:
      mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe ............ -ṁ0.001179
      fees(mv1CQJA6XDWcpVgVbxgSCTa69AW1y8iHbLx5,72) ... +ṁ0.001179
    Transaction:
      Amount: ṁ1
      From: mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe
      To: mv1MbxANFAMxSHb5K1q9ZA9mynzYrZfJ7mHt
      ...
      Balance updates:
        mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe ... -ṁ1
        mv1MbxANFAMxSHb5K1q9ZA9mynzYrZfJ7mHt ... +ṁ1
        mv1E7Ms4p1e3jV2WMehLB3FBFwbV56GiRQfe ... -ṁ0.257

The client does a bit of magic to simplify our life and here we see that many details were automatically set for us. Surprisingly, our transfer operation resulted in two operations, first a revelation, and then a transfer. Alice’s address, obtained from the faucet, is already present on the blockchain, but only in the form of a public key hash mv1Rj...5w. To sign operations, Alice needs to first reveal the public key edpkuk...3X behind the hash, so that other users can verify her signatures. The client is kind enough to prepend a reveal operation before the first transfer of a new address, this has to be done only once, future transfers will consist of a single operation as expected.

Another interesting thing we learn from the receipt is that there are more costs being added on top of the transfer and the burn: fees. To encourage a baker to include our operation, and in general to pay for the cost of running the blockchain, each operation usually includes a fee that goes to the baker. Fees are variable over time and depend on many factors but the Mavkit client selects a default for us.

The last important bit of our receipt is the balance updates that resume which address is being debited or credited a certain amount. We see in this case that baker mv1Ke...yU is being credited one fee for each operation, that Bob’s address mv1Rk...Ph gets 1 mav and that Alice pays the transfer, the burn, and the two fees.

Now that we have a clear picture of what we are going to pay we can execute the transfer for real, without the dry-run option. You will notice that the client hangs for a few seconds before producing the receipt because after injecting the operation in your local node it is waiting for it to be included by some baker on the network. Once it receives a block with the operation inside it will return the receipt.

It is advisable to wait for several blocks to consider the transaction as final. Please refer to the consensus algorithm documentation and analysis to better understand block finality in Mavryk. This page provides concrete values for the number of blocks one should wait.

In the rare case when an operation is lost, how can we be sure that it will not be included in any future block, and then we may re-emit it? After 120 blocks a transaction is considered invalid and can’t be included anymore in a block. Furthermore each operation has a counter that prevents replays so it is usually safe to re-emit an operation that seems lost.

Block Explorers¶

Once your transaction is included in a block, you can retrieve it in one of the public block explorers, which list the whole history of the different Mavryk networks (mainnet or test networks).

Implicit Accounts and Smart Contracts¶

In Mavryk there are two kinds of accounts: implicit accounts and smart contracts (see Accounts and addresses for more details).

Addresses with a mv prefix, like the mv1 public key hashes used above, represent implicit accounts. They are created with a transfer operation to the account’s public key hash.
Smart contracts have addresses starting with KT1 and are created with an origination operation. They don’t have a corresponding secret key and they run Michelson code each time they receive a transaction.

Let’s originate our first contract and call it id:

mavkit-client originate contract id transferring 1 from alice \
             running ./michelson_test_scripts/attic/id.tz \
             --init '"hello"' --burn-cap 0.4

The initial balance is 1 mav, generously provided by implicit account alice. The contract stores a Michelson program id.tz (found in file michelson_test_scripts/attic/id.tz), with Michelson value "hello" as initial storage (the extra quotes are needed to avoid shell expansion). The parameter --burn-cap specifies the maximal fee the user is willing to pay for this operation, while the actual fee is determined by the system.

A Michelson contract is expressed as a pure function, mapping a pair (parameter, storage) to a pair (list_of_operations, storage). However, when this pure function is applied to the blockchain state, it can be seen as an object with a single method taking one parameter (parameter), and with a single attribute (storage). The method updates the state (the storage), and submits operations as a side effect.

For the sake of this example, here is the id.tz contract:

parameter string;
storage string;
code {CAR; NIL operation; PAIR};

It specifies the types for the parameter and storage, and implements a function which updates the storage with the value passed as a parameter and returns this new storage together with an empty list of operations.

Gas and Storage Costs¶

A quick look at the balance updates on the receipt shows that on top of funding the contract with 1 mav, alice was also charged an extra cost that is burnt. This cost comes from the storage and is shown in the line Paid storage size diff: 46 bytes, 41 for the contract and 5 for the string "hello". Given that a contract saves its data on the public blockchain that every node stores, it is necessary to charge a fee per byte to avoid abuse and encourage lean programs.

Let’s see what calling a program with a new argument would look like with the --dry-run option:

mavkit-client transfer 0 from alice to id --arg '"world"' --dry-run

The transaction would successfully update the storage but this time it wouldn’t cost us anything more than the fee, the reason is that the storage for "world" is the same as for "hello", which has already been paid for. To store more we’ll need to pay more, you can try by passing a longer string.

The other cost associated with running contracts is the gas, which measures how long a program takes to compute. Contrary to storage there is no cost per gas unit, a transfer can require as much gas as it wants, however a baker that has to choose among several transactions is much more likely to include a low gas one because it’s cheaper to run and validate. At the same time, bakers also give priority to high fee transactions. This means that there is an implicit cost for gas that is related to the fee offered versus the gas and fees of other transactions.

If you are happy with the gas and storage of your transaction you can run it for real, however it is always a good idea to set an explicit limit for both. The transaction fails if any of the two limits are passed. Note that the storage limit sets an upper bound to the storage size difference, so in our case, it may be 0 because our new value does not increase at all the storage size.

mavkit-client transfer 0 from alice to id --arg '"world"' \
                                         --gas-limit 11375 \
                                         --storage-limit 0

A baker is more likely to include an operation with lower gas and storage limits because it takes fewer resources to execute so it is in the best interest of the user to pick limits that are as close as possible to the actual use. In this case, you may have to specify some fees (using option --fee) as the baker is expecting some for the resource usage. Otherwise, you can force a low fee operation using the --force-low-fee, with the risk that no baker will include it.

More Michelson test scripts can be found in directory michelson_test_scripts/. Advanced documentation of the smart contract language is available here.

Validation¶

The node allows validating an operation before submitting it to the network by simply simulating the application of the operation to the current context. Without this mechanism, if you just send an invalid operation (e.g. sending more tokens than you own), the node would broadcast it and when it is included in a block you would have to pay the usual fee even if it won’t have an effect on the context. To avoid this case the client first asks the node to validate the transaction and only then sends it.

The same validation is used when you pass the option --dry-run: the receipt that you see is actually a simulated one. The only difference is that, when this option is supplied, the transaction is not sent even if it proves to be valid.

Another important use of validation is to determine gas and storage limits. The node first simulates the execution of a Michelson program and tracks the amount of gas and storage that has been consumed. Then the client sends the transaction with the right limits for gas and storage based on those indicated by the node. This is why we were able to submit transactions without specifying these limits: they were computed for us.

More information on validation can be found here.

It’s RPCs all the Way Down¶

The client communicates with the node uniquely through RPC calls so make sure that the node is listening on the right ports and that the ports are open. For example the get timestamp command above is a shortcut for:

mavkit-client rpc get /chains/main/blocks/head/header/shell

The client tries to simplify common tasks as much as possible, however if you want to query the node for more specific information you’ll have to resort to RPCs.

For example to check the value of important constants in Mavryk, which may differ between Mainnet and other test networks, you can use:

mavkit-client rpc get /chains/main/blocks/head/context/constants | jq
{
  "proof_of_work_nonce_size": 8,
  "nonce_length": 32,
  ...
}

Another interesting use of RPCs is to inspect the receipts of the operations of a block:

mavkit-client rpc get /chains/main/blocks/head/operations

It is also possible to review the receipt of the whole block:

mavkit-client rpc get /chains/main/blocks/head/metadata

An interesting block receipt is the one produced at the end of a cycle as many delegates receive back part of their unfrozen accounts.

You can find more info on RPCs in the RPCs’ page.

Other binaries¶

In this short tutorial we will not use some other binaries, but let’s briefly review their roles.

Admin Client¶

The admin client enables you to interact with the peer-to-peer layer in order to:

check the status of the connections
force connections to known peers
ban/unban peers

A useful command to debug a node that is not syncing is:

mavkit-admin-client p2p stat

The admin client uses the same format of configuration file as the client (see Client configuration file).

Codec¶

The Mavkit codec (mavkit-codec) is a utility that:

provides documentation for all the encodings used in the mavkit-node (and other binaries), and
allows to convert from JSON to binary and vice-versa for all these encodings.

It is meant to be used by developers for tests, for generating documentation when writing libraries that share data with the node, for light scripting, etc. For more details on its usage, refer to its online manual and to Encodings.

Protocol compiler¶

The protocol compiler (mavkit-protocol-compiler) can compile protocols within the limited environment that the shell provides. This environment is limited to a restricted set of libraries in order to constrain the possible behavior of the protocols.

It is meant to be used:

by developers to compile the protocol under development,
by the packaging process to compile protocols that are pre-linked in the binaries,
by the Mavkit node when there is an on-chain update to a protocol that is not pre-linked with the binary.

Summary¶

In this tutorial, you have learned:

to start an Mavkit node and set up its basic configuration;
to use the Mavkit client to create implicit accounts and do transfers between them;
to deploy and interact with a simple predefined smart contract;
to distinguish between the various costs associated to transactions such as burnt mav, fees, storage costs, and gas consumption;
some further concepts such as transaction validation and the RPC interface;
the role of other binaries, less frequently used than the client and the node.

You may now explore Mavryk further, and enjoy using it!