Catena is a distributed database based on a blockchain, accessible using SQL. Catena timestamps database transactions (SQL) in a decentralized way between nodes that do not or cannot trust each other, while enforcing modification permissions ('grants') that were agreed upon earlier.
A Catena blockchain contains SQL transactions that, when executed in order, lead to the agreed-upon state of the database. The transactions are automatically replicated to, validated by, and replayed on participating clients. A Catena database can be connected to by client applications using the PostgreSQL wire protocol (pq).
Only SQL statements that modify data or structure are included in the blockchain. This is very similar to replication logs used by e.g. MySQL ('binlog').
Catena builds on macOS. You need a recent version of XCode (>=8.3.2) on your system. Use the following commands to clone the Catena repository and build in debug configuration:
git clone https://github.com/pixelspark/catena.git catena
cd catena
swift build
It is also possible to generate an XCode project and build Catena from it:
swift package generate-xcodeproj
Building on Linux is fully supported. To build, first ensure Swift 4 is installed and is in the PATH. Then ensure clang and required libraries are present:
apt install clang build-essential libicu-dev libcurl4-openssl-dev openssl libssl-dev
git clone https://github.com/pixelspark/catena.git catena
cd catena
swift build
The above was tested on Ubuntu 16.04 as well as Debian Stretch with Swift 4.
Note: Due to the fact that there is no cross-platform WebSocket client implementation in Swift (the current implementation uses Starscream), outgoing peer connections are not supported for the Linux client. Incoming peer connections are possible and can be used by the client to 'talk back', so the client is functional regardless.
A docker image is available at the Docker Hub. To build the Docker image from source (useful if you don't have / can't install Swift locally, for instance):
git clone https://github.com/pixelspark/catena ./catena
cd ./catena
docker build -t pixelspark/catena .
Catena includes a web client, resources from the Resources/ folder. A built version of the web client is
included. To build from scratch, first install the required build tools, then use gulp to compile and bundle files:
cd Resources/
npm install
gulp
Use gulp watch to have gulp recompile files on change.
The following command starts Catena and initializes a new chain (replace 'debug' with 'release' after building a release version):
./.build/debug/Catena -p 8338 -m -c -s 'my seed string'
The -i switch tells Catena to initialize a chain (this deletes any persisted data, which is stored by default in catena.sqlite in the current directory). The -s switch provides Catena with a string that tells it which genesis block to accept. To enable block mining, add the '-m' command line switch.
To start another peer locally, use the following:
./.build/debug/Catena -p 8340 -s 'my seed string' -j ws://NODEID@127.0.0.1:8338 -d peer2.sqlite
Note, the node URL in the command above can be copied from the output of the first node. Only one node is required in order to bootstrap (nodes will perform peer exchange).
docker pull pixelspark/catena
docker run -p 8338:8338 -p 8339:8339 pixelspark/catena [ARGS]
Note: the port number on which Catena listens inside the container must be equal to the port number used outside the container (as Catena advertises it to peers).
Catena provides a web interface on port 8338 (default), which can be used for introspecting the blockchain and performing queries. It also provides a WebSocket service (on the same port) which is used for communication between peers. Provide the --no-web-client command-line option to disable the web client and associated API (note that the currently exposed API does not allow for any mutating actions).
The (private) SQL interface is available on port 8339 (by default). If you set a different HTTP port (using the '-p' command line switch), the SQL interface will assume that port+1. You can connect to the SQL interface using the PostgreSQL command line client:
psql -h localhost -p 8334 -U random
Your username should be the public key (generated by Catena) and your password the private key. Catena will print the public and private key for the 'root' user when initializing a new chain (with the -i option) and will also print a psql command line for you to use to connect as root.
By default, only the 'root' user created during initialization has any rights on the database. Add rows to the 'grants' table to create more 'users' (identified by public key). For example (as root):
CREATE TABLE test(foo INT);
INSERT INTO grants(kind, user, table) VALUES ('insert', $invoker, 'test');
INSERT INTO test(foo) VALUES (1337);
More granular permissions can be granted by using template grants. These grant a user the permission to execute a certain parametrized query with self-chosen parameter values. The template query is hashed and stored in the grants table. Any query whose hash (once parameter values removed) matches that of a template granted to the user can be executed. Template grants can be most easily created through the web client.
The template grant can further restrict the set of allowable parameter values using an IF-statement:
IF ?amount > 0 THEN UPDATE balance SET balance = balance + ?amount WHERE iban = ?iban ELSE FAIL END;
No. The goal of Catena is to make it as easy as possible for developers and administrators that are used to working with SQL to adopt blockchain technology. Catena supports the PostgreSQL (pq) wire protocol to submit queries, which allows Catena to be used from many different languages (such as PHP, Go, C/C++). However, there are fundamental differences between Catena and 'regular' database systems:
- Catena currently does not support many SQL features.
- Catena's consistency model is very different from other databases. In particular, any changes you make are not immediately visible nor confirmed. Transactions may roll back at any time depending on which transactions are included in the 'winning' blockchain.
- Catena will (in the future) check user privileges when changing or adding data, but can never prevent users from seeing all data (all users that are connected to a Catena blockchain can 'see' all transactions). Of course it is possible to set up a private chain.
Catena supports a limited subset of SQL (Catena implements its own SQL parser to sanitize and canonicalize SQL queries). Currently, the following types of statements are supported:
- CREATE TABLE foo (bar TEXT, baz INT);
- INSERT INTO table (x, y, z) VALUES ('text', 1337);
- SELECT DISTINCT *, x, y, 'value', 123 FROM table LEFT JOIN other ON x=y WHERE x=10;
- DELETE FROM foo WHERE x=10;
- UPDATE foo SET bar=baz WHERE bar=1;
- DROP TABLE foo;
Catena uses a Blockchain based on SHA-256 hashes for proof of work, with configurable difficulty. Blocks contain transactions which contain SQL statements. Catena is written from scratch and is therefore completely different from Bitcoin, Ethereum etc.
Catena nodes expose an HTTP/WebSocket interface. A node connects to the WebSocket interface of all other nodes it knows about (initially specified from the command line) to fetch block information and exchange peers. In order for two nodes to be able to communicate, at least one must be able to accept incoming connections (i.e. not be behind NAT or firewall).
SQL statements are grouped in transactions, which become part of a block. Once a block as been accepted in the blockchain and is succeeded by a sufficient number of newer blocks, the block has become an immutable part of the blockchain ledger.
As new blocks still run the risk of being 'replaced' by competing blocks that have been mined (which may or may not include a recent transaction), the most recent transactions run the risk of being rolled back.
Transactions are required to be signed with a private key.
A transaction that modifies any table or row needs to be signed with a private key that has the privilege to modify that specific table or row. Privilege grants are stored in a special 'grants' table (which, in turn, can be modified by those that have a grant to modify that table).
To prevent replay of signed transactions, Catena stores a transaction counter for each public key, which is atomically incremented for every transaction that is executed. A transaction will not execute (again) if it has a lower transaction number than the latest number recorded in the blockchain. To successfully submit a transaction, the invoker must increment the counter by one for each transaction (or use a different key each time).
Catena is Italian for 'chain'.
Chains are identified by their genesis (first) block's hash. To create a private chain, use the '-s' option to specify a different starting seed.
Copyright (c) 2017 Pixelspark, Tommy van der Vorst
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