Rog

A simple distributed commit log inspired by Kafka.

TODOs

• Distribute writes to multiple nodes

Building

To build both the cli and the server you can just run cargo build --release.

Integration tests

The integration tests are written in python with pytest. You can install the dependencies with pip: pip install -r tests/requirements.txt. The tests use protobuf for a few scenarios, so you need the protobuf compiler, you can generated the necessary files running this command:

protoc -I=tests/proto --python_out=tests tests/proto/addressbook.proto

And to execute all tests you can run:

pytest tests

If you don't want to install protoc you can run the tests with the local docker image, this image is used simply to run this tests in an isolated environment.

docker buildx build .

Rog CLI

To interact with the server you can use the rog cli.

Usage: rog-cli --address <ADDRESS> <COMMAND>

Commands:
  create-log
  publish
  fetch
  help        Print this message or the help of the given subcommand(s)

Options:
  -a, --address <ADDRESS>  Rog server address on the format ip:port, e.g.: 127.0.0.1:7878
  -h, --help               Print help

Protocol specification

The Rog protocol is implemented with TCP. In all commands the first byte is the command byte, this is used to identify which command is being sent. There are two client implementations in this repository: one in rust, for the cli and one in python used in the integration tests.

Commands

Create log

Field	Type	Description
Command byte	u8	Fixed value for the create log command, 0
partitions	u8	Number of partitions for the log
Log name size	u8	Size of the log name in bytes
Log name	String	Log name

Successful response

Field	Type	Description
Success byte	u8	Indicates if the response was successful or not, 0

Publish

Field	Type	Description
Command byte	u8	Fixed value for the publish command, 1
partition	u8	Partitions to publish the message
Log name size	u8	Size of the log name in bytes
Log name	String	Log name
Data size	u64	Size of the message in bytes
Data	bytes	The actual content of the message

Successful response

Field	Type	Description
Success byte	u8	Indicates if the response was successful or not, 0

Fetch

Field	Type	Description
Command byte	u8	Fixed value for the fetch command, 2
partition	u8	Partition to fetch the message
Log name size	u8	Size of the log name in bytes
Log name	String	Log name
Group size	u64	Size of the group name
Group	bytes	The group name

Successful response

Field	Type	Description
Success byte	u8	Indicates if the response was successful or not, 0
Message size	u64	Size of the message content
Message	String	Actual message

Ack

Field	Type	Description
Command byte	u8	Fixed value for the ack command, 3
partition	u8	Partition to fetch the message
Log name size	u8	Size of the log name in bytes
Log name	String	Log name
Group size	u64	Size of the group name
Group	bytes	The group name

Successful response

Field	Type	Description
Success byte	u8	Indicates if the response was successful or not, 0

Error response

All commands have the same possible error response.

Field	Type	Description
Success byte	u8	Indicates if the response was successful or not, 1
Message size	u64	Size of the error message
Message	String	Detailed error message

Storage

Rog keeps the messages stored in multiple log files, each file has an approximate max size of 1MiB. When a log is created, Rog creates a directory with name log name and one directory for each partition, the log files are kept inside the partition directory with the extension .log.

Log file format

The file follows a simple structure so that it is easily seekeable so that the fetching process doesn't need to load the whole file into memory. Each message is stored as an "entry" on the file.

Field	Size	Description
id	8 bytes	The message id
entry size	8 bytes	The size of the entry content in bytes
entry	entry size bytes	The entry content