CAS Project Documentation

Project Overview

CAS (Content Addressable Storage) is a peer-to-peer storage system written in Go. It provides:

A TCP-based transport layer for network communication between peers
A file storage system with SHA1-based content addressable path transformation
Support for handshake procedures and custom encoding/decoding

File Reference

main.go

Purpose: Application entry point - initializes and starts the P2P TCP transport server.

Location: /Users/imanimen/Development/go/cas/main.go

Functions:

Function	Signature	Description
OnPeer	`func(peer p2p.Peer) error`	Callback function triggered when a new peer connects. Currently prints peer info.
main	`func()`	Initializes TCP transport with options, starts listening, and consumes messages from the channel.

TCPTransportOption Configuration:

ListenAddr: ":3000" - Port to listen on
HandshakeFunc: p2p.NOPHandshakeFunc - Handshake validation function
Decoder: p2p.DefaultDecoder{} - Message decoder
OnPeer: OnPeer callback function

Commit History:

6f18bc8 - fx: OnPeer method to make the application work

store.go

Purpose: Provides content-addressable file storage with SHA1-based path transformation. Splits hashes into directory paths for efficient file organization.

Location: /Users/imanimen/Development/go/cas/store.go

Types:

Type	Description
`PathTransformFunc`	Function type: `func(string) PathKey` - transforms a key into a path structure
`PathKey`	Struct containing `PathName` (nested directory path) and `FileName` (full hash)
`StoreOptions`	Configuration struct with `PathTransformFunc`
`Store`	Main storage struct holding StoreOptions

Constants/Variables:

Name	Type	Description
`DefaultPathTransformFunc`	`func(key string) string`	Default identity function (returns key as-is)
`CASPathTransformFunc`	`PathTransformFunc`	SHA1-based path transformation (default implementation)

Path Transformation Algorithm (CASPathTransformFunc):

Generate SHA1 hash of the key
Convert hash to hexadecimal string
Split into blocks of 5 characters
Join with "/" to create nested directory structure

Example: momsbestpicture → 6804429f74181a63c50c3d81d733a12f14a353ff → 68044/29f74/181a6/3c50c/3d81d/733a1/2f14a/353ff

Methods:

Method	Signature	Description
CASPathTransformFunc	`func(key string) PathKey`	Transforms a key into PathKey using SHA1 hash
NewStore	`func(options StoreOptions) *Store`	Creates a new Store instance
FullPath	`func(p PathKey) string`	Returns full path: `PathName/FileName`
Read	`func(s *Store, key string) (io.Reader, error)`	Reads file content by key
writeStream	`func(s *Store, key string, r io.Reader) error`	Writes data from reader to disk
readStream	`func(s *Store, key string) (io.ReadCloser, error)`	Opens file for reading
Delete	`func(s *Store, key string) error`	Deletes file and directory structure
Exists	`func(s *Store, key string) bool`	Checks if file exists
FirstPathName	`func(p PathKey) string`	Returns first directory in path

Commit History:

a9a19c0 - chore: filename method and other things
2d38a5d - chore: store is now storing
11747c8 - feat: store implementation

store_test.go

Purpose: Unit tests for the storage functionality.

Location: /Users/imanimen/Development/go/cas/store_test.go

Test Functions:

Function	Description
`TestPathTransformFunc`	Tests SHA1 path transformation with key "momsbestpicture", verifies PathName and FileName
`TestStore`	Integration test: writes data, reads it back, verifies content, then deletes

Commit History:

4d95b9f - chore: latest commits -> delete file + tests

p2p/transport.go

Purpose: Defines core interfaces for P2P communication.

Location: /Users/imanimen/Development/go/cas/p2p/transport.go

Interfaces:

Interface	Description
`Peer`	Represents a remote node. Method: `Close() error`
`Transport`	Handles communication between nodes. Methods: `ListenAndAccept() error`, `Consume() chan<- RPC`

Commit History:

cc4c68c - chore: interfaces

p2p/tcp_transport.go

Purpose: TCP implementation of the Transport interface for peer-to-peer communication.

Location: /Users/imanimen/Development/go/cas/p2p/tcp_transport.go

Types:

Type	Description
`TCPPeer`	Represents a remote node over TCP connection. Has `conn` (net.Conn) and `outbound` bool
`TCPTransportOption`	Configuration: ListenAddr, HandshakeFunc, Decoder, OnPeer callback
`TCPTransport`	Main transport struct with listener, rpcChan, peers map
`Temp`	Unused placeholder type

Methods:

Method	Signature	Description
NewTCPPeer	`func(conn net.Conn, outbound bool) *TCPPeer`	Creates new TCP peer
NewTCPTransport	`func(options TCPTransportOption) *TCPTransport`	Creates new TCP transport
ListenAndAccept	`func(t *TCPTransport) error`	Starts TCP listener and runs acceptor goroutine
Close	`func(p *TCPPeer) error`	Implements Peer interface - closes connection
Consume	`func(t *TCPTransport) <-chan RPC`	Returns channel for incoming messages
acceptor	`func(t *TCPTransport)`	Goroutine accepting incoming connections
connector	`func(t *TCPTransport, conn net.Conn)`	Goroutine handling connection lifecycle: handshake → OnPeer → read loop

Flow:

ListenAndAccept() starts listener and runs acceptor()
acceptor() accepts connections and spawns connector() goroutines
connector() performs handshake, calls OnPeer callback, then enters read loop
Read loop decodes messages and sends to rpcChan

Commit History:

2f27260 - feat: reader is now on
b9571bc - chroe: dropping connection logic
4e47305 - chore: consume method to handle the messages on the channel
c11823f - HOTFIX: TCP option configurations
e979df0 - chore: tcp peer connection is now working
b4e253b - chore: test + listenAndAccept function to handle connector + acceptor
554255f - chore(tests): test the TCP transport
cc4c68c - chore: interfaces (partial)

p2p/tcp_transport_test.go

Purpose: Unit tests for TCP transport.

Location: /Users/imanimen/Development/go/cas/p2p/tcp_transport_test.go

Test Functions:

Function	Description
`TestTCPTransport`	Creates TCP transport, verifies ListenAddr, starts ListenAndAccept

Dependencies: Uses github.com/stretchr/testify/assert

Commit History:

554255f - chore(tests): test the TCP transport

p2p/message.go

Purpose: Defines the RPC message structure for peer-to-peer communication.

Location: /Users/imanimen/Development/go/cas/p2p/message.go

Types:

Type	Description
`RPC`	Struct holding `From` (net.Addr) and `Payload` ([]byte) - arbitrary data sent between peers

Commit History:

f7b2cb1 - chore: from Message to RPC, we have come a long way
cefdf90 - chore: new property in message struct is From
2be32c7 - chore: finally the messages are showing but as bytes
9238f9a - chore: reading bytes in the first place
5e4bcea - chore: add Message.go

p2p/encoding.go

Purpose: Provides message decoding implementations for P2P communication.

Location: /Users/imanimen/Development/go/cas/p2p/encoding.go

Interfaces:

Interface	Description
`Decoder`	Interface with `Decode(io.Reader, *RPC) error` method

Types:

Type	Description
`GOBDecoder`	Uses Go's encoding/gob for structured message decoding
`DefaultDecoder`	Reads raw bytes (1028 byte buffer) - returns payload as-is

Commit History:

88d5612 - chore: Gob Decoder implemented and new TCP options
85748da - chore: decoder
0abebc0 - chore: handshaker & decoder

p2p/handshaker.go

Purpose: Defines handshake functionality for peer connection validation.

Location: /Users/imanimen/Development/go/cas/p2p/handshaker.go

Types/Variables:

Name	Type	Description
`ErrInvalidHandShake`	`error`	Error returned when handshake fails
`HandshakeFunc`	`func(Peer) error`	Function type for handshake validation
`NOPHandshakeFunc`	`HandshakeFunc`	No-op handshake that always succeeds

Commit History:

cfd5184 - chore: handshake func
9680de2 - HOTIFX: shakeHands func
0abebc0 - chore: handshaker & decoder

Git Commit History

Commit	Description
`4d95b9f`	chore: latest commits -> delete file + tests
`bb3a071`	HOTFIX: replace deprecated lib with io.ReadAll()
`2f27260`	feat: reader is now on
`a9a19c0`	chore: filename method and other things
`2d38a5d`	chore: store is now storing
`11747c8`	feat: store implementation
`6f18bc8`	fx: OnPeer method to make the application work
`b9571bc`	chore: dropping connection logic
`4e47305`	chore: consume method to handle the messages on the channel
`5793579`	fix: test is now working
`f7b2cb1`	chore: from Message to RPC, we have come a long way
`cefdf90`	chore: new property in message struct is From
`2be32c7`	chore: finally the messages are showing but as bytes
`9238f9a`	chore: reading bytes in the first place
`5e4bcea`	chore: add Message.go
`c11823f`	HOTFIX: TCP option configurations
`88d5612`	chore: Gob Decoder implemented and new TCP options
`cfd5184`	chore: handshake func
`9680de2`	HOTIFX: shakeHands func
`85748da`	chore: decoder
`0abebc0`	chore: handshaker & decoder
`816b525`	build workflow
`e979df0`	chore: tcp peer connection is now working
`b4e253b`	chore: test + listenAndAccept function to handle connector + acceptor
`554255f`	chore(tests): test the TCP transport
`cc4c68c`	chore: interfaces
`42c7140`	first commit

Architecture Diagram

┌─────────────────────────────────────────────────────────────┐
│                         main.go                             │
│                    (Entry Point)                             │
│  ┌─────────────────────────────────────────────────────┐   │
│  │  TCPTransportOption                                  │   │
│  │  - ListenAddr: ":3000"                              │   │
│  │  - HandshakeFunc                                    │   │
│  │  - Decoder                                          │   │
│  │  - OnPeer callback                                  │   │
│  └─────────────────────────────────────────────────────┘   │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│                    p2p/transport.go                         │
│  ┌─────────────┐              ┌─────────────┐              │
│  │   Peer      │              │  Transport  │              │
│  │  (interface)│              │ (interface) │              │
│  └─────────────┘              └─────────────┘              │
└─────────────────────────────────────────────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│                   p2p/tcp_transport.go                      │
│  ┌─────────────┐  ┌─────────────┐  ┌─────────────────────┐ │
│  │  TCPPeer    │  │TCPTransport │  │ TCPTransportOption  │ │
│  │  - conn     │  │ - listener │  │ - ListenAddr       │ │
│  │  - outbound │  │ - rpcChan  │  │ - HandshakeFunc    │ │
│  └─────────────┘  │ - peers    │  │ - Decoder          │ │
│                   └─────────────┘  │ - OnPeer          │ │
│                                      └─────────────────────┘ │
└─────────────────────────────────────────────────────────────┘
                            │
          ┌─────────────────┼─────────────────┐
          ▼                 ▼                 ▼
┌─────────────────┐ ┌─────────────────┐ ┌─────────────────────┐
│ p2p/encoding.go │ │p2p/handshaker.go│ │   p2p/message.go    │
│  - Decoder      │ │ - HandshakeFunc │ │     - RPC           │
│  - GOBDecoder   │ │ - NOPHandshake  │ │  - From: net.Addr  │
│  - DefaultDec   │ └─────────────────┘ │  - Payload: []byte │
└─────────────────┘                     └─────────────────────┘
                            │
                            ▼
┌─────────────────────────────────────────────────────────────┐
│                        store.go                             │
│  ┌──────────────────────────────────────────────────────┐  │
│  │  Store                                                │  │
│  │  - PathTransformFunc: CASPathTransformFunc (SHA1)   │  │
│  │                                                      │  │
│  │  Methods:                                            │  │
│  │  - Read(key) → io.Reader                            │  │
│  │  - writeStream(key, io.Reader) → error              │  │
│  │  - Delete(key) → error                              │  │
│  │  - Exists(key) → bool                               │  │
│  └──────────────────────────────────────────────────────┘  │
│                                                              │
│  Path Transformation Example:                               │
│  "momsbestpicture" → SHA1 → "6804429f74181a63..."          │
│  → Split(5) → "68044/29f74/181a6/3c50c/3d81d/733a1/..."   │
└─────────────────────────────────────────────────────────────┘

Usage Example

package main

import (
    "fmt"
    "log"

    "github.com/imanimen/cas/p2p"
)

func OnPeer(peer p2p.Peer) error {
    fmt.Printf("New peer connected: %v\n", peer)
    return nil
}

func main() {
    tcpOptions := p2p.TCPTransportOption{
        ListenAddr:    ":3000",
        HandshakeFunc: p2p.NOPHandshakeFunc,
        Decoder:       p2p.DefaultDecoder{},
        OnPeer:        OnPeer,
    }
    tr := p2p.NewTCPTransport(tcpOptions)

    if err := tr.ListenAndAccept(); err != nil {
        log.Fatal(err)
    }

    // Consume messages
    go func() {
        for {
            message := <-tr.Consume()
            fmt.Printf("Message from %v: %v\n", message.From, message.Payload)
        }
    }()

    select {} // Block forever
}

Name		Name	Last commit message	Last commit date
Latest commit History 32 Commits
.github/workflows		.github/workflows
.idea		.idea
bin		bin
p2p		p2p
DOCUMENTATION.md		DOCUMENTATION.md
README.md		README.md
go.mod		go.mod
go.sum		go.sum
main.go		main.go
makefile		makefile
store.go		store.go
store_test.go		store_test.go

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CAS Project Documentation

Project Overview

File Reference

main.go

store.go

store_test.go

p2p/transport.go

p2p/tcp_transport.go

p2p/tcp_transport_test.go

p2p/message.go

p2p/encoding.go

p2p/handshaker.go

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Architecture Diagram

Usage Example

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CAS Project Documentation

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File Reference

main.go

store.go

store_test.go

p2p/transport.go

p2p/tcp_transport.go

p2p/tcp_transport_test.go

p2p/message.go

p2p/encoding.go

p2p/handshaker.go

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