# Decentralized File Storage Module

## Introduction

Decentralized file storage on a blockchain allows for secure and immutable data storage, ensuring data integrity and availability. In this tutorial, we will create a blockchain module for storing and retrieving files using the Ignite CLI and Cosmos SDK.

## Prerequisites

- Basic understanding of blockchain technology.
- Familiarity with Go programming language.
- Ignite CLI installed on your machine.

## Steps to Build the Module

**Step 1: Scaffold a New Blockchain**

First, create a new blockchain project using Ignite CLI:

ignite scaffold chain filechain --no-module && cd filechain

**Step 2: Scaffold the File Storage Module**

Generate the file storage module:

ignite scaffold module filestorage

**Step 3: Define Data Structures**

Define the necessary types for file storage. For instance, a File type:

ignite scaffold single File contentHash data --module filestorage

Here, `contentHash` will be a unique identifier for the file, and data will be the file content.

**Step 4: Implement File Upload Functionality**

In your `x/filestorage/keeper/msg_server_upload_file.go` file, implement the logic to handle file upload transactions:

package keeper

import (
    "context"
    "crypto/sha256"
    "encoding/hex"
    "filechain/x/filestorage/types"
)

func (k Keeper) UploadFile(goCtx context.Context, msg *types.MsgUploadFile) (*types.MsgUploadFileResponse, error) {
    ctx := sdk.UnwrapSDKContext(goCtx)

    // Generate content hash
    hash := sha256.Sum256([]byte(msg.Data))
    contentHash := hex.EncodeToString(hash[:])

    // Create File object
    var file = types.File{
        Creator:    msg.Creator,
        ContentHash: contentHash,
        Data:       msg.Data,
    }

    // Store the file
    k.SetFile(ctx, file)

    return &types.MsgUploadFileResponse{ContentHash: contentHash}, nil
}

**Step 5: Implement File Retrieval Functionality**

Define a query to retrieve files by their content hash in `x/filestorage/keeper/grpc_query_file.go`:

func (k Keeper) File(c context.Context, req *types.QueryGetFileRequest) (*types.QueryGetFileResponse, error) {
    if req == nil {
        return nil, status.Error(codes.InvalidArgument, "invalid request")
    }
    if !k.HasFile(ctx, req.ContentHash) {
        return nil, status.Error(codes.NotFound, "file not found")
    }

    file := k.GetFile(ctx, req.ContentHash)
    return &types.QueryGetFileResponse{File: file}, nil
}

**Step 6: Add CLI and gRPC Configurations**

Ensure your module's CLI commands and gRPC endpoints are properly configured for file upload and retrieval.

**Step 7: Test the Module**

After implementing the module, test uploading and retrieving files using CLI commands or gRPC clients.

## Conclusion

By completing this tutorial, you've built a basic decentralized file storage module. This module can be further expanded to include features like file encryption, access control, and larger data storage mechanisms.

**Next Steps**

- Integrate IPFS or similar decentralized storage solutions for larger file handling.
- Implement access control mechanisms to manage file visibility and access rights.
- Consider adding file encryption for enhanced security.