Initial commit, devnet sponsored tx Dapp

DevnetSponsoredTx/README.md

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+# Concordium Sponsored Transactions Demo
+
+Demo for sponsored transactions on Concordium. Users transfer PLT tokens without paying gas fees - a sponsor wallet covers the cost.
+
+## Project Structure
+
+```
+DevnetSponsoredTx/
+├── docker-compose.yml        # Orchestrates frontend and backend containers
+├── frontend/
+│   ├── Dockerfile            # Multi-stage build, serves with runtime config injection
+│   ├── build-and-serve.sh    # Injects env vars into index.html at container startup
+│   ├── src/
+│   │   └── constants.ts      # Runtime config from window.runtimeConfig
+│   └── index.html            # Contains placeholders for runtime injection
+└── backend/
+    ├── Dockerfile            # Node.js backend build
+    └── wallet/               # Sponsor wallet export file (gitignored)
+```
+
+## Docker
+
+Create a `.env` file in the project root or set default values or secrets in the docker-compose:
+```env
+CONCORDIUM_GRPC_HOST=your-grpc-host
+CCDSCAN_URL=your-ccdscan-url
+```
+
+Add your sponsor wallet export file to `backend/wallet/sponsor.export`, then:
+
+```bash
+docker compose up --build
+```
+
+Open http://localhost:3000 and connect your Browser Wallet.
+
+### Environment Variables
+
+Frontend (runtime injection via `build-and-serve.sh`):
+- `BACKEND_URL` - Backend API URL (default: `http://localhost:3002`)
+- `TOKEN_ID` - Token identifier (default: `EURtest`)
+- `TOKEN_DECIMALS` - Token decimals (default: `6`)
+- `CCDSCAN_URL` - CCDScan URL for transaction links (required)
+
+Backend:
+- `CONCORDIUM_GRPC_HOST` - Concordium node host (required)
+- `CONCORDIUM_GRPC_PORT` - Concordium node port (default: `20000`)
+- `CONCORDIUM_USE_SSL` - Use SSL for gRPC connection (default: `true`)
+- `SPONSOR_WALLET_PATH` - Path to sponsor wallet export file
+- `PORT` - Backend port (default: `3002`)
+
+## Local Development
+
+### Backend
+
+```bash
+cd backend
+npm install
+```
+
+Create `backend/.env`:
+```env
+CONCORDIUM_GRPC_HOST=your-grpc-host
+CONCORDIUM_GRPC_PORT=20000
+CONCORDIUM_USE_SSL=true
+SPONSOR_WALLET_PATH=./wallet/sponsor.export
+PORT=3002
+```
+
+Add your sponsor wallet export file to `backend/wallet/sponsor.export`, then:
+
+```bash
+npm run start:dev
+```
+
+### Frontend
+
+```bash
+cd frontend
+npm install
+npm run build
+npm run start
+```
+
+Open http://localhost:5173 and connect your Browser Wallet.
+
+## How It Works
+
+1. User connects Browser Wallet
+2. User enters recipient and amount
+3. Backend creates the transaction and signs it with the sponsor key
+4. User signs to authorize the token transfer
+5. Sponsor wallet pays the gas fees
+
+## Notes
+
+- Sponsor wallet needs CCD to cover gas fees
+- Wallet export files in `backend/wallet/` are gitignored

DevnetSponsoredTx/backend/.dockerignore

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+node_modules
+dist
+.env
+.env.*
+wallet/*.export

DevnetSponsoredTx/backend/.env.example

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+# Concordium Node Configuration
+CONCORDIUM_GRPC_HOST=grpc.testnet.concordium.com
+CONCORDIUM_GRPC_PORT=20000
+CONCORDIUM_USE_SSL=true
+
+# Token Configuration
+DEFAULT_TOKEN_ID=YOUR_TOKEN_ID
+TOKEN_DECIMALS=6
+
+# Sponsor Wallet
+SPONSOR_WALLET_PATH=./wallet/sponsor.export
+
+# Server Configuration
+PORT=3002
+NODE_ENV=development

DevnetSponsoredTx/backend/.gitignore

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+node_modules/
+dist/
+.env
+wallet/*.export
+wallet/*.json
+*.log
+.DS_Store
+*.tsbuildinfo

DevnetSponsoredTx/backend/Dockerfile

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+FROM node:20-alpine
+
+WORKDIR /app
+
+COPY package*.json ./
+RUN npm install --legacy-peer-deps
+
+COPY . .
+RUN rm -rf dist && npx tsc --incremental false
+
+EXPOSE 3002
+
+CMD ["npm", "run", "start:prod"]