FlowStable Protocol (v1.0.0-alpha)

Abstract

FlowStable serves as an asynchronous, offline-tolerant payment orchestration layer, architected to bridge modern IP-based Unified Payments Interface (UPI) rails with legacy GSM signaling channels (specifically the *99# USSD gateway). It leverages an injected AccessibilityService vector to programmatically intercept, parse, and respond to Session-Oriented Unstructured Supplementary Service Data streams, effectively creating a "Headless Browser" for cellular telephony menus.

Architectural Overview

The system operates on a Finite State Automaton (FSA) model, enforcing deterministic state transitions during the payment handshake.

graph TD
    A["Idle State"] -->|SigInt: *99#| B("USSD Gateway Handshake")
    B -->|ACK: 200 OK| C{"Data Stream Analysis"}
    C -->|Regex Match: 'Send Money'| D["MenuItem Selection Vector"]
    C -->|Regex Match: 'Enter UPI'| E["VPA Injection Protocol"]
    E -->|Payload: VPA| F["Amount Serialization Phase"]
    F -->|Payload: Int64| G["Security Challenge (PIN)"]
    G -->|Manual Input| H["Transaction Finality"]

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System Modules

1. USSDInterceptorDaemon

• Namespace: com.flowstable.upi.ussd.USSDService
• Function: Operates as a background daemon with BIND_ACCESSIBILITY_SERVICE permission.
• Logic: Monitoring TYPE_WINDOW_STATE_CHANGED events to scrape AccessibilityNodeInfo trees. Uses heuristic parsing to identify GSM operator-specific dialects (Airtel vs Jio vs Vi variants).

2. Photonic Data Ingestion (Vision)

• Engine: Google ML Kit (On-device Vision API).
• Protocol: Real-time extraction of pa (Payment Address), pn (Payee Name), and am (Amount) parameters from high-density QR matrices (ISO/IEC 18004).

3. USSDController (The Orchestrator)

A singleton-based State Machine implementing the State pattern.

• States: IDLE, MENU_MAIN, ENTER_UPI, ENTER_AMOUNT, CONFIRM.
• Transition Logic: Deterministic routing based on string tokenization of the incoming USSD buffer.

Deployment Pipeline (CI/CD)

The project utilizes a GitHub Actions workflows for compilation and distribution.

• VM: ubuntu-latest
• JDK: OpenJDK 17 (Temurin Distribution)
• Build System: Gradle 8.2 (Daemonized)
• Artifact Delivery: Curl-based POST request to Telegram Bot API (sendDocument endpoint) for instant binary distribution.

Compiling the Kernel

To build the APK artifact from source, ensure your environment meets the strict minSdk=26 requirement.

# Clone the repository
git clone https://github.com/FlowStablee/flowstable-UPI.git

# Initialize the Gradle Wrapper Daemon
./gradlew --no-daemon

# Compile Debug Build Variant
./gradlew assembleDebug

Security Considerations

• PIN Entry: The system intentionally halts automation at the CONFIRM state (MPIN entry) to maintain a Zero-Trust architecture regarding sensitive user credentials. The AccessibilityService is programmed to yield control to the Human Interface Device (HID) layer at this specific interrupt.

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