Denys

Denys Mulchenko
Software Engineering Intern · Python / SQL / Linux

Poland · [open contact info](look above in the "contact info" section) · [open contact info](look above in the "contact info" section) · github.com/xecce2 · [open contact info](look above in the "contact info" section)

P r o fi l e Third-year Computer Science student (specialization: Cloud Application Programming) who builds
complete applications rather than isolated exercises: layered FastAPI backends with SQLAlchemy and
Alembic, a multi-client banking system written directly on TCP sockets with a protocol I designed
and framed myself, React front ends that consume my own APIs, and a REST service wrapped
around a self-hosted vision model. I test what I write — automated suites with parallel clients and
negative cases — which is how I found and fixed a race condition and a money-creating exploit in my
own code. Comfortable in Linux with Git and Docker, backed by coursework in computer networks,
systems security and parallel programming, and used to handling failure paths explicitly rather than
assuming the happy path. Seeking a software engineering internship where I can contribute to real
code and grow through code review.

Te c h n i c a l S k i l l s Languages — Python, SQL, JavaScript, Bash, C (in progress)
Backend & APIs — FastAPI, REST API design, Pydantic validation, SQLAlchemy ORM, Alembic migra-
tions, asyncio, multiprocessing, threading, TCP sockets, JSON, CORS, HTTP
Databases & SQL — SQL queries, joins and aggregation, relational schema design, normalisation, primary
and foreign keys, constraints, transactions, SQLite, ORM mapping, schema migrations
Frontend — React (components, hooks, state, conditional rendering), JavaScript (ES6+), Vite, npm, HTML
/ CSS, consuming REST APIs from the browser, CORS
Testing & Quality — automated integration and end-to-end test suites, unit tests (unittest), negative-
path testing, concurrency and race-condition testing, REST API testing, logging, defect reproduction and
root-cause analysis
Networking & Protocols — TCP/IP, TCP sockets, application-level protocol design (length-prefixed JSON
framing), HTTP, REST, client–server architecture, packet analysis with Wireshark, scanning with Nmap
Security & Systems — bcrypt password hashing, session handling and server-side authorisation, input
validation, race-condition remediation, firewall and antivirus configuration, backup and recovery, Windows
and Linux troubleshooting, router and Wi-Fi hardening
AI & Data — local vision / LLM inference with Ollama (Gemma 3), structured output parsing and Pydantic
schema validation, batch and parallel processing, benchmarking and result analysis, matplotlib
Tools & Platforms — Linux (daily driver), Bash scripting, Git / GitHub, Docker (images, containers, port
binding), virtual environments (venv), pip / requirements.txt, npm, VS Code, PyCharm
Computer Science — object-oriented programming, data structures and algorithms, concurrency, client–
server architecture, TCP/IP networking, application security

Currently learning — C fundamentals and low-level memory management, machine-learning fundamentals,
Microsoft Azure fundamentals (AZ-900), CI/CD with GitHub Actions

Projects Bank Terminal — Client–Server Banking System
Python · TCP sockets · SQLite · bcrypt · threading · automated testing

• Designed a four-component system — server, client terminal, banker terminal and a shared protocol module
— communicating over a custom length-prefixed JSON protocol on raw TCP.
• Implemented bcrypt password authentication, server-side session handling and role authorisation, and
thread-safe concurrent transactions against a SQLite database.
• Found and fixed a race condition on balance operations using a threading lock and atomic SQL, and closed
a self-transfer exploit that could create money.
• Wrote an automated test suite: 4 parallel client scenarios and 20+ requests covering all 6 API operations
plus 6 negative cases (invalid credentials, insufficient funds, unknown actions).

github.com/xecce2/bank-terminal

Finance Manager — Full-Stack REST API & Dashboard
Python · FastAPI · SQLAlchemy ORM · Pydantic · Alembic · SQLite · React

• Built a layered FastAPI backend (models / schemas / CRUD / database / config) exposing REST endpoints
for categories and transactions, with pagination and HTTP error handling.
• Modelled a relational schema in SQLAlchemy ORM (primary and foreign keys, relationships) and versioned
schema changes with Alembic migrations.
• Wired dependency-injected database sessions, CORS and environment-based configuration, and built the
React dashboard that calls the API, manages component state and renders the data.

github.com/xecce2/finance-manager

OCR Analyzer — REST Service on a Self-Hosted Vision Model
Python · FastAPI · Ollama (Gemma 3) · React (Vite) · REST API

• Built a multipart file-upload endpoint that runs images through a locally hosted vision model and returns
a validated JSON response defined by Pydantic schemas.
• Parsed and validated model output instead of trusting the first response, and handled failure paths explic-
itly.
• Built the React (Vite) front end that uploads files to the API and renders the structured result returned
by the model.

github.com/xecce2/OCR-Analyzer

Parallel Sorting & Amdahl’s Law — Performance Analysis
Python · multiprocessing · matplotlib

• Implemented a split, parallel-sort and merge pipeline and benchmarked it across 3 dataset sizes and 1–8
worker processes, plotting measured speed-up against the theoretical limit.
• Traced misleading results back to measurement artefacts — process cold-start and input data mutated
between runs — and corrected the benchmark methodology.

github.com/xecce2/parallel-sort-with-Amdhali-analysis

Experience BikeCafe — Team Member Poland · Apr 2025 – present

• Customer-facing work in a fast-paced environment: diagnosing and resolving problems on the spot, handling
payments and equipment accurately, and coordinating with the team through peak hours — daily practice
at explaining things to non-technical people under time pressure, in Polish and English.

Education WSB Merito University, Poland 2024 – present

B.Eng. in Computer Science (Informatyka) · Specialization: Cloud Application Programming · 3rd year
• Relevant coursework: parallel programming, databases and SQL, computer networks, systems and network
security, object-oriented programming.

Languages English — B2 · Polish — B2 (degree taught in Polish) · Ukrainian — Native · Russian — Native

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process and future recruitment processes, in accordance with Regulation (EU) 2016/679 (GDPR).