Project 8: Detach/Attach Server Architecture

Build a server that keeps panes alive while clients attach and detach via a Unix socket protocol.

Quick Reference

Attribute Value
Difficulty Level 4: Expert
Time Estimate 2-3 weeks
Main Programming Language C (Alternatives: Rust)
Alternative Programming Languages Rust
Coolness Level Level 5: Persistence Architect
Business Potential 3: The “Infra Tool”
Prerequisites Unix sockets, screen buffers, event loops
Key Topics client-server, snapshot sync, detach/attach

1. Learning Objectives

By completing this project, you will:

  1. Build a working implementation of detach/attach server architecture and verify it with deterministic outputs.
  2. Explain the underlying Unix and terminal primitives involved in the project.
  3. Diagnose common failure modes with logs and targeted tests.
  4. Extend the project with performance and usability improvements.

2. All Theory Needed (Per-Concept Breakdown)

Stateful Client-Server with Snapshot Synchronization

  • Fundamentals Stateful Client-Server with Snapshot Synchronization is the core contract that makes the project behave like a real terminal tool. It sits at the boundary between raw bytes and structured state, so you must treat it as both a protocol and a data model. The goal of the fundamentals is to understand what assumptions the system makes about ordering, buffering, and ownership, and how those assumptions surface as user-visible behavior. Key terms include: attach, detach, snapshot, diff, versioning. In practice, the fastest way to gain intuition is to trace a single input through the pipeline and note where it can be delayed, reordered, or transformed. That exercise reveals why Stateful Client-Server with Snapshot Synchronization needs explicit invariants and why even small mistakes can cascade into broken rendering or stuck input.

  • Deep Dive into the concept A deep understanding of Stateful Client-Server with Snapshot Synchronization requires thinking in terms of state transitions and invariants. You are not just implementing functions; you are enforcing a contract between producers and consumers of bytes, and that contract persists across time. Most failures in this area are caused by violating ordering guarantees, dropping state updates, or misunderstanding how the operating system delivers events. This concept is built from the following pillars: attach, detach, snapshot, diff, versioning. A reliable implementation follows a deterministic flow: Server maintains state even with zero clients -> Client attaches and requests snapshot -> Server sends snapshot, then diffs -> Client detaches without destroying state. From a systems perspective, the tricky part is coordinating concurrency without introducing races. Even in a single-threaded loop, multiple events can arrive in the same tick, so you need deterministic ordering. This is why many implementations keep a strict sequence: read, update state, compute diff, render. Another subtlety is error handling and recovery. A robust design treats errors as part of the normal control flow: EOF is expected, partial reads are expected, and transient failures must be retried or gracefully handled. The deep dive should also cover how to observe the system, because without logs and trace points, you cannot reason about correctness. When you design the project, treat each key term as a source of constraints. For example, if a term implies buffering, decide the buffer size and how overflow is handled. If a term implies state, decide how that state is initialized, updated, and reset. Finally, validate your assumptions with deterministic fixtures so you can reproduce bugs. From a systems perspective, the tricky part is coordinating concurrency without introducing races. Even in a single-threaded loop, multiple events can arrive in the same tick, so you need deterministic ordering. This is why many implementations keep a strict sequence: read, update state, compute diff, render. Another subtlety is error handling and recovery. A robust design treats errors as part of the normal control flow: EOF is expected, partial reads are expected, and transient failures must be retried or gracefully handled. The deep dive should also cover how to observe the system, because without logs and trace points, you cannot reason about correctness. From a systems perspective, the tricky part is coordinating concurrency without introducing races. Even in a single-threaded loop, multiple events can arrive in the same tick, so you need deterministic ordering. This is why many implementations keep a strict sequence: read, update state, compute diff, render. Another subtlety is error handling and recovery. A robust design treats errors as part of the normal control flow: EOF is expected, partial reads are expected, and transient failures must be retried or gracefully handled. The deep dive should also cover how to observe the system, because without logs and trace points, you cannot reason about correctness. From a systems perspective, the tricky part is coordinating concurrency without introducing races. Even in a single-threaded loop, multiple events can arrive in the same tick, so you need deterministic ordering. This is why many implementations keep a strict sequence: read, update state, compute diff, render. Another subtlety is error handling and recovery. A robust design treats errors as part of the normal control flow: EOF is expected, partial reads are expected, and transient failures must be retried or gracefully handled. The deep dive should also cover how to observe the system, because without logs and trace points, you cannot reason about correctness.

  • How this fit on projects This concept is the backbone of the project because it defines how data and control flow move through the system.

  • Definitions & key terms

    • attach -> client operation to connect and receive a snapshot
    • detach -> client operation to disconnect without destroying server state
    • snapshot -> full screen/state transfer sent to a newly attached client
    • diff -> incremental changes relative to the previous frame
    • versioning -> protocol version identifiers used for compatibility checks

  • Mental model diagram (ASCII)

[Input] -> [Stateful Client-Server with Snapshot Synchronization] -> [State] -> [Output]

  • How it works (step-by-step, with invariants and failure modes)

    1. Server maintains state even with zero clients
    2. Client attaches and requests snapshot
    3. Server sends snapshot, then diffs
    4. Client detaches without destroying state

  • Minimal concrete example

ATTACH -> SNAPSHOT -> DIFF* -> DETACH

  • Common misconceptions

    • “Detach means stop server” -> server must remain alive.

  • Check-your-understanding questions

    • What state must be persisted for attach?
    • How do you handle protocol version mismatch?

  • Check-your-understanding answers

    • Screen buffers, layout, focus, and PTY handles must persist.
    • Refuse attach with a version error.

  • Real-world applications

    • tmux detach/attach

  • Where you’ll apply it

  • References

    • TLPI Ch. 57
    • tmux 3 Ch. 4

  • Key insights Stateful Client-Server with Snapshot Synchronization works best when you treat it as a stateful contract with explicit invariants.

  • Summary You now have a concrete mental model for Stateful Client-Server with Snapshot Synchronization and can explain how it affects correctness and usability.

  • Homework/Exercises to practice the concept

    • Design a message header with version and length.

  • Solutions to the homework/exercises

    • Use fixed-size header and network byte order.

3. Project Specification

3.1 What You Will Build

A daemon server that owns PTYs and screen buffers, with a client that can attach/detach and render snapshots.

3.2 Functional Requirements

  1. Requirement 1: Server keeps running after client exit
  2. Requirement 2: Client attach receives full snapshot
  3. Requirement 3: Detach stops updates but keeps state
  4. Requirement 4: Multiple clients can attach

3.3 Non-Functional Requirements

  • Performance: Avoid blocking I/O; batch writes when possible.
  • Reliability: Handle partial reads/writes and cleanly recover from disconnects.
  • Usability: Provide clear CLI errors, deterministic output, and helpful logs.

3.4 Example Usage / Output

    $ ./mytmux-server --socket /tmp/mytmux.sock
[server] session created

$ ./mytmux attach -S /tmp/mytmux.sock
[client] attached
# detach with Ctrl-b d
[client] detached
[exit code: 0]

$ ./mytmux attach -S /tmp/does-not-exist.sock
[error] cannot connect to server
[exit code: 1]

3.5 Data Formats / Schemas / Protocols

    Protocol messages: header(type, len) + payload (snapshot or input).

3.6 Edge Cases

  • Client crashes mid-update
  • Snapshot too large
  • Socket permission denied

3.7 Real World Outcome

This section defines a deterministic, repeatable outcome. Use fixed inputs and set TZ=UTC where time appears.

3.7.1 How to Run (Copy/Paste)

make
./mytmux-server --socket /tmp/mytmux.sock

3.7.2 Golden Path Demo (Deterministic)

The “success” demo below is a fixed scenario with a known outcome. It should always match.

3.7.3 If CLI: provide an exact terminal transcript

    $ ./mytmux-server --socket /tmp/mytmux.sock
[server] session created

$ ./mytmux attach -S /tmp/mytmux.sock
[client] attached
# detach with Ctrl-b d
[client] detached
[exit code: 0]

Failure Demo (Deterministic)

    $ ./mytmux attach -S /tmp/does-not-exist.sock
[error] cannot connect to server
[exit code: 1]

3.7.8 If TUI

At least one ASCII layout for the UI:

    +------------------------------+
    | Detach/Attach Server Architecture           |
    | [content area]               |
    | [status / hints]             |
    +------------------------------+

4. Solution Architecture

4.1 High-Level Design

    +-----------+     +-----------+     +-----------+
    |  Client   | <-> |  Server   | <-> |  PTYs     |
    +-----------+     +-----------+     +-----------+

4.2 Key Components

| Component | Responsibility | Key Decisions | |-----------|----------------|---------------| | Server | Owns PTYs and state. | Single authoritative process. | | Client | Renders snapshots and sends input. | Thin UI process. | | Protocol | Message framing and versioning. | Length-prefixed binary messages. |

4.4 Data Structures (No Full Code)

    struct MsgHeader { uint16_t type; uint32_t len; uint16_t version; };

4.4 Algorithm Overview

Key Algorithm: Attach snapshot sync

  1. Client connects
  2. Client requests attach
  3. Server sends full snapshot
  4. Server sends incremental diffs

Complexity Analysis:

  • O(frame size) snapshot

5. Implementation Guide

5.1 Development Environment Setup

    cc --version
make --version

5.2 Project Structure

    mytmux/
|-- src/
|   |-- server.c
|   |-- client.c
|   `-- protocol.c
`-- Makefile

5.3 The Core Question You’re Answering

“What state must survive when the client disappears?”

5.4 Concepts You Must Understand First

  1. client-server
    • Why it matters and how it impacts correctness.
  2. snapshot sync
    • Why it matters and how it impacts correctness.
  3. detach/attach
    • Why it matters and how it impacts correctness.

5.5 Questions to Guide Your Design

  • How do you serialize screen buffers efficiently?
  • How do you authenticate local clients?

    5.6 Thinking Exercise

List all data you must keep in memory while no clients are attached.

5.7 The Interview Questions They’ll Ask

  • What happens to the PTYs when no clients are attached?
  • How do you avoid losing screen state?

    5.8 Hints in Layers

  • Keep the last frame in memory.

  • Send full snapshot on attach then diffs.

5.9 Books That Will Help

| Topic | Book | Chapter | |——-|——|———| | Unix sockets | The Linux Programming Interface | Ch. 57 |

5.10 Implementation Phases

Phase 1: Foundation (2-3 weeks)

Goals:

  • Establish the core data structures and loop.
  • Prove basic I/O or rendering works.

Tasks:

  1. Implement the core structs and minimal main loop.
  2. Add logging for key events and errors.

Checkpoint: You can run the tool and see deterministic output.

Phase 2: Core Functionality (2-3 weeks)

Goals:

  • Implement the main requirements and pass basic tests.
  • Integrate with OS primitives.

Tasks:

  1. Implement remaining functional requirements.
  2. Add error handling and deterministic test fixtures.

Checkpoint: All functional requirements are met for the golden path.

Phase 3: Polish & Edge Cases (2-3 weeks)

Goals:

  • Handle edge cases and improve UX.
  • Optimize rendering or I/O.

Tasks:

  1. Add edge-case handling and exit codes.
  2. Improve logs and documentation.

Checkpoint: Failure demos behave exactly as specified.

5.11 Key Implementation Decisions

Decision Options Recommendation Rationale
I/O model blocking vs non-blocking non-blocking avoids stalls in multiplexed loops
Logging text vs binary text for v1 easier to inspect and debug

6. Testing Strategy

6.1 Test Categories

Category Purpose Examples
Unit Tests Validate components parser, buffer, protocol
Integration Tests Validate interactions end-to-end CLI flow
Edge Case Tests Handle boundary conditions resize, invalid input

6.2 Critical Test Cases

  1. Attach receives correct snapshot
  2. Detach keeps PTY alive
  3. Multiple clients sync

    6.3 Test Data

text Start server, detach, reattach; expect identical screen content.

7. Common Pitfalls & Debugging

7.1 Frequent Mistakes

| Pitfall | Symptom | Solution | |———|———|———-| | Blank screen on attach | No snapshot sent | Send full snapshot on attach. |

7.2 Debugging Strategies

  • Log message types and sizes for each client.

    7.3 Performance Traps

  • Sending full frames too often instead of diffs.

8. Extensions & Challenges

8.1 Beginner Extensions

  • Add list-sessions command.
  • Add –socket flag.

    8.2 Intermediate Extensions

  • Add compression for snapshots.
  • Add client-side reconnection.

    8.3 Advanced Extensions

  • Add per-client viewports and scaling.

9. Real-World Connections

9.1 Industry Applications

  • Remote session managers
  • tmux

    9.3 Interview Relevance

  • Event loops, terminal I/O, and state machines are common interview topics.

10. Resources

10.1 Essential Reading

11. Self-Assessment Checklist

11.1 Understanding

  • I can explain the core concept without notes
  • I can explain how input becomes output in this tool
  • I can explain the main failure modes

11.2 Implementation

  • All functional requirements are met
  • All test cases pass
  • Code is clean and well-documented
  • Edge cases are handled

11.3 Growth

  • I can identify one thing I’d do differently next time
  • I’ve documented lessons learned
  • I can explain this project in a job interview

12. Submission / Completion Criteria

Minimum Viable Completion:

  • Tool runs and passes the golden-path demo
  • Deterministic output matches expected snapshot
  • Failure demo returns the correct exit code

Full Completion:

  • All minimum criteria plus:
  • Edge cases handled and tested
  • Documentation covers usage and troubleshooting

Excellence (Going Above & Beyond):

  • Add at least one advanced extension
  • Provide a performance profile and improvement notes