PROTOCOL.md

Protocol

The server and the client communicate over TCP using a simple framed protocol with JSON responses.

Framed protocol

Implementation: src/main/java/ru/open/cu/student/protocol/FramedProtocol.java

Message layout:

┌────────────┬─────────────────────────┐
│ Length (4B)│ Payload (UTF-8 bytes)   │
└────────────┴─────────────────────────┘

Length is the payload size in bytes (big-endian). Payload is a UTF-8 string.

Request (Client → Server)

Request payload: the SQL string.

Response (Server → Client)

Response payload: JSON.

Success response

{
  "ok": true,
  "columns": ["id", "name"],
  "rows": [[1, "Alice"], [2, "Bob"]]
}

Error response

{
  "ok": false,
  "errorStage": "PARSER",
  "errorMessage": "Expected SELECT, CREATE or INSERT"
}

errorStage corresponds to the pipeline stage (see PIPELINE.md).

CLI output modes

The CLI can render:

• “pretty” tables (human-readable)
• raw JSON responses (useful for protocol debugging)

Run details: DEVELOPMENT.md.