TCP Protocol Reference

Interface declaration:

db = service("db",
    interface("main", "tcp", 5432),
    ...
)

Methods

send(data="")

Send a line of data over TCP and read the response.

resp = db.main.send(data="PING")
assert_eq(resp, "PONG")

resp = db.main.send(data="SET mykey myvalue")
resp = db.main.send(data="GET mykey")
assert_eq(resp, "myvalue")

Note: send() returns the first line of the response as a string (not a response object). This is a low-level protocol — for structured database access, use the postgres, mysql, or redis protocols instead.

Response

send() returns a string — the first line received from the server.

result = db.main.send(data="PING")
# result is "PONG" (string, not response object)

Fault Rules

TCP has no protocol-level fault rules — it operates at the byte level with no request/response structure. Use syscall-level faults:

db_down = fault_assumption("db_down",
    target = db,
    connect = deny("ECONNREFUSED"),
)

db_slow = fault_assumption("db_slow",
    target = db,
    write = delay("500ms"),
)

Seed / Reset Patterns

For TCP services with simple text protocols:

def seed_db():
    db.main.send(data="SET user:1 alice")
    db.main.send(data="SET user:2 bob")

def reset_db():
    db.main.send(data="FLUSHALL")

db = service("db", BIN + "/mock-db",
    interface("main", "tcp", 5432),
    reuse = True,
    seed = seed_db,
    reset = reset_db,
)