ECHO — Returning Data

Now that PING works, let's add ECHO — a command that returns whatever you send it.

How ECHO Works

ECHO <message> returns the message as a RESP bulk string:

ECHO hello    →  $5\r\nhello\r\n
ECHO foobar   →  $6\r\nfoobar\r\n

Bulk String Encoding

A bulk string has the format: $<length>\r\n<data>\r\n

The length is the number of bytes in the data (important for binary safety — though for ASCII text, bytes = characters).

Examples:

• "" (empty) → $0\r\n\r\n
• "hi" → $2\r\nhi\r\n
• "hello world" → $11\r\nhello world\r\n

Building a RESP Encoder

You should start building helper functions:

encode_bulk_string(s)  → "$<len>\r\n<s>\r\n"
encode_simple_string(s) → "+<s>\r\n"

These will be reused in every future lesson. Write them once, use them everywhere.

Your Task

Add ECHO to your program alongside PING. Both commands must work in the same session.