Merge pull request #413 from codecrafters-io/TropicolX-patch-58

Revise "Receive handshake (2/2) #vm3" (stage 51)

Author: TropicolX

stage_descriptions/replication-09-vm3.md

@@ -1,35 +1,36 @@
 In this stage, you'll add support for receiving the [`PSYNC`](https://redis.io/commands/psync/) command from the replica.
 
-### Handshake (continued from previous stage)
+### Handshake (Recap)
 
-As a recap, there are three parts to the handshake:
+As a recap, the master receives the following for the handshake:
 
-- The master receives a `PING` from the replica (You've already implemented this)
-- The master receives `REPLCONF` twice from the replica (You've already implemented this)
-- The master receives `PSYNC` from the replica (**This stage**)
+1. A `PING` from the replica
+2. `REPLCONF` twice from the replica
+3. `PSYNC` from the replica
 
-After the replica sends `REPLCONF` twice, it'll send a `PSYNC ? -1` command to the master.
+After the replica sends `REPLCONF` twice, it will send a `PSYNC` command with the arguments `? -1` to the master:
 
-- The first argument is `?`
-  - This is the replication ID of the master, it is `?` because this is the first time the replica is connecting to the master.
-- The second argument is `-1`
-  - This is the replication offset, it is `-1` because this is the first time the replica is connecting to the master.
+- The replication ID is `?` because the replica doesn't know the master's ID yet.
+- The offset is `-1` since the replica has no data from the master yet.
 
-The final command you receive will look something like this:
+The final command you'll receive will look something like this:
 
 ```
 *3\r\n$5\r\nPSYNC\r\n$1\r\n?\r\n$2\r\n-1\r\n
 ```
 
-(That's `["PSYNC", "?", "-1"]` encoded as a RESP Array)
+That's `["PSYNC", "?", "-1"]` encoded as a RESP array.
 
-The master needs to respond with `+FULLRESYNC <REPL_ID> 0\r\n` ("FULLRESYNC <REPL_ID> 0" encoded as a RESP Simple String). Here's what
-the response means:
+The master needs to respond with `+FULLRESYNC <REPL_ID> 0\r\n`, which is `FULLRESYNC <REPL_ID> 0` encoded as a simple string. Here's what the response means:
 
-- `FULLRESYNC` means that the master cannot perform incremental replication with the replica, and will thus start a "full" resynchronization.
-- `<REPL_ID>` is the replication ID of the master. You've already set this in the "Replication ID & Offset" stage.
-  - As an example, you can hardcode `8371b4fb1155b71f4a04d3e1bc3e18c4a990aeeb` as the replication ID.
-- `0` is the replication offset of the master. You've already set this in the "Replication ID & Offset" stage.
+- `FULLRESYNC` means that the master cannot perform an incremental update to the replica, and will start a full resynchronization.
+- `<REPL_ID>` is the replication ID of the master (the 40-character string you initialized in a previous stage).
+- `0` is the replication offset of the master (which you initialized in a previous stage).
+
+For example, if your replication ID is `8371b4fb1155b71f4a04d3e1bc3e18c4a990aeeb`, you'd respond with:
+```bash
++FULLRESYNC 8371b4fb1155b71f4a04d3e1bc3e18c4a990aeeb 0\r\n
+```
 
 ### Tests
 
@@ -39,13 +40,13 @@ The tester will execute your program like this:
 ./your_program.sh --port <PORT>
 ```
 
-It'll then connect to your TCP server as a replica and execute the following commands:
+It will then connect to your TCP server as a replica and send the following commands:
 
-1. `PING` (expecting `+PONG\r\n` back)
-2. `REPLCONF listening-port <PORT>` (expecting `+OK\r\n` back)
-3. `REPLCONF capa eof capa psync2` (expecting `+OK\r\n` back)
-4. `PSYNC ? -1` (expecting `+FULLRESYNC <REPL_ID> 0\r\n` back)
+1. `PING` - expecting `+PONG\r\n` back
+2. `REPLCONF listening-port <PORT>` - expecting `+OK\r\n` back
+3. `REPLCONF capa psync2` - expecting `+OK\r\n` back
+4. `PSYNC ? -1` - expecting `+FULLRESYNC <REPL_ID> 0\r\n` back
 
 **Notes**:
 
-- In the response, `<REPL_ID>` needs to be replaced with the replication ID of the master which you've initialized in previous stages.
+- In the response, `<REPL_ID>` needs to be replaced with the replication ID of the master, which you've initialized in previous stages.