Command Processing #yg4

jason-gill00 · December 11, 2024, 4:43am

I’m stuck on Stage #yg4

Not entirely sure how this stage differs from the previous two stages (#zn8, #hd5). But am encountering an error when running the tests. What am I missing?

Here are my logs:

remote: Debug = true
remote:
remote: [tester::#YG4] Running tests for Stage #YG4 (Replication - Command Processing)
remote: [tester::#YG4] Master is running on port 6379
remote: [tester::#YG4] $ ./your_program.sh --port 6380 --replicaof "localhost 6379"
remote: [tester::#YG4] [handshake] master: Waiting for replica to initiate handshake with "PING" command
remote: [tester::#YG4] [handshake] master: Received bytes: "*1\r\n$4\r\nPING\r\n"
remote: [tester::#YG4] [handshake] master: Received RESP array: ["PING"]
remote: [tester::#YG4] [handshake] Received ["PING"]
remote: [tester::#YG4] [handshake] master: Sent "PONG"
remote: [tester::#YG4] [handshake] master: Sent bytes: "+PONG\r\n"
remote: [tester::#YG4] [handshake] master: Waiting for replica to send "REPLCONF listening-port 6380" command
remote: [tester::#YG4] [handshake] master: Received bytes: "*3\r\n$8\r\nREPLCONF\r\n$14\r\nlistening-port\r\n$4\r\n6380\r\n"
remote: [tester::#YG4] [handshake] master: Received RESP array: ["REPLCONF", "listening-port", "6380"]
remote: [tester::#YG4] [handshake] Received ["REPLCONF", "listening-port", "6380"]
remote: [tester::#YG4] [handshake] master: Sent "OK"
remote: [tester::#YG4] [handshake] master: Sent bytes: "+OK\r\n"
remote: [tester::#YG4] [handshake] master: Waiting for replica to send "REPLCONF capa" command
remote: [tester::#YG4] [handshake] master: Received bytes: "*3\r\n$8\r\nREPLCONF\r\n$4\r\ncapa\r\n$6\r\npsync2\r\n"
remote: [tester::#YG4] [handshake] master: Received RESP array: ["REPLCONF", "capa", "psync2"]
remote: [tester::#YG4] [handshake] Received ["REPLCONF", "capa", "psync2"]
remote: [tester::#YG4] [handshake] master: Sent "OK"
remote: [tester::#YG4] [handshake] master: Sent bytes: "+OK\r\n"
remote: [tester::#YG4] [handshake] master: Waiting for replica to send "PSYNC" command
remote: [tester::#YG4] [handshake] master: Received bytes: "*3\r\n$5\r\nPSYNC\r\n$1\r\n?\r\n$2\r\n-1\r\n"
remote: [tester::#YG4] [handshake] master: Received RESP array: ["PSYNC", "?", "-1"]
remote: [tester::#YG4] [handshake] Received ["PSYNC", "?", "-1"]
remote: [tester::#YG4] [handshake] master: Sent "FULLRESYNC 75cd7bc10c49047e0d163660f3b90625b1af31dc 0"
remote: [tester::#YG4] [handshake] master: Sent bytes: "+FULLRESYNC 75cd7bc10c49047e0d163660f3b90625b1af31dc 0\r\n"
remote: [tester::#YG4] [handshake] Sending RDB file...
remote: [tester::#YG4] [handshake] master: Sent bytes: "$88\r\nREDIS0011\xfa\tredis-ver\x057.2.0\xfa\nredis-bits\xc0@\xfa\x05ctime\xc2m\b\xbce\xfa\bused-mem°\xc4\x10\x00\xfa\baof-base\xc0\x00\xff\xf0n;\xfe\xc0\xffZ\xa2"
remote: [tester::#YG4] [handshake] Sent RDB file.
remote: [tester::#YG4] [propagation] master: > SET foo 123
remote: [tester::#YG4] [propagation] master: Sent bytes: "*3\r\n$3\r\nSET\r\n$3\r\nfoo\r\n$3\r\n123\r\n"
remote: [tester::#YG4] [propagation] master: > SET bar 456
remote: [tester::#YG4] [propagation] master: Sent bytes: "*3\r\n$3\r\nSET\r\n$3\r\nbar\r\n$3\r\n456\r\n"
remote: [tester::#YG4] [propagation] master: > SET baz 789
remote: [tester::#YG4] [propagation] master: Sent bytes: "*3\r\n$3\r\nSET\r\n$3\r\nbaz\r\n$3\r\n789\r\n"
remote: [tester::#YG4] [test] Getting key foo
remote: [tester::#YG4] [test] client: $ redis-cli GET foo
remote: [tester::#YG4] [test] client: Sent bytes: "*2\r\n$3\r\nGET\r\n$3\r\nfoo\r\n"
remote: [your_program] 2024/12/11 04:40:58 INFO Received msg from chan info="*2\r\n$3\r\nGET\r\n$3\r\nfoo\r\n"
remote: [your_program] 2024/12/11 04:40:58 INFO No key found with key info="[GET foo]"
remote: [tester::#YG4] Received: "" (no content received)
remote: [tester::#YG4]            ^ error
remote: [tester::#YG4] Error: Expected start of a new RESP2 value (either +, -, :, $ or *)
remote: [your_program] 2024/12/11 04:40:58 ERROR error reading from connection err="read tcp [::1]:6380->[::1]:50442: read: connection reset by peer"
remote: [your_program] 2024/12/11 04:40:58 ERROR error reading from connection err=EOF
remote: [tester::#YG4] Test failed
remote: [tester::#YG4] Terminating program
remote: [tester::#YG4] Program terminated successfully
remote:
remote: View our article on debugging test failures: https://codecrafters.io/debug

And here’s a snippet of my code:

andy1li · December 11, 2024, 5:00am

Hi @jason-gill00, here’s the difference:

Stage
Single-replica propagation #zn8	Your code functions as the master
Multi Replica Command Propagation #hd5	Your code functions as the master
Command Processing #yg4	Your code functions as a replica

jason-gill00 · December 11, 2024, 5:28am

Still not following. In #zn8, it mentions propagating the SET commands from the master to the replica and that the replica should be able to update it’s state. Is that now what’s this stage is asking for?

To test locally, I started the master and replica. Sent SET commands to the master and validated that the replica was updating it’s state by doing: redis-cli -p 3800 GET key (3800 is the port the replica is running on)

Is this not the correct way to test this stage (outside of just running the tests)

andy1li · December 11, 2024, 5:39am

Still not following. In #zn8, it mentions propagating the SET commands from the master to the replica and that the replica should be able to update it’s state. Is that now what’s this stage is asking for?

Yes, in #zn8 your code acted as the master, while the replica was provided by us. In #yg4, it’s your turn to implement the replica.

To test locally, I started the master and replica. Sent SET commands to the master and validated that the replica was updating it’s state by doing: redis-cli -p 3800 GET key (3800 is the port the replica is running on)

Is this not the correct way to test this stage (outside of just running the tests)

That sounds like a valid approach to test locally. If you’d like, I can take a look at your code to help identify any potential issues.

jason-gill00 · December 11, 2024, 5:53am

Yea, that would be very helpful. Thanks. Testing it locally using the method I mentioned seems to be working just fine, so not sure why the tests aren’t passing.

Ah ok. I misunderstood #yg4. In that stage I implemented the replica aswell

andy1li · December 11, 2024, 6:40am

The issue might be related to InitiateHandshake, where most of the responses are not verified. We cannot assume that exactly one command will be read from a connection..

For example, the empty RDB file from the master could slip through and cause troubles.

Additionally, the tests for Stage #VM3 (Replication - Receive handshake (2/2) are failing.

jason-gill00 · December 15, 2024, 7:01pm

I updated my InitateHandshake fn and still can’t quite get this stage to work. What do you mean exactly by the responses are not verified. I fixed my implementation and the previous stages should be passing now

andy1li · December 15, 2024, 8:13pm

I ran your latest code, and it seems to pass the previous stages now!

Could you confirm if your code can handle these scenarios:

Properly processing the RDB file sent by the master.
Handling multiple commands within a single read operation.

What do you mean exactly by the responses are not verified.

Oh, I meant that the responses from the commands below are not being verified.

The responses are simply printed out, but there’s no actual verification to ensure they’re correct:

fmt.Printf("Received response from master: %s\n", string(response[:n]))

jason-gill00 · December 18, 2024, 3:24am

Still stuck on this step. I updated my implementation to validate the responses in the handshake.

How should the replica process the RDB file sent by the master? I don’t think that step was mentioned in the previous stages (as the mentioned RDB file is empty)

My code should handle multiple commands, but not following what you mean by handling multiple commands within a single read operation. Can you clarify?

andy1li · December 21, 2024, 9:44pm

How should the replica process the RDB file sent by the master?

Your code can safely ignore the RDB file since it’s empty. Just make sure it’s skipping the correct number of bytes (88 in this case).

My code should handle multiple commands

Yes, it seems to be working in this respect.

I ran the latest version of your code. It’s no longer passing the #YZ1 (Expiry) stage.

Suggestions:

Use our CLI to test against previous stages by running:

codecrafters test --previous

Focus on fixing the early stages first, as later stages depend on them.

system · December 28, 2024, 12:20am

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