Question about stage EG2 - Fetch Single message from Disk

rajneeshks · October 7, 2025, 7:30pm

I keep getting this error - what is that I am doing wrong?

[tester::#EG2] [tester::#EG2] [client] Idx | Hex [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [Decoder] [tester::#EG2] [tester::#EG2] Hex (bytes 137-144) [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [tester::#EG2] [your_program] received 0 bytes, closing this socket!!
#EG2] [client] Hexdump of received “Fetch” response:
| ASCII
[client] -----±------------------------------------------------±----------------
[client] 0000 | 00 00 00 91 29 fa 4f 2a 00 00 00 00 00 00 00 00 | …).O*…
[client] 0010 | 00 00 00 02 71 a5 9a 51 89 68 4f 8b 93 7e c5 2d | …q..Q.hO..~.-
[client] 0020 | 86 e0 e4 56 02 00 00 00 00 00 00 00 00 00 00 00 | …V…
[client] 0030 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | …
[client] 0040 | 00 00 00 00 00 00 00 00 02 00 00 00 00 00 00 00 | …
[client] 0050 | 00 00 00 00 3d 00 00 00 00 02 56 5c 25 ed 00 00 | …=…V%…
[client] 0060 | 00 00 00 00 00 00 01 91 e0 5b 6d 8b 00 00 01 91 | …[m…
[client] 0070 | e0 5b 6d 8b 00 00 00 00 00 00 00 00 00 00 00 00 | .[m…
[client] 0080 | 00 00 00 00 00 01 16 00 00 00 01 0a 61 70 70 6c | …appl
[client] 0090 | 65 01 00 00 00 | e…
[client]
[Decoder] - FetchResponse
- Header
- CorrelationID (704270122)
- Body
- ThrottleTimeMS (0)
- ErrorCode (0)
- SessionID (0)
- Topics
- Length (2 (Array length(1) + 1))
- Topics[0]
- UUID (71a59a51-8968-4f8b-937e-c52d86e0e456)
- Partitions
- Length (2 (Array length(1) + 1))
- Partitions[0]
- Id (0)
- ErrorCode (0)
- HighWaterMark (0)
- LastStableOffset (0)
- LogStartOffset (0)
- AbortedTransactions
- Length (0 (Null array))
- PreferredReadReplica (0)
- RecordBatches
- Size (2 (Record size(1) + 1))
- RecordBatches[0]
- Offset (0)
- Length (61)
- PartitionLeaderEpoch (0)
- MagicByte (2)
- CRC (1448879597)
- Attributes (0)
- LastOffsetDelta (0)
- FirstTimeStamp (1726045973899)
- MaxTimeStamp (1726045973899)
- ProducerID (0)
- ProducerEpoch (0)
- BaseSequence (0)
- Records
- Length (1)
- Records[0]
- Record
- Length (11)
- Attributes (0)
- TimestampDelta (0)
- OffsetDelta (0)
- KeyLength (-1)
- ValueLength (5)
- Value ([97 112 112 108 101] → UTF-8: (apple))
- HeadersLength (-1)
RecordBatches (decode error)
Received bytes:
| ASCII
------------------------------------------------±-----------------
70 70 6c 65 01 00 00 00 | pple…
^ ^
Expected recordbatches size to be 73, got 1
Test failed
Terminating program
> Program terminated successfully

andy1li · October 8, 2025, 1:35am

Hey @rajneeshks, could you upload your code to GitHub and share the link? It will be much easier to debug if I can run it directly.

rajneeshks · October 8, 2025, 3:48am

Hi @andy1li - uploaded to github:

Specific code block that manages the response:

github.com/saingarhia/codecrafters-kafka-rust

src/kafka/fetch.rs

5527d665d


      
              high_watermark: u64,
              last_stable_offset: u64,
              log_start_offset: u64,
              aborted_transactions: Vec<FetchResponseAbortedTransaction>,
              preferred_read_replica: u32,
              //records: Vec<records::RecordsBatch>,
              records: Vec<u8>,
              tag_buffer: u8,
          }
          
          impl FetchResponsePartition {
              fn new(topic_meta: &metadata::TopicMetadata, partition: u32) -> Self {
                  let aborted_transactions: Vec<FetchResponseAbortedTransaction> = vec![];
                  let log_file_name = format!(
                      "/tmp/kraft-combined-logs/{}-{}/00000000000000000000.log",
                      topic_meta.topic_name, partition
                  );
          
                  println!("***************** LOG FILE: {log_file_name} ********************");
                  let records = std::fs::read(log_file_name).unwrap();
                  println!("Read {} bytes from this file!", records.len());

andy1li · October 8, 2025, 3:16pm

@rajneeshks The issue is caused by the hardcoded RecordBatches size:

github.com/saingarhia/codecrafters-kafka-rust

src/kafka/fetch.rs

5527d665d


      
          // hard code 2 records for now
          writer::write_bytes(resp, &2_u8)?;

Please note that RecordBatches are of type COMPACT_RECORDS:

Let me know if you’d like further clarification!

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Question about stage EG2 - Fetch Single message from Disk

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