"Packet size mismatch!" on dropping mongodb collection

[gedaiu]

Any ideas on how can I fix this issue? It looks like it is a Driver problem:

/// test message error
unittest {
  auto client = connectMongoDB("127.0.0.1");
  auto chunks = client.getCollection("test.fs.chunks");

  chunks.drop;
}

throws:

core.exception.AssertError: Packet size mismatch! Expected 38 bytes, but read 20.
Stack trace:
-------------------
...
0xe058dc _d_assert_msg
0x74d7a4 @safe int vibe.db.mongo.connection.MongoConnection.recvMsg!(true).recvMsg(int, scope void delegate(uint, vibe.data.bson.Bson) @safe, scope void delegate(scope const(char)[], int) @safe, scope void delegate(scope const(char)[], vibe.data.bson.Bson) @safe) (../vibe-d/mongodb/vibe/db/mongo/connection.d:788)
0x74f5bf @safe vibe.data.bson.Bson vibe.db.mongo.connection.MongoConnection.runCommandImpl!(vibe.data.bson.Bson, vibe.db.mongo.connection.MongoDriverException).runCommandImpl(immutable(char)[], vibe.data.bson.Bson, bool, immutable(char)[], immutable(char)[], ulong) (../vibe-d/mongodb/vibe/db/mongo/connection.d:432)
0x74f451 @safe vibe.data.bson.Bson vibe.db.mongo.connection.MongoConnection.runCommand!(vibe.data.bson.Bson, vibe.db.mongo.connection.MongoDriverException).runCommand(immutable(char)[], vibe.data.bson.Bson, immutable(char)[], immutable(char)[], ulong) (../vibe-d/mongodb/vibe/db/mongo/connection.d:387)
0xc5488b @safe vibe.data.bson.Bson vibe.db.mongo.database.MongoDatabase.runCommandChecked!(vibe.db.mongo.collection.MongoCollection.drop().CMD, vibe.db.mongo.connection.MongoDriverException).runCommandChecked(vibe.db.mongo.collection.MongoCollection.drop().CMD, immutable(char)[], immutable(char)[], ulong) (../vibe-d/mongodb/vibe/db/mongo/database.d:160)
0xc3eef5 @safe void vibe.db.mongo.collection.MongoCollection.drop() (../vibe-d/mongodb/vibe/db/mongo/collection.d:1238)
0x964f8f void tests.crate.resources.gridfs.__unittest_L52_C1() (tests/crate/resources/gridfs.d:56)

mongo db logs:

{"t":{"$date":"2025-01-05T12:56:14.368+01:00"},"s":"I",  "c":"NETWORK",  "id":22943,   "ctx":"listener","msg":"Connection accepted","attr":{"remote":"127.0.0.1:38847","uuid":{"uuid":{"$uuid":"21e52944-2c9b-4cb0-896b-08886770842d"}},"connectionId":6,"connectionCount":1}}
{"t":{"$date":"2025-01-05T12:56:14.368+01:00"},"s":"I",  "c":"NETWORK",  "id":51800,   "ctx":"conn6","msg":"client metadata","attr":{"remote":"127.0.0.1:38847","client":"conn6","negotiatedCompressors":[],"doc":{"platform":"Digital Mars D 2.109","os":{"type":"linux","architecture":"x86_64 littleEndian"},"driver":{"version":"2.2.0","name":"vibe.db.mongo"}}}}
{"t":{"$date":"2025-01-05T12:56:14.368+01:00"},"s":"I",  "c":"NETWORK",  "id":6788700, "ctx":"conn6","msg":"Received first command on ingress connection since session start or auth handshake","attr":{"elapsedMillis":0}}
{"t":{"$date":"2025-01-05T12:56:14.368+01:00"},"s":"I",  "c":"COMMAND",  "id":518070,  "ctx":"conn6","msg":"CMD: drop","attr":{"namespace":"test.fs.chunks"}}
{"t":{"$date":"2025-01-05T12:56:14.393+01:00"},"s":"I",  "c":"NETWORK",  "id":22944,   "ctx":"conn6","msg":"Connection ended","attr":{"remote":"127.0.0.1:38847","uuid":{"uuid":{"$uuid":"21e52944-2c9b-4cb0-896b-08886770842d"}},"connectionId":6,"connectionCount":0}}

❯ mongod --version
db version v7.0.16
Build Info: {
    "version": "7.0.16",
    "gitVersion": "18b949444cfdaa88e30b0e10243bc18268251c1f",
    "openSSLVersion": "OpenSSL 3.2.2 4 Jun 2024",
    "modules": [],
    "allocator": "tcmalloc",
    "environment": {
        "distmod": "rhel90",
        "distarch": "x86_64",
        "target_arch": "x86_64"
    }
}

[gedaiu]

@WebFreak001 @s-ludwig, do you have any thoughts on how I can fix this issue?

[WebFreak001]

vibe.d/mongodb/vibe/db/mongo/connection.d

Line 786 in 1dffb74

assert(bytes_read + msglen == m_bytesRead,

seems to be a malformed packet

1. this shouldn't be an assert but an exception/enforce
2. the packet format is defined here: https://github.com/mongodb/specifications/blob/ce35696db1c8da0e15a067b8022c853f1d6d1292/source/message/OP_MSG.md

I think the while code is wrong, instead of
while (m_bytesRead - bytes_read < sectionLength) {
it should probably be
while (m_bytesRead - bytes_read < msglen) {
or instead make the variable bytes_read (which has a bad name) start after all the flags, since that is what sectionLength calculates.

Feel free to try out that while loop instead and see if that fixes it.

If you open a PR, please also rename bytes_read, it's a bad variable name (it should be something like packet_start_index or similar, since it's a snapshot of where we were before reading anything from the packet to see if we read everything)

The sectionLength will most likely be obsolete and can be removed.