OBJ Metadata Headers Json has the wrong format in the v2 Client.

[niklasfp]

Observed behavior

After upgrading some object store code from .net v1 to .net v2 client we run into serialization bugs related to headers.

When trying to get information from a file stored (with headers) from nats cli or nats.net v1 the nats v2 client throws a json serialization exception (see exception below)

Also objects with headers added from the .nats v2 client cannot be read by nats cli:

❯ nats obj info HeaderTest FromV2_txt
nats: error: nats: object-store meta information invalid

And listing the same bucket hangs in the cli

❯ nats obj ls HeaderTest

Exception thrown

System.Text.Json.JsonException
  HResult=0x80131500
  Message=The JSON value could not be converted to System.String. Path: $.headers.abcdef | LineNumber: 0 | BytePositionInLine: 260.
  Source=System.Text.Json
  StackTrace:
   at System.Text.Json.ThrowHelper.ReThrowWithPath(ReadStack& state, Utf8JsonReader& reader, Exception ex)
   at System.Text.Json.Serialization.JsonConverter`1.ReadCore(Utf8JsonReader& reader, JsonSerializerOptions options, ReadStack& state)
   at System.Text.Json.JsonSerializer.Read[TValue](Utf8JsonReader& reader, JsonTypeInfo`1 jsonTypeInfo)
   at NATS.Client.Core.NatsJsonContextSerializer`1.Deserialize(ReadOnlySequence`1& buffer)
   at NATS.Client.Core.NatsJsonContextSerializer`1.NATS.Client.Core.INatsDeserialize<T>.Deserialize(ReadOnlySequence`1& buffer)
   at NATS.Client.ObjectStore.NatsObjStore.<GetInfoAsync>d__21.MoveNext()
   at System.Threading.Tasks.ValueTask`1.get_Result()
   at Program.<<Main>$>d__0.MoveNext() in C:\Source\Repos\NatsConnect\NatsConnect\Program.cs:line 32
   at Program.<<Main>$>d__0.MoveNext() in C:\Source\Repos\NatsConnect\NatsConnect\Program.cs:line 32
   at Program.<<Main>$>d__0.MoveNext() in C:\Source\Repos\NatsConnect\NatsConnect\Program.cs:line 32

  This exception was originally thrown at this call stack:
    [External Code]

Inner Exception 1:
InvalidOperationException: Cannot get the value of a token type 'StartArray' as a string.

The problem is that .nats .net v2 just adds headers as dictionary, where other clients adds them as a dictionary with a string key and of array of string value.

Object meta from object added with nats cli:

{"name":"FromCli_txt","headers":{"abcdef":["123456"]},"options":{"max_chunk_size":131072},"bucket":"HeaderTest","nuid":"iR25m0SOVnMT9BRS0DSn65","size":15,"mtime":"0001-01-01T00:00:00Z","chunks":1,"digest":"SHA-256=krdyOAo_jiepPlfm3uymwB2gf1qtzni7L7sg3hCmaSU="}

Object meta from object added with nats v2 cli:

{"name":"FromV2_txt","description":null,"bucket":"HeaderTest","nuid":"YiKN4TbWcLFuKYk0XZ7Fhq","size":13,"mtime":"2024-03-29T11:24:59.8718469+00:00","chunks":1,"digest":"SHA-256=3_1gIbsr1bCvZ2KQgJ7DpTGR3YHH9wpLKGiKNiGCmG8=","headers":{"abcdef":"123456"},"options":{"max_chunk_size":131072}}

Expected behavior

Nats v2 client can read objects with metadata headers added from other clients.
Nats v2 client can add objects with metadata headers compatible with other clients.

Server and client version

Server: 2.10.12
Cli: v0.1.4

Host environment

Windows 11
Nast server running in docker

Steps to reproduce

Create a bucket for testing

nats obj add HeaderTest

Add an object with headers

 "Hello, World!" > nats obj put HeaderTest --name="FromCli_txt" -H "abcdef:123456"

Run the following csharp code to verify that it breaks.

using NATS.Client.Core;
using NATS.Client.JetStream;
using NATS.Client.ObjectStore;
using NATS.Client.ObjectStore.Models;

const string BucketName = "HeaderTest";
const string FromCliFileName = "FromCli_txt";
const string FromNatsV2FileName = "FromV2_txt";


await using var conn = new NatsConnection();

var storeContext = new NatsObjContext(new NatsJSContext(conn));
var store = await storeContext.GetObjectStoreAsync(BucketName);

var objMeta = new ObjectMetadata()
{
    Name = FromNatsV2FileName,
    Bucket = BucketName,
    Headers = new Dictionary<string, string>()
    {
        { "abcdef", "123456" }
    },

};

// Put object (puts object with headers bad json)
await using var stream = new MemoryStream("Hello, World!"u8.ToArray());
await store.PutAsync(objMeta, stream);

// Get object added from CLI (fails)
var info = await store.GetInfoAsync(FromCliFileName);

After running the csharp code, run the following cli command

nats obj info HeaderTest FromV2_txt

will fail with nats: error: nats: object-store meta information invalid

[mtmk]

thanks @niklasfp. Found the issue. as you probably guessed it was the Headers which ought to be string,string[] rather than string,string.

[niklasfp]

@mtmk when this is fixed and released, it might break for people that only used the v2 client to add headers to objects. Not a problem for us, our problem is that the headers are in the correct format (not v2 compatible) 😉

[mtmk]

yes it's going to be a breaking change unfortunately. as you said, if people have data (with headers) saved and used only with this client, data has to be migrated 😞