9fdc931ff5
Implements binary codec for meta-group snapshots: 2-byte little-endian version header followed by S2-compressed JSON of the stream assignment map. Adds [JsonObjectCreationHandling(Populate)] to StreamAssignment.Consumers so the getter-only dictionary is populated in-place during deserialization. 8 tests covering round-trip, compression ratio, field fidelity, multi-consumer restore, version rejection, and truncation guard. Go reference: jetstream_cluster.go:2075-2145 (encodeMetaSnapshot/decodeMetaSnapshot)
61 lines
2.5 KiB
C#
61 lines
2.5 KiB
C#
using System.Buffers.Binary;
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using System.Text.Json;
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using NATS.Server.JetStream.Storage;
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namespace NATS.Server.JetStream.Cluster;
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/// <summary>
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/// Binary codec for meta-group snapshots.
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/// Format: [2:version_le][N:S2-compressed JSON of assignment map]
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/// Go reference: jetstream_cluster.go:2075-2145 (encodeMetaSnapshot/decodeMetaSnapshot)
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/// </summary>
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internal static class MetaSnapshotCodec
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{
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private const ushort CurrentVersion = 1;
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// Use Populate so the getter-only Consumers dictionary on StreamAssignment
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// is populated in-place by the deserializer rather than requiring a setter.
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// Go reference: jetstream_cluster.go streamAssignment consumers map restoration.
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private static readonly JsonSerializerOptions SerializerOptions = new()
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{
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PreferredObjectCreationHandling = System.Text.Json.Serialization.JsonObjectCreationHandling.Populate,
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};
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/// <summary>
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/// Encodes <paramref name="assignments"/> into the versioned, S2-compressed binary format.
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/// Go reference: jetstream_cluster.go:2075 encodeMetaSnapshot.
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/// </summary>
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public static byte[] Encode(Dictionary<string, StreamAssignment> assignments)
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{
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var json = JsonSerializer.SerializeToUtf8Bytes(assignments, SerializerOptions);
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var compressed = S2Codec.Compress(json);
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var result = new byte[2 + compressed.Length];
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BinaryPrimitives.WriteUInt16LittleEndian(result, CurrentVersion);
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compressed.CopyTo(result, 2);
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return result;
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}
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/// <summary>
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/// Decodes a versioned, S2-compressed binary snapshot into a stream assignment map.
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/// Go reference: jetstream_cluster.go:2100 decodeMetaSnapshot.
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/// </summary>
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/// <exception cref="InvalidOperationException">
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/// Thrown when <paramref name="data"/> is too short or contains an unrecognised version.
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/// </exception>
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public static Dictionary<string, StreamAssignment> Decode(byte[] data)
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{
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if (data.Length < 2)
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throw new InvalidOperationException("Meta snapshot too short to contain version header.");
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var version = BinaryPrimitives.ReadUInt16LittleEndian(data);
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if (version != CurrentVersion)
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throw new InvalidOperationException($"Unknown meta snapshot version: {version}");
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var compressed = data.AsSpan(2);
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var json = S2Codec.Decompress(compressed);
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return JsonSerializer.Deserialize<Dictionary<string, StreamAssignment>>(json, SerializerOptions)
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?? new Dictionary<string, StreamAssignment>();
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}
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}
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