feat(batch15): complete group 6 msgblock/consumerfilestore

dotnet/src/ZB.MOM.NatsNet.Server/JetStream/StoreEnumExtensions.cs

@@ -1,4 +1,5 @@
 using System.Text.Json;
+using IronSnappy;
 
 namespace ZB.MOM.NatsNet.Server;
 
@@ -51,4 +52,38 @@ public static class StoreEnumExtensions
         ArgumentNullException.ThrowIfNull(b);
         UnmarshalJSON(ref alg, b.AsSpan());
     }
+
+    public static (byte[]? Buffer, Exception? Error) Compress(this StoreCompression alg, byte[] buf)
+    {
+        ArgumentNullException.ThrowIfNull(buf);
+
+        const int checksumSize = FileStoreDefaults.RecordHashSize;
+        if (buf.Length < checksumSize)
+            return (null, new InvalidDataException("uncompressed buffer is too short"));
+
+        return alg switch
+        {
+            StoreCompression.NoCompression => (buf, null),
+            StoreCompression.S2Compression => CompressS2(buf, checksumSize),
+            _ => (null, new InvalidOperationException("compression algorithm not known")),
+        };
+    }
+
+    private static (byte[]? Buffer, Exception? Error) CompressS2(byte[] buf, int checksumSize)
+    {
+        try
+        {
+            var bodyLength = buf.Length - checksumSize;
+            var compressedBody = Snappy.Encode(buf.AsSpan(0, bodyLength));
+
+            var output = new byte[compressedBody.Length + checksumSize];
+            Buffer.BlockCopy(compressedBody, 0, output, 0, compressedBody.Length);
+            Buffer.BlockCopy(buf, bodyLength, output, compressedBody.Length, checksumSize);
+            return (output, null);
+        }
+        catch (Exception ex)
+        {
+            return (null, new IOException("error writing to compression writer", ex));
+        }
+    }
 }