ErasureStream

ErasureStream maps one fixed-length byte sequence onto k data streams and m parity streams using systematic Reed-Solomon coding. Members contain only encoded payload: no persistent header, journal, identity, or membership record.

Write and reopen

using TeeForge.ErasureCoding;

var options = new ErasureStreamOptions(leaveOpen: true);
await using (ErasureStream encoded = ErasureStream.Create(
    members, dataShardCount: 4, parityShardCount: 2,
    logicalLength: source.Length, blockSize: 128 * 1024, options))
{
    await source.CopyToAsync(encoded);
    await encoded.CompleteAsync();
}

await using ErasureStream decoded = ErasureStream.Open(
    members, 4, 2, source.Length, 128 * 1024, options);
await decoded.CopyToAsync(destination);

Keep member order, logical length, block size, and data/parity counts externally. For forward-only members, supply fresh readers positioned at payload byte zero. Seekable members are addressed from offset zero. Create truncates seekable writable members; use it only for outputs whose contents may be replaced.

Stream behavior

• Capabilities follow the available member capabilities.
• Ordinary reads/writes use logical Position. Positional operations preserve it; writes to the same codeword serialize.
• One codeword covers k * BlockSize logical bytes. Each member receives one BlockSize payload, including zero padding in the final codeword.
• The logical length is fixed; SetLength is unsupported.
• Forward-only writers must supply exactly the declared length and call CompleteAsync. This emits the final partial codeword and flushes members. Flush does not finalize a partial codeword; disposal does not replace completion.
• The stream owns members unless LeaveOpen is true. Open never initializes or truncates member contents.
• The cache budget controls retained entries. Active operations may temporarily require additional complete codewords, so bound caller concurrency as well.

RequireAllMembers defaults to true. For degraded reads, set it to false and supply a null at each missing member position. At least k readable members are required. Missing members make the stream read-only. Reed-Solomon recovers known missing members; this layout does not identify silently corrupted members.

Partial writes can succeed on some members and fail on others. There is no transactional recovery or safe automatic retry guarantee. Flush behavior is the behavior supplied by the underlying streams.

The default block size remains 128 KiB. Existing benchmark observations are historical evidence; changing defaults requires equivalent sampled comparisons under the benchmark policy.

Run the forward-only sample to encode, reopen, and recover with two missing members.