adding minimal RS 2D tests

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>

tests/codex/testerasure2d.nim

@@ -0,0 +1,94 @@
+import std/sequtils
+from std/math import sqrt
+
+import pkg/asynctest
+import pkg/chronos
+import pkg/libp2p
+import pkg/questionable/results
+
+import pkg/codex/erasure
+import pkg/codex/manifest
+import pkg/codex/stores
+import pkg/codex/blocktype as bt
+import pkg/codex/rng
+
+import ./helpers
+
+suite "2D Erasure encode/decode":
+
+  const BlockSize = 1024
+  const dataSetSize = BlockSize * 123
+
+  var rng: Rng
+  var chunker: Chunker
+  var manifest: Manifest
+  var store: BlockStore
+  var erasure: Erasure
+
+  setup:
+    rng = Rng.instance()
+    chunker = RandomChunker.new(rng, size = dataSetSize, chunkSize = BlockSize)
+    manifest = !Manifest.new(blockSize = BlockSize)
+    store = CacheStore.new(cacheSize = (dataSetSize * 2), chunkSize = BlockSize)
+    erasure = Erasure.new(store, leoEncoderProvider2D, leoDecoderProvider2D)
+
+    while (
+      let chunk = await chunker.getBytes();
+      chunk.len > 0):
+
+      let blk = bt.Block.new(chunk).tryGet()
+      manifest.add(blk.cid)
+      (await store.putBlock(blk)).tryGet()
+
+  proc encode(buffers, parity: int): Future[Manifest] {.async.} =
+    let
+      encoded = (await erasure.encode(
+        manifest,
+        buffers,
+        parity)).tryGet()
+
+    check:
+      encoded.len mod (buffers + parity) == 0
+      encoded.rounded == manifest.len - 1 + buffers - (manifest.len - 1) mod buffers
+      encoded.steps == encoded.rounded div buffers
+
+    echo(manifest.blocks)
+    echo(encoded.blocks)
+
+    return encoded
+
+  test "Should tolerate losing M1 data blocks in a single random column":
+    const
+      k1 = 3
+      k2 = k1
+      m1 = 1
+      m2 = m1
+      buffers = k1 * k2
+      parity = (k1+m1) * (k2+m2) - buffers
+
+    echo "encode"
+
+    let encoded = await encode(buffers, parity)
+
+    var
+      column = rng.rand(encoded.steps - 1) # random column
+      dropped: seq[Cid]
+
+    echo ("steps", encoded.steps)
+    for _ in 0 ..< m1:
+      echo ("column", column)
+      dropped.add(encoded[column])
+      (await store.delBlock(encoded[column])).tryGet()
+      column.inc(encoded.steps)
+
+    var
+      decoded = (await erasure.decode(encoded, parity + buffers - dropped.len)).tryGet()
+
+    check:
+      decoded.cid.tryGet() == manifest.cid.tryGet()
+      decoded.cid.tryGet() == encoded.originalCid
+      decoded.len == encoded.originalLen
+
+    for d in dropped:
+      let present = await store.hasBlock(d)
+      check present.tryGet()