ensures blocks are devisable by number of slots

codex/slotbuilder/slotbuilder.nim

@@ -1,4 +1,6 @@
 import pkg/libp2p
+import pkg/questionable/results
+import pkg/codex/blocktype as bt
 import ../blocktype
 import ../stores
 import ../manifest
@@ -7,16 +9,27 @@ type
   SlotBuilder* = object of RootObj
     blockStore: BlockStore
     manifest: Manifest
+    numberOfSlotBlocks: int
 
 proc new*(
     T: type SlotBuilder,
     blockStore: BlockStore,
     manifest: Manifest
-): SlotBuilder =
-  SlotBuilder(
-    blockStore: blockStore,
-    manifest: manifest
-  )
+): ?!SlotBuilder =
 
-proc getSlotBlockCids*(self: SlotBuilder, datasetSlotIndex: uint64): seq[Cid] =
+  if not manifest.protected:
+    return failure("Can only create SlotBuilder using protected manifests.")
+
+  if (manifest.blocksCount mod manifest.ecK) != 0:
+    return failure("Number of blocks must be devisable by number of slots.")
+
+  let numberOfSlotBlocks = manifest.blocksCount div manifest.ecK
+  success(SlotBuilder(
+    blockStore: blockStore,
+    manifest: manifest,
+    numberOfSlotBlocks: numberOfSlotBlocks
+  ))
+
+proc getSlotBlocks*(self: SlotBuilder, datasetSlotIndex: uint64): seq[bt.Block] =
   raiseAssert("a")
+

tests/codex/slotbuilder/testslotbuilder.nim

@@ -9,6 +9,7 @@ import pkg/codex/chunker
 import pkg/codex/merkletree
 
 import ../helpers
+import ../examples
 
 import codex/slotbuilder/slotbuilder
 
@@ -62,7 +63,31 @@ asyncchecksuite "Slot builder":
   setup:
     await createBlocks()
     await createProtectedManifest()
-    slotBuilder = SlotBuilder.new(localStore, protectedManifest)
+    slotBuilder = SlotBuilder.new(localStore, protectedManifest).tryGet()
+
+  test "Can only create slotBuilder with protected manifest":
+    let unprotectedManifest = Manifest.new(
+      treeCid = Cid.example,
+      blockSize = blockSize.NBytes,
+      datasetSize = datasetSize.NBytes)
+
+    check:
+      SlotBuilder.new(localStore, unprotectedManifest).isErr
+
+  test "Number of blocks must be devisable by number of slots":
+    let mismatchManifest = Manifest.new(
+      manifest = Manifest.new(
+        treeCid = Cid.example,
+        blockSize = blockSize.NBytes,
+        datasetSize = datasetSize.NBytes),
+      treeCid = Cid.example,
+      datasetSize = datasetSize.NBytes,
+      ecK = numberOfSlots - 1,
+      ecM = 0
+    )
+
+    check:
+      SlotBuilder.new(localStore, mismatchManifest).isErr
 
   for i in 0 ..< numberOfSlots:
     test "Can get the protected slot blocks given a slot index (" & $i & ")":
@@ -70,7 +95,7 @@ asyncchecksuite "Slot builder":
         selectStart = i * numberOfSlotBlocks
         selectEnd = selectStart + numberOfSlotBlocks
         expectedCids = datasetBlocks.mapIt(it.cid)[selectStart ..< selectEnd]
-        cids = slotBuilder.getSlotBlockCids(i.uint64)
+        blocks = slotBuilder.getSlotBlocks(i.uint64)
 
       check:
-        cids == expectedCids
+        blocks.mapIt(it.cid) == expectedCids