feat(rln-relay): metadata ffi api

tests/v2/waku_rln_relay/test_waku_rln_relay.nim

@@ -238,6 +238,36 @@ suite "Waku rln relay":
     check:
       rln.removeMember(MembershipIndex(0))
 
+  test "setMetadata rln utils":
+    # create an RLN instance which also includes an empty Merkle tree
+    let rlnInstance = createRLNInstance()
+    require:
+      rlnInstance.isOk()
+    let rln = rlnInstance.get()
+    check:
+      rln.setMetadata(RlnMetadata(lastProcessedBlock: 128)).isOk()
+
+  test "getMetadata rln utils":
+    # create an RLN instance which also includes an empty Merkle tree
+    let rlnInstance = createRLNInstance()
+    require:
+      rlnInstance.isOk()
+    let rln = rlnInstance.get()
+
+    require:
+      rln.setMetadata(RlnMetadata(lastProcessedBlock: 128)).isOk()
+
+    let metadataRes = rln.getMetadata()
+
+    require:
+      metadataRes.isOk()
+
+    let metadata = metadataRes.get()
+
+    check:
+      metadata.lastProcessedBlock == 128
+
+
   test "Merkle tree consistency check between deletion and insertion":
     # create an RLN instance
     let rlnInstance = createRLNInstance()

waku/v2/waku_rln_relay/rln/rln_interface.nim

@@ -175,3 +175,16 @@ proc poseidon*(input_buffer: ptr Buffer,
 ## inputs_buffer holds the hash input as a byte seq
 ## the hash output is generated and populated inside output_buffer
 ## the output_buffer contains 32 bytes hash output
+
+#-------------------------------- Persistent Metadata utils -------------------------------------------
+
+proc set_metadata*(ctx: ptr RLN, input_buffer: ptr Buffer): bool {.importc: "set_metadata".}
+## sets the metadata stored by ctx to the value passed by input_buffer
+## the input_buffer holds a serialized representation of the metadata (format to be defined)
+## input_buffer holds the metadata as a byte seq
+## the return bool value indicates the success or failure of the operation
+
+proc get_metadata*(ctx: ptr RLN, output_buffer: ptr Buffer): bool {.importc: "get_metadata".}
+## gets the metadata stored by ctx and populates the passed pointer output_buffer with it
+## the output_buffer holds the metadata as a byte seq
+## the return bool value indicates the success or failure of the operation

waku/v2/waku_rln_relay/rln/wrappers.nim

@@ -346,3 +346,46 @@ proc getMerkleRoot*(rlnInstance: ptr RLN): MerkleNodeResult =
 
   var rootValue = cast[ptr MerkleNode] (root.`ptr`)[]
   return ok(rootValue)
+
+type
+  RlnMetadata* = object
+    lastProcessedBlock*: uint64
+
+proc serialize(metadata: RlnMetadata): seq[byte] =
+  ## serializes the metadata
+  ## returns the serialized metadata
+  return @(metadata.lastProcessedBlock.toBytes())
+
+proc setMetadata*(rlnInstance: ptr RLN, metadata: RlnMetadata): RlnRelayResult[void] =
+  ## sets the metadata of the RLN instance
+  ## returns an error if the metadata could not be set
+  ## returns void if the metadata is set successfully
+
+  # serialize the metadata
+  let metadataBytes = serialize(metadata)
+  var metadataBuffer = metadataBytes.toBuffer()
+  let metadataBufferPtr = addr metadataBuffer
+
+  # set the metadata
+  let metadataSet = set_metadata(rlnInstance, metadataBufferPtr)
+  if not metadataSet:
+    return err("could not set the metadata")
+  return ok()
+
+proc getMetadata*(rlnInstance: ptr RLN): RlnRelayResult[RlnMetadata] =
+  ## gets the metadata of the RLN instance
+  ## returns an error if the metadata could not be retrieved
+  ## returns the metadata if the metadata is retrieved successfully
+
+  # read the metadata
+  var
+    metadata {.noinit.}: Buffer = Buffer()
+    metadataPtr = addr(metadata)
+    getMetadataSuccessful = get_metadata(rlnInstance, metadataPtr)
+  if not getMetadataSuccessful:
+    return err("could not get the metadata")
+  if not metadata.len == 8:
+    return err("wrong output size")
+
+  var metadataValue = cast[ptr uint64] (metadata.`ptr`)[]
+  return ok(RlnMetadata(lastProcessedBlock: metadataValue))