Nim wrappers for Rln lib (Key and Params generation) (#373)

* adds the initial rln.nim wrapper

* adds test_rln_wrapper

* WIP: initial test (not working)

* changes RLNBn256 data type

* updates parameters type

* adds the wrappers and fixes the bugs

* adds tests

* replaces echo with debug

tests/v2/test_rln_relay_wrappers.nim

@@ -0,0 +1,50 @@
+{.used.}
+
+import
+  std/[unittest],
+  stew/byteutils,
+  chronicles,
+  ../../waku/v2/protocol/waku_rln_relay/rln  
+
+suite "Waku rln relay":
+  test "rln lib: Keygen Nim Wrappers":
+    var 
+      merkleDepth: csize_t = 32
+      # parameters.key contains the parameters related to the Poseidon hasher
+      # to generate this file, clone this repo https://github.com/kilic/rln 
+      # and run the following command in the root directory of the cloned project
+      # cargo run --example export_test_keys
+      # the file is generated separately and copied here
+      parameters = readFile("waku/v2/protocol/waku_rln_relay/parameters.key")
+      pbytes = parameters.toBytes()
+      len : csize_t = uint(pbytes.len)
+      parametersBuffer = Buffer(`ptr`: unsafeAddr(pbytes[0]), len: len)
+    check:
+      # check the parameters.key is not empty
+      pbytes.len != 0
+
+    # ctx holds the information that is going to be used for  the key generation
+    var 
+      obj = RLNBn256()
+      objPtr = unsafeAddr(obj)
+      ctx = objPtr
+    let res = newCircuitFromParams(merkleDepth, unsafeAddr parametersBuffer, ctx)
+    check:
+      # check whether the circuit parameters are generated successfully
+      res == true
+
+    # keysBufferPtr will hold the generated key pairs i.e., secret and public keys 
+    var 
+      keysBufferPtr : Buffer
+      done = keyGen(ctx, keysBufferPtr) 
+    check:
+      # check whether the keys are generated successfully
+      done == true
+
+    if done:
+      var generatedKeys = cast[ptr array[64, byte]](keysBufferPtr.`ptr`)[]
+      check:
+        # the public and secret keys together are 64 bytes
+        generatedKeys.len == 64
+      debug "generated keys: ", generatedKeys 
+    

waku/v2/protocol/waku_rln_relay/rln.nim

@@ -0,0 +1,68 @@
+# this module contains the Nim wrappers for the rln library https://github.com/kilic/rln/blob/3bbec368a4adc68cd5f9bfae80b17e1bbb4ef373/src/ffi.rs
+
+import stew/byteutils, os
+from strutils import rsplit
+
+template sourceDir: string = currentSourcePath.rsplit(DirSep, 1)[0]
+# librln.dylib is the binary executable of rln library (originally implemented in rust with an exposed C API)  
+# contains the key generation and other relevant functions
+# to generate librln.dylib, clone this repo https://github.com/kilic/rln 
+# and run the following command in the root directory of the cloned project
+# cargo build
+# can find the .dylib file under the target/debug directory
+# this file is already generated and copied here
+const libName* = sourceDir / "librln.dylib" # TODO may need to load different libs based on OS
+
+# Data types -----------------------------
+
+# pub struct Buffer {
+#     pub ptr: *const u8,
+#     pub len: usize,
+# }
+
+type
+  Buffer* = object
+    `ptr`*: pointer
+    len*: csize_t
+  RLNBn256* = object
+
+# Procedures ------------------------------
+ # all the following procedures are Nim wrappers for the functions defined in libName
+{.push dynlib: libName.}
+
+# pub extern "C" fn new_circuit_from_params(
+#     merkle_depth: usize,
+#     index: usize,
+#     parameters_buffer: *const Buffer,
+#     ctx: *mut *mut RLN<Bn256>,
+# ) -> bool
+proc newCircuitFromParams*(merkle_depth: csize_t, parameters_buffer: ptr Buffer, ctx: var  ptr RLNBn256): bool{.importc: "new_circuit_from_params".}
+
+# pub extern "C" fn key_gen(ctx: *const RLN<Bn256>, keypair_buffer: *mut Buffer) -> bool
+proc keyGen*(ctx: ptr RLNBn256, keypair_buffer: var Buffer): bool {.importc: "key_gen".}
+
+
+# pub extern "C" fn hash(
+#     ctx: *const RLN<Bn256>,
+#     inputs_buffer: *const Buffer,
+#     input_len: *const usize,
+#     output_buffer: *mut Buffer,
+# ) -> bool 
+proc hash*(ctx: ptr RLNBn256, inputs_buffer:ptr Buffer, input_len: ptr csize_t, output_buffer: ptr Buffer ) {.importc: "hash".} #TODO not tested yet
+
+# pub extern "C" fn verify(
+#     ctx: *const RLN<Bn256>,
+#     proof_buffer: *const Buffer,
+#     public_inputs_buffer: *const Buffer,
+#     result_ptr: *mut u32,
+# ) -> bool
+
+
+
+# pub extern "C" fn generate_proof(
+#     ctx: *const RLN<Bn256>,
+#     input_buffer: *const Buffer,
+#     output_buffer: *mut Buffer,
+# ) -> bool
+
+{.pop.}