add nim ffi and genffi build task

build.nims

@@ -0,0 +1,4 @@
+
+task genffi, "update the nim ffi bindings":
+    exec "cargo install --force nbindgen"
+    exec "nbindgen --crate codex-storage-proofs --output codex_proofs_ffi.nim"

codex_proofs_ffi.nim

@@ -0,0 +1,57 @@
+const EXT_ID_U256_BE* = 51
+
+const EXT_ID_U256_LE* = 50
+
+
+type StorageProofs* {.incompleteStruct.} = object
+
+type Buffer* = object
+  data: ptr uint8
+  len: uint
+
+type ProofCtx* = object
+  proof: Buffer
+  public_inputs: Buffer
+
+## # Safety
+#
+# Use on a valid pointer to ProofCtx or panics
+proc free_proof_ctx*(ctx: ptr ProofCtx) {.importc: "free_proof_ctx".}
+
+## # Safety
+#
+# Use on a valid pointer to StorageProofs or panics
+proc free_prover*(prover: ptr StorageProofs) {.importc: "free_prover".}
+
+## # Safety
+#
+# Construct a StorageProofs object
+proc init*(r1cs: ptr (ptr Buffer),
+           wasm: ptr (ptr Buffer),
+           zkey: ptr (ptr Buffer)): (ptr StorageProofs) {.importc: "init".}
+
+## # Safety
+#
+# Use after constructing a StorageProofs object with init
+proc prove*(prover_ptr: ptr StorageProofs,
+            chunks: ptr Buffer,
+            siblings: ptr Buffer,
+            hashes: ptr Buffer,
+            path: ptr int32,
+            path_len: uint,
+            pubkey: ptr Buffer,
+            root: ptr Buffer,
+            salt: ptr Buffer): (ptr ProofCtx) {.importc: "prove".}
+
+## # Safety
+#
+# Use after constructing a StorageProofs object with init
+proc prove_mpack_ext*(prover_ptr: ptr StorageProofs,
+                      args: ptr Buffer): (ptr ProofCtx) {.importc: "prove_mpack_ext".}
+
+## # Safety
+#
+# Should be called on a valid proof and public inputs previously generated by prove
+proc verify*(prover_ptr: ptr StorageProofs,
+             proof: ptr Buffer,
+             public_inputs: ptr Buffer): bool {.importc: "verify".}

codex_storage_proofs.nim

@@ -20,3 +20,5 @@ static:
 
 
 {.passl: "-lcodex_storage_proofs" & " -L" & libDir.}
+
+proc prove_mpack_ext()

codex_storage_proofs.nimble

@@ -7,3 +7,5 @@ srcDir        = "."
 # Dependencies
 
 requires "nim >= 1.6.14"
+
+include "build.nims"

config.nims

@@ -0,0 +1,2 @@
+
+include "build.nims"