feat: add extractMetadata function

src/rln.ts

@@ -100,6 +100,14 @@ const shareYOffset = shareXOffset + 32;
 const nullifierOffset = shareYOffset + 32;
 const rlnIdentifierOffset = nullifierOffset + 32;
 
+export class ProofMetadata {
+  constructor(
+    public readonly nullifier: Uint8Array,
+    public readonly shareX: Uint8Array,
+    public readonly shareY: Uint8Array,
+    public readonly externalNullifier: Uint8Array
+  ) {}
+}
 export class Proof implements IRateLimitProof {
   readonly proof: Uint8Array;
   readonly merkleRoot: Uint8Array;
@@ -123,6 +131,16 @@ export class Proof implements IRateLimitProof {
       rlnIdentifierOffset
     );
   }
+
+  extractMetadata(): ProofMetadata {
+    const externalNullifier = poseidonHash(this.epoch, this.rlnIdentifier);
+    return new ProofMetadata(
+      this.nullifier,
+      this.shareX,
+      this.shareY,
+      externalNullifier
+    );
+  }
 }
 
 export function proofToBytes(p: IRateLimitProof): Uint8Array {