fix: checking for keystore file existence

tests/waku_rln_relay/test_rln_group_manager_onchain.nim

@@ -223,6 +223,13 @@ suite "Onchain group manager":
                                        rlnInstance: manager.rlnInstance)
     expect(ValueError): await manager2.init()
 
+  asyncTest "should error when keystore path and password are provided but file doesn't exist":
+    let manager = await setup()
+    manager.keystorePath = some("/inexistent/file")
+    manager.keystorePassword = some("password")
+
+    expect(CatchableError): await manager.init()
+
   asyncTest "startGroupSync: should start group sync":
     let manager = await setup()
 

waku/waku_rln_relay/group_manager/on_chain/group_manager.nim

@@ -4,6 +4,7 @@ else:
   {.push raises: [].}
 
 import
+  os,
   web3,
   web3/ethtypes,
   eth/keys as keys,
@@ -630,6 +631,10 @@ method init*(g: OnchainGroupManager): Future[void] {.async.} =
   g.registryContract = some(registryContract)
 
   if g.keystorePath.isSome() and g.keystorePassword.isSome():
+    if not existsFile(g.keystorePath.get()):
+      error "File provided as keystore path does not exist", path=g.keystorePath.get() 
+      raise newException(CatchableError, "missing keystore")
+
     var keystoreQuery = KeystoreMembership(
       membershipContract: MembershipContract(
         chainId: $g.chainId.get(),