From 13762be958b8b007e858dea8679f1e5cf3702e79 Mon Sep 17 00:00:00 2001
From: webwarrior <reg@webwarrior.ws>
Date: Mon, 12 Aug 2024 11:12:53 +0200
Subject: [PATCH] Backend: handle null response from Eth server

Introduce WeirdNullResponseException type and raise it when
response for balance request for Ethereum returns json with
"result" field value of `null`. This way server will be marked
as faulty instead of crashing the application.

Fixes https://github.com/nblockchain/geewallet/issues/282
---
 src/GWallet.Backend/Ether/EtherExceptions.fs | 7 +++++++
 src/GWallet.Backend/Ether/EtherServer.fs     | 4 +++-
 src/GWallet.Backend/ServerManager.fs         | 4 ++++
 3 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/src/GWallet.Backend/Ether/EtherExceptions.fs b/src/GWallet.Backend/Ether/EtherExceptions.fs
index a08d73033..11c6c3fc1 100644
--- a/src/GWallet.Backend/Ether/EtherExceptions.fs
+++ b/src/GWallet.Backend/Ether/EtherExceptions.fs
@@ -95,3 +95,10 @@ type UnhandledWebException =
         }
     new (info: SerializationInfo, context: StreamingContext) =
         { inherit Exception (info, context) }
+
+/// Exception indicating that response JSON contains null value where it should not.
+/// E.g. {"jsonrpc":"2.0","id":1,"result":null}
+type AbnormalNullValueInJsonResponseException(message: string) =
+    inherit CommunicationUnsuccessfulException(message)
+
+    static member BalanceJobErrorMessage = "Abnormal null response from balance job"
diff --git a/src/GWallet.Backend/Ether/EtherServer.fs b/src/GWallet.Backend/Ether/EtherServer.fs
index 3e86bbb9f..acf2b915c 100644
--- a/src/GWallet.Backend/Ether/EtherServer.fs
+++ b/src/GWallet.Backend/Ether/EtherServer.fs
@@ -561,7 +561,9 @@ module Server =
                                 return! Async.AwaitTask task
                             }
                     if Object.ReferenceEquals(balance, null) then
-                        failwith "Weird null response from balance job"
+                        raise <| 
+                            AbnormalNullValueInJsonResponseException 
+                                AbnormalNullValueInJsonResponseException.BalanceJobErrorMessage
                     return UnitConversion.Convert.FromWei(balance.Value, UnitConversion.EthUnit.Ether)
                 }
                 GetRandomizedFuncs currency web3Func
diff --git a/src/GWallet.Backend/ServerManager.fs b/src/GWallet.Backend/ServerManager.fs
index 958ff3d6e..8dd56ef9e 100644
--- a/src/GWallet.Backend/ServerManager.fs
+++ b/src/GWallet.Backend/ServerManager.fs
@@ -128,6 +128,10 @@ module ServerManager =
                 let web3Func (web3: Ether.SomeWeb3): Async<decimal> =
                     async {
                         let! balance = Async.AwaitTask (web3.Eth.GetBalance.SendRequestAsync ETH_GENESISBLOCK_ADDRESS)
+                        if isNull balance then
+                            raise <| 
+                                Ether.AbnormalNullValueInJsonResponseException 
+                                    Ether.AbnormalNullValueInJsonResponseException.BalanceJobErrorMessage
                         return balance.Value |> decimal
                     }