Backend(,Tests): avoid inconsistency ex if no inconsistency

This is the first part of a bugfix for issue 250 [1]. The exception
was misleading because it was not really an inconsistecy but rather
lacking availability.

[1] #250

src/GWallet.Backend.Tests/FaultTolerance.fs

@@ -546,6 +546,39 @@ type FaultTolerance() =
                                           |> ignore<int> )
         Assert.That(inconsistencyEx.Message, IsString.WhichContains "received: 4, consistent: 2, required: 3")
 
+    [<Test>]
+    member __.``should not throw inconsistency exception if received results is less than required``() =
+        let numberOfConsistentResponsesToBeConsideredSafe = 2u
+        let consistencyConfig =
+            SpecificNumberOfConsistentResponsesRequired numberOfConsistentResponsesToBeConsideredSafe |> Some
+        let settings = defaultSettingsForNoConsistencyNoParallelismAndNoRetries consistencyConfig
+
+        let someResult = 1
+
+        let aJob1 =
+            async { return someResult }
+        let aJob2 =
+            async { return raise SomeSpecificException }
+        let aJob3 =
+            async { return raise SomeSpecificException }
+
+        let func1,func2,func3 = serverWithNoHistoryInfoBecauseIrrelevantToThisTest "aJob1" aJob1,
+                                serverWithNoHistoryInfoBecauseIrrelevantToThisTest "aJob2" aJob2,
+                                serverWithNoHistoryInfoBecauseIrrelevantToThisTest "aJob3" aJob3
+
+        let client = FaultTolerantParallelClient<ServerDetails, SomeSpecificException>
+                         dummy_func_to_not_save_server_because_it_is_irrelevant_for_this_test
+
+        let notEngoughAvailableEx =
+            Assert.Throws<NotEnoughAvailableException>(fun _ ->
+                client.Query
+                    settings
+                    [ func1; func2; func3 ]
+                        |> Async.RunSynchronously
+                        |> ignore<int>
+            )
+        Assert.That(notEngoughAvailableEx.Message, IsString.WhichContains "received: 1, unavailable: 2, required: 2")
+
     [<Test>]
     member __.``using an average func instead of consistency``() =
         let job1 =

src/GWallet.Backend/FaultTolerantParallelClient.fs

@@ -10,22 +10,40 @@ open Fsdk
 
 open GWallet.Backend.FSharpUtil.UwpHacks
 
-type ResourcesUnavailabilityException (message: string, innerOrLastException: Exception) =
-    inherit Exception (message, innerOrLastException)
+type ResourcesUnavailabilityException =
+    inherit Exception
+
+    new(message: string, innerException: Exception) = { inherit Exception(message, innerException) }
+    new(message: string) = { inherit Exception(message) }
 
 type private TaskUnavailabilityException (message: string, innerException: Exception) =
     inherit ResourcesUnavailabilityException (message, innerException)
 
-type private ServersUnavailabilityException (message: string, lastException: Exception) =
-    inherit ResourcesUnavailabilityException (message, lastException)
+type ServersUnavailabilityException =
+    inherit ResourcesUnavailabilityException
+
+    new(message: string, innerException: Exception) = { inherit ResourcesUnavailabilityException(message, innerException) }
+    new(message: string) = { inherit ResourcesUnavailabilityException(message) }
 
 type private NoneAvailableException (message:string, lastException: Exception) =
     inherit ServersUnavailabilityException (message, lastException)
 
-type private NotEnoughAvailableException (message:string, lastException: Exception) =
-    inherit ServersUnavailabilityException (message, lastException)
+type NotEnoughAvailableException =
+    inherit ServersUnavailabilityException
+
+    new (message: string, innerException: Exception) =
+        { inherit ServersUnavailabilityException (message, innerException) }
+    new (totalNumberOfSuccesfulResultsObtained: uint32,
+         numberOfServersUnavailable: uint32,
+         numberOfConsistentResultsRequired: uint32) =
+        { inherit ServersUnavailabilityException ("Results obtained were not enough to be considered consistent" +
+                                                      SPrintF3 " (received: %i, unavailable: %i, required: %i)"
+                                                          totalNumberOfSuccesfulResultsObtained
+                                                          numberOfServersUnavailable
+                                                          numberOfConsistentResultsRequired)
+        }
 
-type ResultInconsistencyException (totalNumberOfSuccesfulResultsObtained: int,
+type ResultInconsistencyException (totalNumberOfSuccesfulResultsObtained: uint32,
                                    maxNumberOfConsistentResultsObtained: int,
                                    numberOfConsistentResultsRequired: uint32) =
   inherit Exception ("Results obtained were not enough to be considered consistent" +
@@ -591,7 +609,8 @@ type FaultTolerantParallelClient<'K,'E when 'K: equality and 'K :> ICommunicatio
                                           retriesForInconsistency
                                           cancellationSource
             else
-                let totalNumberOfSuccesfulResultsObtained = executedServers.SuccessfulResults.Length
+                let totalNumberOfSuccesfulResultsObtained = uint executedServers.SuccessfulResults.Length
+                let totalNumberOfUnavailableServers = uint failedFuncs.Length
 
                 // HACK: we do this as a quick fix wrt new OneServerConsistentWithCertainValueOrTwoServers setting, but we should
                 // (TODO) rather throw a specific overload of ResultInconsistencyException about this mode being used
@@ -609,9 +628,18 @@ type FaultTolerantParallelClient<'K,'E when 'K: equality and 'K :> ICommunicatio
                         return failwith "resultsSoFar.Length != 0 but MeasureConsistency returns None, please report this bug"
                     | (_,maxNumberOfConsistentResultsObtained)::_ ->
                         if (retriesForInconsistency = settings.NumberOfRetriesForInconsistency) then
-                            return raise (ResultInconsistencyException(totalNumberOfSuccesfulResultsObtained,
-                                                                       maxNumberOfConsistentResultsObtained,
-                                                                       numberOfConsistentResponsesRequired))
+                            if totalNumberOfSuccesfulResultsObtained >= numberOfConsistentResponsesRequired then
+                                return raise (ResultInconsistencyException(totalNumberOfSuccesfulResultsObtained,
+                                                                           maxNumberOfConsistentResultsObtained,
+                                                                           numberOfConsistentResponsesRequired))
+                            else
+                                return
+                                    raise
+                                    <| NotEnoughAvailableException(
+                                            totalNumberOfSuccesfulResultsObtained,
+                                            totalNumberOfUnavailableServers,
+                                            numberOfConsistentResponsesRequired
+                                    )
                         else
                             return! QueryInternalImplementation
                                                   settings