feat(server): harden hostile input and overload behavior (#15)

src/FinalFactory.Rendezvous.Server/Http/ContractEndpoints.cs

@@ -1,5 +1,6 @@
 using System.Net;
 using FinalFactory.Rendezvous.Contracts;
+using FinalFactory.Rendezvous.Server.Abuse;
 using FinalFactory.Rendezvous.Server.Browser;
 using FinalFactory.Rendezvous.Server.ConnectionOutcomes;
 using FinalFactory.Rendezvous.Server.JoinAttempts;
@@ -20,6 +21,7 @@ internal static class ContractEndpoints
             .Accepts<RegisterSessionRequest>("application/json")
             .Produces<RegisterSessionResponse>(StatusCodes.Status201Created)
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status413PayloadTooLarge)
             .Produces<ApiError>(StatusCodes.Status401Unauthorized)
             .Produces<ApiError>(StatusCodes.Status403Forbidden)
             .Produces<ApiError>(StatusCodes.Status409Conflict)
@@ -31,45 +33,54 @@ internal static class ContractEndpoints
             .Accepts<RenewLeaseRequest>("application/json")
             .Produces<RenewLeaseResponse>()
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status413PayloadTooLarge)
             .Produces<ApiError>(StatusCodes.Status401Unauthorized)
             .Produces<ApiError>(StatusCodes.Status403Forbidden)
             .Produces<ApiError>(StatusCodes.Status404NotFound)
             .Produces<ApiError>(StatusCodes.Status409Conflict)
             .Produces<ApiError>(StatusCodes.Status410Gone)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("RenewSessionLease");
         sessions.MapPut("/{listingId}", UpdateSession)
             .Accepts<UpdateSessionRequest>("application/json")
             .Produces(StatusCodes.Status204NoContent)
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status413PayloadTooLarge)
             .Produces<ApiError>(StatusCodes.Status401Unauthorized)
             .Produces<ApiError>(StatusCodes.Status403Forbidden)
             .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("UpdateSession");
         sessions.MapDelete("/{listingId}", DeleteSession)
             .Accepts<DeleteSessionRequest>("application/json")
             .Produces(StatusCodes.Status204NoContent)
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status413PayloadTooLarge)
             .Produces<ApiError>(StatusCodes.Status401Unauthorized)
             .Produces<ApiError>(StatusCodes.Status403Forbidden)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("DeleteSession");
         sessions.MapGet("/", BrowseSessions)
             .Produces<BrowseSessionsResponse>()
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("BrowseSessions");
         sessions.MapGet("/{listingId}", GetSession)
             .Produces<GetSessionResponse>()
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
             .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("GetSession");
         sessions.MapGet("/{listingId}/join-attempts", BrowseHostJoinAttempts)
             .Produces<BrowseHostJoinAttemptsResponse>()
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
             .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("BrowseHostJoinAttempts");
 
@@ -80,6 +91,7 @@ internal static class ContractEndpoints
             .Accepts<CreateJoinAttemptRequest>("application/json")
             .Produces<CreateJoinAttemptResponse>(StatusCodes.Status201Created)
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status413PayloadTooLarge)
             .Produces<ApiError>(StatusCodes.Status404NotFound)
             .Produces<ApiError>(StatusCodes.Status409Conflict)
             .Produces<ApiError>(StatusCodes.Status410Gone)
@@ -90,14 +102,17 @@ internal static class ContractEndpoints
             .Produces(StatusCodes.Status204NoContent)
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
             .Produces<ApiError>(StatusCodes.Status404NotFound)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("CancelJoinAttempt");
         attempts.MapPost("/{attemptId}/outcome", ReportConnectionOutcome)
             .Accepts<ReportConnectionOutcomeRequest>("application/json")
             .Produces<ReportConnectionOutcomeResponse>()
             .Produces<ApiError>(StatusCodes.Status400BadRequest)
+            .Produces<ApiError>(StatusCodes.Status413PayloadTooLarge)
             .Produces<ApiError>(StatusCodes.Status404NotFound)
             .Produces<ApiError>(StatusCodes.Status409Conflict)
+            .Produces<ApiError>(StatusCodes.Status429TooManyRequests)
             .Produces<ApiError>(StatusCodes.Status503ServiceUnavailable)
             .WithName("ReportConnectionOutcome");
 
@@ -109,6 +124,7 @@ internal static class ContractEndpoints
         [FromHeader(Name = "Authorization")] string? authorizationHeader,
         [FromServices] PrincipalCredentialService credentials,
         [FromServices] SessionLeaseService sessions,
+        [FromServices] AbuseProtectionService abuseProtection,
         [FromServices] IWallClock clock,
         HttpContext httpContext,
         CancellationToken cancellationToken)
@@ -122,13 +138,29 @@ internal static class ContractEndpoints
             return AuthenticationRequired(httpContext);
         }
 
-        SessionServiceResult<RegisterSessionResponse> result = sessions.Register(
-            principal!,
-            request,
-            cancellationToken);
-        return result.Succeeded && result.Value is not null
-            ? Results.Created($"/v1/sessions/{result.Value.ListingId}", result.Value)
-            : Error(result.Error);
+        IPublisherPrincipal publisher = (IPublisherPrincipal)principal!;
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "RegisterSession",
+                Tenant(publisher.GameId, publisher.EnvironmentId),
+                publisher.Subject,
+                null,
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            SessionServiceResult<RegisterSessionResponse> result = sessions.Register(
+                principal!,
+                request,
+                cancellationToken);
+            return result.Succeeded && result.Value is not null
+                ? Results.Created($"/v1/sessions/{result.Value.ListingId}", result.Value)
+                : Error(result.Error);
+        }
     }
 
     private static IResult RenewLease(
@@ -137,6 +169,7 @@ internal static class ContractEndpoints
         [FromHeader(Name = "Authorization")] string? authorizationHeader,
         [FromServices] PrincipalCredentialService credentials,
         [FromServices] SessionLeaseService sessions,
+        [FromServices] AbuseProtectionService abuseProtection,
         [FromServices] IWallClock clock,
         HttpContext httpContext,
         CancellationToken cancellationToken)
@@ -150,14 +183,30 @@ internal static class ContractEndpoints
             return AuthenticationRequired(httpContext);
         }
 
-        SessionServiceResult<RenewLeaseResponse> result = sessions.Renew(
-            principal!,
-            listingId,
-            request,
-            cancellationToken);
-        return result.Succeeded && result.Value is not null
-            ? Results.Ok(result.Value)
-            : Error(result.Error);
+        IPublisherPrincipal publisher = (IPublisherPrincipal)principal!;
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "RenewSessionLease",
+                Tenant(publisher.GameId, publisher.EnvironmentId),
+                publisher.Subject,
+                listingId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            SessionServiceResult<RenewLeaseResponse> result = sessions.Renew(
+                principal!,
+                listingId,
+                request,
+                cancellationToken);
+            return result.Succeeded && result.Value is not null
+                ? Results.Ok(result.Value)
+                : Error(result.Error);
+        }
     }
 
     private static IResult UpdateSession(
@@ -166,6 +215,7 @@ internal static class ContractEndpoints
         [FromHeader(Name = "Authorization")] string? authorizationHeader,
         [FromServices] PrincipalCredentialService credentials,
         [FromServices] SessionLeaseService sessions,
+        [FromServices] AbuseProtectionService abuseProtection,
         [FromServices] IWallClock clock,
         HttpContext httpContext,
         CancellationToken cancellationToken)
@@ -179,12 +229,28 @@ internal static class ContractEndpoints
             return AuthenticationRequired(httpContext);
         }
 
-        SessionServiceResult<bool> result = sessions.Update(
-            principal!,
-            listingId,
-            request,
-            cancellationToken);
-        return result.Succeeded ? Results.NoContent() : Error(result.Error);
+        IPublisherPrincipal publisher = (IPublisherPrincipal)principal!;
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "UpdateSession",
+                Tenant(publisher.GameId, publisher.EnvironmentId),
+                publisher.Subject,
+                listingId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            SessionServiceResult<bool> result = sessions.Update(
+                principal!,
+                listingId,
+                request,
+                cancellationToken);
+            return result.Succeeded ? Results.NoContent() : Error(result.Error);
+        }
     }
 
     private static IResult DeleteSession(
@@ -193,6 +259,7 @@ internal static class ContractEndpoints
         [FromHeader(Name = "Authorization")] string? authorizationHeader,
         [FromServices] PrincipalCredentialService credentials,
         [FromServices] SessionLeaseService sessions,
+        [FromServices] AbuseProtectionService abuseProtection,
         [FromServices] IWallClock clock,
         HttpContext httpContext,
         CancellationToken cancellationToken)
@@ -206,12 +273,28 @@ internal static class ContractEndpoints
             return AuthenticationRequired(httpContext);
         }
 
-        SessionServiceResult<bool> result = sessions.Delete(
-            principal!,
-            listingId,
-            request,
-            cancellationToken);
-        return result.Succeeded ? Results.NoContent() : Error(result.Error);
+        IPublisherPrincipal publisher = (IPublisherPrincipal)principal!;
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "DeleteSession",
+                Tenant(publisher.GameId, publisher.EnvironmentId),
+                publisher.Subject,
+                listingId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            SessionServiceResult<bool> result = sessions.Delete(
+                principal!,
+                listingId,
+                request,
+                cancellationToken);
+            return result.Succeeded ? Results.NoContent() : Error(result.Error);
+        }
     }
 
     private static IResult BrowseSessions(
@@ -224,6 +307,8 @@ internal static class ContractEndpoints
         [FromQuery] bool? excludeFull,
         [FromQuery] string? cursor,
         [FromServices] SessionBrowserService browser,
+        [FromServices] AbuseProtectionService abuseProtection,
+        HttpContext httpContext,
         CancellationToken cancellationToken)
     {
         if (!GameId.TryParse(gameId, out GameId parsedGameId)
@@ -233,20 +318,35 @@ internal static class ContractEndpoints
             return Error(RendezvousErrorCode.InvalidRequest);
         }
 
-        BrowserServiceResult<BrowseSessionsResponse> result = browser.Browse(new()
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "BrowseSessions",
+                Tenant(parsedGameId, parsedEnvironmentId),
+                null,
+                null,
+                out AbuseProtectionService.AbuseLease? abuseLease))
         {
-            ContractVersion = contractVersion,
-            GameId = parsedGameId,
-            EnvironmentId = parsedEnvironmentId,
-            ProtocolVersion = protocolVersion,
-            RegionId = regionId is null ? null : new RegionId(regionId),
-            PageSize = pageSize ?? ContractLimits.BrowserPageMaxItems,
-            ExcludeFull = excludeFull ?? false,
-            Cursor = cursor,
-        }, cancellationToken);
-        return result.Succeeded && result.Value is not null
-            ? Results.Ok(result.Value)
-            : Error(result.Error);
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            BrowserServiceResult<BrowseSessionsResponse> result = browser.Browse(new()
+            {
+                ContractVersion = contractVersion,
+                GameId = parsedGameId,
+                EnvironmentId = parsedEnvironmentId,
+                ProtocolVersion = protocolVersion,
+                RegionId = regionId is null ? null : new RegionId(regionId),
+                PageSize = pageSize ?? ContractLimits.BrowserPageMaxItems,
+                ExcludeFull = excludeFull ?? false,
+                Cursor = cursor,
+            }, cancellationToken);
+            return result.Succeeded && result.Value is not null
+                ? Results.Ok(result.Value)
+                : Error(result.Error);
+        }
     }
 
     private static IResult GetSession(
@@ -256,6 +356,8 @@ internal static class ContractEndpoints
         [FromQuery] string environmentId,
         [FromQuery] uint protocolVersion,
         [FromServices] SessionBrowserService browser,
+        [FromServices] AbuseProtectionService abuseProtection,
+        HttpContext httpContext,
         CancellationToken cancellationToken)
     {
         if (ContractValidation.ValidateContractVersion(contractVersion) != RendezvousErrorCode.None)
@@ -269,15 +371,30 @@ internal static class ContractEndpoints
             return Error(RendezvousErrorCode.InvalidRequest);
         }
 
-        BrowserServiceResult<GetSessionResponse> result = browser.Get(
-            listingId,
-            parsedGameId,
-            parsedEnvironmentId,
-            protocolVersion,
-            cancellationToken);
-        return result.Succeeded && result.Value is not null
-            ? Results.Ok(result.Value)
-            : Error(result.Error);
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "GetSession",
+                Tenant(parsedGameId, parsedEnvironmentId),
+                null,
+                listingId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            BrowserServiceResult<GetSessionResponse> result = browser.Get(
+                listingId,
+                parsedGameId,
+                parsedEnvironmentId,
+                protocolVersion,
+                cancellationToken);
+            return result.Succeeded && result.Value is not null
+                ? Results.Ok(result.Value)
+                : Error(result.Error);
+        }
     }
 
     private static IResult BrowseHostJoinAttempts(
@@ -287,23 +404,41 @@ internal static class ContractEndpoints
         [FromQuery] int? pageSize,
         [FromQuery] string? cursor,
         [FromServices] JoinAttemptService attempts,
+        [FromServices] AbuseProtectionService abuseProtection,
+        HttpContext httpContext,
         CancellationToken cancellationToken)
     {
-        JoinAttemptServiceResult<BrowseHostJoinAttemptsResponse> result = attempts.BrowseForHost(
-            listingId,
-            contractVersion,
-            leaseToken,
-            pageSize ?? ContractLimits.BrowserPageMaxItems,
-            cursor,
-            cancellationToken);
-        return result.Succeeded && result.Value is not null
-            ? Results.Ok(result.Value)
-            : Error(result.Error);
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "BrowseHostJoinAttempts",
+                null,
+                AbuseProtectionService.FingerprintSecret(leaseToken ?? string.Empty),
+                listingId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            JoinAttemptServiceResult<BrowseHostJoinAttemptsResponse> result = attempts.BrowseForHost(
+                listingId,
+                contractVersion,
+                leaseToken,
+                pageSize ?? ContractLimits.BrowserPageMaxItems,
+                cursor,
+                cancellationToken);
+            return result.Succeeded && result.Value is not null
+                ? Results.Ok(result.Value)
+                : Error(result.Error);
+        }
     }
 
     private static IResult CreateJoinAttempt(
         [FromBody] CreateJoinAttemptRequest request,
         [FromServices] JoinAttemptService attempts,
+        [FromServices] AbuseProtectionService abuseProtection,
         HttpContext httpContext,
         CancellationToken cancellationToken)
     {
@@ -313,26 +448,58 @@ internal static class ContractEndpoints
         }
 
         string clientSubject = attempts.CreateAnonymousClientSubject(remoteAddress);
-        JoinAttemptServiceResult<CreateJoinAttemptResponse> result = attempts.Create(
-            clientSubject,
-            request,
-            cancellationToken);
-        return result.Succeeded && result.Value is not null
-            ? Results.Created($"/v1/join-attempts/{result.Value.AttemptId}", result.Value)
-            : Error(result.Error);
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "CreateJoinAttempt",
+                Tenant(request.GameId, request.EnvironmentId),
+                clientSubject,
+                request.ListingId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            JoinAttemptServiceResult<CreateJoinAttemptResponse> result = attempts.Create(
+                clientSubject,
+                request,
+                cancellationToken);
+            return result.Succeeded && result.Value is not null
+                ? Results.Created($"/v1/join-attempts/{result.Value.AttemptId}", result.Value)
+                : Error(result.Error);
+        }
     }
 
     private static IResult CancelJoinAttempt(
         JoinAttemptId attemptId,
         [FromHeader(Name = "X-Rendezvous-Client-Punch-Capability")] string clientPunchCapability,
         [FromServices] JoinAttemptService attempts,
+        [FromServices] AbuseProtectionService abuseProtection,
+        HttpContext httpContext,
         CancellationToken cancellationToken)
     {
-        JoinAttemptServiceResult<bool> result = attempts.Cancel(
-            attemptId,
-            clientPunchCapability,
-            cancellationToken);
-        return result.Succeeded ? Results.NoContent() : Error(result.Error);
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "CancelJoinAttempt",
+                null,
+                AbuseProtectionService.FingerprintSecret(clientPunchCapability ?? string.Empty),
+                attemptId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            JoinAttemptServiceResult<bool> result = attempts.Cancel(
+                attemptId,
+                clientPunchCapability,
+                cancellationToken);
+            return result.Succeeded ? Results.NoContent() : Error(result.Error);
+        }
     }
 
     private static IResult ReportConnectionOutcome(
@@ -340,16 +507,33 @@ internal static class ContractEndpoints
         [FromHeader(Name = "X-Rendezvous-Client-Punch-Capability")] string clientPunchCapability,
         [FromBody] ReportConnectionOutcomeRequest request,
         [FromServices] ConnectionOutcomeService outcomes,
+        [FromServices] AbuseProtectionService abuseProtection,
+        HttpContext httpContext,
         CancellationToken cancellationToken)
     {
-        ConnectionOutcomeServiceResult result = outcomes.Report(
-            attemptId,
-            clientPunchCapability,
-            request,
-            cancellationToken);
-        return result.Succeeded && result.Value is not null
-            ? Results.Ok(result.Value)
-            : Error(result.Error);
+        if (!TryAcquireIdentity(
+                abuseProtection,
+                httpContext,
+                "ReportConnectionOutcome",
+                null,
+                AbuseProtectionService.FingerprintSecret(clientPunchCapability ?? string.Empty),
+                attemptId.ToString(),
+                out AbuseProtectionService.AbuseLease? abuseLease))
+        {
+            return RateLimited(httpContext);
+        }
+
+        using (abuseLease)
+        {
+            ConnectionOutcomeServiceResult result = outcomes.Report(
+                attemptId,
+                clientPunchCapability,
+                request,
+                cancellationToken);
+            return result.Succeeded && result.Value is not null
+                ? Results.Ok(result.Value)
+                : Error(result.Error);
+        }
     }
 
     private static bool TryAuthenticatePublisher(
@@ -377,11 +561,41 @@ internal static class ContractEndpoints
         return true;
     }
 
-    private static IResult Error(RendezvousErrorCode code) => Results.Json(
+    private static bool TryAcquireIdentity(
+        AbuseProtectionService abuseProtection,
+        HttpContext httpContext,
+        string operation,
+        string? tenant,
+        string? principal,
+        string? resource,
+        out AbuseProtectionService.AbuseLease? lease)
+    {
+        if (abuseProtection.TryAcquireHttpIdentity(
+                operation,
+                httpContext.Connection.RemoteIpAddress,
+                tenant,
+                principal,
+                resource,
+                out lease,
+                out int retryAfterSeconds))
+        {
+            return true;
+        }
+
+        httpContext.Response.Headers.RetryAfter = retryAfterSeconds.ToString(
+            System.Globalization.CultureInfo.InvariantCulture);
+        return false;
+    }
+
+    private static string Tenant(GameId gameId, EnvironmentId environmentId) =>
+        $"{gameId.Value}/{environmentId.Value}";
+
+    private static IResult Error(RendezvousErrorCode code, int? retryAfterSeconds = null) => Results.Json(
         new ApiError
         {
             Code = code,
             Message = ErrorMessage(code),
+            RetryAfterSeconds = retryAfterSeconds,
         },
         ContractJson.Options,
         statusCode: ErrorStatus(code));
@@ -392,6 +606,18 @@ internal static class ContractEndpoints
         return Error(RendezvousErrorCode.AuthenticationRequired);
     }
 
+    private static IResult RateLimited(HttpContext context)
+    {
+        int? retryAfterSeconds = int.TryParse(
+            context.Response.Headers.RetryAfter,
+            System.Globalization.NumberStyles.None,
+            System.Globalization.CultureInfo.InvariantCulture,
+            out int parsed)
+            ? Math.Clamp(parsed, 1, 60)
+            : null;
+        return Error(RendezvousErrorCode.RateLimited, retryAfterSeconds);
+    }
+
     private static int ErrorStatus(RendezvousErrorCode code) => code switch
     {
         RendezvousErrorCode.AuthenticationRequired => StatusCodes.Status401Unauthorized,
@@ -417,6 +643,7 @@ internal static class ContractEndpoints
         RendezvousErrorCode.Expired => "The session lease has expired.",
         RendezvousErrorCode.StaleHost => "The session has no fresh host presence.",
         RendezvousErrorCode.IncompatibleProtocol => "The gameplay protocol is not enabled for this game.",
+        RendezvousErrorCode.RateLimited => "The request rate limit was exceeded.",
         RendezvousErrorCode.CapacityExceeded => "The configured session capacity is currently exhausted.",
         RendezvousErrorCode.ServiceUnavailable => "Session state is temporarily unavailable.",
         RendezvousErrorCode.UnsupportedContractVersion => "The requested contract version is not supported.",