Cryptic Error when ReferenceExpression value looks like a JSON object

[afscrome]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

If you try to create a reference expression encapsulating another expression in a json value (e.g. ReferenceExpression.Create($@"{{""url"": ""{app.GetEndpoint("http")}""}}), your resoruce will fail to start with a cryptic error of Failed to apply configuration value 'JsonifiedReference'. A dependency may have failed to start.

Further investigation suggested the root cause is an escaping problem, however aspire only logs the error at debug level, so you probably don't see the inner exception making determining the root cause a pain.

aspire/src/Aspire.Hosting/Dcp/ApplicationExecutor.cs

Line 1399 in 4494825

resourceLogger.LogCritical("Failed to apply configuration value '{ConfigKey}'. A dependency may have failed to start.", c.Key);

aspire/src/Aspire.Hosting/Dcp/ApplicationExecutor.cs

Line 1676 in 4494825

resourceLogger.LogCritical("Failed to apply configuration value '{ConfigKey}'. A dependency may have failed to start.", kvp.Key);

aspire/src/Aspire.Hosting/Dcp/ApplicationExecutor.cs

Line 1357 in 4494825

resourceLogger.LogCritical("Failed to apply arguments. A dependency may have failed to start.");

aspire/src/Aspire.Hosting/Dcp/ApplicationExecutor.cs

Line 1746 in 4494825

resourceLogger.LogCritical("Failed to apply container arguments '{ConfigKey}'. A dependency may have failed to start.", arg);

Expected Behavior

I'd have expected aspire to provide a clearer error that would have let me work out the issue was due to escaping, not a

Steps To Reproduce

For a more real world repo

var app = builder.AddExecutable("app", "pwsh", ".")
    .WithHttpEndpoint();
app.WithEnvironment("ENV VAR NAME", ReferenceExpression.Create($@"{{""url"": ""{app.GetEndpoint("http")}""}}"));

A simpler repo can be seen with

var expression = ReferenceExpression.Create($"{{");
var x = expression.ValueExpression; // Throws

Exceptions (if any)

Failed to apply configuration value 'JsonifiedReference'. A dependency may have failed to start.

If you turn on debug logging, you'll see an error more like:

System.FormatException: Input string was not in a correct format. Failure to parse near offset 1. Format item ends prematurely.
at System.Text.ValueStringBuilder.AppendFormatHelper(IFormatProvider provider, String format, ReadOnlySpan1 args) at System.String.FormatHelper(IFormatProvider provider, String format, ReadOnlySpan1 args)
at System.String.Format(IFormatProvider provider, String format, Object[] args)
at Aspire.Hosting.ApplicationModel.ReferenceExpression.get_ValueExpression() in /_/src/Aspire.Hosting/ApplicationModel/ReferenceExpression.cs:line 49
at Program.

$(String[] args) in S:\AspireApp2\AspireApp2.AppHost\Program.cs:line 18

.NET Version info

.NET SDK:
 Version:           9.0.100
 Commit:            59db016f11
 Workload version:  9.0.100-manifests.c6f19616
 MSBuild version:   17.12.7+5b8665660

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.22621
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\9.0.100\

.NET workloads installed:
 [aspire]
   Installation Source: VS 17.12.35514.174
   Manifest Version:    8.2.2/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.aspire\8.2.2\WorkloadManifest.json
   Install Type:              Msi

Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.0
  Architecture: x64
  Commit:       9d5a6a9aa4

.NET SDKs installed:
  6.0.428 [C:\Program Files\dotnet\sdk]
  8.0.404 [C:\Program Files\dotnet\sdk]
  9.0.100 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
  Not set

global.json file:
  Not found

Learn more:
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Anything else?

[afscrome]

I've opened a PR to exposing the underlying exception in #7032, although leaving this issue open to see if there's anything to improve the error message in this particular case. Whilst Input string was not in a correct format. Failure to parse near offset 1. Format item ends prematurely. is better than nothing, it's not immediately obvious it's related to escaping of curley braces.