Error UseHealthChecksUI Unexpected character encountered - .net-core

Question

I'm trying to implement the ASP.NET Core 2.2 health check feature. Setting up the health check itself isn't the problem, but I also want to be able to use the UI feature in other project to monitoring all my apis. Right now I get the exception message
Unexpected character encountered while parsing value: <.
What I'm doing bad?
API Project:
var healthCheckOptions = new HealthCheckOptions
{
Predicate = _ => true,
ResponseWriter = async (c, r) =>
{
c.Response.ContentType = MediaTypeNames.Application.Json;
var result = JsonConvert.SerializeObject(
new
{
Checks = r.Entries.Select(e =>
new
{
Description = e.Key,
Status = e.Value.Status.ToString(),
ResponseTime = e.Value.Duration.TotalMilliseconds
}),
TotalResponseTime = r.TotalDuration.TotalMilliseconds
});
await c.Response.WriteAsync(result);
}
};
app.UseHealthChecks("/live", new HealthCheckOptions
{
Predicate = _ => true
});
app.UseHealthChecks("/hc", healthCheckOptions);
app.UseHealthChecksUI(options => options.UIPath = "/healtcheck");
// Registers required services for health checks
services
.AddHealthChecks()
.AddCheck("self", () => HealthCheckResult.Healthy())
.AddCheck("ComunContext Database", new SqlServerHealthCheck(configuration["ConnectionStrings:ComunContext"]));
Web project:
services.AddHealthChecksUI();
app.UseHealthChecksUI(config =>
{
config.UIPath = "/healthcheck";
});
appsettings.json
{
"HealthChecks-UI": {
"HealthChecks": [
{
"Name": "Local",
"Uri": "http://localhost:27365/hc"
}
],
"EvaluationTimeOnSeconds": 10,
"MinimumSecondsBetweenFailureNotifications": 60
}
}

Answer 1

Try adding a ResponseWriter:
public void Configure(IApplicationBuilder app, IHostingEnvironment env)
{
app.UseHealthChecks("/healthchecks", new HealthCheckOptions
{
ResponseWriter = async (context, report) =>
{
context.Response.ContentType = "application/json; charset=utf-8";
var bytes = Encoding.UTF8.GetBytes(JsonConvert.SerializeObject(report));
await context.Response.Body.WriteAsync(bytes);
}
});
app.UseHealthChecksUI();
}

Answer 2

After a few days struggling with this parser error, I've figured out that there are 2 problems:
1 - If you have an Exception, Health UI tries to convert Exception object field, resulting on error;
2 - If you try to pass your own anonymous object, Health UI fails to convert Entries collection, because it need to be an specific anonymous Dictionary.
Try this:
var healthCheckOptions = new HealthCheckOptions
{
Predicate = _ => true,
ResponseWriter = async (c, r) =>
{
c.Response.ContentType = MediaTypeNames.Application.Json;
var result = JsonConvert.SerializeObject(
new
{
Checks = r.Entries.ToDictionary(
e => e.Key,
e =>
new
{
Description = e.Key,
Status = e.Value.Status.ToString(),
ResponseTime = e.Value.Duration.TotalMilliseconds
}),
TotalResponseTime = r.TotalDuration.TotalMilliseconds
});
await c.Response.WriteAsync(result);
}
};