Error handling

Errors are modeled as message descriptions. Each error type is listed in Services.MessageDescription table (also ServiceMessage.Instance). There is human-readable template text and machine-readable identifier number. Error messages are easily logged, stored, indexed, serialized, transmitted, and converted into other formats, such as .json.

IMessageDescription describes error type.

// Choose message description
IMessageDescription messageDescription = Services.MessageDescription.BadQueryNoValue;
// Write description
Console.Error.WriteLine(messageDescription);
// MessageDescription(Code=A0AAC059, Key=Avalanche.Service.BadQueryNoValue, HResult=A0AAC059, Severity=, Template="{request}: No value.", "No value")

IMessage is attached to thrown Exceptions (message).

// Create handler
Delegate decorator = (IQuery<string, string> q) => q.Response.SetValue(q.Request + "-Suffix");
// Create service
IService service = Services.Create(decorator);

try
{
    // Issue request that is not handled
    service.GetRequired<int, int>(5);
}
// Get e.Data[MessageExceptionExtensions.Key] as IMessage
catch (Exception e) when (e.TryGetAttachedMessage(out IMessage message))
{
    // Print message
    string print = message.Print();
    // Write event with arguments
    Console.Error.WriteLine(print);
    // Let it fly
    throw;
}

.HResult contains identifier of the occured error. HResult number is allocated under the bit mask for third party codes.

// Create handler
Delegate decorator = (IQuery<string, string> q) => q.Response.SetValue(q.Request + "-Suffix");
// Create service
IService service = Services.Create(decorator);
try
{
    // Issue request that is not handled
    service.GetRequired<int, int>(5);
}
catch (Exception e) when (e.HResult == Services.MessageDescription.BadQueryNoValue.HResult)
{
    Console.Error.WriteLine("Query was not handled.");
}

QueryLogger is a handler that prints query results into a ILogger.

Full Example

Full example

using System;
using Avalanche.Service;
using Avalanche.Utilities;
using Avalanche.Message;
using Avalanche.Template;

public class articles_errorhandling
{
    public static void Run()
    {
        {
            // <01>
            // Choose message description
            IMessageDescription messageDescription = Services.MessageDescription.BadQueryNoValue;
            // Write description
            Console.Error.WriteLine(messageDescription);
            // MessageDescription(Code=A0AAC059, Key=Avalanche.Service.BadQueryNoValue, HResult=A0AAC059, Severity=, Template="{request}: No value.", "No value")
            // </01>
        }

        {
            try
            {
                // <02>
                // Create handler
                Delegate decorator = (IQuery<string, string> q) => q.Response.SetValue(q.Request + "-Suffix");
                // Create service
                IService service = Services.Create(decorator);

                try
                {
                    // Issue request that is not handled
                    service.GetRequired<int, int>(5);
                }
                // Get e.Data[MessageExceptionExtensions.Key] as IMessage
                catch (Exception e) when (e.TryGetAttachedMessage(out IMessage message))
                {
                    // Print message
                    string print = message.Print();
                    // Write event with arguments
                    Console.Error.WriteLine(print);
                    // Let it fly
                    throw;
                }
                // </02>
            }
            catch (Exception) { }

            try
            {
                // <03>
                // Create handler
                Delegate decorator = (IQuery<string, string> q) => q.Response.SetValue(q.Request + "-Suffix");
                // Create service
                IService service = Services.Create(decorator);
                try
                {
                    // Issue request that is not handled
                    service.GetRequired<int, int>(5);
                }
                catch (Exception e) when (e.HResult == Services.MessageDescription.BadQueryNoValue.HResult)
                {
                    Console.Error.WriteLine("Query was not handled.");
                }
                // </03>
            } catch (Exception) { }
        }
    }
}