SetExternalEvents Method Implementation Notes

• Action Name: SetExternalEvents
• Action Parameters: A JSON encoded string containing an array of SafetyEvent objects.
• Returns: string.Empty

//Example 1 - One event active
[
    {
        "Source":"ASCOM Sentinel at My Observatory",
        "Name":"Observing conditions SkyBrightness",
        "Id":"723e775aab_SkyBrightness",
        "Type":"SkyBrightness",
        "Trigger":"AboveThreshold",
        "Description":"SkyBrightness rule 1 violated: Value 85.83 is greater than 0.25.",
        "EventTimeUtc":"2026-04-15T08:05:03.2139641Z"
    }
]

// Example 2 - Two events active
[
    {
        "Source":"ASCOM Sentinel at My Observatory",
        "Name":"Observing conditions SkyBrightness",
        "Id":"723e775aab_SkyBrightness",
        "Type":"SkyBrightness",
        "Trigger":"AboveThreshold",
        "Description":"SkyBrightness rule 1 violated: Value 85.83 is greater than 0.25.",
        "EventTimeUtc":"2026-04-15T08:05:03.2139641Z"
    },
    {
        "Source":"ASCOM Sentinel at My Observatory",
        "Name":"Observing conditions StarFWHM",
        "Id":"723e775aab_StarFWHM",
        "Type":"StarFWHM",
        "Trigger":"AboveThreshold",
        "Description":"StarFWHM rule 1 violated: Value 1.03 is greater than 0.8.",
        "EventTimeUtc":"2026-04-15T08:05:03.2147037Z"
    }
]

The response has been whitespace formatted for readability, but the actual response should be a single line of JSON text without unnecessary whitespace.

Alpaca clients must send an HTTP PUT request to the safety monitor's action endpoint as described here: Alpaca Action Endpoint with application/x-www-form-urlencoded body parameters:

• ActionName = "SetExternalEvents"
• ActionParameters = A string containing a JSON encoded array of SafetyEvent objects.

Alpaca devices must return a standard Alpaca response object with:

• Value = "" and ErrorNumber = 0 if the request was successful
• Value = "" and ErrorNumber ≠ 0 and a descriptive ErrorMessage if they cannot complete the request.

{
    "Value":"",
    "ClientTransactionID":66,
    "ServerTransactionID":428,
    "ErrorNumber":0,
    "ErrorMessage":""
}

The response has been whitespace formatted for readability, but the actual response should be a single line of JSON text without unnecessary whitespace.

On receipt, the client should check the ErrorNumber field:

• = 0 - The values provided have been successfully set.
  • IsSafe will return false.
• ≠ 0 - An error occurred and the ErrorMessage field should be examined to determine the cause of the error.

COM clients should call the safety monitor instance's Action method with ActionName = "SetExternalEvents" and ActionParameters = A string containing a JSON encoded array of SafetyEvent objects as shown above.

COM devices should return an empty string. If the device cannot complete the request, it should throw an exception with a message describing the cause of the error.

On return from the call, COM clients should:

• No exception - The values were accepted and IsSafe will return false.
• Exception - Catch and handle any exception thrown by the safety monitor.