fix(mtconnect): share MTConnectError text extraction; pin hollow-error refusal

2026-08-05 06:23:08 -04:00
parent 9f17d7efa2
commit 3b8b5a77e1
3 changed files with 93 additions and 21 deletions
@@ -127,6 +127,40 @@ internal static class MTConnectXml
            return message;
        }

+        var errors = ExtractErrorText(root);
+
+        return errors is null ? message : $"{message} The Agent reported: {errors}";
+    }
+
+    /// <summary>
+    ///     The Agent's own words from an <c>MTConnectError</c> document: every <c>&lt;Error&gt;</c>
+    ///     beneath <paramref name="root"/>, rendered <c>errorCode: text</c> where a code is present
+    ///     and joined with <c>"; "</c>. <c>null</c> when the document carries no readable error
+    ///     detail at all (no <c>&lt;Error&gt;</c> elements, or only blank ones).
+    /// </summary>
+    /// <remarks>
+    ///     <para>
+    ///         <b>Shared because both callers must read the same document the same way.</b> An
+    ///         Agent's objection reaches this driver through two unrelated doors — a read path that
+    ///         got an error document where it expected a model
+    ///         (<see cref="DescribeUnexpectedRoot"/>), and the write path deciding whether a 200
+    ///         actually accepted the observation. Two copies of this walk would drift on the same
+    ///         two silent rules the type-level remarks describe, and on the write side a missed
+    ///         <c>&lt;Error&gt;</c> does not merely degrade a message: it reads as a successful
+    ///         write.
+    ///     </para>
+    ///     <para>
+    ///         <b><c>null</c> means "no readable detail", NOT "not an error document".</b> Only the
+    ///         caller knows which document it is holding — check the root name first. A caller that
+    ///         treats a <c>null</c> here as "no error occurred" turns a hollow
+    ///         <c>&lt;MTConnectError/&gt;</c> into a success.
+    ///     </para>
+    /// </remarks>
+    /// <param name="root">The <c>MTConnectError</c> document's root element.</param>
+    public static string? ExtractErrorText(XElement root)
+    {
+        ArgumentNullException.ThrowIfNull(root);
+
        var errors = root.Descendants()
            .Where(e => IsNamed(e, "Error"))
            .Select(e =>
@@ -139,8 +173,6 @@ internal static class MTConnectXml
            .Where(text => text.Length > 0)
            .ToList();

-        return errors.Count == 0
-            ? message
-            : $"{message} The Agent reported: {string.Join("; ", errors)}";
+        return errors.Count == 0 ? null : string.Join("; ", errors);
    }
 }