refactor(inboundapi): pool the request audit buffer + reset Position in finally

src/ScadaLink.InboundAPI/Middleware/AuditWriteMiddleware.cs

@@ -1,3 +1,4 @@
+using System.Buffers;
 using System.Diagnostics;
 using System.Text;
 using System.Text.Json;
@@ -279,14 +280,18 @@ public sealed class AuditWriteMiddleware
             return (null, false);
         }
 
+        // Read AT MOST cap + 1 bytes — the extra byte tells us the body was
+        // over the cap without forcing us to allocate the whole payload. Rent
+        // the scratch buffer from the shared ArrayPool so we don't allocate
+        // (and immediately discard) `cap + 1` bytes per request — the pool
+        // may hand back a buffer LARGER than `limit`, so we treat `limit`
+        // (not `buffer.Length`) as the read ceiling.
+        var limit = capBytes + 1;
+        var buffer = ArrayPool<byte>.Shared.Rent(limit);
         try
         {
             request.Body.Position = 0;
 
-            // Read AT MOST cap + 1 bytes — the extra byte tells us the body was
-            // over the cap without forcing us to allocate the whole payload.
-            var limit = capBytes + 1;
-            var buffer = new byte[limit];
             var total = 0;
             while (total < limit)
             {
@@ -299,7 +304,6 @@ public sealed class AuditWriteMiddleware
                 }
                 total += read;
             }
-            request.Body.Position = 0;
 
             if (total == 0)
             {
@@ -318,6 +322,15 @@ public sealed class AuditWriteMiddleware
             // outcome.
             return (null, false);
         }
+        finally
+        {
+            // Even on a thrown read, the downstream handler must see the full
+            // body from position 0 — never let a failed audit copy leak a
+            // truncated view. A rewind failure is swallowed: best-effort,
+            // same philosophy as the rest of the file.
+            try { request.Body.Position = 0; } catch { /* swallow */ }
+            ArrayPool<byte>.Shared.Return(buffer);
+        }
     }
 
     /// <summary>