Support large large objects.

Fixes #1865.

large_objects_private_test.go

@@ -0,0 +1,20 @@
+package pgx
+
+import (
+	"testing"
+)
+
+// SetMaxLargeObjectMessageLength sets internal maxLargeObjectMessageLength variable
+// to the given length for the duration of the test.
+//
+// Tests using this helper should not use t.Parallel().
+func SetMaxLargeObjectMessageLength(t *testing.T, length int) {
+	t.Helper()
+
+	original := maxLargeObjectMessageLength
+	t.Cleanup(func() {
+		maxLargeObjectMessageLength = original
+	})
+
+	maxLargeObjectMessageLength = length
+}