bring subcommand abstraction in line with main command abstraction

src/PSOProtocol.cc

@@ -207,3 +207,19 @@ void print_received_command(
 
   print_data(stderr, w.str());
 }
+
+void check_size_v(size_t size, size_t min_size, size_t max_size) {
+  if (size < min_size) {
+    throw std::runtime_error(string_printf(
+        "command too small (expected at least 0x%zX bytes, received 0x%zX bytes)",
+        min_size, size));
+  }
+  if (max_size < min_size) {
+    max_size = min_size;
+  }
+  if (size > max_size) {
+    throw std::runtime_error(string_printf(
+        "command too large (expected at most 0x%zX bytes, received 0x%zX bytes)",
+        max_size, size));
+  }
+}