Give network.xmlrpc.size_limit.set a floor

A limit below any valid request rejects the request that would raise it again.

src/rpc/rpc_manager.cc

@@ -172,6 +172,9 @@ RpcManager::set_size_limit(uint64_t size) {
   if (size > SCgiTask::max_content_size)
     throw torrent::input_error("XMLRPC size limit cannot exceed the SCGI content size limit.");
 
+  if (size < min_size_limit)
+    throw torrent::input_error("XMLRPC size limit is too small to hold a request.");
+
   m_xmlrpc.set_size_limit(size);
 }
 

src/rpc/rpc_manager.h

@@ -53,6 +53,10 @@ public:
   enum RPCType { XML,
                  JSON };
 
+  // A limit below the shortest useful request rejects every request, the one
+  // that would raise it again included.
+  static constexpr uint64_t min_size_limit = 1024;
+
   RpcManager()  = default;
   ~RpcManager() = default;
 

test/Makefile.am

@@ -52,7 +52,9 @@ rtorrent_Test_Rpc_SOURCES = $(rtorrent_Test_Common) \
 	rpc/test_object_storage.cc \
 	rpc/test_object_storage.h \
 	rpc/test_parse_options.cc \
-	rpc/test_parse_options.h
+	rpc/test_parse_options.h \
+	rpc/test_rpc_manager.cc \
+	rpc/test_rpc_manager.h
 
 rtorrent_Test_Src_SOURCES = $(rtorrent_Test_Common) \
 	src/test_command_dynamic.cc \

test/rpc/test_rpc_manager.cc

@@ -0,0 +1,21 @@
+#include "config.h"
+
+#include "test/rpc/test_rpc_manager.h"
+
+#include <torrent/exceptions.h>
+
+#include "rpc/scgi_task.h"
+
+CPPUNIT_TEST_SUITE_REGISTRATION(TestRpcManager);
+
+// A size limit too small to hold any request rejects every request, including
+// the one that would put it back, so it can only be undone by a restart.
+void
+TestRpcManager::test_size_limit_bounds() {
+  CPPUNIT_ASSERT_THROW(m_rpc_manager.set_size_limit(0), torrent::input_error);
+  CPPUNIT_ASSERT_THROW(m_rpc_manager.set_size_limit(rpc::RpcManager::min_size_limit - 1), torrent::input_error);
+  CPPUNIT_ASSERT_THROW(m_rpc_manager.set_size_limit(rpc::SCgiTask::max_content_size + 1), torrent::input_error);
+
+  CPPUNIT_ASSERT_NO_THROW(m_rpc_manager.set_size_limit(rpc::RpcManager::min_size_limit));
+  CPPUNIT_ASSERT_NO_THROW(m_rpc_manager.set_size_limit(rpc::SCgiTask::max_content_size));
+}

test/rpc/test_rpc_manager.h

@@ -0,0 +1,17 @@
+#include "test/helpers/test_fixture.h"
+
+#include "rpc/rpc_manager.h"
+
+class TestRpcManager : public test_fixture {
+  CPPUNIT_TEST_SUITE(TestRpcManager);
+
+  CPPUNIT_TEST(test_size_limit_bounds);
+
+  CPPUNIT_TEST_SUITE_END();
+
+public:
+  void test_size_limit_bounds();
+
+private:
+  rpc::RpcManager m_rpc_manager;
+};