Validate cuOptGetErrorString buffer size

cpp/src/pdlp/cuopt_c.cpp

@@ -1182,6 +1182,7 @@ cuopt_int_t cuOptGetErrorString(cuOptSolution solution,
 {
   if (solution == nullptr) { return CUOPT_INVALID_ARGUMENT; }
   if (error_string_ptr == nullptr) { return CUOPT_INVALID_ARGUMENT; }
+  if (error_string_size <= 0) { return CUOPT_INVALID_ARGUMENT; }
   solution_and_stream_view_t* solution_and_stream_view =
     static_cast<solution_and_stream_view_t*>(solution);
   std::string error_string = solution_and_stream_view->get_solution()->get_error_status().what();

cpp/tests/linear_programming/c_api_tests/c_api_test.c

@@ -129,6 +129,77 @@ cuopt_int_t test_bad_parameter_name()
   return status;
 }
 
+cuopt_int_t test_error_string_invalid_buffer_size()
+{
+  cuOptOptimizationProblem problem = NULL;
+  cuOptSolverSettings settings     = NULL;
+  cuOptSolution solution           = NULL;
+  cuopt_int_t status;
+
+  cuopt_float_t objective[] = {1.0};
+  cuopt_int_t row_offsets[] = {0, 1};
+  cuopt_int_t column_indices[] = {0};
+  cuopt_float_t values[]    = {1.0};
+  char constraint_sense[]   = {CUOPT_LESS_THAN};
+  cuopt_float_t rhs[]       = {1.0};
+  cuopt_float_t lower_bounds[] = {0.0};
+  cuopt_float_t upper_bounds[] = {1.0};
+  char variable_types[]     = {CUOPT_CONTINUOUS};
+  char error_string[8]      = "unset";
+
+  status = cuOptCreateProblem(1,
+                              1,
+                              CUOPT_MINIMIZE,
+                              0.0,
+                              objective,
+                              row_offsets,
+                              column_indices,
+                              values,
+                              constraint_sense,
+                              rhs,
+                              lower_bounds,
+                              upper_bounds,
+                              variable_types,
+                              &problem);
+  if (status != CUOPT_SUCCESS) {
+    printf("Error creating optimization problem\n");
+    goto DONE;
+  }
+
+  status = cuOptCreateSolverSettings(&settings);
+  if (status != CUOPT_SUCCESS) {
+    printf("Error creating solver settings\n");
+    goto DONE;
+  }
+
+  status = cuOptSolve(problem, settings, &solution);
+  if (status != CUOPT_SUCCESS) {
+    printf("Error solving problem\n");
+    goto DONE;
+  }
+
+  status = cuOptGetErrorString(solution, error_string, 0);
+  if (status != CUOPT_INVALID_ARGUMENT) {
+    printf("Error: expected invalid argument for zero error buffer size, but got %d\n", status);
+    goto DONE;
+  }
+
+  status = cuOptGetErrorString(solution, error_string, -1);
+  if (status != CUOPT_INVALID_ARGUMENT) {
+    printf("Error: expected invalid argument for negative error buffer size, but got %d\n",
+           status);
+    goto DONE;
+  }
+
+  status = CUOPT_SUCCESS;
+
+DONE:
+  cuOptDestroyProblem(&problem);
+  cuOptDestroySolverSettings(&settings);
+  cuOptDestroySolution(&solution);
+  return status;
+}
+
 typedef struct mip_callback_context_t {
   cuopt_int_t n_variables;
   int get_calls;

cpp/tests/linear_programming/c_api_tests/c_api_tests.cpp

@@ -107,6 +107,11 @@ TEST(c_api, solve_time_bb_preemption)
 
 TEST(c_api, bad_parameter_name) { EXPECT_EQ(test_bad_parameter_name(), CUOPT_INVALID_ARGUMENT); }
 
+TEST(c_api, error_string_invalid_buffer_size)
+{
+  EXPECT_EQ(test_error_string_invalid_buffer_size(), CUOPT_SUCCESS);
+}
+
 TEST(c_api, mip_get_callbacks_only) { EXPECT_EQ(test_mip_get_callbacks_only(), CUOPT_SUCCESS); }
 
 TEST(c_api, mip_get_set_callbacks) { EXPECT_EQ(test_mip_get_set_callbacks(), CUOPT_SUCCESS); }

cpp/tests/linear_programming/c_api_tests/c_api_tests.h

@@ -28,6 +28,7 @@ cuopt_int_t solve_mps_file(const char* filename,
 cuopt_int_t test_missing_file();
 cuopt_int_t test_infeasible_problem();
 cuopt_int_t test_bad_parameter_name();
+cuopt_int_t test_error_string_invalid_buffer_size();
 cuopt_int_t test_mip_get_callbacks_only();
 cuopt_int_t test_mip_get_set_callbacks();
 cuopt_int_t test_ranged_problem(cuopt_int_t* termination_status_ptr, cuopt_float_t* objective_ptr);