New test helper mbedtls_test_fork_run_child()

Run some code in a child process. Propagate output from the child if the
test succeeds, and propagate the test result information otherwise.

Signed-off-by: Gilles Peskine <[email protected]>

tests/include/test/fork_helpers.h

@@ -0,0 +1,59 @@
+/** Helper functions for testing with subprocesses.
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+ */
+
+#ifndef TEST_FORK_HELPERS_H
+#define TEST_FORK_HELPERS_H
+
+#include "test/helpers.h"
+
+/** Type of a function to run in a child process.
+ *
+ * The function can mark the test case as failed by calling
+ * mbedtls_test_fail(). This information will be reported to the parent.
+ *
+ * \param param         Parameter passed to the callback.
+ * \param[out] output   Buffer for data to pass to the parent.
+ *                      This data is ignored if the test case is marked
+ *                      as failed.
+ * \param output_size   Size of \p output in bytes.
+ * \param[out] output_length    Number of bytes written to \p output, to be
+ *                              passed to the parent. The default is \c 0.
+ */
+typedef void mbedtls_test_fork_child_callback_t(
+    void *param,
+    unsigned char *output, size_t output_size, size_t *output_length);
+
+/* Fork a child process and wait for it to collect some data.
+ *
+ * This is similar to backquotes or `$(...)` in a shell.
+ *
+ * This function blocks until the child exits.
+ *
+ * If the child marks the test as failed or skipped, the child's test
+ * information (test result and failure location) is propagated to the
+ * parent.
+ *
+ * \param child_callback        Callback function to run in the child.
+ * \param param                 Parameter to pass to the callback function.
+ * \param[out] child_output     On success, data retrieved from the child.
+ *                              Note that the data is only available if the
+ *                              child did not mark the test case as failed
+ *                              or skipped.
+ * \param child_output_size     Size of \p child_output in bytes.
+ * \param[out] child_output_length  On success, the number of bytes collected
+ *                                  from the child in \c child_output.
+ *
+ * \return \c 0 on success.
+ *         A nonzero value if the test case is marked as failed or skipped.
+ */
+int mbedtls_test_fork_run_child(
+    mbedtls_test_fork_child_callback_t *child_callback,
+    void *param,
+    unsigned char *child_output, size_t child_output_size,
+    size_t *child_output_length);
+
+#endif /* TEST_FORK_HELPERS_H */

tests/include/test/helpers.h

@@ -147,6 +147,25 @@ void mbedtls_test_get_line1(char *line);
  */
 void mbedtls_test_get_line2(char *line);
 
+/**
+ * \brief           Get a copy of the test result information.
+ *
+ * \param[out] out  On output, contains a copy of the current test info.
+ */
+void mbedtls_test_info_save(mbedtls_test_info_t *out);
+
+/**
+ * \brief           Overwrite the test result information.
+ *                  This is intended for some unusual scenarios.
+ *                  You probably shouldn't use this in a test function.
+ *
+ * \param[in] replacement
+ *                  The test info to use instead of the current one.
+ *                  The function copies the data, so the pointer does
+ *                  not need to be valid after this function returns.
+ */
+void mbedtls_test_info_overwrite(const mbedtls_test_info_t *replacement);
+
 #if defined(MBEDTLS_TEST_MUTEX_USAGE)
 /**
  * \brief           Get the current mutex usage error message