newlib: add test for st_blksize and FILE buffer size

Inspired by https://github.com/joltwallet/esp_littlefs/pull/91/files#r935872478

components/newlib/test_apps/main/CMakeLists.txt

@@ -2,5 +2,6 @@ idf_component_register(SRCS
                         "test_newlib_main.c"
                         "test_stdatomic.c"
                         "test_misc.c"
+                        "test_file.c"
                        REQUIRES test_utils
-                       PRIV_REQUIRES unity)
+                       PRIV_REQUIRES unity vfs)

components/newlib/test_apps/main/test_file.c

@@ -0,0 +1,94 @@
+/*
+ * SPDX-FileCopyrightText: 2022 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+#include <stdio.h>
+#include <stdio_ext.h>
+#include <string.h>
+#include <fcntl.h>
+#include <errno.h>
+#include "esp_vfs.h"
+#include "unity.h"
+#include "unity_fixture.h"
+
+TEST_GROUP(file);
+
+TEST_SETUP(file)
+{
+}
+
+TEST_TEAR_DOWN(file)
+{
+}
+
+/* This test checks that st_blksize value set in struct stat correctly affects the
+ * FILE structure:
+ * - _blksize field should be equal to st_blksize
+ * - buffer size should be equal to st_blksize if it is nonzero, and __BUFSIZ__ otherwise.
+ * This is more of an integration test since some of the functions responsible for this are
+ * in ROM, and have been built without HAVE_BLKSIZE feature for the ESP32 chip.
+ */
+
+typedef struct {
+    unsigned blksize;
+} blksize_test_ctx_t;
+
+static int blksize_test_open(void* ctx, const char * path, int flags, int mode)
+{
+    return 1;
+}
+
+static int blksize_test_fstat(void* ctx, int fd, struct stat * st)
+{
+    blksize_test_ctx_t* test_ctx = (blksize_test_ctx_t*) ctx;
+    memset(st, 0, sizeof(*st));
+    st->st_mode = S_IFREG;
+    st->st_blksize = test_ctx->blksize;
+    return 0;
+}
+
+static ssize_t blksize_test_write(void* ctx, int fd, const void * data, size_t size)
+{
+    return size;
+}
+
+TEST(file, blksize)
+{
+    FILE* f;
+    blksize_test_ctx_t ctx = {};
+    const char c = 42;
+    const esp_vfs_t desc = {
+        .flags = ESP_VFS_FLAG_CONTEXT_PTR,
+        .open_p = blksize_test_open,
+        .fstat_p = blksize_test_fstat,
+        .write_p = blksize_test_write,
+    };
+
+    TEST_ESP_OK(esp_vfs_register("/test", &desc, &ctx));
+
+    /* test with zero st_blksize (=not set) */
+    ctx.blksize = 0;
+    f = fopen("/test/path", "w");
+    TEST_ASSERT_NOT_NULL(f);
+    fwrite(&c, 1, 1, f);
+    TEST_ASSERT_EQUAL(0, f->_blksize);
+    TEST_ASSERT_EQUAL(__BUFSIZ__, __fbufsize(f));
+    fclose(f);
+
+    /* test with non-zero st_blksize */
+    ctx.blksize = 4096;
+    f = fopen("/test/path", "w");
+    TEST_ASSERT_NOT_NULL(f);
+    fwrite(&c, 1, 1, f);
+    TEST_ASSERT_EQUAL(ctx.blksize, f->_blksize);
+    TEST_ASSERT_EQUAL(ctx.blksize, __fbufsize(f));
+    fclose(f);
+
+    TEST_ESP_OK(esp_vfs_unregister("/test"));
+}
+
+TEST_GROUP_RUNNER(file)
+{
+    RUN_TEST_CASE(file, blksize)
+}

components/newlib/test_apps/main/test_newlib_main.c

@@ -10,6 +10,7 @@ static void run_all_tests(void)
 {
     RUN_TEST_GROUP(stdatomic);
     RUN_TEST_GROUP(misc);
+    RUN_TEST_GROUP(file);
 }
 
 void app_main(void)