expat: add source of entropy

components/newlib/random.c

@@ -0,0 +1,52 @@
+// Copyright 2018 Espressif Systems (Shanghai) PTE LTD
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <sys/random.h>
+#include <sys/param.h>
+#include <assert.h>
+#include <errno.h>
+#include <string.h>
+#include "esp_system.h"
+#include "esp_log.h"
+
+static const char *TAG = "RANDOM";
+
+ssize_t getrandom(void *buf, size_t buflen, unsigned int flags)
+{
+    // Flags are ignored because:
+    // - esp_random is non-blocking so it works for both blocking and non-blocking calls,
+    // - don't have opportunity so set som other source of entropy.
+
+    ESP_LOGD(TAG, "getrandom(buf=0x%x, buflen=%d, flags=%u)", (int) buf, buflen, flags);
+
+    if (buf == NULL) {
+        errno = EFAULT;
+        ESP_LOGD(TAG, "getrandom returns -1 (EFAULT)");
+        return -1;
+    }
+
+    uint8_t *dst = (uint8_t *) buf;
+    ssize_t ret = 0;
+
+    while (ret < buflen) {
+        const uint32_t random = esp_random();
+        const int needed = buflen - ret;
+        const int copy_len = MIN(sizeof(random), needed);
+        memcpy(dst + ret, &random, copy_len);
+        ret += copy_len;
+    }
+
+    ESP_LOGD(TAG, "getrandom returns %d", ret);
+    return ret;
+}