Fix rand_bytes in Android

CMakeLists.txt

@@ -113,6 +113,8 @@ if (WIN32)
 	list(APPEND src src/rand_win.c)
 elseif (APPLE)
 	list(APPEND src src/rand_apple.c)
+elseif (ANDROID)
+	list(APPEND src src/rand.c)
 else()
 	list(APPEND src src/rand_unix.c)
 endif()

src/rand.c

@@ -0,0 +1,45 @@
+/*
+ *  Copyright 2014-2022 The GmSSL Project. All Rights Reserved.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the License); you may
+ *  not use this file except in compliance with the License.
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ */
+
+
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#include <gmssl/rand.h>
+#include <gmssl/error.h>
+
+#define RAND_MAX_BUF_SIZE 4096
+
+int rand_bytes(uint8_t *buf, size_t len)
+{
+	FILE *fp;
+	if (!buf) {
+		error_print();
+		return -1;
+	}
+	if (len > RAND_MAX_BUF_SIZE) {
+		error_print();
+		return -1;
+	}
+	if (!len) {
+		return 0;
+	}
+
+	if (!(fp = fopen("/dev/urandom", "rb"))) {
+		error_print();
+		return -1;
+	}
+	if (fread(buf, 1, len, fp) != len) {
+		error_print();
+		fclose(fp);
+		return -1;
+	}
+	fclose(fp);
+	return 1;
+}