add mqttclient to the component, and add fire stm32f429 board demo.

components/connectivity/mqttclient/common/random.c

@@ -0,0 +1,64 @@
+/*
+ * @Author: jiejie
+ * @Github: https://github.com/jiejieTop
+ * @Date: 2020-01-09 19:25:05
+ * @LastEditTime : 2020-01-10 08:54:24
+ * @Description: the code belongs to jiejie, please keep the author information and source code according to the license.
+ */
+#include <stdlib.h>
+#include "random.h"
+#include "platform_timer.h"
+#include "platform_memory.h"
+
+static unsigned int last_seed = 1;
+
+static int do_random(unsigned int seed)
+{
+    srand(seed);
+    return rand();
+}
+
+int random_number(void)
+{
+    unsigned int seed = (unsigned int) platform_timer_now();
+    last_seed += (seed >> ((seed ^ last_seed) % 3));
+    return do_random(last_seed ^ seed);
+}
+
+char *random_string(unsigned int len)
+{
+    unsigned int i, flag, seed, random;
+
+    char *str = platform_memory_alloc((size_t)(len + 1));
+    if (NULL == str)
+        return NULL;
+    
+    seed = (unsigned int) random_number();
+    seed += (unsigned int) ((size_t)str ^ seed);
+    
+    random = (unsigned int)do_random(seed);
+    
+	for (i = 0; i < len; i++) {
+        random = do_random(seed ^ random);
+		flag = (unsigned int)random % 3;
+		switch (flag) {
+            case 0:
+                str[i] = 'A' + do_random(random ^ (i & flag)) % 26;
+                break;
+            case 1:
+                str[i] = 'a' + do_random(random ^ (i & flag)) % 26;
+                break;
+            case 2:
+                str[i] = '0' + do_random(random ^ (i & flag)) % 10;
+                break;
+            default:
+                str[i] = 'x';
+                break;
+		}
+        random += ((0xb433e5c6 ^ random)  << (i & flag));
+	}
+
+    str[len] = '\0';
+	return str;
+}
+