Introduced esprandom

esprandom.h

@@ -0,0 +1,42 @@
+#pragma once
+
+// system includes
+#include <limits>
+#include <random>
+
+// esp-idf includes
+#include <esp_system.h>
+
+namespace espcpputils {
+namespace {
+
+class esp_random_device
+{
+public:
+    using result_type = decltype(esp_random()); // should be uint32_t
+
+    result_type operator()() const { return esp_random(); }
+
+    double entropy() const { return 1.; }
+    result_type min() const { return std::numeric_limits<result_type>::min(); }
+    result_type max() const { return std::numeric_limits<result_type>::max(); }
+};
+
+std::string randomString(std::size_t length)
+{
+    static constexpr auto chars =
+        "0123456789"
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+        "abcdefghijklmnopqrstuvwxyz";
+
+    auto rng = esp_random_device{};
+
+    auto dist = std::uniform_int_distribution{{}, std::strlen(chars) - 1};
+
+    auto result = std::string(length, '\0');
+    std::generate_n(std::begin(result), length, [&]() { return chars[dist(rng)]; });
+    return result;
+}
+
+} // namespace
+} // namespace espcpputils

esputils.h

@@ -8,7 +8,6 @@
 #include <cstring>
 #include <string>
 #include <string_view>
-#include <random>
 
 /*
    Avoid "unused parameter" warnings
@@ -229,18 +228,5 @@ bool is_in(First &&first, T && ... t)
     return ((first == t) || ...);
 }
 
-std::string randomString(std::size_t length)
-{
-    static constexpr auto chars =
-        "0123456789"
-        "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
-        "abcdefghijklmnopqrstuvwxyz";
-    thread_local auto rng = std::default_random_engine();
-    auto dist = std::uniform_int_distribution{{}, std::strlen(chars) - 1};
-    auto result = std::string(length, '\0');
-    std::generate_n(std::begin(result), length, [&]() { return chars[dist(rng)]; });
-    return result;
-}
-
 } // namespace
 } // namespace espcpputils