fix: remove modulo bias from random helper

include/session/random.hpp

@@ -3,6 +3,10 @@
 #include <sodium/randombytes.h>
 
 #include <algorithm>
+#include <cstdint>
+#include <limits>
+#include <random>
+#include <type_traits>
 
 #include "util.hpp"
 
@@ -77,11 +81,16 @@ std::string unique_id(std::string_view prefix);
 /// - A random integer in the specified range
 template <typename T>
 T get_uniform_distribution(T min, T max) {
+    static_assert(std::is_integral_v<T>, "get_uniform_distribution requires an integral type");
+
     if (min > max)
         return min;
 
-    const uint64_t range = static_cast<uint64_t>(max) - static_cast<uint64_t>(min) + 1;
-    return static_cast<T>(static_cast<uint64_t>(min) + (csrng() % range));
+    using dist_type = std::conditional_t<std::is_signed_v<T>, int64_t, uint64_t>;
+    std::uniform_int_distribution<dist_type> dist{
+            static_cast<dist_type>(min), static_cast<dist_type>(max)};
+
+    return static_cast<T>(dist(csrng));
 }
 
 }  // namespace session::random

tests/test_random.cpp

@@ -1,4 +1,6 @@
 #include <catch2/catch_test_macros.hpp>
+#include <cstdint>
+#include <limits>
 
 #include "session/random.h"
 #include "session/random.hpp"
@@ -14,3 +16,21 @@ TEST_CASE("Random generation", "[random][random]") {
     CHECK(rand3.size() == 20);
     CHECK(rand1 != rand2);
 }
+
+TEST_CASE("Random uniform distribution", "[random][uniform]") {
+    CHECK(session::random::get_uniform_distribution<int>(7, 7) == 7);
+    CHECK(session::random::get_uniform_distribution<int>(9, 3) == 9);
+    CHECK_NOTHROW(session::random::get_uniform_distribution<uint64_t>(
+            0, std::numeric_limits<uint64_t>::max()));
+    CHECK_NOTHROW(session::random::get_uniform_distribution<int64_t>(
+            std::numeric_limits<int64_t>::min(), std::numeric_limits<int64_t>::max()));
+
+    for (int i = 0; i < 1000; ++i) {
+        const auto signed_value = session::random::get_uniform_distribution<int>(-5, 5);
+        CHECK(signed_value >= -5);
+        CHECK(signed_value <= 5);
+
+        const auto unsigned_value = session::random::get_uniform_distribution<size_t>(0, 10);
+        CHECK(unsigned_value <= 10);
+    }
+}