refactor: use tr_rand_buf() in tr_bandwidth::phaseOne() (#4404) (#4411)

libtransmission/bandwidth.cc

@@ -4,7 +4,6 @@
 // License text can be found in the licenses/ folder.
 
 #include <algorithm>
-#include <random> // for std::mt19937
 #include <utility> // for std::swap()
 #include <vector>
 
@@ -13,6 +12,7 @@
 #include "transmission.h"
 
 #include "bandwidth.h"
+#include "crypto-utils.h"
 #include "log.h"
 #include "peer-io.h"
 #include "tr-assert.h"
@@ -164,19 +164,19 @@ void tr_bandwidth::allocateBandwidth(
     }
 }
 
-void tr_bandwidth::phaseOne(std::vector<tr_peerIo*>& peer_array, tr_direction dir)
+void tr_bandwidth::phaseOne(std::vector<tr_peerIo*>& peers, tr_direction dir)
 {
     // First phase of IO. Tries to distribute bandwidth fairly to keep faster
     // peers from starving the others.
-    tr_logAddTrace(fmt::format("{} peers to go round-robin for {}", peer_array.size(), dir == TR_UP ? "upload" : "download"));
+    tr_logAddTrace(fmt::format("{} peers to go round-robin for {}", peers.size(), dir == TR_UP ? "upload" : "download"));
 
     // Shuffle the peers so they all have equal chance to be first in line.
-    thread_local auto random_engine = std::mt19937{ std::random_device{}() };
-    std::shuffle(std::begin(peer_array), std::end(peer_array), random_engine);
+    thread_local auto urbg = tr_urbg<size_t>{};
+    std::shuffle(std::begin(peers), std::end(peers), urbg);
 
     // Give each peer `Increment` bandwidth bytes to use. Repeat this
     // process until we run out of bandwidth and/or peers that can use it.
-    for (size_t n_unfinished = std::size(peer_array); n_unfinished > 0U;)
+    for (size_t n_unfinished = std::size(peers); n_unfinished > 0U;)
     {
         for (size_t i = 0; i < n_unfinished;)
         {
@@ -185,13 +185,13 @@ void tr_bandwidth::phaseOne(std::vector<tr_peerIo*>& peer_array, tr_direction di
             // out in a timely manner.
             static auto constexpr Increment = size_t{ 3000 };
 
-            auto const bytes_used = peer_array[i]->flush(dir, Increment);
+            auto const bytes_used = peers[i]->flush(dir, Increment);
             tr_logAddTrace(fmt::format("peer #{} of {} used {} bytes in this pass", i, n_unfinished, bytes_used));
 
             if (bytes_used != Increment)
             {
                 // peer is done writing for now; move it to the end of the list
-                std::swap(peer_array[i], peer_array[n_unfinished - 1]);
+                std::swap(peers[i], peers[n_unfinished - 1]);
                 --n_unfinished;
             }
             else

libtransmission/bandwidth.h

@@ -252,7 +252,7 @@ private:
 
     [[nodiscard]] size_t clamp(uint64_t now, tr_direction dir, size_t byte_count) const;
 
-    static void phaseOne(std::vector<tr_peerIo*>& peer_array, tr_direction dir);
+    static void phaseOne(std::vector<tr_peerIo*>& peers, tr_direction dir);
 
     void allocateBandwidth(
         tr_priority_t parent_priority,

libtransmission/crypto-utils.h

@@ -9,6 +9,7 @@
 #include <array>
 #include <cstddef> // size_t
 #include <cstdint>
+#include <limits>
 #include <memory>
 #include <optional>
 #include <string>
@@ -187,6 +188,34 @@ private:
     std::array<T, N> buf;
 };
 
+// UniformRandomBitGenerator impl that uses `tr_rand_buffer()`.
+// See https://en.cppreference.com/w/cpp/named_req/UniformRandomBitGenerator
+template<typename T, size_t N = 1024U>
+class tr_urbg
+{
+public:
+    using result_type = T;
+    static_assert(!std::numeric_limits<T>::is_signed);
+
+    [[nodiscard]] static constexpr T min() noexcept
+    {
+        return std::numeric_limits<T>::min();
+    }
+
+    [[nodiscard]] static constexpr T max() noexcept
+    {
+        return std::numeric_limits<T>::max();
+    }
+
+    [[nodiscard]] T operator()() noexcept
+    {
+        return buf_();
+    }
+
+private:
+    tr_salt_shaker<T, N> buf_;
+};
+
 /** @} */
 
 #endif /* TR_CRYPTO_UTILS_H */

tests/libtransmission/crypto-test-ref.h

@@ -30,6 +30,7 @@
 #define tr_ssha1_test tr_ssha1_test_
 #define tr_ssl_ctx_t tr_ssl_ctx_t_
 #define tr_ssl_get_x509_store tr_ssl_get_x509_store_
+#define tr_urbg tr_urbg_
 #define tr_x509_cert_free tr_x509_cert_free_
 #define tr_x509_cert_new tr_x509_cert_new_
 #define tr_x509_cert_t tr_x509_cert_t_
@@ -63,6 +64,7 @@
 #undef tr_ssha1_test
 #undef tr_ssl_ctx_t
 #undef tr_ssl_get_x509_store
+#undef tr_urbg
 #undef tr_x509_cert_free
 #undef tr_x509_cert_new
 #undef tr_x509_cert_t
@@ -99,6 +101,7 @@
 #define tr_ssha1_test_ tr_ssha1_test
 #define tr_ssl_ctx_t_ tr_ssl_ctx_t
 #define tr_ssl_get_x509_store_ tr_ssl_get_x509_store
+#define tr_urbg_ tr_urbg
 #define tr_x509_cert_free_ tr_x509_cert_free
 #define tr_x509_cert_new_ tr_x509_cert_new
 #define tr_x509_cert_t_ tr_x509_cert_t