perf: avoid string allocations by using fixed-width hash strings (#5725)

libtransmission/crypto-utils.cc

@@ -25,6 +25,7 @@ extern "C"
 
 #include "libtransmission/crypto-utils.h"
 #include "libtransmission/tr-assert.h"
+#include "libtransmission/tr-strbuf.h"
 #include "libtransmission/utils.h"
 
 using namespace std::literals;
@@ -150,24 +151,16 @@ namespace
 namespace hex_impl
 {
 
-constexpr void tr_binary_to_hex(void const* vinput, void* voutput, size_t byte_length)
+template<typename InIt, typename OutIt>
+constexpr void tr_binary_to_hex(InIt begin, InIt end, OutIt out)
 {
     auto constexpr Hex = "0123456789abcdef"sv;
 
-    auto const* input = static_cast<uint8_t const*>(vinput);
-    auto* output = static_cast<char*>(voutput);
-
-    /* go from back to front to allow for in-place conversion */
-    input += byte_length;
-    output += byte_length * 2;
-
-    *output = '\0';
-
-    while (byte_length-- > 0)
+    while (begin != end)
     {
-        unsigned int const val = *(--input);
-        *(--output) = Hex[val & 0xf];
-        *(--output) = Hex[val >> 4];
+        auto const val = static_cast<unsigned int>(*begin++);
+        *out++ = Hex[val >> 4];
+        *out++ = Hex[val & 0xF];
     }
 }
 
@@ -188,21 +181,23 @@ constexpr void tr_hex_to_binary(char const* input, void* voutput, size_t byte_le
 } // namespace hex_impl
 } // namespace
 
-std::string tr_sha1_to_string(tr_sha1_digest_t const& digest)
+tr_sha1_string tr_sha1_to_string(tr_sha1_digest_t const& digest)
 {
     using namespace hex_impl;
 
-    auto str = std::string(std::size(digest) * 2, '?');
-    tr_binary_to_hex(digest.data(), str.data(), std::size(digest));
+    auto str = tr_sha1_string{};
+    tr_binary_to_hex(std::begin(digest), std::end(digest), std::back_inserter(str));
+    TR_ASSERT(std::size(str) == TrSha1DigestStrlen);
     return str;
 }
 
-std::string tr_sha256_to_string(tr_sha256_digest_t const& digest)
+tr_sha256_string tr_sha256_to_string(tr_sha256_digest_t const& digest)
 {
     using namespace hex_impl;
 
-    auto str = std::string(std::size(digest) * 2, '?');
-    tr_binary_to_hex(digest.data(), str.data(), std::size(digest));
+    auto str = tr_sha256_string{};
+    tr_binary_to_hex(std::begin(digest), std::end(digest), std::back_inserter(str));
+    TR_ASSERT(std::size(str) == TrSha256DigestStrlen);
     return str;
 }
 

libtransmission/crypto-utils.h

@@ -16,7 +16,9 @@
 #include <string>
 #include <string_view>
 
-#include "transmission.h" // tr_sha1_digest_t
+#include "libtransmission/transmission.h" // tr_sha1_digest_t
+
+#include "libtransmission/tr-strbuf.h"
 
 /**
  * @addtogroup utils Utilities
@@ -133,20 +135,24 @@ T tr_rand_obj()
  */
 [[nodiscard]] std::string tr_base64_decode(std::string_view input);
 
+using tr_sha1_string = tr_strbuf<char, sizeof(tr_sha1_digest_t) * 2U + 1U>;
+
 /**
  * @brief Generate an ascii hex string for a sha1 digest.
  */
-[[nodiscard]] std::string tr_sha1_to_string(tr_sha1_digest_t const&);
+[[nodiscard]] tr_sha1_string tr_sha1_to_string(tr_sha1_digest_t const&);
 
 /**
  * @brief Generate a sha1 digest from a hex string.
  */
 [[nodiscard]] std::optional<tr_sha1_digest_t> tr_sha1_from_string(std::string_view hex);
 
+using tr_sha256_string = tr_strbuf<char, sizeof(tr_sha256_digest_t) * 2U + 1U>;
+
 /**
  * @brief Generate an ascii hex string for a sha256 digest.
  */
-[[nodiscard]] std::string tr_sha256_to_string(tr_sha256_digest_t const&);
+[[nodiscard]] tr_sha256_string tr_sha256_to_string(tr_sha256_digest_t const&);
 
 /**
  * @brief Generate a sha256 digest from a hex string.

libtransmission/magnet-metainfo.h

@@ -13,6 +13,7 @@
 #include "transmission.h"
 
 #include "announce-list.h"
+#include "crypto-utils.h"
 #include "tr-strbuf.h" // tr_urlbuf
 #include "utils.h" // tr_strv_convert_utf8()
 
@@ -58,12 +59,12 @@ public:
         return announce_list_;
     }
 
-    [[nodiscard]] constexpr std::string const& info_hash_string() const noexcept
+    [[nodiscard]] constexpr auto const& info_hash_string() const noexcept
     {
         return info_hash_str_;
     }
 
-    [[nodiscard]] constexpr std::string const& info_hash2_string() const noexcept
+    [[nodiscard]] constexpr auto const& info_hash2_string() const noexcept
     {
         return info_hash2_str_;
     }
@@ -80,7 +81,7 @@ protected:
     std::vector<std::string> webseed_urls_;
     tr_sha1_digest_t info_hash_ = {};
     tr_sha256_digest_t info_hash2_ = {};
-    std::string info_hash_str_;
-    std::string info_hash2_str_;
+    tr_sha1_string info_hash_str_;
+    tr_sha256_string info_hash2_str_;
     std::string name_;
 };

libtransmission/tr-strbuf.h

@@ -33,8 +33,16 @@ public:
         ensure_sz();
     }
 
-    tr_strbuf(tr_strbuf const& other) = delete;
-    tr_strbuf& operator=(tr_strbuf const& other) = delete;
+    tr_strbuf(tr_strbuf const& other)
+    {
+        assign(other.sv());
+    }
+
+    tr_strbuf& operator=(tr_strbuf const& other)
+    {
+        assign(other.sv());
+        return *this;
+    }
 
     tr_strbuf(tr_strbuf&& other)
         : buffer_{ std::move(other.buffer_) }

qt/AddData.cc

@@ -43,7 +43,8 @@ QString getNameFromMagnet(QString const& magnet)
         return QString::fromStdString(tmp.name());
     }
 
-    return QString::fromStdString(tmp.info_hash_string());
+    auto const& hashstr = tmp.info_hash_string();
+    return QString::fromUtf8(std::data(hashstr), std::size(hashstr));
 }
 
 } // namespace

qt/Torrent.h

@@ -105,6 +105,7 @@ class TorrentHash
 {
 private:
     tr_sha1_digest_t data_ = {};
+    QString data_str_;
 
 public:
     TorrentHash() = default;
@@ -119,6 +120,9 @@ public:
         if (auto const hash = tr_sha1_from_string(str != nullptr ? str : ""); hash)
         {
             data_ = *hash;
+
+            auto const tmpstr = tr_sha1_to_string(data_);
+            data_str_ = QString::fromUtf8(std::data(tmpstr), std::size(tmpstr));
         }
     }
 
@@ -127,6 +131,9 @@ public:
         if (auto const hash = tr_sha1_from_string(str.toStdString()); hash)
         {
             data_ = *hash;
+
+            auto const tmpstr = tr_sha1_to_string(data_);
+            data_str_ = QString::fromUtf8(std::data(tmpstr), std::size(tmpstr));
         }
     }
 
@@ -145,9 +152,9 @@ public:
         return data_ < that.data_;
     }
 
-    QString toString() const
+    [[nodiscard]] constexpr auto& toString() const noexcept
     {
-        return QString::fromStdString(tr_sha1_to_string(data_));
+        return data_str_;
     }
 };