From cc649f38eee35b95af5901832c5dd043081b3a09 Mon Sep 17 00:00:00 2001
From: PastaPastaPasta <6443210+PastaPastaPasta@users.noreply.github.com>
Date: Thu, 5 Dec 2024 23:38:55 -0600
Subject: [PATCH] feat: serialize on the stack (#75)

* feat: implement std::array based serialization

* fixup add const

* add SerializeToArray for PrivateKey

* simplify G1Element::Serialize by using G1Element::SerializeToArray

* refactor: continued reduced duplication

* fixup: apply code review comments
---
 include/dashbls/elements.hpp   |  3 +++
 include/dashbls/privatekey.hpp |  1 +
 src/elements.cpp               | 28 ++++++++++++++++++++++++----
 src/privatekey.cpp             |  7 +++++++
 4 files changed, 35 insertions(+), 4 deletions(-)

diff --git a/include/dashbls/elements.hpp b/include/dashbls/elements.hpp
index 6832b31f3..95937f62d 100644
--- a/include/dashbls/elements.hpp
+++ b/include/dashbls/elements.hpp
@@ -59,6 +59,7 @@ class G1Element {
     GTElement Pair(const G2Element &b) const;
     uint32_t GetFingerprint(bool fLegacy = false) const;
     std::vector<uint8_t> Serialize(bool fLegacy = false) const;
+    std::array<uint8_t, SIZE> SerializeToArray(bool fLegacy = false) const;
     G1Element Copy();
 
     friend bool operator==(const G1Element &a, const G1Element &b);
@@ -102,6 +103,7 @@ class G2Element {
     G2Element Negate() const;
     GTElement Pair(const G1Element &a) const;
     std::vector<uint8_t> Serialize(bool fLegacy = false) const;
+    std::array<uint8_t, G2Element::SIZE> SerializeToArray(bool fLegacy = false) const;
     G2Element Copy();
 
     friend bool operator==(G2Element const &a, G2Element const &b);
@@ -127,6 +129,7 @@ class GTElement {
 
     void Serialize(uint8_t *buffer) const;
     std::vector<uint8_t> Serialize() const;
+    std::array<uint8_t, SIZE> SerializeToArray() const;
 
     friend bool operator==(GTElement const &a, GTElement const &b);
     friend bool operator!=(GTElement const &a, GTElement const &b);
diff --git a/include/dashbls/privatekey.hpp b/include/dashbls/privatekey.hpp
index beebbb05a..d02a7d292 100644
--- a/include/dashbls/privatekey.hpp
+++ b/include/dashbls/privatekey.hpp
@@ -82,6 +82,7 @@ class PrivateKey {
     // Serialize the key into bytes
     void Serialize(uint8_t *buffer) const;
     std::vector<uint8_t> Serialize(bool fLegacy = false) const;
+    std::array<uint8_t, PrivateKey::PRIVATE_KEY_SIZE> SerializeToArray(bool fLegacy = false) const;
 
     G2Element SignG2(
         const uint8_t *msg,
diff --git a/src/elements.cpp b/src/elements.cpp
index 278af8cd8..b0c747af8 100644
--- a/src/elements.cpp
+++ b/src/elements.cpp
@@ -171,11 +171,16 @@ uint32_t G1Element::GetFingerprint(const bool fLegacy) const
 }
 
 std::vector<uint8_t> G1Element::Serialize(const bool fLegacy) const {
+    const auto arr = G1Element::SerializeToArray(fLegacy);
+    return std::vector<uint8_t>{arr.begin(), arr.end()};
+}
+
+std::array<uint8_t, G1Element::SIZE> G1Element::SerializeToArray(const bool fLegacy) const {
     uint8_t buffer[G1Element::SIZE + 1];
     g1_write_bin(buffer, G1Element::SIZE + 1, p, 1);
 
+    std::array<uint8_t, G1Element::SIZE> result{};
     if (buffer[0] == 0x00) {  // infinity
-        std::vector<uint8_t> result(G1Element::SIZE, 0);
         result[0] = 0xc0;
         return result;
     }
@@ -187,7 +192,9 @@ std::vector<uint8_t> G1Element::Serialize(const bool fLegacy) const {
     if (!fLegacy) {
         buffer[1] |= 0x80;  // indicate compression
     }
-    return std::vector<uint8_t>(buffer + 1, buffer + 1 + G1Element::SIZE);
+
+    std::copy_n(buffer + 1, G1Element::SIZE, result.begin());
+    return result;
 }
 
 bool operator==(const G1Element & a, const G1Element &b)
@@ -386,11 +393,18 @@ G2Element G2Element::Negate() const
 GTElement G2Element::Pair(const G1Element& a) const { return a & (*this); }
 
 std::vector<uint8_t> G2Element::Serialize(const bool fLegacy) const {
+    const auto arr = G2Element::SerializeToArray(fLegacy);
+    return std::vector<uint8_t>{arr.begin(), arr.end()};
+}
+
+std::array<uint8_t, G2Element::SIZE> G2Element::SerializeToArray(const bool fLegacy) const {
     uint8_t buffer[G2Element::SIZE + 1];
     g2_write_bin(buffer, G2Element::SIZE + 1, (g2_st*)q, 1);
 
+    std::array<uint8_t, G2Element::SIZE> result{};
+
     if (buffer[0] == 0x00) {  // infinity
-        std::vector<uint8_t> result(G2Element::SIZE, 0);
+        result.fill(0);
         result[0] = 0xc0;
         return result;
     }
@@ -410,7 +424,6 @@ std::vector<uint8_t> G2Element::Serialize(const bool fLegacy) const {
         }
     }
 
-    std::vector<uint8_t> result(G2Element::SIZE, 0);
     if (fLegacy) {
         std::memcpy(result.data(), buffer + 1, G2Element::SIZE);
     } else {
@@ -551,4 +564,11 @@ std::vector<uint8_t> GTElement::Serialize() const
     return data;
 }
 
+std::array<uint8_t, GTElement::SIZE> GTElement::SerializeToArray() const
+{
+    std::array<uint8_t, GTElement::SIZE> data{};
+    Serialize(data.data());
+    return data;
+}
+
 }  // end namespace bls
diff --git a/src/privatekey.cpp b/src/privatekey.cpp
index 865507dfc..d4dd32d11 100644
--- a/src/privatekey.cpp
+++ b/src/privatekey.cpp
@@ -284,6 +284,13 @@ std::vector<uint8_t> PrivateKey::Serialize(const bool fLegacy) const
     return data;
 }
 
+std::array<uint8_t, PrivateKey::PRIVATE_KEY_SIZE> PrivateKey::SerializeToArray(bool fLegacy) const
+{
+    std::array<uint8_t, PRIVATE_KEY_SIZE> data{};
+    Serialize(data.data());
+    return data;
+}
+
 G2Element PrivateKey::SignG2(
     const uint8_t *msg,
     size_t len,