From 73c4c1b27c9028c5404c39c58ab8afa303251e6b Mon Sep 17 00:00:00 2001
From: Malay Satapathy <satapathymalay.95@gmail.com>
Date: Fri, 16 Oct 2026 00:22:02 +0530
Subject: [PATCH] Fix #207: FR: Add CopyBytesFrom for array types

---
 runtime/cpp/emboss_array_view.h            | 23 +++++++++++++
 runtime/cpp/test/emboss_array_view_test.cc | 38 ++++++++++++++++++++++
 2 files changed, 61 insertions(+)

diff --git a/runtime/cpp/emboss_array_view.h b/runtime/cpp/emboss_array_view.h
index fa8ccd38..4960d118 100644
--- a/runtime/cpp/emboss_array_view.h
+++ b/runtime/cpp/emboss_array_view.h
@@ -258,6 +258,29 @@ class GenericArrayView final {
     WriteArrayToTextStream(this, stream, options);
   }
 
+  template <class Container, int N = 0>
+  typename ::std::enable_if<
+      ((void)N, kAddressableUnitSize * kElementSize == 8), void>::type
+  CopyBytesFrom(const Container &source) const {
+    EMBOSS_CHECK(IsComplete());
+    EMBOSS_CHECK(static_cast<::std::size_t>(source.size()) == ElementCount());
+    auto it = source.begin();
+    for (::std::size_t i = 0; i < ElementCount(); ++i, ++it) {
+      (*this)[i].Write(static_cast<typename ElementView::ValueType>(*it));
+    }
+  }
+
+  template <typename T, ::std::size_t N, int M = 0>
+  typename ::std::enable_if<
+      ((void)M, kAddressableUnitSize * kElementSize == 8), void>::type
+  CopyBytesFrom(const T (&source)[N]) const {
+    EMBOSS_CHECK(IsComplete());
+    EMBOSS_CHECK(N == ElementCount());
+    for (::std::size_t i = 0; i < ElementCount(); ++i) {
+      (*this)[i].Write(static_cast<typename ElementView::ValueType>(source[i]));
+    }
+  }
+
   static constexpr bool IsAggregate() { return true; }
 
   BufferType BackingStorage() const { return buffer_; }
diff --git a/runtime/cpp/test/emboss_array_view_test.cc b/runtime/cpp/test/emboss_array_view_test.cc
index 1f632e89..10e98b9f 100644
--- a/runtime/cpp/test/emboss_array_view_test.cc
+++ b/runtime/cpp/test/emboss_array_view_test.cc
@@ -16,6 +16,7 @@
 
 #include <string>
 #include <type_traits>
+#include <array>
 
 #include "absl/strings/str_format.h"
 #include "gtest/gtest.h"
@@ -89,6 +90,43 @@ TEST(ArrayView, Methods) {
   EXPECT_FALSE((ArrayView<FixedUIntView<32>, ReadWriteContiguousBuffer, 1>{
       ReadWriteContiguousBuffer{
           nullptr}}.Ok()));
+
+  // Test CopyBytesFrom
+  ::std::array<::std::uint8_t, 4> new_bytes = {0xaa, 0xbb, 0xcc, 0xdd};
+  auto dest_array = ArrayView<FixedUIntView<8>, ReadWriteContiguousBuffer, 1>{
+      ReadWriteContiguousBuffer{bytes, 4}};
+  dest_array.CopyBytesFrom(new_bytes);
+  EXPECT_EQ(0xaa, bytes[0]);
+  EXPECT_EQ(0xbb, bytes[1]);
+  EXPECT_EQ(0xcc, bytes[2]);
+  EXPECT_EQ(0xdd, bytes[3]);
+
+  // Test CopyBytesFrom with signed elements to ensure values >= 128 do not abort
+  bytes[0] = 0;
+  bytes[1] = 0;
+  bytes[2] = 0;
+  bytes[3] = 0;
+  auto dest_signed_array =
+      ArrayView<FixedIntView<8>, ReadWriteContiguousBuffer, 1>{
+          ReadWriteContiguousBuffer{bytes, 4}};
+  dest_signed_array.CopyBytesFrom(new_bytes);
+  EXPECT_EQ(0xaa, bytes[0]);
+  EXPECT_EQ(0xbb, bytes[1]);
+  EXPECT_EQ(0xcc, bytes[2]);
+  EXPECT_EQ(0xdd, bytes[3]);
+
+  // Test CopyBytesFrom with a raw C-style array
+  const ::std::uint8_t raw_bytes[4] = {0x11, 0x22, 0x33, 0x44};
+  dest_array.CopyBytesFrom(raw_bytes);
+  EXPECT_EQ(0x11, bytes[0]);
+  EXPECT_EQ(0x22, bytes[1]);
+  EXPECT_EQ(0x33, bytes[2]);
+  EXPECT_EQ(0x44, bytes[3]);
+
+#if EMBOSS_CHECK_ABORTS
+  ::std::array<::std::uint8_t, 3> wrong_size_bytes = {0xaa, 0xbb, 0xcc};
+  EXPECT_DEATH(dest_array.CopyBytesFrom(wrong_size_bytes), "");
+#endif  // EMBOSS_CHECK_ABORTS
 }
 
 TEST(ArrayView, Ok) {