feat: Construct a builder from a FFI builder

CMakeLists.txt

@@ -14,7 +14,7 @@
 cmake_minimum_required(VERSION 3.27)
 
 # This is the current version of this C++ project
-project(c2pa-c VERSION 0.18.1)
+project(c2pa-c VERSION 0.18.2)
 
 # Set the version of the c2pa_rs library used
 set(C2PA_VERSION "0.78.4")

include/c2pa.hpp

@@ -840,6 +840,11 @@ namespace c2pa
         [[deprecated("Use Builder(IContextProvider& context, manifest_json) instead")]]
         Builder(const std::string &manifest_json);
 
+        /// @brief Create a Builder from a raw C FFI builder.
+        /// @param builder Raw C2paBuilder pointer to wrap.
+        /// @throws C2paException if builder is nullptr.
+        explicit Builder(C2paBuilder *builder);
+
         Builder(const Builder&) = delete;
 
         Builder& operator=(const Builder&) = delete;

src/c2pa_builder.cpp

@@ -21,6 +21,15 @@
 
 namespace c2pa
 {
+    Builder::Builder(C2paBuilder *builder)
+        : builder(builder)
+    {
+        if (this->builder == nullptr)
+        {
+            throw C2paException("Invalid builder pointer");
+        }
+    }
+
     Builder::Builder(IContextProvider& context)
         : builder(nullptr)
     {

tests/builder.test.cpp

@@ -166,6 +166,22 @@ TEST_F(BuilderTest, exposes_raw_pointer) {
     ASSERT_NE(builder.c2pa_builder(), nullptr);
 }
 
+TEST_F(BuilderTest, wraps_c_ffi_builder) {
+    fs::path current_dir = fs::path(__FILE__).parent_path();
+    fs::path manifest_path = current_dir / "../tests/fixtures/training.json";
+    auto manifest = c2pa_test::read_text_file(manifest_path);
+
+    C2paBuilder* ffi_builder = c2pa_builder_from_json(manifest.c_str());
+    ASSERT_NE(ffi_builder, nullptr);
+
+    auto builder = c2pa::Builder(ffi_builder);
+    EXPECT_EQ(builder.c2pa_builder(), ffi_builder);
+}
+
+TEST_F(BuilderTest, wraps_null_c_ffi_builder_throws) {
+    EXPECT_THROW(c2pa::Builder(nullptr), c2pa::C2paException);
+}
+
 // Test fixture for basic signature validations with automatic cleanup
 class BuilderSmokeSignTest : public BuilderTest, public ::testing::WithParamInterface<std::string> {
 public: