CXX-595 Implement a basic from_json

Author: acmorrow

src/bsoncxx/json.cpp

@@ -20,6 +20,8 @@
 #include <sstream>
 #include <vector>
 
+#include <bson.h>
+
 #include <bsoncxx/document/view.hpp>
 #include <bsoncxx/stdx/make_unique.hpp>
 #include <bsoncxx/stdx/string_view.hpp>
@@ -33,6 +35,10 @@ BSONCXX_INLINE_NAMESPACE_BEGIN
 
 namespace {
 
+void bson_free_deleter(std::uint8_t* ptr) {
+    bson_free(ptr);
+}
+
 class json_visitor {
    public:
     json_visitor(std::ostream& out, bool is_array, std::size_t padding)
@@ -275,5 +281,19 @@ std::string to_json(types::value value) {
     return ss.str();
 }
 
+stdx::optional<document::value> from_json(stdx::string_view json) {
+    bson_error_t error;
+    bson_t* result = bson_new_from_json(
+        reinterpret_cast<const uint8_t*>(json.data()), json.size(), &error);
+
+    if (!result)
+        return stdx::nullopt;
+
+    std::uint32_t length;
+    std::uint8_t* buf = bson_destroy_with_steal(result, true, &length);
+
+    return document::value{buf, length, bson_free_deleter};
+}
+
 BSONCXX_INLINE_NAMESPACE_END
 }  // namespace bsoncxx

src/bsoncxx/json.hpp

@@ -18,7 +18,9 @@
 
 #include <string>
 
+#include <bsoncxx/document/value.hpp>
 #include <bsoncxx/document/view.hpp>
+#include <bsoncxx/stdx/optional.hpp>
 
 namespace bsoncxx {
 BSONCXX_INLINE_NAMESPACE_BEGIN
@@ -55,6 +57,16 @@ BSONCXX_API std::string to_json(document::element element);
 ///
 BSONCXX_API std::string to_json(types::value value);
 
+///
+/// Constructs a new document::value from the provided JSON text
+///
+/// @param 'json'
+///  A string_view into a JSON document
+///
+/// @returns An engaged optional containing a document::value if conversion worked.
+///
+BSONCXX_API stdx::optional<document::value> from_json(stdx::string_view json);
+
 BSONCXX_INLINE_NAMESPACE_END
 }  // namespace bsoncxx
 

src/bsoncxx/test/CMakeLists.txt

@@ -3,10 +3,11 @@ include_directories(
 )
 
 add_executable(test_bson
+    bson_builder.cpp
     bson_util_itoa.cpp
     bson_validate.cpp
+    json.cpp
     new_tests.cpp
-    bson_builder.cpp
 )
 
 target_link_libraries(test_bson bsoncxx_static)

src/bsoncxx/test/json.cpp

@@ -0,0 +1,32 @@
+#include "catch.hpp"
+
+#include <bsoncxx/builder/stream/document.hpp>
+#include <bsoncxx/json.hpp>
+
+namespace {
+    constexpr auto k_invalid_json = R"({])";
+    constexpr auto k_valid_json = R"({ "a" : 1, "b" : 2.0 })";
+}
+
+TEST_CASE("invalid json returns disengaged optional") {
+    using namespace bsoncxx;
+    REQUIRE(!from_json(k_invalid_json));
+}
+
+TEST_CASE("valid json returns an engaged optional") {
+    using namespace bsoncxx;
+    REQUIRE(from_json(k_valid_json));
+}
+
+TEST_CASE("valid json is converted to equivalent BSON") {
+    using namespace bsoncxx;
+
+    const auto expected = builder::stream::document{} << "a" << 1 << "b" << 2.0 << builder::stream::finalize;
+    const auto expected_view = expected.view();
+
+    const auto actual = from_json(k_valid_json);
+    const auto actual_view = actual->view();
+
+    REQUIRE(expected_view.length() == actual_view.length());
+    REQUIRE(0 == memcmp(expected_view.data(), actual_view.data(), expected_view.length()));
+}