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refactor: Implement FDv2 Wire Format + Payload Parser (#514)
This is a pretty straightforward port of `FDv2ChangeSet` and related classes from Java, as well as the protocol objects, such as `PutObject`, `DeleteObject`, etc. * Adds `FDv2Change`, `FDv2ChangeSet` objects for use in data system. * Adds `ServerIntent`, `PutObject`, etc methods for parsing messages from backend. * Adds `tag_invoke` methods based on the existing json deserialization code. * Adds tests for all of the JSON parsing. <!-- CURSOR_SUMMARY --> --- > [!NOTE] > **Medium Risk** > Introduces new protocol-level JSON deserialization and data model types that will be used for streaming/data-sync, so schema/compatibility mistakes could affect data updates despite being mostly additive and covered by unit tests. > > **Overview** > Adds initial FDv2 wire-format support by introducing `Selector`, `FDv2Change`, and `FDv2ChangeSet` types for representing full/partial/no-op data updates. > > Implements JSON deserialization (Boost.JSON `tag_invoke`) for FDv2 protocol messages—`IntentCode`, `ServerIntent`, `PutObject`, `DeleteObject`, `PayloadTransferred`, `Goodbye`, and `FDv2Error`—and wires the new parser into the internal build (`serialization/json_fdv2_events.cpp`). > > Adds comprehensive unit tests (`fdv2_serialization_test.cpp`) validating successful parsing, null handling, and schema-failure behavior for missing/invalid fields. > > <sup>Written by [Cursor Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit 11be538. This will update automatically on new commits. Configure [here](https://cursor.com/dashboard?tab=bugbot).</sup> <!-- /CURSOR_SUMMARY -->
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‎libs/internal/include/launchdarkly/data_model/fdv2_change.hpp‎

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#pragma once
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#include <launchdarkly/data_model/flag.hpp>
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#include <launchdarkly/data_model/item_descriptor.hpp>
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#include <launchdarkly/data_model/segment.hpp>
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#include <launchdarkly/data_model/selector.hpp>
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#include <string>
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#include <variant>
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#include <vector>
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namespace launchdarkly::data_model {
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struct FDv2Change {
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std::string key;
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std::variant<ItemDescriptor<Flag>, ItemDescriptor<Segment>> object;
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};
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struct FDv2ChangeSet {
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enum class Type {
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kFull = 0,
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kPartial = 1,
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kNone = 2,
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};
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Type type;
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std::vector<FDv2Change> changes;
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Selector selector;
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};
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} // namespace launchdarkly::data_model

‎libs/internal/include/launchdarkly/data_model/selector.hpp‎

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#pragma once
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#include <cstdint>
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#include <optional>
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#include <string>
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namespace launchdarkly::data_model {
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/**
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* Identifies a specific version of data in the LaunchDarkly backend, used to
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* request incremental updates from a known point. <p> A selector is either
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* empty or contains a version number and state string that
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* were provided by a LaunchDarkly data source. Empty selectors signal that the
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* client has no existing data and requires a full payload. <p> <strong>For SDK
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* consumers implementing custom data sources:</strong> you should always use
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* std::nullopt when constructing a ChangeSet. Non-empty selectors are
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* set by LaunchDarkly's own data sources based on state received from the
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* LaunchDarkly backend, and are not meaningful when constructed externally.
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*/
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struct Selector {
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struct State {
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std::int64_t version;
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std::string state;
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};
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std::optional<State> value;
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};
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} // namespace launchdarkly::data_model

‎libs/internal/include/launchdarkly/serialization/json_fdv2_events.hpp‎

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#pragma once
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#include <launchdarkly/detail/serialization/json_errors.hpp>
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#include <boost/json/value.hpp>
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#include <tl/expected.hpp>
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#include <cstdint>
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#include <optional>
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#include <string>
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#include <vector>
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namespace launchdarkly {
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enum class IntentCode { kNone, kTransferFull, kTransferChanges, kUnknown };
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struct ServerIntentPayload {
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std::string id;
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std::int64_t target;
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IntentCode intent_code;
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std::optional<std::string> reason;
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};
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struct ServerIntent {
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std::vector<ServerIntentPayload> payloads;
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};
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struct PutObject {
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std::int64_t version;
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std::string kind;
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std::string key;
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boost::json::value object;
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};
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struct DeleteObject {
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std::int64_t version;
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std::string kind;
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std::string key;
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};
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struct PayloadTransferred {
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std::string state;
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std::int64_t version;
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};
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struct Goodbye {
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std::optional<std::string> reason;
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};
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struct FDv2Error {
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std::optional<std::string> id;
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std::string reason;
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};
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tl::expected<std::optional<IntentCode>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<IntentCode>, JsonError>> const& unused,
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boost::json::value const& json_value);
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tl::expected<std::optional<ServerIntentPayload>, JsonError> tag_invoke(
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boost::json::value_to_tag<tl::expected<std::optional<ServerIntentPayload>,
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JsonError>> const& unused,
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boost::json::value const& json_value);
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tl::expected<std::optional<ServerIntent>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<ServerIntent>, JsonError>> const& unused,
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boost::json::value const& json_value);
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tl::expected<std::optional<PutObject>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<PutObject>, JsonError>> const& unused,
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boost::json::value const& json_value);
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tl::expected<std::optional<DeleteObject>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<DeleteObject>, JsonError>> const& unused,
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boost::json::value const& json_value);
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tl::expected<std::optional<PayloadTransferred>, JsonError> tag_invoke(
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boost::json::value_to_tag<tl::expected<std::optional<PayloadTransferred>,
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JsonError>> const& unused,
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boost::json::value const& json_value);
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tl::expected<std::optional<Goodbye>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<Goodbye>, JsonError>> const& unused,
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boost::json::value const& json_value);
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tl::expected<std::optional<FDv2Error>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<FDv2Error>, JsonError>> const& unused,
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boost::json::value const& json_value);
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} // namespace launchdarkly

‎libs/internal/src/CMakeLists.txt‎

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serialization/json_evaluation_reason.cpp
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serialization/value_mapping.cpp
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serialization/json_evaluation_result.cpp
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serialization/json_fdv2_events.cpp
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serialization/json_sdk_data_set.cpp
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serialization/json_segment.cpp
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serialization/json_primitives.cpp

‎libs/internal/src/serialization/json_fdv2_events.cpp‎

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#include <boost/core/ignore_unused.hpp>
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#include <boost/json.hpp>
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#include <launchdarkly/serialization/json_fdv2_events.hpp>
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#include <launchdarkly/serialization/value_mapping.hpp>
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#include <tl/expected.hpp>
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namespace launchdarkly {
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tl::expected<std::optional<IntentCode>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<IntentCode>, JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_STRING(json_value);
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auto const& str = json_value.as_string();
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if (str == "none") {
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return IntentCode::kNone;
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} else if (str == "xfer-full") {
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return IntentCode::kTransferFull;
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} else if (str == "xfer-changes") {
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return IntentCode::kTransferChanges;
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} else {
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return IntentCode::kUnknown;
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}
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}
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tl::expected<std::optional<ServerIntentPayload>, JsonError> tag_invoke(
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boost::json::value_to_tag<tl::expected<std::optional<ServerIntentPayload>,
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JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_OBJECT(json_value);
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auto const& obj = json_value.as_object();
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ServerIntentPayload payload{};
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PARSE_REQUIRED_FIELD(payload.id, obj, "id");
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PARSE_REQUIRED_FIELD(payload.target, obj, "target");
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PARSE_REQUIRED_FIELD(payload.intent_code, obj, "intentCode");
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PARSE_CONDITIONAL_FIELD(payload.reason, obj, "reason");
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return payload;
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}
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tl::expected<std::optional<ServerIntent>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<ServerIntent>, JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_OBJECT(json_value);
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auto const& obj = json_value.as_object();
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ServerIntent intent{};
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PARSE_REQUIRED_FIELD(intent.payloads, obj, "payloads");
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return intent;
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}
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tl::expected<std::optional<PutObject>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<PutObject>, JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_OBJECT(json_value);
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auto const& obj = json_value.as_object();
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PutObject put{};
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PARSE_REQUIRED_FIELD(put.version, obj, "version");
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PARSE_REQUIRED_FIELD(put.kind, obj, "kind");
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PARSE_REQUIRED_FIELD(put.key, obj, "key");
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auto const& it = obj.find("object");
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if (it == obj.end()) {
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return tl::make_unexpected(JsonError::kSchemaFailure);
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}
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put.object = it->value();
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return put;
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}
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tl::expected<std::optional<DeleteObject>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<DeleteObject>, JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_OBJECT(json_value);
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auto const& obj = json_value.as_object();
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DeleteObject del{};
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PARSE_REQUIRED_FIELD(del.version, obj, "version");
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PARSE_REQUIRED_FIELD(del.kind, obj, "kind");
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PARSE_REQUIRED_FIELD(del.key, obj, "key");
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return del;
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}
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tl::expected<std::optional<PayloadTransferred>, JsonError> tag_invoke(
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boost::json::value_to_tag<tl::expected<std::optional<PayloadTransferred>,
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JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_OBJECT(json_value);
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auto const& obj = json_value.as_object();
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PayloadTransferred transferred{};
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PARSE_REQUIRED_FIELD(transferred.state, obj, "state");
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PARSE_REQUIRED_FIELD(transferred.version, obj, "version");
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return transferred;
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}
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tl::expected<std::optional<Goodbye>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<Goodbye>, JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_OBJECT(json_value);
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auto const& obj = json_value.as_object();
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Goodbye goodbye{};
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PARSE_CONDITIONAL_FIELD(goodbye.reason, obj, "reason");
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return goodbye;
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}
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tl::expected<std::optional<FDv2Error>, JsonError> tag_invoke(
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boost::json::value_to_tag<
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tl::expected<std::optional<FDv2Error>, JsonError>> const& unused,
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boost::json::value const& json_value) {
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boost::ignore_unused(unused);
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REQUIRE_OBJECT(json_value);
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auto const& obj = json_value.as_object();
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FDv2Error error{};
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PARSE_REQUIRED_FIELD(error.reason, obj, "reason");
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PARSE_CONDITIONAL_FIELD(error.id, obj, "id");
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return error;
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}
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} // namespace launchdarkly

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