WIP: use Boost::json for incremental parsing and reflection

gpt4all-backend-test/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.29)
+cmake_minimum_required(VERSION 3.28...3.31)
 project(gpt4all-backend-test VERSION 0.1 LANGUAGES CXX)
 
 set(G4A_TEST_OLLAMA_URL "http://localhost:11434/" CACHE STRING "The base URL of the Ollama server to use.")

gpt4all-backend-test/src/main.cpp

@@ -23,9 +23,9 @@ static void run()
     LLMProvider provider(OLLAMA_URL);
     auto version = QCoro::waitFor(provider.getVersion());
     if (version) {
-        fmt::print("Server version: {}\n", *version);
+        fmt::print("Server version: {}\n", version->version);
     } else {
-        fmt::print("Network error: {}\n", version.error().errorString);
+        fmt::print("Error retrieving version: {}\n", version.error().errorString);
         return QCoreApplication::exit(1);
     }
     QCoreApplication::exit(0);

gpt4all-backend/CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.28)
+cmake_minimum_required(VERSION 3.28...3.31)
 project(gpt4all-backend VERSION 0.1 LANGUAGES CXX)
 
 set(CMAKE_CXX_STANDARD 23)  # make sure fmt is compiled with the same C++ version as us
@@ -7,6 +7,7 @@ include(../common/common.cmake)
 find_package(Qt6 6.8 COMPONENTS Concurrent Core Network REQUIRED)
 
 add_subdirectory(../deps common_deps)
+add_subdirectory(deps)
 add_subdirectory(src)
 
 target_sources(gpt4all-backend PUBLIC

gpt4all-backend/deps/CMakeLists.txt

@@ -0,0 +1,14 @@
+include(FetchContent)
+
+set(BUILD_SHARED_LIBS OFF)
+
+# suppress warnings during boost build
+add_compile_definitions($<$<COMPILE_LANGUAGE:CXX>:BOOST_ALLOW_DEPRECATED_HEADERS>)
+
+set(GPT4ALL_BOOST_TAG 1.87.0)
+FetchContent_Declare(
+    boost
+    URL "https://github.com/boostorg/boost/releases/download/boost-${GPT4ALL_BOOST_TAG}/boost-${GPT4ALL_BOOST_TAG}-cmake.tar.xz"
+    URL_HASH "SHA256=7da75f171837577a52bbf217e17f8ea576c7c246e4594d617bfde7fafd408be5"
+)
+FetchContent_MakeAvailable(boost)

gpt4all-backend/include/gpt4all-backend/main.h

@@ -1,6 +1,7 @@
 #pragma once
 
 #include <QCoro/QCoroTask> // IWYU pragma: keep
+#include <boost/describe/class.hpp>
 
 #include <QJsonParseError>
 #include <QNetworkReply>
@@ -19,7 +20,7 @@ struct ResponseError {
 private:
     using ErrorCode = std::variant<
         QNetworkReply::NetworkError,
-        QJsonParseError::ParseError
+        std::exception_ptr
     >;
 
 public:
@@ -33,17 +34,19 @@ public:
         assert(reply->error());
     }
 
-    ResponseError(const QJsonParseError &err)
-        : error(err.error)
-        , errorString(err.errorString())
+    ResponseError(const std::exception &e, std::exception_ptr err)
+        : error(std::move(err))
+        , errorString(e.what())
     {
-        assert(err.error);
+        assert(std::get<std::exception_ptr>(error));
     }
 };
 
 template <typename T>
 using DataOrRespErr = std::expected<T, ResponseError>;
 
+struct VersionResponse { QString version; };
+BOOST_DESCRIBE_STRUCT(VersionResponse, (), (version))
 
 class LLMProvider {
 public:
@@ -55,10 +58,11 @@ public:
     void getBaseUrl(QUrl value) { m_baseUrl = std::move(value); }
 
     /// Retrieve the Ollama version, e.g. "0.5.1"
-    auto getVersion() const -> QCoro::Task<DataOrRespErr<QString>>;
+    auto getVersion() -> QCoro::Task<DataOrRespErr<VersionResponse>>;
 
 private:
-    QUrl m_baseUrl;
+    QUrl                  m_baseUrl;
+    QNetworkAccessManager m_nam;
 };
 
 } // namespace gpt4all::backend

gpt4all-backend/src/CMakeLists.txt

@@ -1,13 +1,27 @@
 set(TARGET gpt4all-backend)
 
 add_library(${TARGET} STATIC
+    json_helpers.cpp
     main.cpp
 )
 target_compile_features(${TARGET} PUBLIC cxx_std_23)
 gpt4all_add_warning_options(${TARGET})
+target_include_directories(${TARGET} PRIVATE
+    .
+    ../include/gpt4all-backend
+)
 target_link_libraries(${TARGET} PUBLIC
-    QCoro6::Coro Qt6::Core Qt6::Network
+    Boost::describe
+    QCoro6::Coro
+    Qt6::Core
+    Qt6::Network
 )
 target_link_libraries(${TARGET} PRIVATE
-    QCoro6::Network fmt::fmt
+    QCoro6::Network
+    fmt::fmt
 )
+
+# link Boost::json as -isystem to suppress -Wundef
+get_target_property(LIB_INCLUDE_DIRS Boost::json INTERFACE_INCLUDE_DIRECTORIES)
+target_include_directories(${TARGET} SYSTEM PRIVATE ${LIB_INCLUDE_DIRS})
+target_link_libraries(${TARGET} PRIVATE Boost::json)

gpt4all-backend/src/json_helpers.cpp

@@ -0,0 +1,12 @@
+#include "json_helpers.h"
+
+#include <boost/json.hpp>
+
+#include <QString>
+
+
+QString tag_invoke(const boost::json::value_to_tag<QString> &, const boost::json::value &value)
+{
+    auto &s = value.as_string();
+    return QString::fromUtf8(s.data(), s.size());
+}

gpt4all-backend/src/json_helpers.h

@@ -0,0 +1,11 @@
+#pragma once
+
+class QString;
+namespace boost::json {
+    class value;
+    template <typename T> struct value_to_tag;
+}
+
+
+/// Allows JSON strings to be deserialized as QString.
+QString tag_invoke(const boost::json::value_to_tag<QString> &, const boost::json::value &value);

gpt4all-backend/src/main.cpp

@@ -1,43 +1,45 @@
-#include <gpt4all-backend/main.h>
+#include "main.h"
 
+#include "json_helpers.h"
+
+#include <QCoro/QCoroIODevice> // IWYU pragma: keep
 #include <QCoro/QCoroNetworkReply> // IWYU pragma: keep
+#include <boost/json.hpp>
 
 #include <QByteArray>
-#include <QJsonDocument>
 #include <QNetworkAccessManager>
 #include <QNetworkRequest>
-#include <QJsonObject>
-#include <QJsonValue>
 
 #include <coroutine>
 #include <expected>
 #include <memory>
 
 using namespace Qt::Literals::StringLiterals;
+namespace json = boost::json;
 
 
 namespace gpt4all::backend {
 
-auto LLMProvider::getVersion() const -> QCoro::Task<DataOrRespErr<QString>>
+auto LLMProvider::getVersion() -> QCoro::Task<DataOrRespErr<VersionResponse>>
 {
-    QNetworkAccessManager nam;
-    std::unique_ptr<QNetworkReply> reply(co_await nam.get(QNetworkRequest(m_baseUrl.resolved(u"/api/version"_s))));
+    std::unique_ptr<QNetworkReply> reply(m_nam.get(QNetworkRequest(m_baseUrl.resolved(u"/api/version"_s))));
     if (reply->error())
         co_return std::unexpected(reply.get());
 
-    QJsonParseError error;
-    auto doc = QJsonDocument::fromJson(reply->readAll(), &error);
-    if (doc.isNull())
-        co_return std::unexpected(error);
+    try {
+        json::parser p;
+        auto coroReply = qCoro(*reply);
+        do {
+            auto chunk = co_await coroReply.readAll();
+            if (reply->error())
+                co_return std::unexpected(reply.get());
+            p.write(chunk.data(), chunk.size());
+        } while (!reply->atEnd());
 
-    assert(doc.isObject());
-    auto obj = doc.object();
-
-    auto version = std::as_const(obj).find("version"_L1);
-    assert(version != obj.constEnd());
-
-    assert(version->isString());
-    co_return version->toString();
+        co_return json::value_to<VersionResponse>(p.release());
+    } catch (const std::exception &e) {
+        co_return std::unexpected(ResponseError(e, std::current_exception()));
+    }
 }
 
 } // namespace gpt4all::backend