easy.hpp

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#pragma once
 
/// @file userver/easy.hpp
/// @brief Headers of an library for `easy` prototyping
 
#include <functional>
#include <string>
#include <string_view>
#include <type_traits>
 
#include <userver/clients/http/client.hpp>
#include <userver/components/component_base.hpp>
#include <userver/components/component_list.hpp>
#include <userver/formats/json.hpp>
#include <userver/http/content_type.hpp>
#include <userver/server/handlers/exceptions.hpp>  // out of the box support for server::handlers::ClientError
#include <userver/server/http/http_request.hpp>
#include <userver/server/request/request_context.hpp>
#include <userver/utils/meta_light.hpp>
 
#include <userver/storages/postgres/cluster.hpp>
#include <userver/storages/query.hpp>
 
USERVER_NAMESPACE_BEGIN
 
/// @brief Top namespace for `easy` library
namespace easy {
 
namespace impl {
 
class DependenciesBase : public components::ComponentBase {
public:
    static constexpr std::string_view kName = "easy-dependencies";
    using components::ComponentBase::ComponentBase;
    ~DependenciesBase() override;
};
 
/// @cond
template <class T>
struct FirstFunctionArgument;
 
template <class Return, class First, class... Args>
struct FirstFunctionArgument<Return(First, Args...) noexcept> {
    using type = First;
};
 
template <class Return, class First, class... Args>
struct FirstFunctionArgument<Return(First, Args...)> {
    using type = First;
};
 
template <class Return, class Class, class First, class... Args>
struct FirstFunctionArgument<Return (Class::*)(First, Args...)> {
    using type = First;
};
 
template <class Return, class Class, class First, class... Args>
struct FirstFunctionArgument<Return (Class::*)(First, Args...) const> {
    using type = First;
};
 
template <class T>
struct FirstFunctionArgument : FirstFunctionArgument<decltype(&std::decay_t<T>::operator())> {};
/// @endcond
 
template <typename T>
concept HasFromJsonString = requires {
    {
        FromJsonString(std::string_view{}, formats::parse::To<T>{})
    } -> std::same_as<T>;
};
 
template <typename T>
T ParseFromJsonString(std::string_view json) {
    if constexpr (HasFromJsonString<T>) {
        return FromJsonString(json, formats::parse::To<T>{});
    } else {
        return formats::json::FromString(json).As<T>();
    }
}
 
template <typename T>
std::string FormatToJsonString(const T& value) {
    if constexpr (requires { ToJsonString(value); }) {
        return ToJsonString(value);
    } else {
        return formats::json::ToString(formats::json::ValueBuilder{value}.ExtractValue());
    }
}
 
}  // namespace impl
 
/// @ingroup userver_components
///
/// @brief Factory component for the dependencies from easy library.
///
/// This component can be registered in the component list and used by any client. For example:
///
/// @snippet samples/easy/6_pg_service_template_no_http_with/src/main.cpp  main
template <class Dependencies>
class DependenciesComponent : public impl::DependenciesBase {
public:
    /// @ingroup userver_component_names
    /// @brief The default name of easy::DependenciesComponent
    static constexpr std::string_view kName = "easy-dependencies";
 
    DependenciesComponent(const components::ComponentConfig& config, const components::ComponentContext& context)
        : DependenciesBase(config, context),
          dependencies_(context)
    {}
 
    Dependencies GetDependencies() const { return dependencies_; }
 
private:
    Dependencies dependencies_;
};
 
/// @brief easy::HttpWith like class with erased dependencies information that should be used only in dependency
/// registration functions; use easy::HttpWith if not making a new dependency class.
class HttpBase final {
public:
    struct Callback {
        std::function<std::string(const server::http::HttpRequest&, const impl::DependenciesBase&)> function;
        std::optional<http::ContentType> content_type;
    };
 
    /// Sets the default Content-Type header for all the routes
    void DefaultContentType(http::ContentType content_type);
 
    /// Register an HTTP handler by `path` that supports the `methods` HTTP methods
    void Route(std::string_view path, Callback&& func, std::initializer_list<server::http::HttpMethod> methods);
 
    /// Append a component to the component list of a service
    template <class Component>
    bool TryAddComponent(std::string_view name, std::string_view config) {
        if (component_list_.Contains(name)) {
            return false;
        }
 
        component_list_.Append<Component>(name);
        AddComponentConfig(name, config);
        return true;
    }
 
    template <class Component>
    bool TryAddComponent(std::string_view name) {
        if (component_list_.Contains(name)) {
            return false;
        }
 
        component_list_.Append<Component>(name);
        return true;
    }
 
    /// Stores the schema for further retrieval from GetDbSchema()
    void DbSchema(std::string_view schema);
 
    /// @returns the \b last schema that was provided to the easy::HttpWith or easy::HttpBase
    static const std::string& GetDbSchema() noexcept;
 
    /// Set the HTTP server listen port, default is 8080.
    void Port(std::uint16_t port);
 
    /// Set the logging level for the service
    void LogLevel(logging::Level level);
 
private:
    template <class>
    friend class HttpWith;
 
    void AddComponentConfig(std::string_view name, std::string_view config);
 
    HttpBase(int argc, const char* const argv[]);
    ~HttpBase();
 
    class Handle;
 
    const int argc_;
    const char* const* argv_;
    std::string static_config_;
    components::ComponentList component_list_;
 
    std::uint16_t port_ = 8080;
    logging::Level level_ = logging::Level::kDebug;
};
 
/// Class that combines dependencies passed to HttpWith into a single type, that is passed to callbacks.
///
/// @see @ref scripts/docs/en/userver/libraries/easy.md
template <class... Dependency>
class Dependencies final : public Dependency... {
public:
    explicit Dependencies(const components::ComponentContext& context) : Dependency{context}... {}
 
    static void RegisterOn(HttpBase& app) { (Dependency::RegisterOn(app), ...); }
};
 
/// @brief Class for describing the service functionality in simple declarative way that generates static configs,
/// applies schemas.
///
/// @see @ref scripts/docs/en/userver/libraries/easy.md
template <class Dependency = Dependencies<>>
class HttpWith final {
public:
    /// Helper class that can store any callback of the following signatures:
    ///
    /// * formats::json::Value(formats::json::Value, const Dependency&)
    /// * formats::json::Value(formats::json::Value)
    /// * formats::json::Value(const HttpRequest&, const Dependency&)
    /// * std::string(const HttpRequest&, const Dependency&)
    /// * formats::json::Value(const HttpRequest&)
    /// * std::string(const HttpRequest&)
    /// * JsonSerializableStructure(JsonParseableStructure, const Dependency&)
    /// * JsonSerializableStructure(JsonParseableStructure)
    ///
    /// If callback returns formats::json::Value or accepts a JSON parsable structure then the default content type
    /// is set to `application/json`.
    class Callback final {
    public:
        template <class Function>
        Callback(Function func);
 
        HttpBase::Callback Extract() && noexcept { return std::move(callback_); }
 
    private:
        static Dependency GetDependencies(const impl::DependenciesBase& deps) {
            return static_cast<const DependenciesComponent&>(deps).GetDependencies();
        };
        HttpBase::Callback callback_;
    };
 
    HttpWith(int argc, const char* const argv[])
        : impl_(argc, argv)
    {
        impl_.TryAddComponent<DependenciesComponent>(DependenciesComponent::kName);
    }
    ~HttpWith() { Dependency::RegisterOn(impl_); }
 
    /// @copydoc HttpBase::DefaultContentType
    HttpWith& DefaultContentType(http::ContentType content_type) {
        return (impl_.DefaultContentType(content_type), *this);
    }
 
    /// @copydoc HttpBase::Route
    HttpWith& Route(
        std::string_view path,
        Callback&& func,
        std::initializer_list<server::http::HttpMethod> methods =
            {
                server::http::HttpMethod::kGet,
                server::http::HttpMethod::kPost,
                server::http::HttpMethod::kDelete,
                server::http::HttpMethod::kPut,
                server::http::HttpMethod::kPatch,
            }
    ) {
        impl_.Route(path, std::move(func).Extract(), methods);
        return *this;
    }
 
    /// Register an HTTP handler by `path` that supports the HTTP GET method.
    HttpWith& Get(std::string_view path, Callback&& func) {
        impl_.Route(path, std::move(func).Extract(), {server::http::HttpMethod::kGet});
        return *this;
    }
 
    /// Register an HTTP handler by `path` that supports the HTTP POST method.
    HttpWith& Post(std::string_view path, Callback&& func) {
        impl_.Route(path, std::move(func).Extract(), {server::http::HttpMethod::kPost});
        return *this;
    }
 
    /// Register an HTTP handler by `path` that supports the HTTP DELETE method.
    HttpWith& Del(std::string_view path, Callback&& func) {
        impl_.Route(path, std::move(func).Extract(), {server::http::HttpMethod::kDelete});
        return *this;
    }
 
    /// Register an HTTP handler by `path` that supports the HTTP PUT method.
    HttpWith& Put(std::string_view path, Callback&& func) {
        impl_.Route(path, std::move(func).Extract(), {server::http::HttpMethod::kPut});
        return *this;
    }
 
    /// Register an HTTP handler by `path` that supports the HTTP PATCH method.
    HttpWith& Patch(std::string_view path, Callback&& func) {
        impl_.Route(path, std::move(func).Extract(), {server::http::HttpMethod::kPatch});
        return *this;
    }
 
    /// @copydoc HttpBase::DbSchema
    HttpWith& DbSchema(std::string_view schema) {
        impl_.DbSchema(schema);
        return *this;
    }
 
    /// @copydoc HttpBase::Port
    HttpWith& Port(std::uint16_t port) {
        impl_.Port(port);
        return *this;
    }
 
    /// @copydoc HttpBase::LogLevel
    HttpWith& LogLevel(logging::Level level) {
        impl_.LogLevel(level);
        return *this;
    }
 
private:
    using DependenciesComponent = easy::DependenciesComponent<Dependency>;
    HttpBase impl_;
};
 
template <class Dependency>
template <class Function>
HttpWith<Dependency>::Callback::Callback(Function func) {
    using server::http::HttpRequest;
 
    constexpr unsigned kMatches =
        (std::is_invocable_r_v<formats::json::Value, Function, formats::json::Value, const Dependency&> << 0) |
        (std::is_invocable_r_v<formats::json::Value, Function, formats::json::Value> << 1) |
        (std::is_invocable_r_v<formats::json::Value, Function, const HttpRequest&, const Dependency&> << 2) |
        (std::is_invocable_r_v<std::string, Function, const HttpRequest&, const Dependency&> << 3) |
        (std::is_invocable_r_v<formats::json::Value, Function, const HttpRequest&> << 4) |
        (std::is_invocable_r_v<std::string, Function, const HttpRequest&> << 5);
    constexpr bool has_single_match = (kMatches == 0 || ((kMatches & (kMatches - 1)) == 0));
    static_assert(
        has_single_match,
        "Found more than one matching signature, probably due to `auto` usage in parameters. See "
        "the easy::HttpWith::Callback docs for info on supported signatures"
    );
 
    if constexpr (kMatches & 1) {
        callback_.content_type = http::content_type::kApplicationJson;
        callback_.function = [f = std::move(func)](const HttpRequest& req, const impl::DependenciesBase& deps) {
            return formats::json::ToString(f(formats::json::FromString(req.RequestBody()), GetDependencies(deps)));
        };
    } else if constexpr (kMatches & 2) {
        callback_.content_type = http::content_type::kApplicationJson;
        callback_.function = [f = std::move(func)](const HttpRequest& req, const impl::DependenciesBase&) {
            return formats::json::ToString(f(formats::json::FromString(req.RequestBody())));
        };
    } else if constexpr (kMatches & 4) {
        callback_.content_type = http::content_type::kApplicationJson;
        callback_.function = [f = std::move(func)](const HttpRequest& req, const impl::DependenciesBase& deps) {
            return formats::json::ToString(f(req, GetDependencies(deps)));
        };
    } else if constexpr (kMatches & 8) {
        callback_.content_type = http::content_type::kApplicationJson;
        callback_.function = [f = std::move(func)](const HttpRequest& req, const impl::DependenciesBase& deps) {
            return f(req, GetDependencies(deps));
        };
    } else if constexpr (kMatches & 16) {
        callback_.content_type = http::content_type::kApplicationJson;
        callback_.function = [f = std::move(func)](const HttpRequest& req, const impl::DependenciesBase&) {
            return formats::json::ToString(f(req));
        };
    } else if constexpr (kMatches & 32) {
        callback_.function = [f = std::move(func)](const HttpRequest& req, const impl::DependenciesBase&) {
            return f(req);
        };
    } else {
        using FirstArgument = std::decay_t<typename impl::FirstFunctionArgument<Function>::type>;
        static_assert(
            std::is_class_v<FirstArgument>,
            "First function argument should be a class or structure that is JSON pareseable"
        );
 
        callback_.content_type = http::content_type::kApplicationJson;
        callback_.function = [f = std::move(func)](const HttpRequest& req, const impl::DependenciesBase& deps) {
            auto arg = impl::ParseFromJsonString<FirstArgument>(req.RequestBody());
 
            if constexpr (std::is_invocable_v<Function, FirstArgument, const Dependency&>) {
                return impl::FormatToJsonString(f(std::move(arg), GetDependencies(deps)));
            } else {
                static_assert(
                    std::is_invocable_v<Function, FirstArgument>,
                    "Found no matching signature, probably due to second argument of the provided function. See "
                    "the easy::HttpWith::Callback docs for info on supported signatures"
                );
                return impl::FormatToJsonString(f(std::move(arg)));
            }
        };
    }
}
 
/// @brief Dependency class that provides a PostgreSQL cluster client.
class PgDep {
public:
    explicit PgDep(const components::ComponentContext& context);
    storages::postgres::Cluster& pg() const noexcept { return *pg_cluster_; }
    static void RegisterOn(HttpBase& app);
 
private:
    storages::postgres::ClusterPtr pg_cluster_;
};
 
/// @brief Dependency class that provides a Http client.
class HttpDep {
public:
    explicit HttpDep(const components::ComponentContext& context);
    clients::http::Client& http() { return http_; }
    static void RegisterOn(HttpBase& app);
 
private:
    clients::http::Client& http_;
};
 
}  // namespace easy
 
template <class Dependencies>
inline constexpr auto
    components::kConfigFileMode<easy::DependenciesComponent<Dependencies>> = ConfigFileMode::kNotRequired;
 
USERVER_NAMESPACE_END