samples/http_caching/http_caching.cpp

#include <userver/utils/assert.hpp>
 
#include <userver/cache/caching_component_base.hpp>
#include <userver/clients/dns/component.hpp>
#include <userver/clients/http/component.hpp>
#include <userver/components/component.hpp>
#include <userver/components/minimal_server_component_list.hpp>
#include <userver/http/url.hpp>
#include <userver/server/handlers/http_handler_base.hpp>
#include <userver/server/handlers/tests_control.hpp>
#include <userver/testsuite/testsuite_support.hpp>
#include <userver/utils/daemon_run.hpp>
#include <userver/yaml_config/merge_schemas.hpp>
 
#include <userver/utest/using_namespace_userver.hpp>
 
namespace samples::http_cache {
 
struct KeyLang {
    std::string key;
    std::string language;
};
 
struct KeyLangEq {
    bool operator()(const KeyLang& x, const KeyLang& y) const noexcept;
};
 
struct KeyLangHash {
    bool operator()(const KeyLang& x) const noexcept;
};
 
using KeyLangToTranslation = std::unordered_map<KeyLang, std::string, KeyLangHash, KeyLangEq>;
 
}  // namespace samples::http_cache
 
namespace samples::http_cache {
 
bool KeyLangEq::operator()(const KeyLang& x, const KeyLang& y) const noexcept {
    return x.key == y.key && x.language == y.language;
}
 
bool KeyLangHash::operator()(const KeyLang& x) const noexcept {
    std::string data;
    data.append(x.key);
    data.append(x.language);
    return std::hash<std::string>{}(data);
}
 
}  // namespace samples::http_cache
 
namespace samples::http_cache {
 
class HttpCachedTranslations final : public components::CachingComponentBase<KeyLangToTranslation> {
public:
    static constexpr std::string_view kName = "cache-http-translations";
 
    HttpCachedTranslations(const components::ComponentConfig& config, const components::ComponentContext& context);
    ~HttpCachedTranslations() override;
 
    void Update(
        cache::UpdateType type,
        [[maybe_unused]] const std::chrono::system_clock::time_point& last_update,
        [[maybe_unused]] const std::chrono::system_clock::time_point& now,
        cache::UpdateStatisticsScope& stats_scope
    ) override;
 
    static yaml_config::Schema GetStaticConfigSchema();
 
private:
    clients::http::Client& http_client_;
    const std::string translations_url_;
    std::string last_update_remote_;
 
    formats::json::Value GetAllData() const;
    formats::json::Value GetUpdatedData() const;
 
    void MergeAndSetData(
        KeyLangToTranslation&& content,
        formats::json::Value json,
        cache::UpdateStatisticsScope& stats_scope
    );
};
 
}  // namespace samples::http_cache
 
namespace samples::http_cache {
 
HttpCachedTranslations::HttpCachedTranslations(
    const components::ComponentConfig& config,
    const components::ComponentContext& context
)
    : CachingComponentBase(config, context),
      http_client_(context.FindComponent<components::HttpClient>().GetHttpClient()),
      translations_url_(config["translations-url"].As<std::string>()) {
    CacheUpdateTrait::StartPeriodicUpdates();
}
 
HttpCachedTranslations::~HttpCachedTranslations() { CacheUpdateTrait::StopPeriodicUpdates(); }
 
void HttpCachedTranslations::Update(
    cache::UpdateType type,
    [[maybe_unused]] const std::chrono::system_clock::time_point& last_update,
    [[maybe_unused]] const std::chrono::system_clock::time_point& now,
    cache::UpdateStatisticsScope& stats_scope
) {
    formats::json::Value json;
    switch (type) {
        case cache::UpdateType::kFull:
            json = GetAllData();
            break;
        case cache::UpdateType::kIncremental:
            json = GetUpdatedData();
            break;
        default:
            UASSERT(false);
    }
 
    if (json.IsEmpty()) {
        stats_scope.FinishNoChanges();
        return;
    }
 
    KeyLangToTranslation content;
    if (type == cache::UpdateType::kIncremental) {
        const auto snapshot = Get();  // smart pointer to a shared cache data
        content = *snapshot;          // copying the shared data
    }
 
    MergeAndSetData(std::move(content), json, stats_scope);
}
 
formats::json::Value HttpCachedTranslations::GetAllData() const {
    auto response = http_client_.CreateRequest()
                        .get(translations_url_)  // HTTP GET translations_url_ URL
                        .retry(2)                // retry once in case of error
                        .timeout(std::chrono::milliseconds{500})
                        .perform();  // start performing the request
    response->raise_for_status();
    return formats::json::FromString(response->body_view());
}
 
formats::json::Value HttpCachedTranslations::GetUpdatedData() const {
    const auto url = http::MakeUrl(translations_url_, {{"last_update", last_update_remote_}});
    auto response = http_client_.CreateRequest().get(url).retry(2).timeout(std::chrono::milliseconds{500}).perform();
    response->raise_for_status();
    return formats::json::FromString(response->body_view());
}
 
void HttpCachedTranslations::MergeAndSetData(
    KeyLangToTranslation&& content,
    formats::json::Value json,
    cache::UpdateStatisticsScope& stats_scope
) {
    for (const auto& [key, value] : Items(json["content"])) {
        for (const auto& [lang, text] : Items(value)) {
            content.insert_or_assign(KeyLang{key, lang}, text.As<std::string>());
        }
        stats_scope.IncreaseDocumentsReadCount(value.GetSize());
    }
 
    auto update_time = json["update_time"].As<std::string>();
 
    const auto size = content.size();
    Set(std::move(content));
    last_update_remote_ = std::move(update_time);
    stats_scope.Finish(size);
}
 
class GreetUser final : public server::handlers::HttpHandlerBase {
public:
    static constexpr std::string_view kName = "handler-greet-user";
 
    GreetUser(const components::ComponentConfig& config, const components::ComponentContext& context)
        : HttpHandlerBase(config, context), cache_(context.FindComponent<HttpCachedTranslations>()) {}
 
    std::string HandleRequestThrow(const server::http::HttpRequest& request, server::request::RequestContext&)
        const override {
        const auto cache_snapshot = cache_.Get();
 
        using samples::http_cache::KeyLang;
        const auto& hello = cache_snapshot->at(KeyLang{"hello", "ru"});
        const auto& welcome = cache_snapshot->at(KeyLang{"welcome", "ru"});
        request.GetHttpResponse().SetContentType(http::content_type::kTextPlain);
        return fmt::format("{}, {}! {}", hello, request.GetArg("username"), welcome);
    }
 
private:
    samples::http_cache::HttpCachedTranslations& cache_;
};
 
yaml_config::Schema HttpCachedTranslations::GetStaticConfigSchema() {
    return yaml_config::MergeSchemas<components::CachingComponentBase<KeyLangToTranslation>>(R"(
type: object
description: HTTP caching sample component
additionalProperties: false
properties:
    translations-url:
        type: string
        description: some other microservice listens on this URL
)");
}
 
}  // namespace samples::http_cache
 
int main(int argc, char* argv[]) {
    const auto component_list = components::MinimalServerComponentList()
                                    .Append<samples::http_cache::HttpCachedTranslations>()
                                    .Append<samples::http_cache::GreetUser>()
                                    .Append<components::TestsuiteSupport>()
                                    .Append<server::handlers::TestsControl>()
                                    .Append<clients::dns::Component>()
                                    .Append<components::HttpClient>();
    return utils::DaemonMain(argc, argv, component_list);
}