YT-19324: move YT provider to ydb/library/yql

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This commit has zero effect on all projects that depend on YQL.

The summary of changes:
- `yql/providers/yt -> ydb/library/yql/providers/yt `- the whole implementation of YT provider is moved into YDB code base for further export as a part of YT YQL plugin shared library;
- `yql/providers/stat/{expr_nodes,uploader} -> ydb/library/yql/providers/stat/{expr_nodes,uploader}` - a small interface without implementation and the description of stat expr nodes;
- `yql/core/extract_predicate/ut -> ydb/library/yql/core/extract_predicate/ut`;
- `yql/core/{ut,ut_common} -> ydb/library/yql/core/{ut,ut_common}`;
- `yql/core` is gone;
- `yql/library/url_preprocessing -> ydb/library/yql/core/url_preprocessing`.

**NB**: all new targets inside `ydb/` are under `IF (NOT CMAKE_EXPORT)` clause which disables them from open-source cmake generation and ya make build. They will be enabled in the subsequent commits.

1 files changed, 140 insertions, 0 deletions

diff --git a/yt/cpp/mapreduce/http/host_manager.cpp b/yt/cpp/mapreduce/http/host_manager.cpp
new file mode 100644
index 0000000000..a239dde769
--- /dev/null
+++ b/yt/cpp/mapreduce/http/host_manager.cpp
@@ -0,0 +1,140 @@
+#include "host_manager.h"
+
+#include "context.h"
+#include "helpers.h"
+#include "http.h"
+#include "http_client.h"
+#include "requests.h"
+
+#include <yt/cpp/mapreduce/interface/logging/yt_log.h>
+
+#include <yt/cpp/mapreduce/interface/config.h>
+
+#include <library/cpp/json/json_reader.h>
+
+#include <util/generic/guid.h>
+#include <util/generic/vector.h>
+#include <util/generic/singleton.h>
+#include <util/generic/ymath.h>
+
+#include <util/random/random.h>
+
+#include <util/string/vector.h>
+
+namespace NYT::NPrivate {
+
+////////////////////////////////////////////////////////////////////////////////
+
+static TVector<TString> ParseJsonStringArray(const TString& response)
+{
+    NJson::TJsonValue value;
+    TStringInput input(response);
+    NJson::ReadJsonTree(&input, &value);
+
+    const NJson::TJsonValue::TArray& array = value.GetArray();
+    TVector<TString> result;
+    result.reserve(array.size());
+    for (size_t i = 0; i < array.size(); ++i) {
+        result.push_back(array[i].GetString());
+    }
+    return result;
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+class THostManager::TClusterHostList
+{
+public:
+    explicit TClusterHostList(TVector<TString> hosts)
+        : Hosts_(std::move(hosts))
+        , Timestamp_(TInstant::Now())
+    { }
+
+    explicit TClusterHostList(std::exception_ptr error)
+        : Error_(std::move(error))
+        , Timestamp_(TInstant::Now())
+    { }
+
+    TString ChooseHostOrThrow() const
+    {
+        if (Error_) {
+            std::rethrow_exception(Error_);
+        }
+
+        if (Hosts_.empty()) {
+            ythrow yexception() << "fetched list of proxies is empty";
+        }
+
+        return Hosts_[RandomNumber<size_t>(Hosts_.size())];
+    }
+
+    TDuration GetAge() const
+    {
+        return TInstant::Now() - Timestamp_;
+    }
+
+private:
+    TVector<TString> Hosts_;
+    std::exception_ptr Error_;
+    TInstant Timestamp_;
+};
+
+////////////////////////////////////////////////////////////////////////////////
+
+THostManager& THostManager::Get()
+{
+    return *Singleton<THostManager>();
+}
+
+void THostManager::Reset()
+{
+    auto guard = Guard(Lock_);
+    ClusterHosts_.clear();
+}
+
+TString THostManager::GetProxyForHeavyRequest(const TClientContext& context)
+{
+    auto cluster = context.ServerName;
+    {
+        auto guard = Guard(Lock_);
+        auto it = ClusterHosts_.find(cluster);
+        if (it != ClusterHosts_.end() && it->second.GetAge() < context.Config->HostListUpdateInterval) {
+            return it->second.ChooseHostOrThrow();
+        }
+    }
+
+    auto hostList = GetHosts(context);
+    auto result = hostList.ChooseHostOrThrow();
+    {
+        auto guard = Guard(Lock_);
+        ClusterHosts_.emplace(cluster, std::move(hostList));
+    }
+    return result;
+}
+
+THostManager::TClusterHostList THostManager::GetHosts(const TClientContext& context)
+{
+    TString hostsEndpoint = context.Config->Hosts;
+    while (hostsEndpoint.StartsWith("/")) {
+        hostsEndpoint = hostsEndpoint.substr(1);
+    }
+    THttpHeader header("GET", hostsEndpoint, false);
+
+    try {
+        auto hostName = context.ServerName;
+        auto requestId = CreateGuidAsString();
+        // TODO: we need to set socket timeout here
+        auto response = context.HttpClient->Request(GetFullUrl(hostName, context, header), requestId, header);
+        auto hosts = ParseJsonStringArray(response->GetResponse());
+        for (auto& host : hosts) {
+            host = CreateHostNameWithPort(host, context);
+        }
+        return TClusterHostList(std::move(hosts));
+    } catch (const std::exception& e) {
+        return TClusterHostList(std::current_exception());
+    }
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
+} // namespace NYT::NPrivate