ISSUES-5436 support custom http

dbms/src/Interpreters/CustomHTTP/HTTPMatchExecutor.cpp

@@ -0,0 +1,259 @@
+#include <Interpreters/CustomHTTP/HTTPMatchExecutor.h>
+
+#include <ext/scope_guard.h>
+#include <Common/Exception.h>
+#include <Common/SettingsChanges.h>
+#include <Core/ExternalTable.h>
+#include <Interpreters/Context.h>
+#include <Interpreters/CustomHTTP/HTTPMatchExecutorDefault.h>
+#include <Poco/Net/HTTPBasicCredentials.h>
+#include <IO/CascadeWriteBuffer.h>
+#include <IO/MemoryReadWriteBuffer.h>
+#include <IO/WriteBufferFromTemporaryFile.h>
+#include <Compression/CompressedWriteBuffer.h>
+#include <IO/ReadBufferFromIStream.h>
+#include <IO/BrotliReadBuffer.h>
+#include <IO/ReadBufferFromString.h>
+#include <IO/ZlibInflatingReadBuffer.h>
+#include <DataStreams/IBlockInputStream.h>
+#include <Poco/Net/HTTPServerRequestImpl.h>
+#include <Compression/CompressedReadBuffer.h>
+#include <Interpreters/CustomHTTP/HTTPStreamsWithInput.h>
+#include <Interpreters/CustomHTTP/HTTPStreamsWithOutput.h>
+
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int SYNTAX_ERROR;
+    extern const int LOGICAL_ERROR;
+    extern const int REQUIRED_PASSWORD;
+    extern const int INVALID_SESSION_TIMEOUT;
+    extern const int UNKNOWN_COMPRESSION_METHOD;
+}
+
+
+namespace
+{
+    duration parseSessionTimeout(const HTMLForm & params, size_t default_session_timeout, size_t max_session_timeout)
+    {
+        size_t session_timeout = default_session_timeout;
+
+        if (params.has("session_timeout"))
+        {
+            std::string session_timeout_str = params.get("session_timeout");
+
+            ReadBufferFromString buf(session_timeout_str);
+            if (!tryReadIntText(session_timeout, buf) || !buf.eof())
+                throw Exception("Invalid session timeout: '" + session_timeout_str + "'", ErrorCodes::INVALID_SESSION_TIMEOUT);
+
+            if (session_timeout > max_session_timeout)
+                throw Exception(
+                    "Session timeout '" + session_timeout_str + "' is larger than max_session_timeout: " + toString(max_session_timeout) +
+                    ". Maximum session timeout could be modified in configuration file.", ErrorCodes::INVALID_SESSION_TIMEOUT);
+        }
+
+        return std::chrono::seconds(session_timeout);
+    }
+}
+
+
+void HTTPMatchExecutor::execute(Context & context, HTTPServerRequest & request, HTTPServerResponse & response, HTMLForm & params, HTTPStreamsWithOutput & used_output) const
+{
+    authentication(context, request, params);
+
+    std::shared_ptr<Context> session_context;
+    String session_id = params.get("session_id", "");
+    duration session_timeout = parseSessionTimeout(params, 1800, 3600);
+
+    SCOPE_EXIT({ detachSessionContext(session_context, session_id, session_timeout); });
+    session_context = attachSessionContext(context, params, session_id, session_timeout);
+
+    initClientInfo(context, request);
+    used_output.attachRequestAndResponse(context, request, response, params, /* TODO: keep_alive_time_out */ 0);
+
+    HTTPStreamsWithInput used_input(request, params);
+    collectParamsAndApplySettings(request, params, context);
+
+    Settings & query_settings = context.getSettingsRef();
+    used_input.attachSettings(context, query_settings, request);
+    used_output.attachSettings(context, query_settings, request);
+
+    String execute_query_string = getExecuteQuery(params);
+    ReadBufferPtr query_in_buffer = std::make_shared<ReadBufferFromString>(execute_query_string);
+
+    ReadBufferPtr in = query_in_buffer;
+    if (!needParsePostBody(request, params) || !context.getExternalTables().empty())
+        in = std::make_shared<ConcatReadBuffer>(*query_in_buffer, *used_input.in_maybe_internal_compressed);
+
+    executeQuery(*in, *used_output.out_maybe_delayed_and_compressed, /* allow_into_outfile = */ false, context,
+        [&response] (const String & content_type) { response.setContentType(content_type); },
+        [&response] (const String & current_query_id) { response.add("X-ClickHouse-Query-Id", current_query_id); });
+
+    used_output.finalize();
+}
+
+void HTTPMatchExecutor::initClientInfo(Context & context, HTTPServerRequest & request) const
+{
+
+    ClientInfo & client_info = context.getClientInfo();
+    client_info.query_kind = ClientInfo::QueryKind::INITIAL_QUERY;
+    client_info.interface = ClientInfo::Interface::HTTP;
+
+    /// Query sent through HTTP interface is initial.
+    client_info.initial_user = client_info.current_user;
+    client_info.initial_query_id = client_info.current_query_id;
+    client_info.initial_address = client_info.current_address;
+
+    ClientInfo::HTTPMethod http_method = ClientInfo::HTTPMethod::UNKNOWN;
+    if (request.getMethod() == Poco::Net::HTTPServerRequest::HTTP_GET)
+        http_method = ClientInfo::HTTPMethod::GET;
+    else if (request.getMethod() == Poco::Net::HTTPServerRequest::HTTP_POST)
+        http_method = ClientInfo::HTTPMethod::POST;
+
+    client_info.http_method = http_method;
+    client_info.http_user_agent = request.get("User-Agent", "");
+}
+
+void HTTPMatchExecutor::authentication(Context & context, HTTPServerRequest & request, HTMLForm & params) const
+{
+    auto user = request.get("X-ClickHouse-User", "");
+    auto password = request.get("X-ClickHouse-Key", "");
+    auto quota_key = request.get("X-ClickHouse-Quota", "");
+
+    if (user.empty() && password.empty() && quota_key.empty())
+    {
+        /// User name and password can be passed using query parameters
+        /// or using HTTP Basic auth (both methods are insecure).
+        if (request.hasCredentials())
+        {
+            Poco::Net::HTTPBasicCredentials credentials(request);
+
+            user = credentials.getUsername();
+            password = credentials.getPassword();
+        }
+        else
+        {
+            user = params.get("user", "default");
+            password = params.get("password", "");
+        }
+
+        quota_key = params.get("quota_key", "");
+    }
+    else
+    {
+        /// It is prohibited to mix different authorization schemes.
+        if (request.hasCredentials()
+            || params.has("user")
+            || params.has("password")
+            || params.has("quota_key"))
+        {
+            throw Exception("Invalid authentication: it is not allowed to use X-ClickHouse HTTP headers and other authentication methods simultaneously", ErrorCodes::REQUIRED_PASSWORD);
+        }
+    }
+
+    std::string query_id = params.get("query_id", "");
+    context.setUser(user, password, request.clientAddress(), quota_key);
+    context.setCurrentQueryId(query_id);
+}
+
+std::shared_ptr<Context> HTTPMatchExecutor::attachSessionContext(
+    Context & context, HTMLForm & params, const String & session_id, const duration & session_timeout) const
+{
+    if (!session_id.empty())
+    {
+        std::string session_check = params.get("session_check", "");
+        auto session_context = context.acquireSession(session_id, session_timeout, session_check == "1");
+
+        context = *session_context;
+        context.setSessionContext(*session_context);
+        return session_context;
+    }
+    return {};
+}
+
+void HTTPMatchExecutor::detachSessionContext(std::shared_ptr<Context> & session_context, const String & session_id, const duration & session_timeout) const
+{
+    if (session_context)
+        session_context->releaseSession(session_id, session_timeout);
+}
+
+void HTTPMatchExecutor::collectParamsAndApplySettings(HTTPServerRequest & request, HTMLForm & params, Context & context) const
+{
+    static const NameSet reserved_param_names{
+        "compress", "decompress", "user", "password", "quota_key", "query_id", "stacktrace", "buffer_size", "wait_end_of_query",
+        "session_id", "session_timeout", "session_check"};
+
+    Names reserved_param_suffixes;
+
+    auto param_could_be_skipped = [&] (const String & name)
+    {
+        if (reserved_param_names.count(name))
+            return true;
+
+        for (const String & suffix : reserved_param_suffixes)
+        {
+            if (endsWith(name, suffix))
+                return true;
+        }
+
+        return false;
+    };
+
+    /// Settings can be overridden in the query.
+    /// Some parameters (database, default_format, everything used in the code above) do not
+    /// belong to the Settings class.
+
+    /// 'readonly' setting values mean:
+    /// readonly = 0 - any query is allowed, client can change any setting.
+    /// readonly = 1 - only readonly queries are allowed, client can't change settings.
+    /// readonly = 2 - only readonly queries are allowed, client can change any setting except 'readonly'.
+
+    /// In theory if initially readonly = 0, the client can change any setting and then set readonly
+    /// to some other value.
+    /// Only readonly queries are allowed for HTTP GET requests.
+    if (request.getMethod() == Poco::Net::HTTPRequest::HTTP_GET)
+    {
+        Settings & settings = context.getSettingsRef();
+
+        if (settings.readonly == 0)
+            settings.readonly = 2;
+    }
+
+    bool has_multipart = startsWith(request.getContentType().data(), "multipart/form-data");
+
+    if (has_multipart || needParsePostBody(request, params))
+    {
+        ExternalTablesHandler handler(context, params);
+        params.load(request, request.stream(), handler);
+
+        if (has_multipart)
+        {
+            /// Skip unneeded parameters to avoid confusing them later with context settings or query parameters.
+            reserved_param_suffixes.reserve(3);
+            /// It is a bug and ambiguity with `date_time_input_format` and `low_cardinality_allow_in_native_format` formats/settings.
+            reserved_param_suffixes.emplace_back("_format");
+            reserved_param_suffixes.emplace_back("_types");
+            reserved_param_suffixes.emplace_back("_structure");
+        }
+    }
+
+    SettingsChanges settings_changes;
+    for (const auto & [key, value] : params)
+    {
+        if (key == "database")
+            context.setCurrentDatabase(value);
+        else if (key == "default_format")
+            context.setDefaultFormat(value);
+        else if (!param_could_be_skipped(key) && !acceptQueryParam(context, key, value))
+            settings_changes.push_back({key, value}); /// All other query parameters are treated as settings.
+    }
+
+    /// For external data we also want settings
+    context.checkSettingsConstraints(settings_changes);
+    context.applySettingsChanges(settings_changes);
+}
+
+}

dbms/src/Interpreters/CustomHTTP/HTTPMatchExecutor.h

@@ -0,0 +1,55 @@
+#pragma once
+
+#include <Core/Types.h>
+#include <Common/HTMLForm.h>
+#include <Common/Exception.h>
+#include <Poco/Net/HTTPServerRequest.h>
+#include <Poco/Net/HTTPServerResponse.h>
+#include <Poco/Util/AbstractConfiguration.h>
+#include <IO/ReadBuffer.h>
+
+namespace DB
+{
+
+class Context;
+class HTTPMatchExecutor;
+struct HTTPStreamsWithInput;
+struct HTTPStreamsWithOutput;
+
+using duration = std::chrono::steady_clock::duration;
+using HTTPMatchExecutorPtr = std::shared_ptr<HTTPMatchExecutor>;
+
+class HTTPMatchExecutor
+{
+public:
+    using HTTPServerRequest = Poco::Net::HTTPServerRequest;
+    using HTTPServerResponse = Poco::Net::HTTPServerResponse;
+
+    bool match(HTTPServerRequest & request, HTMLForm & params) const { return matchImpl(request, params); };
+
+    void execute(Context & context, HTTPServerRequest & request, HTTPServerResponse & response, HTMLForm & params, HTTPStreamsWithOutput & used_output) const;
+
+    virtual ~HTTPMatchExecutor() = default;
+protected:
+
+    virtual bool matchImpl(HTTPServerRequest & request, HTMLForm & params) const = 0;
+
+    virtual String getExecuteQuery(HTMLForm & params) const = 0;
+
+    virtual bool needParsePostBody(HTTPServerRequest & request, HTMLForm & params) const = 0;
+
+    virtual bool acceptQueryParam(Context & context, const String & key, const String & value) const = 0;
+
+    void initClientInfo(Context & context, HTTPServerRequest & request) const;
+
+    void authentication(Context & context, HTTPServerRequest & request, HTMLForm & params) const;
+
+    void detachSessionContext(std::shared_ptr<Context> & context, const String & session_id, const duration & session_timeout) const;
+
+    std::shared_ptr<Context> attachSessionContext(Context & context, HTMLForm & params, const String & session_id, const duration & session_timeout) const;
+
+    void collectParamsAndApplySettings(HTTPServerRequest & request, HTMLForm & params, Context & context) const;
+
+};
+
+}

dbms/src/Interpreters/CustomHTTP/HTTPMatchExecutorDefault.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include <Interpreters/CustomHTTP/HTTPMatchExecutor.h>
+#include <IO/ConcatReadBuffer.h>
+#include <IO/ReadBufferFromString.h>
+#include <Interpreters/executeQuery.h>
+
+
+namespace DB
+{
+
+class HTTPMatchExecutorDefault : public HTTPMatchExecutor
+{
+protected:
+
+    bool matchImpl(HTTPServerRequest & /*request*/, HTMLForm & /*params*/) const override { return true; }
+
+    bool needParsePostBody(HTTPServerRequest & /*request*/, HTMLForm & /*params*/) const override { return false; }
+
+    String getExecuteQuery(HTMLForm & params) const override
+    {
+        String execute_query;
+        for (const auto & [key, value] : params)
+        {
+            if (key == "query")
+                execute_query += value;
+        }
+
+        return execute_query;
+    }
+
+    bool acceptQueryParam(Context &context, const String &key, const String &value) const override
+    {
+        if (startsWith(key, "param_"))
+        {
+            /// Save name and values of substitution in dictionary.
+            context.setQueryParameter(key.substr(strlen("param_")), value);
+            return true;
+        }
+
+        return key == "query";
+    }
+
+};
+
+}

dbms/src/Interpreters/CustomHTTP/HTTPStreamsWithInput.cpp

@@ -0,0 +1,73 @@
+#include <Interpreters/CustomHTTP/HTTPStreamsWithInput.h>
+
+#include <IO/ReadBufferFromIStream.h>
+#include <IO/ZlibInflatingReadBuffer.h>
+#include <Compression/CompressedReadBuffer.h>
+#include "HTTPStreamsWithInput.h"
+
+
+namespace DB
+{
+
+namespace ErrorCodes
+{
+    extern const int UNKNOWN_COMPRESSION_METHOD;
+}
+
+HTTPStreamsWithInput::HTTPStreamsWithInput(HTTPServerRequest & request, HTMLForm & from)
+    : in(createRawInBuffer(request))
+    , in_maybe_compressed(createCompressedBuffer(request, in))
+    , in_maybe_internal_compressed(createInternalCompressedBuffer(from, in_maybe_compressed))
+{
+}
+
+ReadBufferPtr HTTPStreamsWithInput::createRawInBuffer(HTTPServerRequest & request) const
+{
+    return std::make_unique<ReadBufferFromIStream>(request.stream());
+}
+
+ReadBufferPtr HTTPStreamsWithInput::createCompressedBuffer(HTTPServerRequest & request, ReadBufferPtr & raw_buffer) const
+{
+    /// Request body can be compressed using algorithm specified in the Content-Encoding header.
+    String http_compressed_method = request.get("Content-Encoding", "");
+
+    if (!http_compressed_method.empty())
+    {
+        if (http_compressed_method == "gzip")
+            return std::make_shared<ZlibInflatingReadBuffer>(*raw_buffer, CompressionMethod::Gzip);
+        else if (http_compressed_method == "deflate")
+            return std::make_shared<ZlibInflatingReadBuffer>(*raw_buffer, CompressionMethod::Zlib);
+#if USE_BROTLI
+            else if (http_compressed_method == "br")
+            return std::make_shared<BrotliReadBuffer>(*raw_buffer);
+#endif
+        else
+            throw Exception("Unknown Content-Encoding of HTTP request: " + http_compressed_method, ErrorCodes::UNKNOWN_COMPRESSION_METHOD);
+    }
+
+    return raw_buffer;
+}
+
+ReadBufferPtr HTTPStreamsWithInput::createInternalCompressedBuffer(HTMLForm & params, ReadBufferPtr & http_maybe_encoding_buffer) const
+{
+    /// The data can also be compressed using incompatible internal algorithm. This is indicated by
+    /// 'decompress' query parameter.
+    std::unique_ptr<ReadBuffer> in_post_maybe_compressed;
+    if (params.getParsed<bool>("decompress", false))
+        return std::make_unique<CompressedReadBuffer>(*http_maybe_encoding_buffer);
+
+    return http_maybe_encoding_buffer;
+}
+
+void HTTPStreamsWithInput::attachSettings(Context & /*context*/, Settings & settings, HTTPServerRequest & /*request*/)
+{
+    /// If 'http_native_compression_disable_checksumming_on_decompress' setting is turned on,
+    /// checksums of client data compressed with internal algorithm are not checked.
+    if (settings.http_native_compression_disable_checksumming_on_decompress)
+    {
+        if(CompressedReadBuffer * compressed_buffer = typeid_cast<CompressedReadBuffer *>(in_maybe_internal_compressed.get()))
+            compressed_buffer->disableChecksumming();
+    }
+}
+
+}

dbms/src/Interpreters/CustomHTTP/HTTPStreamsWithInput.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <Core/Types.h>
+#include <IO/ReadBuffer.h>
+#include <Common/HTMLForm.h>
+#include <Interpreters/Context.h>
+#include <Poco/Net/HTTPServerRequest.h>
+
+namespace DB
+{
+
+using HTTPServerRequest = Poco::Net::HTTPServerRequest;
+
+struct HTTPStreamsWithInput
+{
+    std::shared_ptr<ReadBuffer> in;
+    std::shared_ptr<ReadBuffer> in_maybe_compressed;
+    std::shared_ptr<ReadBuffer> in_maybe_internal_compressed;
+
+    HTTPStreamsWithInput(HTTPServerRequest & request, HTMLForm & from);
+
+    void attachSettings(Context & context, Settings & settings, HTTPServerRequest & request);
+
+    ReadBufferPtr createRawInBuffer(HTTPServerRequest & request) const;
+    ReadBufferPtr createCompressedBuffer(HTTPServerRequest & request, ReadBufferPtr & raw_buffer) const;
+    ReadBufferPtr createInternalCompressedBuffer(HTMLForm & params, ReadBufferPtr & http_maybe_encoding_buffer) const;
+};
+
+}

dbms/src/Interpreters/CustomHTTP/HTTPStreamsWithOutput.cpp

@@ -0,0 +1,217 @@
+#include <Interpreters/CustomHTTP/HTTPStreamsWithOutput.h>
+#include <Compression/CompressedWriteBuffer.h>
+#include <IO/copyData.h>
+#include <IO/CascadeWriteBuffer.h>
+#include <IO/MemoryReadWriteBuffer.h>
+#include <DataStreams/IBlockInputStream.h>
+#include <Poco/Net/HTTPServerRequestImpl.h>
+#include <IO/WriteBufferFromTemporaryFile.h>
+#include <Compression/CompressedReadBuffer.h>
+#include <IO/ConcatReadBuffer.h>
+
+
+namespace DB
+{
+
+namespace
+{
+    inline void listeningProgress(Context & context, ProgressCallback listener)
+    {
+        auto prev = context.getProgressCallback();
+        context.setProgressCallback([prev, listener] (const Progress & progress)
+        {
+            if (prev)
+                prev(progress);
+
+            listener(progress);
+        });
+    }
+
+    inline ProgressCallback cancelListener(Context & context, Poco::Net::StreamSocket & socket)
+    {
+        /// Assume that at the point this method is called no one is reading data from the socket any more.
+        /// True for read-only queries.
+        return [&context, &socket](const Progress &)
+        {
+            try
+            {
+                char b;
+                int status = socket.receiveBytes(&b, 1, MSG_DONTWAIT | MSG_PEEK);
+                if (status == 0)
+                    context.killCurrentQuery();
+            }
+            catch (Poco::TimeoutException &)
+            {
+            }
+            catch (...)
+            {
+                context.killCurrentQuery();
+            }
+        };
+    }
+}
+
+void HTTPStreamsWithOutput::attachSettings(Context & context, Settings & settings, HTTPServerRequest & request)
+{
+    /// HTTP response compression is turned on only if the client signalled that they support it
+    /// (using Accept-Encoding header) and 'enable_http_compression' setting is turned on.
+    out->setCompression(out->getCompression() && settings.enable_http_compression);
+    if (out->getCompression())
+        out->setCompressionLevel(settings.http_zlib_compression_level);
+
+    out->setSendProgressInterval(settings.http_headers_progress_interval_ms);
+
+    /// Add CORS header if 'add_http_cors_header' setting is turned on and the client passed
+    /// Origin header.
+    out->addHeaderCORS(settings.add_http_cors_header && !request.get("Origin", "").empty());
+
+    /// While still no data has been sent, we will report about query execution progress by sending HTTP headers.
+    if (settings.send_progress_in_http_headers)
+        listeningProgress(context, [this] (const Progress & progress) { out->onProgress(progress); });
+
+    if (settings.readonly > 0 && settings.cancel_http_readonly_queries_on_client_close)
+    {
+        Poco::Net::StreamSocket & socket = dynamic_cast<Poco::Net::HTTPServerRequestImpl &>(request).socket();
+
+        listeningProgress(context, cancelListener(context, socket));
+    }
+}
+
+void HTTPStreamsWithOutput::attachRequestAndResponse(
+    Context & context, HTTPServerRequest & request, HTTPServerResponse & response, HTMLForm & form, size_t keep_alive_timeout)
+{
+    out = createEndpoint(request, response, keep_alive_timeout);
+    out_maybe_compressed = createMaybeCompressionEndpoint(form, out);
+    out_maybe_delayed_and_compressed = createMaybeDelayedAndCompressionEndpoint(context, form, out_maybe_compressed);
+}
+
+std::shared_ptr<WriteBufferFromHTTPServerResponse> HTTPStreamsWithOutput::createEndpoint(
+    HTTPServerRequest & request, HTTPServerResponse & response, size_t keep_alive_timeout)
+{
+    /// The client can pass a HTTP header indicating supported compression method (gzip or deflate).
+    String http_response_compression_methods = request.get("Accept-Encoding", "");
+
+    if (!http_response_compression_methods.empty())
+    {
+        /// Both gzip and deflate are supported. If the client supports both, gzip is preferred.
+        /// NOTE parsing of the list of methods is slightly incorrect.
+        if (std::string::npos != http_response_compression_methods.find("gzip"))
+            return std::make_shared<WriteBufferFromHTTPServerResponse>(
+                request, response, keep_alive_timeout, true, CompressionMethod::Gzip, DBMS_DEFAULT_BUFFER_SIZE);
+        else if (std::string::npos != http_response_compression_methods.find("deflate"))
+            return std::make_shared<WriteBufferFromHTTPServerResponse>(
+                request, response, keep_alive_timeout, true, CompressionMethod::Zlib, DBMS_DEFAULT_BUFFER_SIZE);
+#if USE_BROTLI
+        else if (http_response_compression_methods == "br")
+            return std::make_shared<WriteBufferFromHTTPServerResponse>(
+                request, response, keep_alive_timeout, true, CompressionMethod::Brotli, DBMS_DEFAULT_BUFFER_SIZE);
+#endif
+    }
+
+    return std::make_shared<WriteBufferFromHTTPServerResponse>(
+        request, response, keep_alive_timeout, false, CompressionMethod{}, DBMS_DEFAULT_BUFFER_SIZE);
+}
+
+WriteBufferPtr HTTPStreamsWithOutput::createMaybeCompressionEndpoint(HTMLForm & form, std::shared_ptr<WriteBufferFromHTTPServerResponse> & endpoint)
+{
+    /// Client can pass a 'compress' flag in the query string. In this case the query result is
+    /// compressed using internal algorithm. This is not reflected in HTTP headers.
+    bool internal_compression = form.getParsed<bool>("compress", false);
+    return internal_compression ? std::make_shared<CompressedWriteBuffer>(*endpoint) : WriteBufferPtr(endpoint);
+}
+
+WriteBufferPtr HTTPStreamsWithOutput::createMaybeDelayedAndCompressionEndpoint(Context & context, HTMLForm & form, WriteBufferPtr & endpoint)
+{
+    /// If it is specified, the whole result will be buffered.
+    ///  First ~buffer_size bytes will be buffered in memory, the remaining bytes will be stored in temporary file.
+    bool buffer_until_eof = form.getParsed<bool>("wait_end_of_query", false);
+
+    /// At least, we should postpone sending of first buffer_size result bytes
+    size_t buffer_size_total = std::max(form.getParsed<size_t>("buffer_size", DBMS_DEFAULT_BUFFER_SIZE), static_cast<size_t>(DBMS_DEFAULT_BUFFER_SIZE));
+
+    size_t buffer_size_memory = (buffer_size_total > DBMS_DEFAULT_BUFFER_SIZE) ? buffer_size_total : 0;
+
+    if (buffer_size_memory > 0 || buffer_until_eof)
+    {
+        CascadeWriteBuffer::WriteBufferPtrs cascade_buffer1;
+        CascadeWriteBuffer::WriteBufferConstructors cascade_buffer2;
+
+        if (buffer_size_memory > 0)
+            cascade_buffer1.emplace_back(std::make_shared<MemoryWriteBuffer>(buffer_size_memory));
+
+        if (buffer_until_eof)
+        {
+            std::string tmp_path_template = context.getTemporaryPath() + "http_buffers/";
+
+            auto create_tmp_disk_buffer = [tmp_path_template] (const WriteBufferPtr &)
+            {
+                return WriteBufferFromTemporaryFile::create(tmp_path_template);
+            };
+
+            cascade_buffer2.emplace_back(std::move(create_tmp_disk_buffer));
+        }
+        else
+        {
+            auto push_memory_buffer_and_continue = [next_buffer = endpoint] (const WriteBufferPtr & prev_buf)
+            {
+                auto prev_memory_buffer = typeid_cast<MemoryWriteBuffer *>(prev_buf.get());
+                if (!prev_memory_buffer)
+                    throw Exception("Expected MemoryWriteBuffer", ErrorCodes::LOGICAL_ERROR);
+
+                auto rdbuf = prev_memory_buffer->tryGetReadBuffer();
+                copyData(*rdbuf , *next_buffer);
+
+                return next_buffer;
+            };
+
+            cascade_buffer2.emplace_back(push_memory_buffer_and_continue);
+        }
+
+        return std::make_shared<CascadeWriteBuffer>(std::move(cascade_buffer1), std::move(cascade_buffer2));
+    }
+
+    return endpoint;
+}
+
+void HTTPStreamsWithOutput::finalize() const
+{
+    if (out_maybe_delayed_and_compressed != out_maybe_compressed)
+    {
+        /// TODO: set Content-Length if possible
+        std::vector<WriteBufferPtr> write_buffers;
+        std::vector<ReadBufferPtr> read_buffers;
+        std::vector<ReadBuffer *> read_buffers_raw_ptr;
+
+        auto cascade_buffer = typeid_cast<CascadeWriteBuffer *>(out_maybe_delayed_and_compressed.get());
+        if (!cascade_buffer)
+            throw Exception("Expected CascadeWriteBuffer", ErrorCodes::LOGICAL_ERROR);
+
+        cascade_buffer->getResultBuffers(write_buffers);
+
+        if (write_buffers.empty())
+            throw Exception("At least one buffer is expected to overwrite result into HTTP response", ErrorCodes::LOGICAL_ERROR);
+
+        for (auto & write_buf : write_buffers)
+        {
+            IReadableWriteBuffer * write_buf_concrete;
+            ReadBufferPtr reread_buf;
+
+            if (write_buf
+                && (write_buf_concrete = dynamic_cast<IReadableWriteBuffer *>(write_buf.get()))
+                && (reread_buf = write_buf_concrete->tryGetReadBuffer()))
+            {
+                read_buffers.emplace_back(reread_buf);
+                read_buffers_raw_ptr.emplace_back(reread_buf.get());
+            }
+        }
+
+        ConcatReadBuffer concat_read_buffer(read_buffers_raw_ptr);
+        copyData(concat_read_buffer, *out_maybe_compressed);
+    }
+
+    /// Send HTTP headers with code 200 if no exception happened and the data is still not sent to
+    /// the client.
+    out->finalize();
+}
+
+}

dbms/src/Interpreters/CustomHTTP/HTTPStreamsWithOutput.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include <Core/Types.h>
+#include <IO/WriteBuffer.h>
+#include <Common/HTMLForm.h>
+#include <Poco/Net/HTTPServerRequest.h>
+#include <Poco/Net/HTTPServerResponse.h>
+#include <IO/WriteBufferFromHTTPServerResponse.h>
+
+namespace DB
+{
+
+using HTTPServerRequest = Poco::Net::HTTPServerRequest;
+using HTTPServerResponse = Poco::Net::HTTPServerResponse;
+
+
+/* Raw data
+ * ↓
+ * CascadeWriteBuffer out_maybe_delayed_and_compressed (optional)
+ * ↓ (forwards data if an overflow is occur or explicitly via pushDelayedResults)
+ * CompressedWriteBuffer out_maybe_compressed (optional)
+ * ↓
+ * WriteBufferFromHTTPServerResponse out
+ */
+struct HTTPStreamsWithOutput
+{
+    using HTTPResponseBufferPtr = std::shared_ptr<WriteBufferFromHTTPServerResponse>;
+
+    HTTPResponseBufferPtr out;
+    /// Points to 'out' or to CompressedWriteBuffer(*out), depending on settings.
+    std::shared_ptr<WriteBuffer> out_maybe_compressed;
+    /// Points to 'out' or to CompressedWriteBuffer(*out) or to CascadeWriteBuffer.
+    std::shared_ptr<WriteBuffer> out_maybe_delayed_and_compressed;
+
+    void finalize() const;
+
+    WriteBufferPtr createMaybeDelayedAndCompressionEndpoint(Context & context, HTMLForm & form, WriteBufferPtr & endpoint);
+
+    WriteBufferPtr createMaybeCompressionEndpoint(HTMLForm & form, std::shared_ptr<WriteBufferFromHTTPServerResponse> & endpoint);
+
+    HTTPResponseBufferPtr createEndpoint(HTTPServerRequest & request, HTTPServerResponse & response, size_t keep_alive_timeout);
+
+    void attachSettings(Context & context, Settings & settings, HTTPServerRequest & request);
+
+    void attachRequestAndResponse(Context & context, HTTPServerRequest & request, HTTPServerResponse & response, HTMLForm & form, size_t keep_alive_timeout);
+};
+
+}

programs/server/HTTPHandler.cpp

@@ -216,7 +216,7 @@ void HTTPHandler::processQuery(
     Poco::Net::HTTPServerRequest & request,
     HTMLForm & params,
     Poco::Net::HTTPServerResponse & response,
-    Output & used_output)
+    HTTPStreamsWithOutput & used_output)
 {
     Context context = server.context();
 
@@ -224,6 +224,12 @@ void HTTPHandler::processQuery(
 
     LOG_TRACE(log, "Request URI: " << request.getURI());
 
+    if (context.getSettingsRef().allow_experimental_custom_http)
+    {
+        context.getHTTPMatchExecutor()->execute(context, request, response, params, used_output);
+        return;
+    }
+
     std::istream & istr = request.stream();
 
     /// Part of the query can be passed in the 'query' parameter and the rest in the request body
@@ -605,20 +611,14 @@ void HTTPHandler::processQuery(
         }
     );
 
-    if (used_output.hasDelayed())
-    {
-        /// TODO: set Content-Length if possible
-        pushDelayedResults(used_output);
-    }
-
     /// Send HTTP headers with code 200 if no exception happened and the data is still not sent to
     /// the client.
-    used_output.out->finalize();
+    used_output.finalize();
 }
 
 void HTTPHandler::trySendExceptionToClient(const std::string & s, int exception_code,
     Poco::Net::HTTPServerRequest & request, Poco::Net::HTTPServerResponse & response,
-    Output & used_output)
+    HTTPStreamsWithOutput & used_output)
 {
     try
     {
@@ -655,7 +655,7 @@ void HTTPHandler::trySendExceptionToClient(const std::string & s, int exception_
         else if (used_output.out_maybe_compressed)
         {
             /// Destroy CascadeBuffer to actualize buffers' positions and reset extra references
-            if (used_output.hasDelayed())
+            if (used_output.out_maybe_delayed_and_compressed != used_output.out_maybe_compressed)
                 used_output.out_maybe_delayed_and_compressed.reset();
 
             /// Send the error message into already used (and possibly compressed) stream.
@@ -691,7 +691,7 @@ void HTTPHandler::handleRequest(Poco::Net::HTTPServerRequest & request, Poco::Ne
     setThreadName("HTTPHandler");
     ThreadStatus thread_status;
 
-    Output used_output;
+    HTTPStreamsWithOutput used_output;
 
     /// In case of exception, send stack trace to client.
     bool with_stacktrace = false;

programs/server/HTTPHandler.h

@@ -7,6 +7,8 @@
 #include <Common/CurrentMetrics.h>
 #include <Common/HTMLForm.h>
 
+#include <Interpreters/CustomHTTP/HTTPStreamsWithOutput.h>
+
 
 namespace CurrentMetrics
 {
@@ -68,14 +70,14 @@ private:
         Poco::Net::HTTPServerRequest & request,
         HTMLForm & params,
         Poco::Net::HTTPServerResponse & response,
-        Output & used_output);
+        HTTPStreamsWithOutput & used_output);
 
     void trySendExceptionToClient(
         const std::string & s,
         int exception_code,
         Poco::Net::HTTPServerRequest & request,
         Poco::Net::HTTPServerResponse & response,
-        Output & used_output);
+        HTTPStreamsWithOutput & used_output);
 
     static void pushDelayedResults(Output & used_output);
 };

src/IO/WriteBufferFromHTTPServerResponse.h

@@ -113,6 +113,11 @@ public:
         compress = enable_compression;
     }
 
+    bool getCompression()
+    {
+        return compress;
+    }
+
     /// Set compression level if the compression is turned on.
     /// The setting has any effect only if HTTP headers haven't been sent yet.
     void setCompressionLevel(int level)

src/Interpreters/Context.cpp

@@ -44,6 +44,7 @@
 #include <Interpreters/SystemLog.h>
 #include <Interpreters/Context.h>
 #include <Interpreters/DDLWorker.h>
+#include <Interpreters/CustomHTTP/HTTPMatchExecutorDefault.h>
 #include <Common/DNSResolver.h>
 #include <IO/ReadBufferFromFile.h>
 #include <IO/UncompressedCache.h>
@@ -348,6 +349,7 @@ struct ContextShared
     std::unique_ptr<Clusters> clusters;
     ConfigurationPtr clusters_config;                        /// Stores updated configs
     mutable std::mutex clusters_mutex;                        /// Guards clusters and clusters_config
+    mutable std::mutex match_executor_mutex;                  /// Guards match executor and their config
 
 #if USE_EMBEDDED_COMPILER
     std::shared_ptr<CompiledExpressionCache> compiled_expression_cache;
@@ -1543,6 +1545,10 @@ void Context::setCluster(const String & cluster_name, const std::shared_ptr<Clus
     shared->clusters->setCluster(cluster_name, cluster);
 }
 
+HTTPMatchExecutorPtr Context::getHTTPMatchExecutor()
+{
+    return std::make_shared<HTTPMatchExecutorDefault>();
+}
 
 void Context::initializeSystemLogs()
 {

src/Interpreters/Context.h

@@ -490,6 +490,8 @@ public:
 
     Compiler & getCompiler();
 
+    HTTPMatchExecutorPtr getHTTPMatchExecutor();
+
     /// Call after initialization before using system logs. Call for global context.
     void initializeSystemLogs();