scylladb/alternator/executor.hh

/*
 * Copyright 2019-present ScyllaDB
 */

/*
 * SPDX-License-Identifier: LicenseRef-ScyllaDB-Source-Available-1.0
 */

#pragma once

#include <seastar/core/future.hh>
#include "seastarx.hh"
#include <seastar/core/sharded.hh>
#include <seastar/util/noncopyable_function.hh>

#include "service/migration_manager.hh"
#include "service/client_state.hh"
#include "service_permit.hh"
#include "db/timeout_clock.hh"

#include "alternator/error.hh"
#include "stats.hh"
#include "utils/rjson.hh"
#include "utils/updateable_value.hh"

#include "tracing/trace_state.hh"

namespace db {
    class system_distributed_keyspace;
}

namespace query {
class partition_slice;
class result;
}

namespace cql3::selection {
    class selection;
}

namespace service {
    class storage_proxy;
}

namespace cdc {
    class metadata;
}

namespace gms {

class gossiper;

}

class schema_builder;

namespace alternator {

class rmw_operation;

schema_ptr get_table(service::storage_proxy& proxy, const rjson::value& request);
bool is_alternator_keyspace(const sstring& ks_name);
// Wraps the db::get_tags_of_table and throws if the table is missing the tags extension.
const std::map<sstring, sstring>& get_tags_of_table_or_throw(schema_ptr schema);

// An attribute_path_map object is used to hold data for various attributes
// paths (parsed::path) in a hierarchy of attribute paths. Each attribute path
// has a root attribute, and then modified by member and index operators -
// for example in "a.b[2].c" we have "a" as the root, then ".b" member, then
// "[2]" index, and finally ".c" member.
// Data can be added to an attribute_path_map using the add() function, but
// requires that attributes with data not be *overlapping* or *conflicting*:
//
// 1. Two attribute paths which are identical or an ancestor of one another
//    are considered *overlapping* and not allowed. If a.b.c has data,
//    we can't add more data in a.b.c or any of its descendants like a.b.c.d.
//
// 2. Two attribute paths which need the same parent to have both a member and
//    an index are considered *conflicting* and not allowed. E.g., if a.b has
//    data, you can't add a[1]. The meaning of adding both would be that the
//    attribute a is both a map and an array, which isn't sensible.
//
// These two requirements are common to the two places where Alternator uses
// this abstraction to describe how a hierarchical item is to be transformed:
//
// 1. In ProjectExpression: for filtering from a full top-level attribute
//    only the parts for which user asked in ProjectionExpression.
//
// 2. In UpdateExpression: for taking the previous value of a top-level
//    attribute, and modifying it based on the instructions in the user
//    wrote in UpdateExpression.

template<typename T>
class attribute_path_map_node {
public:
    using data_t = T;
    // We need the extra unique_ptr<> here because libstdc++ unordered_map
    // doesn't work with incomplete types :-(
    using members_t =  std::unordered_map<std::string, std::unique_ptr<attribute_path_map_node<T>>>;
    // The indexes list is sorted because DynamoDB requires handling writes
    // beyond the end of a list in index order.
    using indexes_t = std::map<unsigned, std::unique_ptr<attribute_path_map_node<T>>>;
    // The prohibition on "overlap" and "conflict" explained above means
    // That only one of data, members or indexes is non-empty.
    std::optional<std::variant<data_t, members_t, indexes_t>> _content;

    bool is_empty() const { return !_content; }
    bool has_value() const { return _content && std::holds_alternative<data_t>(*_content); }
    bool has_members() const { return _content && std::holds_alternative<members_t>(*_content); }
    bool has_indexes() const { return _content && std::holds_alternative<indexes_t>(*_content); }
    // get_members() assumes that has_members() is true
    members_t& get_members() { return std::get<members_t>(*_content); }
    const members_t& get_members() const { return std::get<members_t>(*_content); }
    indexes_t& get_indexes() { return std::get<indexes_t>(*_content); }
    const indexes_t& get_indexes() const { return std::get<indexes_t>(*_content); }
    T& get_value() { return std::get<T>(*_content); }
    const T& get_value() const { return std::get<T>(*_content); }
};

template<typename T>
using attribute_path_map = std::unordered_map<std::string, attribute_path_map_node<T>>;

using attrs_to_get_node = attribute_path_map_node<std::monostate>;
// attrs_to_get lists which top-level attribute are needed, and possibly also
// which part of the top-level attribute is really needed (when nested
// attribute paths appeared in the query).
// Most code actually uses optional<attrs_to_get>. There, a disengaged
// optional means we should get all attributes, not specific ones.
using attrs_to_get = attribute_path_map<std::monostate>;

namespace parsed {
class expression_cache;
}

class executor : public peering_sharded_service<executor> {
    gms::gossiper& _gossiper;
    service::storage_proxy& _proxy;
    service::migration_manager& _mm;
    db::system_distributed_keyspace& _sdks;
    cdc::metadata& _cdc_metadata;
    utils::updateable_value<bool> _enforce_authorization;
    utils::updateable_value<bool> _warn_authorization;
    // An smp_service_group to be used for limiting the concurrency when
    // forwarding Alternator request between shards - if necessary for LWT.
    smp_service_group _ssg;

    std::unique_ptr<parsed::expression_cache> _parsed_expression_cache;

public:
    using client_state = service::client_state;
    // request_return_type is the return type of the executor methods, which
    // can be one of:
    // 1. A string, which is the response body for the request.
    // 2. A body_writer, an asynchronous function (returning future<>) that
    //    takes an output_stream and writes the response body into it.
    // 3. An api_error, which is an error response that should be returned to
    //    the client.
    // The body_writer is used for streaming responses, where the response body
    // is written in chunks to the output_stream. This allows for efficient
    // handling of large responses without needing to allocate a large buffer
    // in memory.
    using body_writer = noncopyable_function<future<>(output_stream<char>&&)>;
    using request_return_type = std::variant<std::string, body_writer, api_error>;
    stats _stats;
    // The metric_groups object holds this stat object's metrics registered
    // as long as the stats object is alive.
    seastar::metrics::metric_groups _metrics;
    static constexpr auto ATTRS_COLUMN_NAME = ":attrs";
    static constexpr auto KEYSPACE_NAME_PREFIX = "alternator_";
    static constexpr std::string_view INTERNAL_TABLE_PREFIX = ".scylla.alternator.";

    executor(gms::gossiper& gossiper,
             service::storage_proxy& proxy,
             service::migration_manager& mm,
             db::system_distributed_keyspace& sdks,
             cdc::metadata& cdc_metadata,
             smp_service_group ssg,
             utils::updateable_value<uint32_t> default_timeout_in_ms);
    ~executor();

    future<request_return_type> create_table(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> describe_table(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> delete_table(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> update_table(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> put_item(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> get_item(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> delete_item(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> update_item(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> list_tables(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> scan(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> describe_endpoints(client_state& client_state, service_permit permit, rjson::value request, std::string host_header);
    future<request_return_type> batch_write_item(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> batch_get_item(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> query(client_state& client_state, tracing::trace_state_ptr trace_state, service_permit permit, rjson::value request);
    future<request_return_type> tag_resource(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> untag_resource(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> list_tags_of_resource(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> update_time_to_live(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> describe_time_to_live(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> list_streams(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> describe_stream(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> get_shard_iterator(client_state& client_state, service_permit permit, rjson::value request);
    future<request_return_type> get_records(client_state& client_state, tracing::trace_state_ptr, service_permit permit, rjson::value request);
    future<request_return_type> describe_continuous_backups(client_state& client_state, service_permit permit, rjson::value request);

    future<> start();
    future<> stop();

    static sstring table_name(const schema&);
    static db::timeout_clock::time_point default_timeout();
private:
    static thread_local utils::updateable_value<uint32_t> s_default_timeout_in_ms;
public:
    static schema_ptr find_table(service::storage_proxy&, std::string_view table_name);
    static schema_ptr find_table(service::storage_proxy&, const rjson::value& request);

private:
    friend class rmw_operation;

    static void describe_key_schema(rjson::value& parent, const schema&, std::unordered_map<std::string,std::string> * = nullptr, const std::map<sstring, sstring> *tags = nullptr);

public:
    static void describe_key_schema(rjson::value& parent, const schema& schema, std::unordered_map<std::string,std::string>&, const std::map<sstring, sstring> *tags = nullptr);

    static std::optional<rjson::value> describe_single_item(schema_ptr,
        const query::partition_slice&,
        const cql3::selection::selection&,
        const query::result&,
        const std::optional<attrs_to_get>&,
        uint64_t* = nullptr);

    // Converts a multi-row selection result to JSON compatible with DynamoDB.
    // For each row, this method calls item_callback, which takes the size of
    // the item as the parameter.
    static future<std::vector<rjson::value>> describe_multi_item(schema_ptr schema,
        const query::partition_slice&& slice,
        shared_ptr<cql3::selection::selection> selection,
        foreign_ptr<lw_shared_ptr<query::result>> query_result,
        shared_ptr<const std::optional<attrs_to_get>> attrs_to_get,
        noncopyable_function<void(uint64_t)> item_callback = {});

    static void describe_single_item(const cql3::selection::selection&,
        const std::vector<managed_bytes_opt>&,
        const std::optional<attrs_to_get>&,
        rjson::value&,
        uint64_t* item_length_in_bytes = nullptr,
        bool = false);

    static bool add_stream_options(const rjson::value& stream_spec, schema_builder&, service::storage_proxy& sp);
    static void supplement_table_info(rjson::value& descr, const schema& schema, service::storage_proxy& sp);
    static void supplement_table_stream_info(rjson::value& descr, const schema& schema, const service::storage_proxy& sp);
};

// is_big() checks approximately if the given JSON value is "bigger" than
// the given big_size number of bytes. The goal is to *quickly* detect
// oversized JSON that, for example, is too large to be serialized to a
// contiguous string - we don't need an accurate size for that. Moreover,
// as soon as we detect that the JSON is indeed "big", we can return true
// and don't need to continue calculating its exact size.
// For simplicity, we use a recursive implementation. This is fine because
// Alternator limits the depth of JSONs it reads from inputs, and doesn't
// add more than a couple of levels in its own output construction.
bool is_big(const rjson::value& val, int big_size = 100'000);

// Check CQL's Role-Based Access Control (RBAC) permission (MODIFY,
// SELECT, DROP, etc.) on the given table. When permission is denied an
// appropriate user-readable api_error::access_denied is thrown.
future<> verify_permission(bool enforce_authorization, bool warn_authorization, const service::client_state&, const schema_ptr&, auth::permission, alternator::stats& stats);

/**
 * Make return type for serializing the object "streamed",
 * i.e. direct to HTTP output stream. Note: only useful for
 * (very) large objects as there are overhead issues with this
 * as well, but for massive lists of return objects this can
 * help avoid large allocations/many re-allocs
 */
executor::body_writer make_streamed(rjson::value&&);

}