src/lib-sql/driver-cassandra.c

	driver-cassandra.c revision b23a8d3514760899ac1094f2a8103a057ae6416d
/* Copyright (c) 2015 Dovecot authors, see the included COPYING file */

#include "lib.h"
#include "array.h"
#include "str.h"
#include "ioloop.h"
#include "write-full.h"
#include "sql-api-private.h"

#ifdef BUILD_CASSANDRA
#include <unistd.h>
#include <cassandra.h>

#define IS_CONNECTED(db) \
    ((db)->api.state != SQL_DB_STATE_DISCONNECTED && \
     (db)->api.state != SQL_DB_STATE_CONNECTING)

typedef void driver_cassandra_callback_t(CassFuture *future, void *context);

struct cassandra_callback {
    unsigned int id;
    CassFuture *future;
    struct cassandra_db *db;
    driver_cassandra_callback_t *callback;
    void *context;
};

struct cassandra_db {
    struct sql_db api;

    char *hosts, *keyspace;
    CassConsistency consistency;
    CassLogLevel log_level;

    CassCluster *cluster;
    CassSession *session;

    int fd_pipe[2];
    struct io *io_pipe;
    ARRAY(struct cassandra_callback *) callbacks;
    unsigned int callback_ids;

    struct cassandra_result *cur_result;
    struct ioloop *ioloop, *orig_ioloop;
    struct sql_result *sync_result;

    char *error;

    unsigned int set_consistency:1;
};

struct cassandra_result {
    struct sql_result api;
    CassStatement *statement;
    const CassResult *result;
    CassIterator *iterator;
    char *query;
    char *error;

    pool_t row_pool;
    ARRAY_TYPE(const_string) fields;

    sql_query_callback_t *callback;
    void *context;

    unsigned int finished:1;
};

struct cassandra_transaction_context {
    struct sql_transaction_context ctx;
    int refcount;

    sql_commit_callback_t *callback;
    void *context;

    pool_t query_pool;
    const char *error;

    unsigned int begin_succeeded:1;
    unsigned int begin_failed:1;
    unsigned int failed:1;
};

extern const struct sql_db driver_cassandra_db;
extern const struct sql_result driver_cassandra_result;

static struct {
    CassConsistency consistency;
    const char *name;
} cass_consistency_names[] = {
    { CASS_CONSISTENCY_ANY, "any" },
    { CASS_CONSISTENCY_ONE, "one" },
    { CASS_CONSISTENCY_TWO, "two" },
    { CASS_CONSISTENCY_THREE, "three" },
    { CASS_CONSISTENCY_QUORUM, "" },
    { CASS_CONSISTENCY_ALL, "all" },
    { CASS_CONSISTENCY_QUORUM, "" },
    { CASS_CONSISTENCY_ALL, "all" },
    { CASS_CONSISTENCY_LOCAL_QUORUM, "local-quorum" },
    { CASS_CONSISTENCY_EACH_QUORUM, "each-quorum" },
    { CASS_CONSISTENCY_SERIAL, "serial" },
    { CASS_CONSISTENCY_LOCAL_SERIAL, "local-serial" },
    { CASS_CONSISTENCY_LOCAL_ONE, "local-one" }
};

static struct {
    CassLogLevel log_level;
    const char *name;
} cass_log_level_names[] = {
    { CASS_LOG_CRITICAL, "critical" },
    { CASS_LOG_ERROR, "error" },
    { CASS_LOG_WARN, "warn" },
    { CASS_LOG_INFO, "info" },
    { CASS_LOG_DEBUG, "debug" },
    { CASS_LOG_TRACE, "trace" }
};

static void result_finish(struct cassandra_result *result);

static int consistency_parse(const char *str, CassConsistency *consistency_r)
{
    unsigned int i;

    for (i = 0; i < N_ELEMENTS(cass_consistency_names); i++) {
        if (strcmp(cass_consistency_names[i].name, str) == 0) {
            *consistency_r = cass_consistency_names[i].consistency;
            return 0;
        }
    }
    return -1;
}

static int log_level_parse(const char *str, CassLogLevel *log_level_r)
{
    unsigned int i;

    for (i = 0; i < N_ELEMENTS(cass_log_level_names); i++) {
        if (strcmp(cass_log_level_names[i].name, str) == 0) {
            *log_level_r = cass_log_level_names[i].log_level;
            return 0;
        }
    }
    return -1;
}

static void driver_cassandra_set_state(struct cassandra_db *db, enum sql_db_state state)
{
    i_assert(state == SQL_DB_STATE_BUSY || db->cur_result == NULL);

    /* switch back to original ioloop in case the caller wants to
       add/remove timeouts */
    if (db->ioloop != NULL)
        io_loop_set_current(db->orig_ioloop);
    sql_db_set_state(&db->api, state);
    if (db->ioloop != NULL)
        io_loop_set_current(db->ioloop);
}

static void driver_cassandra_close(struct cassandra_db *db)
{
    if (db->io_pipe != NULL)
        io_remove(&db->io_pipe);
    if (db->fd_pipe[0] != -1) {
        i_close_fd(&db->fd_pipe[0]);
        i_close_fd(&db->fd_pipe[1]);
    }
    driver_cassandra_set_state(db, SQL_DB_STATE_DISCONNECTED);

    if (db->ioloop != NULL) {
        /* running a sync query, stop it */
        io_loop_stop(db->ioloop);
    }
}

static void driver_cassandra_log_error(CassFuture *future, const char *str)
{
    const char *message;
    size_t size;

    cass_future_error_message(future, &message, &size);
    i_error("cassandra: %s: %.*s", str, (int)size, message);
}

static void driver_cassandra_future_callback(CassFuture *future ATTR_UNUSED,
                         void *context)
{
    struct cassandra_callback *cb = context;

    /* this isn't the main thread - communicate with main thread by
       writing the callback id to the pipe */
    if (write_full(cb->db->fd_pipe[1], &cb->id, sizeof(cb->id)) < 0)
        i_error("cassandra: write(pipe) failed: %m");
}

static void cassandra_callback_run(struct cassandra_callback *cb)
{
    cb->callback(cb->future, cb->context);
    cass_future_free(cb->future);
    i_free(cb);
}

static void driver_cassandra_input_id(struct cassandra_db *db, unsigned int id)
{
    struct cassandra_callback *cb, *const *cbp;

    /* usually there are only a few callbacks, so don't bother with using
       a hash table */
    array_foreach(&db->callbacks, cbp) {
        cb = *cbp;
        if (cb->id == id) {
            array_delete(&db->callbacks,
                     array_foreach_idx(&db->callbacks, cbp), 1);
            cassandra_callback_run(cb);
            return;
        }
    }
    i_panic("cassandra: Received unknown ID %u", id);
}

static void driver_cassandra_input(struct cassandra_db *db)
{
    unsigned int ids[1024];
    ssize_t ret;

    ret = read(db->fd_pipe[0], ids, sizeof(ids));
    if (ret < 0)
        i_error("cassandra: read(pipe) failed: %m");
    else if (ret == 0)
        i_error("cassandra: read(pipe) failed: EOF");
    else if (ret % sizeof(ids[0]) != 0)
        i_error("cassandra: read(pipe) returned wrong amount of data");
    else {
        /* success */
        unsigned int i, count = ret / sizeof(ids[0]);

        for (i = 0; i < count && db->api.state != SQL_DB_STATE_DISCONNECTED; i++)
            driver_cassandra_input_id(db, ids[i]);
        return;
    }
    driver_cassandra_close(db);
}

static void
driver_cassandra_set_callback(CassFuture *future, struct cassandra_db *db,
                  driver_cassandra_callback_t *callback,
                  void *context)
{
    struct cassandra_callback *cb;

    cb = i_new(struct cassandra_callback, 1);
    cb->id = ++db->callback_ids;
    cb->future = future;
    cb->callback = callback;
    cb->context = context;
    cb->db = db;
    array_append(&db->callbacks, &cb, 1);

    cass_future_set_callback(future, driver_cassandra_future_callback, cb);
}

static void connect_callback(CassFuture *future, void *context)
{
    struct cassandra_db *db = context;
    CassError rc;

    if ((rc = cass_future_error_code(future)) != CASS_OK) {
        driver_cassandra_log_error(future,
                       "Couldn't connect to Cassandra");
        driver_cassandra_close(db);
        return;
    }
    driver_cassandra_set_state(db, SQL_DB_STATE_IDLE);
    if (db->ioloop != NULL) {
        /* driver_cassandra_sync_init() waiting for connection to
           finish */
        io_loop_stop(db->ioloop);
    }
}

static int driver_cassandra_connect(struct sql_db *_db)
{
    struct cassandra_db *db = (struct cassandra_db *)_db;
    CassFuture *future;

    i_assert(db->api.state == SQL_DB_STATE_DISCONNECTED);

    if (pipe(db->fd_pipe) < 0) {
        i_error("pipe() failed: %m");
        return -1;
    }
    db->io_pipe = io_add(db->fd_pipe[0], IO_READ,
                 driver_cassandra_input, db);
    driver_cassandra_set_state(db, SQL_DB_STATE_CONNECTING);

    future = cass_session_connect_keyspace(db->session, db->cluster, db->keyspace);
    driver_cassandra_set_callback(future, db, connect_callback, db);
    return 0;
}

static void driver_cassandra_disconnect(struct sql_db *_db)
{
    struct cassandra_db *db = (struct cassandra_db *)_db;

    if (db->cur_result != NULL && !db->cur_result->finished) {
        if (db->cur_result->error == NULL)
            db->cur_result->error = i_strdup("disconnecting");
        result_finish(db->cur_result);
    }
    driver_cassandra_close(db);
}

static const char *
driver_cassandra_escape_string(struct sql_db *db ATTR_UNUSED,
                   const char *string)
{
    string_t *escaped;
    unsigned int i;

    if (strchr(string, '\'') == NULL)
        return string;
    escaped = t_str_new(strlen(string)+10);
    for (i = 0; string[i] != '\0'; i++) {
        if (string[i] == '\'')
            str_append_c(escaped, '\'');
        str_append_c(escaped, string[i]);
    }
    return str_c(escaped);
}

static void driver_cassandra_parse_connect_string(struct cassandra_db *db,
                          const char *connect_string)
{
    const char *const *args, *key, *value;
    string_t *hosts = t_str_new(64);

    db->log_level = CASS_LOG_WARN;

    args = t_strsplit_spaces(connect_string, " ");
    for (; *args != NULL; args++) {
        value = strchr(*args, '=');
        if (value == NULL) {
            i_fatal("cassandra: Missing value in connect string: %s",
                *args);
        }
        key = t_strdup_until(*args, value++);

        if (strcmp(key, "host") == 0) {
            if (str_len(hosts) > 0)
                str_append_c(hosts, ',');
            str_append(hosts, value);
        } else if (strcmp(key, "dbname") == 0 ||
               strcmp(key, "keyspace") == 0) {
            i_free(db->keyspace);
            db->keyspace = i_strdup(value);
        } else if (strcmp(key, "consistency") == 0) {
            if (consistency_parse(value, &db->consistency) < 0)
                i_fatal("cassandra: Unknown consistency: %s", value);
            db->set_consistency = TRUE;
        } else if (strcmp(key, "log_level") == 0) {
            if (log_level_parse(value, &db->log_level) < 0)
                i_fatal("cassandra: Unknown log_level: %s", value);
        } else {
            i_fatal("cassandra: Unknown connect string: %s", key);
        }
    }

    if (str_len(hosts) == 0)
        i_fatal("cassandra: No hosts given in connect string");
    if (db->keyspace == NULL)
        i_fatal("cassandra: No dbname given in connect string");
    db->hosts = i_strdup(str_c(hosts));
}

static struct sql_db *driver_cassandra_init_v(const char *connect_string)
{
    struct cassandra_db *db;

    db = i_new(struct cassandra_db, 1);
    db->api = driver_cassandra_db;
    db->fd_pipe[0] = db->fd_pipe[1] = -1;

    T_BEGIN {
        driver_cassandra_parse_connect_string(db, connect_string);
    } T_END;
    cass_log_set_level(db->log_level);

    db->cluster = cass_cluster_new();
    cass_cluster_set_connect_timeout(db->cluster, SQL_CONNECT_TIMEOUT_SECS * 1000);
    cass_cluster_set_request_timeout(db->cluster, SQL_QUERY_TIMEOUT_SECS * 1000);
    cass_cluster_set_contact_points(db->cluster, db->hosts);
    db->session = cass_session_new();
    i_array_init(&db->callbacks, 16);
    return &db->api;
}

static void driver_cassandra_deinit_v(struct sql_db *_db)
{
    struct cassandra_db *db = (struct cassandra_db *)_db;

    if (db->cur_result != NULL && !db->cur_result->finished) {
        if (db->cur_result->error == NULL)
            db->cur_result->error = i_strdup("deinitializing");
        result_finish(db->cur_result);
    }
        driver_cassandra_close(db);

    i_assert(array_count(&db->callbacks) == 0);
    array_free(&db->callbacks);

    cass_session_free(db->session);
    cass_cluster_free(db->cluster);
    i_free(db->hosts);
    i_free(db->error);
    i_free(db->keyspace);
    array_free(&_db->module_contexts);
    i_free(db);
}

static void driver_cassandra_set_idle(struct cassandra_db *db)
{
    i_assert(db->api.state == SQL_DB_STATE_BUSY);

    driver_cassandra_set_state(db, SQL_DB_STATE_IDLE);
}

static void driver_cassandra_result_free(struct sql_result *_result)
{
    struct cassandra_db *db = (struct cassandra_db *)_result->db;
        struct cassandra_result *result = (struct cassandra_result *)_result;

    if (result->api.callback) {
        /* we're coming here from a user's sql_result_free() that's
           being called from a callback. we'll do this later,
           so ignore. */
        return;
    }

    i_assert(db->cur_result == result);
    i_assert(result->callback == NULL);

    if (_result == db->sync_result)
        db->sync_result = NULL;
    db->cur_result = NULL;

    driver_cassandra_set_idle(db);
    if (result->result != NULL)
        cass_result_free(result->result);
    if (result->iterator != NULL)
        cass_iterator_free(result->iterator);
    cass_statement_free(result->statement);
    pool_unref(&result->row_pool);
    i_free(result->query);
    i_free(result->error);
    i_free(result);
}

static void result_finish(struct cassandra_result *result)
{
    struct cassandra_db *db = (struct cassandra_db *)result->api.db;
    bool free_result = TRUE;

    result->finished = TRUE;

    if (db->log_level >= CASS_LOG_DEBUG) {
        i_debug("cassandra: Finished query '%s': %s", result->query,
            result->error != NULL ? result->error : "success");
    }

    i_assert((result->error != NULL) == (result->iterator == NULL));

    result->api.callback = TRUE;
    T_BEGIN {
        result->callback(&result->api, result->context);
    } T_END;
    result->api.callback = FALSE;
    result->callback = NULL;

    free_result = db->sync_result != &result->api;
    if (db->ioloop != NULL)
        io_loop_stop(db->ioloop);

    if (free_result)
        sql_result_unref(&result->api);
}

static void query_callback(CassFuture *future, void *context)
{
    struct cassandra_result *result = context;

    if (cass_future_error_code(future) != CASS_OK) {
        const char *errmsg;
        size_t errsize;

        cass_future_error_message(future, &errmsg, &errsize);
        i_free(result->error);
        result->error = i_strdup_printf("Query '%s' failed: %.*s",
                        result->query,
                        (int)errsize, errmsg);
        result_finish(result);
        return;
    }
    result->result = cass_future_get_result(future);
    result->iterator = cass_iterator_from_result(result->result);
    result_finish(result);
}

static void do_query(struct cassandra_result *result, const char *query)
{
        struct cassandra_db *db = (struct cassandra_db *)result->api.db;
    CassFuture *future;

    i_assert(SQL_DB_IS_READY(&db->api));
    i_assert(db->cur_result == NULL);

    driver_cassandra_set_state(db, SQL_DB_STATE_BUSY);
    db->cur_result = result;

    result->query = i_strdup(query);
    result->row_pool = pool_alloconly_create("cassandra result", 512);
    result->statement = cass_statement_new(query, 0);
    if (db->set_consistency)
        cass_statement_set_consistency(result->statement, db->consistency);
    future = cass_session_execute(db->session, result->statement);
    driver_cassandra_set_callback(future, db, query_callback, result);
}

static void exec_callback(struct sql_result *_result ATTR_UNUSED,
              void *context ATTR_UNUSED)
{
}

static void driver_cassandra_exec(struct sql_db *db, const char *query)
{
    struct cassandra_result *result;

    result = i_new(struct cassandra_result, 1);
    result->api = driver_cassandra_result;
    result->api.db = db;
    result->api.refcount = 1;
    result->callback = exec_callback;
    do_query(result, query);
}

static void driver_cassandra_query(struct sql_db *db, const char *query,
                   sql_query_callback_t *callback, void *context)
{
    struct cassandra_result *result;

    result = i_new(struct cassandra_result, 1);
    result->api = driver_cassandra_result;
    result->api.db = db;
    result->api.refcount = 1;
    result->callback = callback;
    result->context = context;
    do_query(result, query);
}

static void cassandra_query_s_callback(struct sql_result *result, void *context)
{
        struct cassandra_db *db = context;

    db->sync_result = result;
}

static void driver_cassandra_sync_init(struct cassandra_db *db)
{
    if (sql_connect(&db->api) < 0)
        return;
    db->orig_ioloop = current_ioloop;
    db->ioloop = io_loop_create();
    if (IS_CONNECTED(db))
        return;
    i_assert(db->api.state == SQL_DB_STATE_CONNECTING);

    db->io_pipe = io_loop_move_io(&db->io_pipe);
    /* wait for connecting to finish */
    io_loop_run(db->ioloop);
}

static void driver_cassandra_sync_deinit(struct cassandra_db *db)
{
    if (db->orig_ioloop == NULL)
        return;
    if (db->io_pipe != NULL) {
        io_loop_set_current(db->orig_ioloop);
        db->io_pipe = io_loop_move_io(&db->io_pipe);
        io_loop_set_current(db->ioloop);
    }
    io_loop_destroy(&db->ioloop);
}

static struct sql_result *
driver_cassandra_sync_query(struct cassandra_db *db, const char *query)
{
    struct sql_result *result;

    i_assert(db->sync_result == NULL);

    switch (db->api.state) {
    case SQL_DB_STATE_CONNECTING:
    case SQL_DB_STATE_BUSY:
        i_unreached();
    case SQL_DB_STATE_DISCONNECTED:
        sql_not_connected_result.refcount++;
        return &sql_not_connected_result;
    case SQL_DB_STATE_IDLE:
        break;
    }

    driver_cassandra_query(&db->api, query, cassandra_query_s_callback, db);
    if (db->sync_result == NULL) {
        db->io_pipe = io_loop_move_io(&db->io_pipe);
        io_loop_run(db->ioloop);
    }

    result = db->sync_result;
    if (result == &sql_not_connected_result) {
        /* we don't end up in cassandra's free function, so sync_result
           won't be set to NULL if we don't do it here. */
        db->sync_result = NULL;
    } else if (result == NULL) {
        result = &sql_not_connected_result;
        result->refcount++;
    }
    return result;
}

static struct sql_result *
driver_cassandra_query_s(struct sql_db *_db, const char *query)
{
    struct cassandra_db *db = (struct cassandra_db *)_db;
    struct sql_result *result;

    driver_cassandra_sync_init(db);
    result = driver_cassandra_sync_query(db, query);
    driver_cassandra_sync_deinit(db);
    return result;
}

static int
driver_cassandra_get_value(struct cassandra_result *result,
               const CassValue *value, const char **str_r)
{
    const char *output;
    size_t output_size;
    CassError rc;

    if (cass_value_is_null(value)) {
        *str_r = NULL;
        return 0;
    }

    rc = cass_value_get_string(value, &output, &output_size);
    if (rc != CASS_OK) {
        i_free(result->error);
        result->error = i_strdup_printf("Couldn't get value as string (code=%d)", rc);
        return -1;
    }
    *str_r = p_strndup(result->row_pool, output, output_size);
    return 0;
}

static int driver_cassandra_result_next_row(struct sql_result *_result)
{
    struct cassandra_result *result = (struct cassandra_result *)_result;
    const CassRow *row;
    const CassValue *value;
    const char *str;
    unsigned int i;
    int ret = 1;

    if (result->iterator == NULL)
        return -1;

    if (!cass_iterator_next(result->iterator))
        return 0;

    p_clear(result->row_pool);
    p_array_init(&result->fields, result->row_pool, 8);

    row = cass_iterator_get_row(result->iterator);
    for (i = 0; (value = cass_row_get_column(row, i)) != NULL; i++) {
        if (driver_cassandra_get_value(result, value, &str) < 0) {
            ret = -1;
            break;
        }
        array_append(&result->fields, &str, 1);
    }
    return ret;
}

static unsigned int
driver_cassandra_result_get_fields_count(struct sql_result *_result)
{
    struct cassandra_result *result = (struct cassandra_result *)_result;

    return array_count(&result->fields);
}

static const char *
driver_cassandra_result_get_field_name(struct sql_result *_result ATTR_UNUSED,
                       unsigned int idx ATTR_UNUSED)
{
    i_unreached();
}

static int
driver_cassandra_result_find_field(struct sql_result *_result ATTR_UNUSED,
                   const char *field_name ATTR_UNUSED)
{
    i_unreached();
}

static const char *
driver_cassandra_result_get_field_value(struct sql_result *_result,
                    unsigned int idx)
{
    struct cassandra_result *result = (struct cassandra_result *)_result;
    const char *const *strp;

    strp = array_idx(&result->fields, idx);
    return *strp;
}

static const unsigned char *
driver_cassandra_result_get_field_value_binary(struct sql_result *_result ATTR_UNUSED,
                           unsigned int idx ATTR_UNUSED,
                           size_t *size_r ATTR_UNUSED)
{
    i_unreached();
}

static const char *
driver_cassandra_result_find_field_value(struct sql_result *result ATTR_UNUSED,
                     const char *field_name ATTR_UNUSED)
{
    i_unreached();
}

static const char *const *
driver_cassandra_result_get_values(struct sql_result *_result)
{
    struct cassandra_result *result = (struct cassandra_result *)_result;

    return array_idx(&result->fields, 0);
}

static const char *driver_cassandra_result_get_error(struct sql_result *_result)
{
    struct cassandra_result *result = (struct cassandra_result *)_result;

    if (result->error != NULL)
        return result->error;
    return "FIXME";
}

static struct sql_transaction_context *
driver_cassandra_transaction_begin(struct sql_db *db)
{
    struct cassandra_transaction_context *ctx;

    ctx = i_new(struct cassandra_transaction_context, 1);
    ctx->ctx.db = db;
    ctx->refcount = 1;
    /* we need to be able to handle multiple open transactions, so at least
       for now just keep them in memory until commit time. */
    ctx->query_pool = pool_alloconly_create("cassandra transaction", 1024);
    return &ctx->ctx;
}

static void
driver_cassandra_transaction_unref(struct cassandra_transaction_context *ctx)
{
    i_assert(ctx->refcount > 0);
    if (--ctx->refcount > 0)
        return;

    pool_unref(&ctx->query_pool);
    i_free(ctx);
}

static void
transaction_begin_callback(struct sql_result *result,
               struct cassandra_transaction_context *ctx)
{
    if (sql_result_next_row(result) < 0) {
        ctx->begin_failed = TRUE;
        ctx->failed = TRUE;
        ctx->error = sql_result_get_error(result);
    } else {
        ctx->begin_succeeded = TRUE;
    }
    driver_cassandra_transaction_unref(ctx);
}

static void
transaction_commit_callback(struct sql_result *result,
                struct cassandra_transaction_context *ctx)
{
    if (sql_result_next_row(result) < 0)
        ctx->callback(sql_result_get_error(result), ctx->context);
    else
        ctx->callback(NULL, ctx->context);
    driver_cassandra_transaction_unref(ctx);
}

static void
transaction_update_callback(struct sql_result *result,
                struct sql_transaction_query *query)
{
    struct cassandra_transaction_context *ctx =
        (struct cassandra_transaction_context *)query->trans;

    if (sql_result_next_row(result) < 0) {
        ctx->failed = TRUE;
        ctx->error = sql_result_get_error(result);
    }
    driver_cassandra_transaction_unref(ctx);
}

static void
driver_cassandra_transaction_commit(struct sql_transaction_context *_ctx,
                sql_commit_callback_t *callback, void *context)
{
    struct cassandra_transaction_context *ctx =
        (struct cassandra_transaction_context *)_ctx;

    ctx->callback = callback;
    ctx->context = context;

    if (ctx->failed || _ctx->head == NULL) {
        callback(ctx->failed ? ctx->error : NULL, context);
        driver_cassandra_transaction_unref(ctx);
    } else if (_ctx->head->next == NULL) {
        /* just a single query, send it */
        sql_query(_ctx->db, _ctx->head->query,
              transaction_commit_callback, ctx);
    } else {
        /* multiple queries, use a transaction */
        ctx->refcount++;
        sql_query(_ctx->db, "BEGIN", transaction_begin_callback, ctx);
        while (_ctx->head != NULL) {
            ctx->refcount++;
            sql_query(_ctx->db, _ctx->head->query,
                  transaction_update_callback, _ctx->head);
            _ctx->head = _ctx->head->next;
        }
        sql_query(_ctx->db, "COMMIT", transaction_commit_callback, ctx);
    }
}

static void
commit_multi_fail(struct cassandra_transaction_context *ctx,
          struct sql_result *result, const char *query)
{
    ctx->failed = TRUE;
    ctx->error = t_strdup_printf("%s (query: %s)",
                     sql_result_get_error(result), query);
    sql_result_unref(result);
}

static int
driver_cassandra_transaction_commit_multi(struct cassandra_transaction_context *ctx,
                      struct sql_result **result_r)
{
    struct cassandra_db *db = (struct cassandra_db *)ctx->ctx.db;
    struct sql_result *result;
    struct sql_transaction_query *query;
    int ret = 0;

    result = driver_cassandra_sync_query(db, "BEGIN");
    if (sql_result_next_row(result) < 0) {
        commit_multi_fail(ctx, result, "BEGIN");
        return -1;
    }
    sql_result_unref(result);

    /* send queries */
    for (query = ctx->ctx.head; query != NULL; query = query->next) {
        result = driver_cassandra_sync_query(db, query->query);
        if (sql_result_next_row(result) < 0) {
            commit_multi_fail(ctx, result, query->query);
            ret = -1;
            break;
        }
        sql_result_unref(result);
    }

    *result_r = driver_cassandra_sync_query(db, ctx->failed ?
                        "ROLLBACK" : "COMMIT");
    return ret;
}

static void
driver_cassandra_try_commit_s(struct cassandra_transaction_context *ctx,
                  const char **error_r)
{
    struct sql_transaction_context *_ctx = &ctx->ctx;
    struct cassandra_db *db = (struct cassandra_db *)_ctx->db;
    struct sql_transaction_query *single_query = NULL;
    struct sql_result *result = NULL;
    int ret = 0;

    if (_ctx->head->next == NULL) {
        /* just a single query, send it */
        single_query = _ctx->head;
        result = sql_query_s(_ctx->db, single_query->query);
    } else {
        /* multiple queries, use a transaction */
        driver_cassandra_sync_init(db);
        ret = driver_cassandra_transaction_commit_multi(ctx, &result);
        i_assert(ret == 0 || ctx->failed);
        driver_cassandra_sync_deinit(db);
    }

    if (ctx->failed) {
        i_assert(ctx->error != NULL);
        *error_r = ctx->error;
    } else {
        if (sql_result_next_row(result) < 0) {
            ctx->failed = TRUE;
            *error_r = sql_result_get_error(result);
            i_assert(*error_r != NULL);
        }
    }
    *error_r = t_strdup(*error_r);
    if (result != NULL)
        sql_result_unref(result);
}

static int
driver_cassandra_transaction_commit_s(struct sql_transaction_context *_ctx,
                      const char **error_r)
{
    struct cassandra_transaction_context *ctx =
        (struct cassandra_transaction_context *)_ctx;

    *error_r = NULL;

    if (_ctx->head != NULL)
        driver_cassandra_try_commit_s(ctx, error_r);

    i_assert(ctx->refcount == 1);
    i_assert((*error_r != NULL) == ctx->failed);
    driver_cassandra_transaction_unref(ctx);
    return *error_r == NULL ? 0 : -1;
}

static void
driver_cassandra_transaction_rollback(struct sql_transaction_context *_ctx)
{
    struct cassandra_transaction_context *ctx =
        (struct cassandra_transaction_context *)_ctx;

    i_assert(ctx->refcount == 1);
    driver_cassandra_transaction_unref(ctx);
}

static void
driver_cassandra_update(struct sql_transaction_context *_ctx, const char *query,
            unsigned int *affected_rows)
{
    struct cassandra_transaction_context *ctx =
        (struct cassandra_transaction_context *)_ctx;

    i_assert(affected_rows == NULL);

    sql_transaction_add_query(_ctx, ctx->query_pool, query, affected_rows);
}

const struct sql_db driver_cassandra_db = {
    .name = "cassandra",
    .flags = 0,

    .v = {
        driver_cassandra_init_v,
        driver_cassandra_deinit_v,
        driver_cassandra_connect,
        driver_cassandra_disconnect,
        driver_cassandra_escape_string,
        driver_cassandra_exec,
        driver_cassandra_query,
        driver_cassandra_query_s,

        driver_cassandra_transaction_begin,
        driver_cassandra_transaction_commit,
        driver_cassandra_transaction_commit_s,
        driver_cassandra_transaction_rollback,

        driver_cassandra_update
    }
};

const struct sql_result driver_cassandra_result = {
    .v = {
        driver_cassandra_result_free,
        driver_cassandra_result_next_row,
        driver_cassandra_result_get_fields_count,
        driver_cassandra_result_get_field_name,
        driver_cassandra_result_find_field,
        driver_cassandra_result_get_field_value,
        driver_cassandra_result_get_field_value_binary,
        driver_cassandra_result_find_field_value,
        driver_cassandra_result_get_values,
        driver_cassandra_result_get_error
    }
};

const char *driver_cassandra_version = DOVECOT_ABI_VERSION;

void driver_cassandra_init(void);
void driver_cassandra_deinit(void);

void driver_cassandra_init(void)
{
    sql_driver_register(&driver_cassandra_db);
}

void driver_cassandra_deinit(void)
{
    sql_driver_unregister(&driver_cassandra_db);
}

#endif