datafusion-postgres 0.17.0

use std::collections::HashMap;
use std::sync::Arc;

use async_trait::async_trait;
use datafusion::arrow::datatypes::DataType;
use datafusion::common::ParamValues;
use datafusion::logical_expr::LogicalPlan;
use datafusion::prelude::*;
use datafusion::sql::parser::Statement;
use datafusion::sql::sqlparser;
use log::info;
use pgwire::api::auth::StartupHandler;
use pgwire::api::auth::noop::NoopStartupHandler;
use pgwire::api::cancel::{CancelHandler, DefaultCancelHandler};
use pgwire::api::portal::{Format, Portal};
use pgwire::api::query::{ExtendedQueryHandler, SimpleQueryHandler};
use pgwire::api::results::{FieldInfo, Response, Tag};
use pgwire::api::stmt::QueryParser;
use pgwire::api::store::PortalStore;
use pgwire::api::{
    ClientInfo, ClientPortalStore, ConnectionManager, ErrorHandler, PgWireServerHandlers, Type,
};
use pgwire::error::{PgWireError, PgWireResult};
use pgwire::messages::PgWireBackendMessage;
use pgwire::types::format::FormatOptions;

use crate::hooks::QueryHook;
use crate::hooks::cursor::CursorStatementHook;
use crate::hooks::set_show::SetShowHook;
use crate::hooks::transactions::TransactionStatementHook;
use crate::{client, planner};
use arrow_pg::datatypes::df;
use arrow_pg::datatypes::{arrow_schema_to_pg_fields, into_pg_type};
use datafusion_pg_catalog::sql::PostgresCompatibilityParser;

/// Simple startup handler that does no authentication
pub struct SimpleStartupHandler {
    connection_manager: Arc<ConnectionManager>,
}

#[async_trait::async_trait]
impl NoopStartupHandler for SimpleStartupHandler {
    fn connection_manager(&self) -> Option<Arc<ConnectionManager>> {
        Some(self.connection_manager.clone())
    }
}

pub struct HandlerFactory {
    pub session_service: Arc<DfSessionService>,
    cancel_handler: Arc<DefaultCancelHandler>,
    startup_handler: Arc<SimpleStartupHandler>,
}

impl HandlerFactory {
    pub fn new(session_context: Arc<SessionContext>) -> Self {
        let session_service = Arc::new(DfSessionService::new(session_context));
        let connection_manager = Arc::new(ConnectionManager::new());
        HandlerFactory {
            session_service,
            cancel_handler: Arc::new(DefaultCancelHandler::new(connection_manager.clone())),
            startup_handler: Arc::new(SimpleStartupHandler {
                connection_manager: connection_manager.clone(),
            }),
        }
    }

    pub fn new_with_hooks(
        session_context: Arc<SessionContext>,
        query_hooks: Vec<Arc<dyn QueryHook>>,
    ) -> Self {
        let session_service = Arc::new(DfSessionService::new_with_hooks(
            session_context,
            query_hooks,
        ));
        let connection_manager = Arc::new(ConnectionManager::new());
        HandlerFactory {
            session_service,
            cancel_handler: Arc::new(DefaultCancelHandler::new(connection_manager.clone())),
            startup_handler: Arc::new(SimpleStartupHandler {
                connection_manager: connection_manager.clone(),
            }),
        }
    }
}

impl PgWireServerHandlers for HandlerFactory {
    fn simple_query_handler(&self) -> Arc<impl SimpleQueryHandler> {
        self.session_service.clone()
    }

    fn extended_query_handler(&self) -> Arc<impl ExtendedQueryHandler> {
        self.session_service.clone()
    }

    fn startup_handler(&self) -> Arc<impl StartupHandler> {
        self.startup_handler.clone()
    }

    fn error_handler(&self) -> Arc<impl ErrorHandler> {
        Arc::new(LoggingErrorHandler)
    }

    fn cancel_handler(&self) -> Arc<impl CancelHandler> {
        self.cancel_handler.clone()
    }
}

struct LoggingErrorHandler;

impl ErrorHandler for LoggingErrorHandler {
    fn on_error<C>(&self, _client: &C, error: &mut PgWireError)
    where
        C: ClientInfo,
    {
        info!("Sending error: {error}")
    }
}

/// The pgwire handler backed by a datafusion `SessionContext`
pub struct DfSessionService {
    session_context: Arc<SessionContext>,
    parser: Arc<Parser>,
    query_hooks: Vec<Arc<dyn QueryHook>>,
}

impl DfSessionService {
    pub fn new(session_context: Arc<SessionContext>) -> DfSessionService {
        let hooks: Vec<Arc<dyn QueryHook>> = vec![
            Arc::new(CursorStatementHook),
            Arc::new(SetShowHook),
            Arc::new(TransactionStatementHook),
        ];
        Self::new_with_hooks(session_context, hooks)
    }

    pub fn new_with_hooks(
        session_context: Arc<SessionContext>,
        query_hooks: Vec<Arc<dyn QueryHook>>,
    ) -> DfSessionService {
        let parser = Arc::new(Parser {
            session_context: session_context.clone(),
            sql_parser: PostgresCompatibilityParser::new(),
            query_hooks: query_hooks.clone(),
        });
        DfSessionService {
            session_context,
            parser,
            query_hooks,
        }
    }
}

#[async_trait]
impl SimpleQueryHandler for DfSessionService {
    async fn do_query<C>(&self, client: &mut C, query: &str) -> PgWireResult<Vec<Response>>
    where
        C: ClientInfo
            + ClientPortalStore
            + futures::Sink<PgWireBackendMessage>
            + Unpin
            + Send
            + Sync,
        C::PortalStore: PortalStore,
        C::Error: std::fmt::Debug,
        PgWireError: From<<C as futures::Sink<PgWireBackendMessage>>::Error>,
    {
        log::debug!("Received query: {query}");

        let statements = self
            .parser
            .sql_parser
            .parse(query)
            .map_err(|e| PgWireError::ApiError(Box::new(e)))?;

        // empty query
        if statements.is_empty() {
            return Ok(vec![Response::EmptyQuery]);
        }

        let mut results = vec![];
        'stmt: for statement in statements {
            // Call query hooks with the parsed statement
            for hook in &self.query_hooks {
                if let Some(result) = hook
                    .handle_simple_query(&statement, &self.session_context, client)
                    .await
                {
                    results.push(result?);
                    continue 'stmt;
                }
            }

            let df_result = {
                let query = statement.to_string();

                let timeout = client::get_statement_timeout(client);
                if let Some(timeout_duration) = timeout {
                    tokio::time::timeout(timeout_duration, self.session_context.sql(&query))
                        .await
                        .map_err(|_| {
                            PgWireError::UserError(Box::new(pgwire::error::ErrorInfo::new(
                                "ERROR".to_string(),
                                "57014".to_string(), // query_canceled error code
                                "canceling statement due to statement timeout".to_string(),
                            )))
                        })?
                } else {
                    self.session_context.sql(&query).await
                }
            };

            // Handle query execution errors and transaction state
            let df = match df_result {
                Ok(df) => df,
                Err(e) => {
                    return Err(PgWireError::ApiError(Box::new(e)));
                }
            };

            if matches!(statement, sqlparser::ast::Statement::Insert(_)) {
                let resp = map_rows_affected_for_insert(&df).await?;
                results.push(resp);
            } else {
                // For non-INSERT queries, return a regular Query response
                let format_options =
                    Arc::new(FormatOptions::from_client_metadata(client.metadata()));
                let resp =
                    df::encode_dataframe(df, &Format::UnifiedText, Some(format_options)).await?;
                results.push(Response::Query(resp));
            }
        }
        Ok(results)
    }
}

#[async_trait]
impl ExtendedQueryHandler for DfSessionService {
    type Statement = (String, Option<(sqlparser::ast::Statement, LogicalPlan)>);
    type QueryParser = Parser;

    fn query_parser(&self) -> Arc<Self::QueryParser> {
        self.parser.clone()
    }

    async fn do_query<C>(
        &self,
        client: &mut C,
        portal: &Portal<Self::Statement>,
        _max_rows: usize,
    ) -> PgWireResult<Response>
    where
        C: ClientInfo
            + ClientPortalStore
            + futures::Sink<PgWireBackendMessage>
            + Unpin
            + Send
            + Sync,
        C::PortalStore: PortalStore,
        C::Error: std::fmt::Debug,
        PgWireError: From<<C as futures::Sink<PgWireBackendMessage>>::Error>,
    {
        let query = &portal.statement.statement.0;
        log::debug!("Received execute extended query: {query}");
        // Check query hooks first
        if !self.query_hooks.is_empty()
            && let (_, Some((statement, plan))) = &portal.statement.statement
        {
            // TODO: in the case where query hooks all return None, we do the param handling again later.
            let param_types = planner::get_inferred_parameter_types(plan)
                .map_err(|e| PgWireError::ApiError(Box::new(e)))?;

            let param_values: ParamValues =
                df::deserialize_parameters(portal, &ordered_param_types(&param_types))?;

            for hook in &self.query_hooks {
                if let Some(result) = hook
                    .handle_extended_query(
                        statement,
                        plan,
                        &param_values,
                        &self.session_context,
                        client,
                    )
                    .await
                {
                    return result;
                }
            }
        }

        if let (_, Some((statement, plan))) = &portal.statement.statement {
            let param_types = planner::get_inferred_parameter_types(plan)
                .map_err(|e| PgWireError::ApiError(Box::new(e)))?;

            let param_values =
                df::deserialize_parameters(portal, &ordered_param_types(&param_types))?;

            let plan = plan
                .clone()
                .replace_params_with_values(&param_values)
                .map_err(|e| PgWireError::ApiError(Box::new(e)))?;
            let optimised = self
                .session_context
                .state()
                .optimize(&plan)
                .map_err(|e| PgWireError::ApiError(Box::new(e)))?;

            let dataframe = {
                let timeout = client::get_statement_timeout(client);
                if let Some(timeout_duration) = timeout {
                    tokio::time::timeout(
                        timeout_duration,
                        self.session_context.execute_logical_plan(optimised),
                    )
                    .await
                    .map_err(|_| {
                        PgWireError::UserError(Box::new(pgwire::error::ErrorInfo::new(
                            "ERROR".to_string(),
                            "57014".to_string(), // query_canceled error code
                            "canceling statement due to statement timeout".to_string(),
                        )))
                    })?
                    .map_err(|e| PgWireError::ApiError(Box::new(e)))?
                } else {
                    self.session_context
                        .execute_logical_plan(optimised)
                        .await
                        .map_err(|e| PgWireError::ApiError(Box::new(e)))?
                }
            };

            if matches!(statement, sqlparser::ast::Statement::Insert(_)) {
                let resp = map_rows_affected_for_insert(&dataframe).await?;

                Ok(resp)
            } else {
                // For non-INSERT queries, return a regular Query response
                let format_options =
                    Arc::new(FormatOptions::from_client_metadata(client.metadata()));
                let resp = df::encode_dataframe(
                    dataframe,
                    &portal.result_column_format,
                    Some(format_options),
                )
                .await?;
                Ok(Response::Query(resp))
            }
        } else {
            Ok(Response::EmptyQuery)
        }
    }
}

async fn map_rows_affected_for_insert(df: &DataFrame) -> PgWireResult<Response> {
    // For INSERT queries, we need to execute the query to get the row count
    // and return an Execution response with the proper tag
    let result = df
        .clone()
        .collect()
        .await
        .map_err(|e| PgWireError::ApiError(Box::new(e)))?;

    // Extract count field from the first batch
    let rows_affected = result
        .first()
        .and_then(|batch| batch.column_by_name("count"))
        .and_then(|col| {
            col.as_any()
                .downcast_ref::<datafusion::arrow::array::UInt64Array>()
        })
        .map_or(0, |array| array.value(0) as usize);

    // Create INSERT tag with the affected row count
    let tag = Tag::new("INSERT").with_oid(0).with_rows(rows_affected);
    Ok(Response::Execution(tag))
}

pub struct Parser {
    session_context: Arc<SessionContext>,
    sql_parser: PostgresCompatibilityParser,
    query_hooks: Vec<Arc<dyn QueryHook>>,
}

#[async_trait]
impl QueryParser for Parser {
    type Statement = (String, Option<(sqlparser::ast::Statement, LogicalPlan)>);

    async fn parse_sql<C>(
        &self,
        client: &C,
        sql: &str,
        _types: &[Option<Type>],
    ) -> PgWireResult<Self::Statement>
    where
        C: ClientInfo + Unpin + Send + Sync,
    {
        log::debug!("Received parse extended query: {sql}");
        let mut statements = self
            .sql_parser
            .parse(sql)
            .map_err(|e| PgWireError::ApiError(Box::new(e)))?;
        if statements.is_empty() {
            return Ok((sql.to_string(), None));
        }

        let statement = statements.remove(0);
        let query = statement.to_string();

        let context = &self.session_context;
        let state = context.state();

        for hook in &self.query_hooks {
            if let Some(logical_plan) = hook
                .handle_extended_parse_query(&statement, context, client)
                .await
            {
                return Ok((query, Some((statement, logical_plan?))));
            }
        }

        let logical_plan = state
            .statement_to_plan(Statement::Statement(Box::new(statement.clone())))
            .await
            .map_err(|e| PgWireError::ApiError(Box::new(e)))?;
        Ok((query, Some((statement, logical_plan))))
    }

    fn get_parameter_types(&self, stmt: &Self::Statement) -> PgWireResult<Vec<Type>> {
        if let (_, Some((_, plan))) = stmt {
            let params = planner::get_inferred_parameter_types(plan)
                .map_err(|e| PgWireError::ApiError(Box::new(e)))?;

            let mut param_types = Vec::with_capacity(params.len());
            for param_type in ordered_param_types(&params).iter() {
                if let Some(datatype) = param_type {
                    let pgtype = into_pg_type(datatype)?;
                    param_types.push(pgtype);
                } else {
                    param_types.push(Type::UNKNOWN);
                }
            }

            Ok(param_types)
        } else {
            Ok(vec![])
        }
    }

    fn get_result_schema(
        &self,
        stmt: &Self::Statement,
        column_format: Option<&Format>,
    ) -> PgWireResult<Vec<FieldInfo>> {
        if let (_, Some((_, plan))) = stmt {
            if !matches!(plan, LogicalPlan::Ddl(_) | LogicalPlan::Dml(_)) {
                let schema = plan.schema();
                let fields = arrow_schema_to_pg_fields(
                    schema.as_arrow(),
                    column_format.unwrap_or(&Format::UnifiedText),
                    None,
                )?;

                Ok(fields)
            } else {
                Ok(vec![])
            }
        } else {
            Ok(vec![])
        }
    }
}

fn ordered_param_types(types: &HashMap<String, Option<DataType>>) -> Vec<Option<&DataType>> {
    // Datafusion stores the parameters as a map.  In our case, the keys will be
    // `$1`, `$2` etc.  The values will be the parameter types.
    let mut types = types.iter().collect::<Vec<_>>();
    types.sort_by(|a, b| a.0.cmp(b.0));
    types.into_iter().map(|pt| pt.1.as_ref()).collect()
}

#[cfg(test)]
mod tests {
    use datafusion::prelude::SessionContext;

    use super::*;
    use crate::testing::MockClient;

    use crate::hooks::HookClient;

    struct TestHook;

    #[async_trait]
    impl QueryHook for TestHook {
        async fn handle_simple_query(
            &self,
            statement: &sqlparser::ast::Statement,
            _ctx: &SessionContext,
            _client: &mut dyn HookClient,
        ) -> Option<PgWireResult<Response>> {
            if statement.to_string().contains("magic") {
                Some(Ok(Response::EmptyQuery))
            } else {
                None
            }
        }

        async fn handle_extended_parse_query(
            &self,
            _statement: &sqlparser::ast::Statement,
            _session_context: &SessionContext,
            _client: &(dyn ClientInfo + Send + Sync),
        ) -> Option<PgWireResult<LogicalPlan>> {
            None
        }

        async fn handle_extended_query(
            &self,
            _statement: &sqlparser::ast::Statement,
            _logical_plan: &LogicalPlan,
            _params: &ParamValues,
            _session_context: &SessionContext,
            _client: &mut dyn HookClient,
        ) -> Option<PgWireResult<Response>> {
            None
        }
    }

    #[tokio::test]
    async fn test_query_hooks() {
        let hook = TestHook;
        let ctx = SessionContext::new();
        let mut client = MockClient::new();

        // Parse a statement that contains "magic"
        let parser = PostgresCompatibilityParser::new();
        let statements = parser.parse("SELECT magic").unwrap();
        let stmt = &statements[0];

        // Hook should intercept
        let result = hook.handle_simple_query(stmt, &ctx, &mut client).await;
        assert!(result.is_some());

        // Parse a normal statement
        let statements = parser.parse("SELECT 1").unwrap();
        let stmt = &statements[0];

        // Hook should not intercept
        let result = hook.handle_simple_query(stmt, &ctx, &mut client).await;
        assert!(result.is_none());
    }

    #[tokio::test]
    async fn test_multiple_statements_with_hook_continue() {
        // Bug #227: when a hook returned a result, the code used `break 'stmt`
        // which would exit the entire statement loop, preventing subsequent statements
        // from being processed.
        let session_context = Arc::new(SessionContext::new());

        let hooks: Vec<Arc<dyn QueryHook>> = vec![Arc::new(TestHook)];
        let service = DfSessionService::new_with_hooks(session_context, hooks);

        let mut client = MockClient::new();

        // Mix of queries with hooks and those without
        let query = "SELECT magic; SELECT 1; SELECT magic; SELECT 1";

        let results =
            <DfSessionService as SimpleQueryHandler>::do_query(&service, &mut client, query)
                .await
                .unwrap();

        assert_eq!(results.len(), 4, "Expected 4 responses");

        assert!(matches!(results[0], Response::EmptyQuery));
        assert!(matches!(results[1], Response::Query(_)));
        assert!(matches!(results[2], Response::EmptyQuery));
        assert!(matches!(results[3], Response::Query(_)));
    }

    #[tokio::test]
    async fn test_set_sends_parameter_status_via_sink() {
        use pgwire::messages::PgWireBackendMessage;

        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        let test_cases = vec![
            ("SET datestyle = 'ISO, MDY'", "DateStyle", "ISO, MDY"),
            (
                "SET intervalstyle = 'postgres'",
                "IntervalStyle",
                "postgres",
            ),
            ("SET bytea_output = 'hex'", "bytea_output", "hex"),
            (
                "SET application_name = 'myapp'",
                "application_name",
                "myapp",
            ),
            ("SET search_path = 'public'", "search_path", "public"),
            ("SET extra_float_digits = '2'", "extra_float_digits", "2"),
            (
                "SET TIME ZONE 'America/New_York'",
                "TimeZone",
                "America/New_York",
            ),
        ];

        for (sql, expected_key, expected_value) in test_cases {
            client.sent_messages.clear();

            let responses =
                <DfSessionService as SimpleQueryHandler>::do_query(&service, &mut client, sql)
                    .await
                    .unwrap();

            assert!(
                matches!(responses[0], Response::Execution(_)),
                "Expected SET tag for {sql}"
            );

            let ps_msgs: Vec<_> = client
                .sent_messages()
                .iter()
                .filter_map(|m| match m {
                    PgWireBackendMessage::ParameterStatus(ps) => Some(ps),
                    _ => None,
                })
                .collect();

            assert_eq!(ps_msgs.len(), 1, "Expected 1 ParameterStatus for {sql}");
            assert_eq!(ps_msgs[0].name, expected_key, "Wrong key for {sql}");
            assert_eq!(ps_msgs[0].value, expected_value, "Wrong value for {sql}");
        }
    }

    #[tokio::test]
    async fn test_set_statement_timeout_no_parameter_status() {
        use pgwire::messages::PgWireBackendMessage;

        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "SET statement_timeout TO '5000ms'",
        )
        .await
        .unwrap();

        let has_ps = client
            .sent_messages()
            .iter()
            .any(|m| matches!(m, PgWireBackendMessage::ParameterStatus(_)));

        assert!(!has_ps, "statement_timeout should not send ParameterStatus");
    }

    fn assert_execution_tag(response: &Response, expected: &str) {
        match response {
            Response::Execution(tag) => {
                let cc = pgwire::messages::response::CommandComplete::from(tag.clone());
                assert_eq!(cc.tag, expected, "Unexpected execution tag");
            }
            other => panic!("Expected Execution response, got: {other:?}"),
        }
    }

    async fn assert_query_response_empty(response: &mut Response) {
        use futures::StreamExt;

        let Response::Query(qr) = response else {
            panic!("Expected Query response, got: {response:?}");
        };

        let mut count = 0;
        while qr.data_rows().next().await.is_some() {
            count += 1;
        }
        assert_eq!(count, 0, "Expected no rows from exhausted cursor");
    }

    #[tokio::test]
    async fn test_declare_fetch_close_cursor() {
        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        let responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "DECLARE test_cursor CURSOR FOR SELECT 1 AS col",
        )
        .await
        .unwrap();

        assert_eq!(responses.len(), 1);
        assert_execution_tag(&responses[0], "DECLARE CURSOR");

        let responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH NEXT FROM test_cursor",
        )
        .await
        .unwrap();

        assert_eq!(responses.len(), 1);
        assert!(
            matches!(&responses[0], Response::Query(_)),
            "Expected Query response for FETCH"
        );

        let mut responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH NEXT FROM test_cursor",
        )
        .await
        .unwrap();

        assert_eq!(responses.len(), 1);
        assert_query_response_empty(&mut responses[0]).await;

        let responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "CLOSE test_cursor",
        )
        .await
        .unwrap();

        assert_eq!(responses.len(), 1);
        assert_execution_tag(&responses[0], "CLOSE CURSOR");
    }

    #[tokio::test]
    async fn test_fetch_nonexistent_cursor() {
        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        let result = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH NEXT FROM nonexistent",
        )
        .await;

        assert!(result.is_err());
    }

    #[tokio::test]
    async fn test_close_all_portals() {
        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "DECLARE c1 CURSOR FOR SELECT 1",
        )
        .await
        .unwrap();

        <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "DECLARE c2 CURSOR FOR SELECT 2",
        )
        .await
        .unwrap();

        let responses =
            <DfSessionService as SimpleQueryHandler>::do_query(&service, &mut client, "CLOSE ALL")
                .await
                .unwrap();

        assert!(matches!(&responses[0], Response::Execution(_)),);

        let result = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH NEXT FROM c1",
        )
        .await;
        assert!(result.is_err(), "c1 should be closed");
    }

    #[tokio::test]
    async fn test_fetch_forward_n() {
        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "CREATE TABLE nums AS SELECT 1 AS n UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5",
        )
        .await
        .unwrap();

        <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "DECLARE mycur CURSOR FOR SELECT n FROM nums ORDER BY n",
        )
        .await
        .unwrap();

        let responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH FORWARD 3 FROM mycur",
        )
        .await
        .unwrap();

        assert!(
            matches!(&responses[0], Response::Query(_)),
            "Expected Query response for FORWARD 3"
        );

        let responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH FORWARD ALL FROM mycur",
        )
        .await
        .unwrap();

        let resp_desc = match &responses[0] {
            Response::Query(_) => "Query".to_string(),
            Response::Execution(tag) => {
                let cc = pgwire::messages::response::CommandComplete::from(tag.clone());
                format!("Execution({})", cc.tag)
            }
            other => format!("{:?}", other),
        };
        assert!(
            matches!(&responses[0], Response::Query(_)),
            "Expected Query response for remaining rows, got: {resp_desc}"
        );

        let mut responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH NEXT FROM mycur",
        )
        .await
        .unwrap();

        assert_query_response_empty(&mut responses[0]).await;
    }

    #[tokio::test]
    async fn test_scroll_cursor_error() {
        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "DECLARE mycur CURSOR FOR SELECT 1",
        )
        .await
        .unwrap();

        let result = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH PRIOR FROM mycur",
        )
        .await;

        assert!(result.is_err(), "PRIOR should fail on forward-only cursor");
    }

    #[tokio::test]
    async fn test_move_cursor() {
        let service = crate::testing::setup_handlers();
        let mut client = MockClient::new();

        <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "DECLARE mycur CURSOR FOR SELECT generate_series(1, 5) AS n",
        )
        .await
        .unwrap();

        let responses = <DfSessionService as SimpleQueryHandler>::do_query(
            &service,
            &mut client,
            "FETCH FORWARD 3 FROM mycur",
        )
        .await
        .unwrap();

        assert!(matches!(&responses[0], Response::Query(_)));
    }
}