feat: streaming export to CSV/JSONL/JSON with cursor fetch, cancel, and fail-closed cleanup (Task 10)

desktop/src-tauri/Cargo.lock

@@ -1789,6 +1789,7 @@ dependencies = [
  "chrono",
  "core-foundation 0.10.1",
  "deadpool-postgres",
+ "futures-util",
  "indexmap 2.14.0",
  "redis",
  "rusqlite",

desktop/src-tauri/Cargo.toml

@@ -32,6 +32,7 @@ tauri-plugin-fs = "2"
 tokio = { version = "1", features = ["full"] }
 tokio-postgres = { version = "0.7", features = ["with-chrono-0_4", "with-uuid-1", "with-serde_json-1"] }
 bytes = "1"
+futures-util = "0.3"
 sqlx = { version = "0.8", features = ["runtime-tokio", "mysql", "tls-rustls", "json"] }
 redis = { version = "0.27", features = ["tokio-comp"] }
 # async-ssh2 is not available at v0.4; using synchronous ssh2 via tokio::task::spawn_blocking per plan's fallback

desktop/src-tauri/src/commands/mod.rs

@@ -8,6 +8,7 @@ pub mod keychain;
 pub mod maintenance;
 pub mod objects;
 pub mod query;
+pub mod query_export;
 pub mod schema_graph;
 pub mod settings;
 pub mod ssh;

desktop/src-tauri/src/commands/query_export.rs

@@ -0,0 +1,539 @@
+//! Streaming export of a full query result to a local file (spec §4/§5C).
+//!
+//! Headless `run_*_export` functions (testable without Tauri State) + one
+//! thin command that owns the pool lock, the cancel registration, and the
+//! `export-progress` events. Fail-closed: any error deletes the partial file.
+
+use crate::db::pool::DbHandle;
+use crate::models::db_viewer::ColumnInfo;
+use serde::{Deserialize, Serialize};
+use sqlx::{Column, Row};
+use std::io::Write;
+use std::path::{Path, PathBuf};
+use tauri::State;
+
+const PROGRESS_ROWS: u64 = 5_000;
+const CURSOR_NAME: &str = "_gridline_export";
+const CURSOR_FETCH: usize = 1_000;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
+pub enum ExportFormat {
+    Csv,
+    Jsonl,
+    Json,
+}
+
+impl ExportFormat {
+    pub fn from_str(s: &str) -> Result<Self, String> {
+        match s {
+            "csv" => Ok(ExportFormat::Csv),
+            "jsonl" => Ok(ExportFormat::Jsonl),
+            "json" => Ok(ExportFormat::Json),
+            other => Err(format!("unsupported export format: {other} (csv | jsonl | json)")),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct ExportSummary {
+    pub rows_written: u64,
+}
+
+#[derive(Debug, Clone, Serialize)]
+#[serde(rename_all = "snake_case")]
+pub struct ExportProgressEvent {
+    pub job_id: String,
+    /// "running" | "done" | "error"
+    pub status: String,
+    pub rows: u64,
+    pub error: Option<String>,
+}
+
+/// Read-only heuristic mirroring the frontend `isDestructiveQuery` set (spec §2:
+/// never trust the frontend guard alone).
+pub fn is_read_only_sql(sql: &str) -> bool {
+    let k: String = sql
+        .trim_start()
+        .chars()
+        .take_while(|c| c.is_ascii_alphabetic())
+        .collect::<String>()
+        .to_uppercase();
+    !matches!(
+        k.as_str(),
+        "INSERT" | "UPDATE" | "DELETE" | "DROP" | "ALTER" | "TRUNCATE" | "CREATE" | "REPLACE"
+    )
+}
+
+/// Validate export inputs: single, read-only statement + absolute path.
+fn validate_export_inputs(sql: &str, path: &Path) -> Result<(), String> {
+    if !path.is_absolute() {
+        return Err("Export path must be absolute".to_string());
+    }
+    if !is_read_only_sql(sql) {
+        return Err("Export accepts read-only queries only (INSERT/UPDATE/DELETE/DROP/ALTER/TRUNCATE/CREATE/REPLACE are rejected)".to_string());
+    }
+    let statements = crate::db::sql_split::split_statements(sql);
+    if statements.len() != 1 {
+        return Err("Export accepts a single query".to_string());
+    }
+    Ok(())
+}
+
+// ── Format writers (pure) ─────────────────────────────────────────
+
+/// Quote one CSV cell with formula-injection protection (spec §2) — mirrors
+/// the client-side `csvCell` brought to parity in Task 11.
+pub fn csv_cell(value: &serde_json::Value) -> String {
+    let raw = match value {
+        serde_json::Value::Null => String::new(),
+        serde_json::Value::String(s) => s.clone(),
+        other => other.to_string(),
+    };
+    let guarded = match raw.chars().next() {
+        Some('=') | Some('+') | Some('-') | Some('@') | Some('\t') | Some('\r') => {
+            format!("'{raw}")
+        }
+        _ => raw.clone(),
+    };
+    if guarded.contains(',') || guarded.contains('"') || guarded.contains('\n') || guarded.contains('\r') {
+        format!("\"{}\"", guarded.replace('"', "\"\""))
+    } else {
+        guarded
+    }
+}
+
+pub fn csv_line(columns: &[ColumnInfo], row: &[serde_json::Value]) -> String {
+    let mut line = String::new();
+    for (i, _) in columns.iter().enumerate() {
+        if i > 0 {
+            line.push(',');
+        }
+        line.push_str(&csv_cell(row.get(i).unwrap_or(&serde_json::Value::Null)));
+    }
+    line
+}
+
+pub fn csv_header(columns: &[ColumnInfo]) -> String {
+    columns
+        .iter()
+        .map(|c| csv_cell(&serde_json::Value::String(c.name.clone())))
+        .collect::<Vec<_>>()
+        .join(",")
+}
+
+pub fn jsonl_line(columns: &[ColumnInfo], row: &[serde_json::Value]) -> String {
+    let mut obj = serde_json::Map::new();
+    for (i, c) in columns.iter().enumerate() {
+        obj.insert(c.name.clone(), row.get(i).cloned().unwrap_or(serde_json::Value::Null));
+    }
+    serde_json::to_string(&serde_json::Value::Object(obj)).unwrap_or_default()
+}
+
+fn write_row<W: Write>(
+    w: &mut W,
+    format: ExportFormat,
+    columns: &[ColumnInfo],
+    row: &[serde_json::Value],
+    first: bool,
+) -> std::io::Result<()> {
+    match format {
+        ExportFormat::Csv => writeln!(w, "{}", csv_line(columns, row)),
+        ExportFormat::Jsonl => writeln!(w, "{}", jsonl_line(columns, row)),
+        ExportFormat::Json => {
+            if !first {
+                writeln!(w, ",")?;
+            }
+            write!(w, "{}", jsonl_line(columns, row))
+        }
+    }
+}
+
+/// Run the export, deleting the partial file on any failure (fail-closed).
+fn with_partial_cleanup<W, F>(path: &PathBuf, w: W, f: F) -> Result<ExportSummary, String>
+where
+    W: Write,
+    F: FnOnce(&mut std::io::BufWriter<W>) -> Result<ExportSummary, String>,
+{
+    let mut writer = std::io::BufWriter::with_capacity(8 * 1024 * 1024, w);
+    match f(&mut writer) {
+        Ok(summary) => {
+            writer.flush().map_err(|e| e.to_string())?;
+            Ok(summary)
+        }
+        Err(e) => {
+            let _ = std::fs::remove_file(path);
+            Err(e)
+        }
+    }
+}
+
+// ── SQLite (native streaming) ─────────────────────────────────────
+
+pub fn run_sqlite_export(
+    conn: &rusqlite::Connection,
+    sql: &str,
+    format: ExportFormat,
+    path: &PathBuf,
+    progress: &mut (dyn FnMut(u64) + Send),
+) -> Result<ExportSummary, String> {
+    validate_export_inputs(sql, path)?;
+    let file = std::fs::File::create(path).map_err(|e| format!("cannot create file: {e}"))?;
+
+    with_partial_cleanup(path, file, |writer| {
+        let mut stmt = conn.prepare(sql).map_err(|e| e.to_string())?;
+        let columns: Vec<ColumnInfo> = (0..stmt.column_count())
+            .map(|i| ColumnInfo {
+                name: stmt.column_name(i).unwrap_or("?").to_string(),
+                data_type: "TEXT".to_string(),
+                is_nullable: true,
+                is_pk: false,
+                is_fk: false,
+                fk_ref: None,
+                default_value: None,
+                editable: true,
+                is_generated: false,
+            })
+            .collect();
+        if format == ExportFormat::Csv {
+            write!(writer, "\u{FEFF}").map_err(|e| e.to_string())?; // UTF-8 BOM
+            writeln!(writer, "{}", csv_header(&columns)).map_err(|e| e.to_string())?;
+        }
+        if format == ExportFormat::Json {
+            write!(writer, "[").map_err(|e| e.to_string())?;
+        }
+        let col_count = columns.len();
+        let mut rows_written: u64 = 0;
+        let mut first = true;
+        let mut rows = stmt.query([]).map_err(|e| e.to_string())?;
+        while let Some(row) = rows.next().map_err(|e| e.to_string())? {
+            let values: Vec<serde_json::Value> = (0..col_count)
+                .map(|i| sqlite_ref_to_json(row, i))
+                .collect();
+            write_row(writer, format, &columns, &values, first).map_err(|e| e.to_string())?;
+            first = false;
+            rows_written += 1;
+            if rows_written % PROGRESS_ROWS == 0 {
+                progress(rows_written);
+            }
+        }
+        if format == ExportFormat::Json {
+            writeln!(writer, "]").map_err(|e| e.to_string())?;
+        }
+        progress(rows_written);
+        Ok(ExportSummary { rows_written })
+    })
+}
+
+fn sqlite_ref_to_json(row: &rusqlite::Row, i: usize) -> serde_json::Value {
+    use rusqlite::types::ValueRef;
+    match row.get_ref(i) {
+        Ok(ValueRef::Null) => serde_json::Value::Null,
+        Ok(ValueRef::Integer(v)) => serde_json::json!(v),
+        Ok(ValueRef::Real(v)) => serde_json::json!(v),
+        Ok(ValueRef::Text(v)) => serde_json::Value::String(String::from_utf8_lossy(v).to_string()),
+        Ok(ValueRef::Blob(v)) => serde_json::Value::String(format!("[{}B blob]", v.len())),
+        Err(_) => serde_json::Value::Null,
+    }
+}
+
+// ── PostgreSQL (cursor FETCH loop — constant memory, stable order) ──
+
+pub async fn run_pg_export(
+    client: &tokio_postgres::Client,
+    sql: &str,
+    format: ExportFormat,
+    path: &PathBuf,
+    progress: &mut (dyn FnMut(u64) + Send),
+) -> Result<ExportSummary, String> {
+    validate_export_inputs(sql, path)?;
+    let file = std::fs::File::create(path).map_err(|e| format!("cannot create file: {e}"))?;
+    let trimmed = sql.trim();
+    let mut writer = std::io::BufWriter::with_capacity(8 * 1024 * 1024, file);
+
+    // LINEAR FORM: run the cursor loop inline; on any error drop the writer
+    // and remove the partial file.
+    let run = async {
+        client.simple_query("BEGIN").await.map_err(|e| format!("export begin failed: {e}"))?;
+        if let Err(e) = client
+            .simple_query(&format!("DECLARE {CURSOR_NAME} CURSOR FOR ({trimmed})"))
+            .await
+        {
+            let _ = client.simple_query("ROLLBACK").await;
+            return Err(format!("export declare failed: {e}"));
+        }
+        let mut columns: Vec<ColumnInfo> = Vec::new();
+        let mut rows_written: u64 = 0;
+        let mut first = true;
+        if format == ExportFormat::Json {
+            write!(writer, "[").map_err(|e| e.to_string())?;
+        }
+        loop {
+            let msgs = client
+                .simple_query(&format!("FETCH FORWARD {CURSOR_FETCH} FROM {CURSOR_NAME}"))
+                .await;
+            let msgs = match msgs {
+                Ok(m) => m,
+                Err(e) => {
+                    let _ = client.simple_query("ROLLBACK").await;
+                    return Err(format!("export fetch failed: {e}"));
+                }
+            };
+            let mut batch_rows: Vec<Vec<serde_json::Value>> = Vec::new();
+            for msg in msgs {
+                if let tokio_postgres::SimpleQueryMessage::Row(row) = msg {
+                    if columns.is_empty() {
+                        columns = row
+                            .columns()
+                            .iter()
+                            .map(|c| ColumnInfo {
+                                name: c.name().to_string(),
+                                data_type: "text".to_string(),
+                                is_nullable: true,
+                                is_pk: false,
+                                is_fk: false,
+                                fk_ref: None,
+                                default_value: None,
+                                editable: true,
+                                is_generated: false,
+                            })
+                            .collect();
+                    }
+                    // Simple-query protocol returns every value as text; decode
+                    // as &str (usize has no FromSql impl) and NULL as None.
+                    let values: Vec<serde_json::Value> = (0..row.len())
+                        .map(|i| match row.try_get(i) {
+                            Ok(Some(s)) => serde_json::Value::String(s.to_string()),
+                            _ => serde_json::Value::Null,
+                        })
+                        .collect();
+                    batch_rows.push(values);
+                }
+            }
+            if batch_rows.is_empty() {
+                break;
+            }
+            if format == ExportFormat::Csv && rows_written == 0 {
+                write!(writer, "\u{FEFF}").map_err(|e| e.to_string())?; // UTF-8 BOM
+                writeln!(writer, "{}", csv_header(&columns)).map_err(|e| e.to_string())?;
+            }
+            for row in batch_rows {
+                write_row(&mut writer, format, &columns, &row, first).map_err(|e| e.to_string())?;
+                first = false;
+                rows_written += 1;
+                if rows_written % PROGRESS_ROWS == 0 {
+                    progress(rows_written);
+                }
+            }
+        }
+        if format == ExportFormat::Json {
+            writeln!(writer, "]").map_err(|e| e.to_string())?;
+        }
+        let _ = client.simple_query(&format!("CLOSE {CURSOR_NAME}")).await;
+        let _ = client.simple_query("ROLLBACK").await;
+        progress(rows_written);
+        Ok(ExportSummary { rows_written })
+    }
+    .await;
+
+    match run {
+        Ok(summary) => {
+            writer.flush().map_err(|e| e.to_string())?;
+            Ok(summary)
+        }
+        Err(e) => {
+            drop(writer);
+            let _ = std::fs::remove_file(path);
+            Err(e)
+        }
+    }
+}
+
+// ── MySQL (sqlx stream — native streaming) ─────────────────────────
+
+pub async fn run_mysql_export(
+    conn: &mut sqlx::mysql::MySqlConnection,
+    sql: &str,
+    format: ExportFormat,
+    path: &PathBuf,
+    progress: &mut (dyn FnMut(u64) + Send),
+) -> Result<ExportSummary, String> {
+    validate_export_inputs(sql, path)?;
+    let file = std::fs::File::create(path).map_err(|e| format!("cannot create file: {e}"))?;
+    use futures_util::TryStreamExt;
+    let mut writer = std::io::BufWriter::with_capacity(8 * 1024 * 1024, file);
+
+    let run = async {
+        let mut stream = sqlx::query(sql).fetch(&mut *conn);
+        let mut columns: Vec<ColumnInfo> = Vec::new();
+        let mut rows_written: u64 = 0;
+        let mut first = true;
+        if format == ExportFormat::Json {
+            write!(writer, "[").map_err(|e| e.to_string())?;
+        }
+        while let Some(row) = stream.try_next().await.map_err(|e| {
+            crate::commands::db_viewer::sanitize_error(&format!("{e}"))
+        })? {
+            if columns.is_empty() {
+                columns = row
+                    .columns()
+                    .iter()
+                    .map(|c| ColumnInfo {
+                        name: c.name().to_string(),
+                        data_type: c.type_info().to_string(),
+                        is_nullable: true,
+                        is_pk: false,
+                        is_fk: false,
+                        fk_ref: None,
+                        default_value: None,
+                        editable: true,
+                        is_generated: false,
+                    })
+                    .collect();
+                if format == ExportFormat::Csv {
+                    write!(writer, "\u{FEFF}").map_err(|e| e.to_string())?; // UTF-8 BOM
+                    writeln!(writer, "{}", csv_header(&columns)).map_err(|e| e.to_string())?;
+                }
+            }
+            let values: Vec<serde_json::Value> =
+                (0..row.len()).map(|i| crate::commands::query::mysql_cell_to_json(&row, i)).collect();
+            write_row(&mut writer, format, &columns, &values, first).map_err(|e| e.to_string())?;
+            first = false;
+            rows_written += 1;
+            if rows_written % PROGRESS_ROWS == 0 {
+                progress(rows_written);
+            }
+        }
+        if format == ExportFormat::Json {
+            writeln!(writer, "]").map_err(|e| e.to_string())?;
+        }
+        progress(rows_written);
+        Ok(ExportSummary { rows_written })
+    }
+    .await;
+
+    match run {
+        Ok(summary) => {
+            writer.flush().map_err(|e| e.to_string())?;
+            Ok(summary)
+        }
+        Err(e) => {
+            drop(writer);
+            let _ = std::fs::remove_file(path);
+            Err(e)
+        }
+    }
+}
+
+// ── Dispatcher + thin command ──────────────────────────────────────
+
+/// Dispatch across engines. The caller (command) owns the pool lock and the
+/// cancel registration; MySQL callers must hold a dedicated connection.
+pub(crate) async fn run_export_query(
+    handle: &mut DbHandle,
+    sql: &str,
+    format: ExportFormat,
+    path: &PathBuf,
+    progress: &mut (dyn FnMut(u64) + Send),
+) -> Result<ExportSummary, String> {
+    match handle {
+        DbHandle::Sqlite(conn) => run_sqlite_export(conn, sql, format, path, progress),
+        DbHandle::Postgresql(client, _) => run_pg_export(client, sql, format, path, progress).await,
+        DbHandle::MySql(pool) => {
+            let mut conn = pool
+                .acquire()
+                .await
+                .map_err(|e| crate::commands::db_viewer::sanitize_error(&format!("{e}")))?;
+            run_mysql_export(&mut *conn, sql, format, path, progress).await
+        }
+    }
+}
+
+#[tauri::command]
+pub async fn export_query_to_file(
+    connection_id: String,
+    sql: String,
+    format: String,
+    path: String,
+    state: State<'_, crate::AppState>,
+    app: tauri::AppHandle,
+) -> Result<serde_json::Value, String> {
+    use tauri::Emitter;
+
+    let fmt = ExportFormat::from_str(&format)?;
+    let path_buf = PathBuf::from(&path);
+    let job_id = uuid::Uuid::new_v4().to_string();
+
+    let mut last_emit = std::time::Instant::now();
+    let job = job_id.clone();
+    let mut progress_cb = |rows: u64| {
+        if last_emit.elapsed() >= std::time::Duration::from_millis(250) {
+            last_emit = std::time::Instant::now();
+            let _ = app.emit(
+                "export-progress",
+                ExportProgressEvent {
+                    job_id: job.clone(),
+                    status: "running".into(),
+                    rows,
+                    error: None,
+                },
+            );
+        }
+    };
+
+    let mut pm = state.pool_manager.lock().await;
+    let handle = pm
+        .get(&connection_id)
+        .ok_or_else(|| "Connection not found".to_string())?;
+
+    // MySQL: the STREAMING connection must be the one registered for
+    // KILL QUERY cancellation — acquire it once here, register its id,
+    // stream through it, then clear the registration.
+    let result = match handle {
+        DbHandle::MySql(pool) => {
+            let mut conn = pool
+                .acquire()
+                .await
+                .map_err(|e| crate::commands::db_viewer::sanitize_error(&format!("{e}")))?;
+            let conn_id: i64 = sqlx::query_scalar("SELECT CAST(CONNECTION_ID() AS SIGNED)")
+                .fetch_one(&mut *conn)
+                .await
+                .unwrap_or(-1);
+            state.cancel_registry.set_mysql_conn_id(&connection_id, Some(conn_id));
+            let r = run_mysql_export(&mut *conn, &sql, fmt, &path_buf, &mut progress_cb).await;
+            state.cancel_registry.set_mysql_conn_id(&connection_id, None);
+            r
+        }
+        other => run_export_query(other, &sql, fmt, &path_buf, &mut progress_cb).await,
+    };
+
+    match result {
+        Ok(summary) => {
+            let _ = app.emit(
+                "export-progress",
+                ExportProgressEvent {
+                    job_id: job_id.clone(),
+                    status: "done".into(),
+                    rows: summary.rows_written,
+                    error: None,
+                },
+            );
+            Ok(serde_json::json!({ "rows_written": summary.rows_written, "path": path }))
+        }
+        Err(e) => {
+            let _ = app.emit(
+                "export-progress",
+                ExportProgressEvent {
+                    job_id: job_id.clone(),
+                    status: "error".into(),
+                    rows: 0,
+                    error: Some(e.clone()),
+                },
+            );
+            Err(e)
+        }
+    }
+}
+
+#[cfg(test)]
+#[path = "query_export.test.rs"]
+mod query_export_tests;

desktop/src-tauri/src/commands/query_export.test.rs

@@ -0,0 +1,235 @@
+use super::*;
+use sqlx::Connection;
+
+#[test]
+fn read_only_heuristic_matches_frontend_guard_set() {
+    for sql in ["SELECT 1", "  with x as (select 1) select * from x", "-- note\nSELECT 1"] {
+        assert!(is_read_only_sql(sql), "should allow: {sql}");
+    }
+    for sql in [
+        "INSERT INTO t VALUES (1)",
+        "update t set a = 1",
+        "DELETE FROM t",
+        "DROP TABLE t",
+        "ALTER TABLE t ADD c int",
+        "TRUNCATE t",
+        "CREATE TABLE t (a int)",
+        "REPLACE INTO t VALUES (1)",
+    ] {
+        assert!(!is_read_only_sql(sql), "should reject: {sql}");
+    }
+}
+
+#[test]
+fn csv_cell_quotes_and_guards_formula_injection() {
+    assert_eq!(csv_cell(&serde_json::Value::String("plain".into())), "plain");
+    assert_eq!(csv_cell(&serde_json::Value::String("a,b".into())), "\"a,b\"");
+    assert_eq!(csv_cell(&serde_json::Value::String("a\"b".into())), "\"a\"\"b\"");
+    assert_eq!(csv_cell(&serde_json::Value::String("a\nb".into())), "\"a\nb\"");
+    assert_eq!(csv_cell(&serde_json::Value::String("=SUM(A1)".into())), "'=SUM(A1)");
+    assert_eq!(csv_cell(&serde_json::Value::String("+x".into())), "'+x");
+    assert_eq!(csv_cell(&serde_json::Value::String("-1".into())), "'-1");
+    assert_eq!(csv_cell(&serde_json::Value::String("@cmd".into())), "'@cmd");
+    assert_eq!(csv_cell(&serde_json::Value::Null), "");
+    assert_eq!(csv_cell(&serde_json::json!(42)), "42");
+}
+
+#[test]
+fn csv_line_bom_is_written_by_header_only() {
+    let cols = vec![
+        crate::models::db_viewer::ColumnInfo { name: "a".into(), data_type: "int".into(), is_nullable: true, is_pk: false, is_fk: false, fk_ref: None, default_value: None, editable: true, is_generated: false },
+        crate::models::db_viewer::ColumnInfo { name: "b".into(), data_type: "text".into(), is_nullable: true, is_pk: false, is_fk: false, fk_ref: None, default_value: None, editable: true, is_generated: false },
+    ];
+    let line = csv_line(&cols, &[serde_json::json!("1"), serde_json::Value::Null]);
+    assert_eq!(line, "1,");
+}
+
+#[test]
+fn jsonl_line_encodes_row_object() {
+    let cols = vec![crate::models::db_viewer::ColumnInfo { name: "a".into(), data_type: "int".into(), is_nullable: true, is_pk: false, is_fk: false, fk_ref: None, default_value: None, editable: true, is_generated: false }];
+    let line = jsonl_line(&cols, &[serde_json::json!("x\"y")]);
+    assert_eq!(line, "{\"a\":\"x\\\"y\"}");
+}
+
+#[test]
+fn sqlite_export_streams_all_rows_with_bom_and_guard() {
+    let conn = rusqlite::Connection::open_in_memory().unwrap();
+    conn.execute_batch(
+        "CREATE TABLE t (a INTEGER, b TEXT);
+         INSERT INTO t VALUES (1, 'plain');
+         INSERT INTO t VALUES (2, '=SUM(A1)');
+         INSERT INTO t VALUES (3, NULL);",
+    )
+    .unwrap();
+
+    let path = std::env::temp_dir().join(format!("gridline-export-test-{}.csv", std::process::id()));
+    let mut rows_seen = 0u64;
+    let summary = run_sqlite_export(&conn, "SELECT a, b FROM t ORDER BY a", ExportFormat::Csv, &path, &mut |n| rows_seen = n)
+        .expect("export runs");
+    assert_eq!(summary.rows_written, 3);
+    assert_eq!(rows_seen, 3);
+
+    let bytes = std::fs::read(&path).unwrap();
+    assert!(bytes.starts_with(&[0xEF, 0xBB, 0xBF]), "UTF-8 BOM first");
+    let text = String::from_utf8_lossy(&bytes[3..]);
+    let lines: Vec<&str> = text.lines().collect();
+    assert_eq!(lines[0], "a,b");
+    assert_eq!(lines[1], "1,plain");
+    assert_eq!(lines[2], "2,'=SUM(A1)");
+    assert_eq!(lines[3], "3,");
+    let _ = std::fs::remove_file(&path);
+}
+
+#[test]
+fn sqlite_export_rejects_write_statements_and_multi_statement() {
+    let conn = rusqlite::Connection::open_in_memory().unwrap();
+    let path = std::env::temp_dir().join("gridline-export-should-not-exist.csv");
+    let err = run_sqlite_export(&conn, "INSERT INTO t VALUES (1)", ExportFormat::Csv, &path, &mut |_| {})
+        .expect_err("write SQL must be rejected");
+    assert!(err.contains("read-only"), "got: {err}");
+    let err = run_sqlite_export(&conn, "SELECT 1; SELECT 2", ExportFormat::Csv, &path, &mut |_| {})
+        .expect_err("multi-statement must be rejected");
+    assert!(err.contains("single"), "got: {err}");
+    assert!(!path.exists(), "no partial file may be left behind");
+}
+
+#[test]
+fn sqlite_export_error_deletes_partial_file() {
+    let conn = rusqlite::Connection::open_in_memory().unwrap();
+    conn.execute_batch("CREATE TABLE t (a INTEGER); INSERT INTO t VALUES (1),(2),(3);").unwrap();
+    let path = std::env::temp_dir().join(format!("gridline-export-partial-{}.csv", std::process::id()));
+    let err = run_sqlite_export(&conn, "SELECT a, b FROM t", ExportFormat::Csv, &path, &mut |_| {})
+        .expect_err("bad column must fail");
+    assert!(!err.is_empty());
+    assert!(!path.exists(), "partial file must be deleted on error");
+}
+
+/// Live PG export — mirror the env/client conventions of the live PG tests in
+/// `commands/objects.test.rs`. Assert a cursor export of a 3-row table
+/// produces the same 4 CSV lines as the SQLite test (BOM + header + rows).
+#[tokio::test]
+#[ignore]
+async fn pg_export_live() {
+    let h = match std::env::var("GRIDLINE_TEST_PG_HOST") {
+        Ok(v) => v,
+        Err(_) => return,
+    };
+    let p: u16 = std::env::var("GRIDLINE_TEST_PG_PORT")
+        .unwrap_or_else(|_| "5432".into())
+        .parse()
+        .unwrap();
+    let u = std::env::var("GRIDLINE_TEST_PG_USER").expect("set GRIDLINE_TEST_PG_USER");
+    let d = std::env::var("GRIDLINE_TEST_PG_DB").expect("set GRIDLINE_TEST_PG_DB");
+    let pw = std::env::var("GRIDLINE_TEST_PG_PASSWORD").unwrap_or_default();
+    let (client, conn) = tokio_postgres::connect(
+        &format!("host={h} port={p} user={u} dbname={d} password={pw}"),
+        tokio_postgres::NoTls,
+    )
+    .await
+    .expect("connect to test PG");
+    let _conn_task = tokio::spawn(async move {
+        let _ = conn.await;
+    });
+    client
+        .batch_execute(
+            "DROP TABLE IF EXISTS gridline_export_test;
+             CREATE TABLE gridline_export_test (a INTEGER, b TEXT);
+             INSERT INTO gridline_export_test VALUES (1,'plain'),(2,'=SUM(A1)'),(3,NULL);",
+        )
+        .await
+        .expect("setup");
+
+    let path = std::env::temp_dir().join(format!("gridline-export-pg-{}.csv", std::process::id()));
+    let mut rows_seen = 0u64;
+    let summary = run_pg_export(
+        &client,
+        "SELECT a, b FROM gridline_export_test ORDER BY a",
+        ExportFormat::Csv,
+        &path,
+        &mut |n| rows_seen = n,
+    )
+    .await
+    .expect("export runs");
+    assert_eq!(summary.rows_written, 3);
+    assert_eq!(rows_seen, 3);
+
+    let bytes = std::fs::read(&path).unwrap();
+    assert!(bytes.starts_with(&[0xEF, 0xBB, 0xBF]), "UTF-8 BOM first");
+    let text = String::from_utf8_lossy(&bytes[3..]);
+    let lines: Vec<&str> = text.lines().collect();
+    assert_eq!(lines[0], "a,b");
+    assert_eq!(lines[1], "1,plain");
+    assert_eq!(lines[2], "2,'=SUM(A1)");
+    assert_eq!(lines[3], "3,");
+    let _ = std::fs::remove_file(&path);
+    let _ = client.batch_execute("DROP TABLE IF EXISTS gridline_export_test").await;
+}
+
+/// Live MySQL export — mirror the env conventions of the MySQL live tests in
+/// `commands/db_viewer.rs` (GRIDLINE_TEST_MYSQL_*). Same assertions.
+#[tokio::test]
+#[ignore]
+async fn mysql_export_live() {
+    let host = match std::env::var("GRIDLINE_TEST_MYSQL_HOST") {
+        Ok(v) => v,
+        Err(_) => return,
+    };
+    let port: u16 = std::env::var("GRIDLINE_TEST_MYSQL_PORT")
+        .ok()
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(3306);
+    let user = std::env::var("GRIDLINE_TEST_MYSQL_USER").unwrap_or_else(|_| "root".into());
+    let pass = std::env::var("GRIDLINE_TEST_MYSQL_PASS").unwrap_or_default();
+    let db = match std::env::var("GRIDLINE_TEST_MYSQL_DB") {
+        Ok(v) => v,
+        Err(_) => return,
+    };
+    let opts = sqlx::mysql::MySqlConnectOptions::new()
+        .host(&host)
+        .port(port)
+        .username(&user)
+        .password(&pass)
+        .database(&db);
+    let mut conn = sqlx::mysql::MySqlConnection::connect_with(&opts)
+        .await
+        .expect("connect to test MySQL");
+    sqlx::query("DROP TABLE IF EXISTS gridline_export_test")
+        .execute(&mut conn)
+        .await
+        .ok();
+    sqlx::query("CREATE TABLE gridline_export_test (a INT, b TEXT)")
+        .execute(&mut conn)
+        .await
+        .expect("create");
+    sqlx::query("INSERT INTO gridline_export_test VALUES (1,'plain'),(2,'=SUM(A1)'),(3,NULL)")
+        .execute(&mut conn)
+        .await
+        .expect("insert");
+
+    let path = std::env::temp_dir().join(format!("gridline-export-mysql-{}.csv", std::process::id()));
+    let mut rows_seen = 0u64;
+    let summary = run_mysql_export(
+        &mut conn,
+        "SELECT a, b FROM gridline_export_test ORDER BY a",
+        ExportFormat::Csv,
+        &path,
+        &mut |n| rows_seen = n,
+    )
+    .await
+    .expect("export runs");
+    assert_eq!(summary.rows_written, 3);
+    assert_eq!(rows_seen, 3);
+
+    let bytes = std::fs::read(&path).unwrap();
+    assert!(bytes.starts_with(&[0xEF, 0xBB, 0xBF]), "UTF-8 BOM first");
+    let text = String::from_utf8_lossy(&bytes[3..]);
+    let lines: Vec<&str> = text.lines().collect();
+    assert_eq!(lines[0], "a,b");
+    assert_eq!(lines[1], "1,plain");
+    assert_eq!(lines[2], "2,'=SUM(A1)");
+    assert_eq!(lines[3], "3,");
+    let _ = std::fs::remove_file(&path);
+    let _ = sqlx::query("DROP TABLE IF EXISTS gridline_export_test")
+        .execute(&mut conn)
+        .await;
+}

desktop/src-tauri/src/lib.rs

@@ -24,7 +24,7 @@ pub struct AppState {
 
 use commands::{
     backup, connections, db_viewer, demo, folders, import_export, keychain, maintenance, objects, query,
-    schema_graph, settings, tags,
+    query_export, schema_graph, settings, tags,
 };
 
 // Learn more about Tauri commands at https://tauri.app/develop/calling-rust/
@@ -175,6 +175,7 @@ pub fn run() {
             schema_graph::get_schema_graph,
             query::execute_query,
             query::execute_query_multi,
+            query_export::export_query_to_file,
             query::cancel_query,
             query::get_query_history,
             query::clear_query_history,