datapress-core 0.4.1

//! Shared safety gate for the raw-SQL endpoint (`POST /api/v1/sql`).
//!
//! Raw SQL is a much larger attack surface than the structured `/query`
//! endpoint, so every statement is parsed and validated *before* it is
//! handed to a backend engine. The same gate runs for DuckDB and
//! DataFusion, giving both backends identical safety semantics — and
//! keeping the "which tables may this query touch?" policy in one place.
//!
//! Guarantees enforced by [`validate`]:
//! - exactly one statement, and it is a read-only `SELECT` / `WITH … SELECT`,
//! - every referenced table is a registered dataset — no file-reading
//!   table functions (`read_parquet`, `read_csv`, …), no unknown tables,
//! - no file-reading scalar functions (`read_text`, `read_blob`, …),
//! - at most `max_datasets` distinct datasets are referenced. Phase 1
//!   passes `1`, enforcing the single-dataset rule; raising this bound is
//!   all that's needed to allow cross-dataset joins later.
//!
//! CTE-defined names are tracked per query scope and excluded from the
//! dataset allowlist check, so `WITH t AS (SELECT … FROM events) SELECT …`
//! is accepted (it still only touches `events`).

use std::collections::{HashMap, HashSet};
use std::ops::ControlFlow;

use sqlparser::ast::{
    Expr, Ident, ObjectName, ObjectNamePart, Query, Statement, Visit, VisitMut, Visitor,
    VisitorMut,
};
use sqlparser::dialect::GenericDialect;
use sqlparser::parser::Parser;

use crate::errors::AppError;

/// File-reading / external-access functions that must never run through
/// the SQL endpoint, in either table or scalar position. Table-position
/// functions are already blocked by the relation allowlist; this list
/// closes the scalar-position gap (e.g. `SELECT read_text('/etc/passwd')`).
const DENIED_FUNCTIONS: &[&str] = &[
    "read_text",
    "read_blob",
    "read_csv",
    "read_csv_auto",
    "read_parquet",
    "parquet_scan",
    "read_json",
    "read_json_auto",
    "read_json_objects",
    "read_ndjson",
    "read_ndjson_auto",
    "read_ndjson_objects",
    "sniff_csv",
    "glob",
];

/// A validated, ready-to-execute SQL query.
#[derive(Debug)]
pub struct ValidatedSql {
    /// The trimmed, semicolon-free SQL string, safe to wrap and execute.
    pub sql: String,
    /// The distinct dataset names the query references (lowercased). Empty
    /// for table-less queries such as `SELECT 1`.
    pub datasets: Vec<String>,
}

/// Validate `sql` for the raw-SQL endpoint.
///
/// `allowed` is the set of registered dataset names, **lowercased** by the
/// caller (matching is case-insensitive). `max_datasets` caps how many
/// distinct datasets a single statement may touch (phase 1 = `1`).
///
/// On success returns the cleaned SQL ready to be wrapped in an outer
/// `LIMIT` and executed by the backend.
pub fn validate(
    sql: &str,
    allowed: &HashSet<String>,
    max_datasets: usize,
) -> Result<ValidatedSql, AppError> {
    let trimmed = sql.trim().trim_end_matches(';').trim();
    if trimmed.is_empty() {
        return Err(AppError::InvalidValue("sql must not be empty".into()));
    }

    let statements = Parser::parse_sql(&GenericDialect {}, trimmed)
        .map_err(|e| AppError::InvalidValue(format!("could not parse SQL: {e}")))?;
    if statements.len() != 1 {
        return Err(AppError::InvalidValue(
            "exactly one SQL statement is allowed".into(),
        ));
    }
    let stmt = &statements[0];
    if !matches!(stmt, Statement::Query(_)) {
        return Err(AppError::InvalidValue(
            "only read-only SELECT queries are allowed".into(),
        ));
    }

    let mut checker = ScopeCheck {
        allowed,
        cte_names: HashSet::new(),
        referenced: HashSet::new(),
        violation: None,
    };
    let _ = stmt.visit(&mut checker);
    if let Some(err) = checker.violation {
        return Err(AppError::InvalidValue(err));
    }

    let mut datasets: Vec<String> = checker.referenced.into_iter().collect();
    datasets.sort();
    if datasets.len() > max_datasets {
        return Err(AppError::InvalidValue(format!(
            "this endpoint allows at most {max_datasets} dataset(s) per query; \
             the statement references {}",
            datasets.len()
        )));
    }

    Ok(ValidatedSql {
        sql: trimmed.to_string(),
        datasets,
    })
}

/// Rewrite references to registered tables and their columns so they
/// match **case-insensitively**, the way DuckDB does.
///
/// DataFusion lowercases unquoted identifiers by default, so a query like
/// `SELECT State FROM accidents` is looked up as `state` and fails against
/// a case-sensitive Parquet column literally named `State`. Rather than
/// disable normalization globally (which would also make *aliases* and
/// *CTE names* case-sensitive), we rewrite only the identifiers that name
/// a known dataset or column into their **canonical casing, quoted**.
/// Quoted identifiers bypass the engine's lowercasing and match the stored
/// name exactly, while every other identifier (aliases, CTE names, …) is
/// left untouched so the engine's normal case-insensitive handling still
/// applies.
///
/// `tables` and `columns` map a **lowercased** name to its canonical
/// spelling. On any parse failure the input is returned unchanged so the
/// backend can surface a meaningful error.
pub fn canonicalize_identifiers(
    sql: &str,
    tables: &HashMap<String, String>,
    columns: &HashMap<String, String>,
) -> String {
    let mut statements = match Parser::parse_sql(&GenericDialect {}, sql) {
        Ok(s) if s.len() == 1 => s,
        _ => return sql.to_string(),
    };
    let mut canon = Canonicalizer { tables, columns };
    let _ = VisitMut::visit(&mut statements[0], &mut canon);
    statements[0].to_string()
}

struct Canonicalizer<'a> {
    tables: &'a HashMap<String, String>,
    columns: &'a HashMap<String, String>,
}

impl Canonicalizer<'_> {
    /// If `ident` (case-folded) names something in `map`, replace it with
    /// the canonical spelling and force double-quoting so the engine keeps
    /// the exact case.
    fn rewrite(ident: &mut Ident, map: &HashMap<String, String>) {
        if let Some(canonical) = map.get(&ident.value.to_lowercase()) {
            ident.value = canonical.clone();
            ident.quote_style = Some('"');
        }
    }
}

impl VisitorMut for Canonicalizer<'_> {
    type Break = ();

    fn pre_visit_relation(&mut self, relation: &mut ObjectName) -> ControlFlow<Self::Break> {
        for part in relation.0.iter_mut() {
            if let ObjectNamePart::Identifier(ident) = part {
                Self::rewrite(ident, self.tables);
            }
        }
        ControlFlow::Continue(())
    }

    fn pre_visit_expr(&mut self, expr: &mut Expr) -> ControlFlow<Self::Break> {
        match expr {
            // Bare column reference: `State`.
            Expr::Identifier(ident) => Self::rewrite(ident, self.columns),
            // Qualified reference: `accidents.State` / `a.State`. The last
            // part is the column; earlier parts qualify it with a table or
            // alias (only real table names are rewritten).
            Expr::CompoundIdentifier(idents) => {
                if let Some((column, qualifiers)) = idents.split_last_mut() {
                    Self::rewrite(column, self.columns);
                    for qualifier in qualifiers {
                        Self::rewrite(qualifier, self.tables);
                    }
                }
            }
            _ => {}
        }
        ControlFlow::Continue(())
    }
}

struct ScopeCheck<'a> {
    allowed: &'a HashSet<String>,
    cte_names: HashSet<String>,
    referenced: HashSet<String>,
    violation: Option<String>,
}

impl Visitor for ScopeCheck<'_> {
    type Break = ();

    fn pre_visit_query(&mut self, query: &Query) -> ControlFlow<Self::Break> {
        // Record CTE names *before* visiting the query body so references
        // to them inside the body are recognised and not mistaken for
        // unknown tables. Nested `WITH` clauses are handled the same way
        // as the visitor descends into subqueries.
        if let Some(with) = &query.with {
            for cte in &with.cte_tables {
                self.cte_names.insert(cte.alias.name.value.to_lowercase());
            }
        }
        ControlFlow::Continue(())
    }

    fn pre_visit_relation(&mut self, relation: &ObjectName) -> ControlFlow<Self::Break> {
        let ident = relation
            .0
            .last()
            .and_then(|p| p.as_ident())
            .map(|i| i.value.to_lowercase())
            .unwrap_or_default();

        if self.cte_names.contains(&ident) {
            return ControlFlow::Continue(());
        }
        if let Some(name) = self.allowed.get(&ident) {
            self.referenced.insert(name.clone());
            return ControlFlow::Continue(());
        }
        self.violation = Some(format!(
            "table '{ident}' is not a registered dataset accessible from the SQL endpoint"
        ));
        ControlFlow::Break(())
    }

    fn pre_visit_expr(&mut self, expr: &Expr) -> ControlFlow<Self::Break> {
        if let Expr::Function(func) = expr {
            let fname = func
                .name
                .0
                .last()
                .and_then(|p| p.as_ident())
                .map(|i| i.value.to_lowercase())
                .unwrap_or_default();
            if DENIED_FUNCTIONS.contains(&fname.as_str()) {
                self.violation =
                    Some(format!("function '{fname}' is not allowed in the SQL endpoint"));
                return ControlFlow::Break(());
            }
        }
        ControlFlow::Continue(())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn allowed(names: &[&str]) -> HashSet<String> {
        names.iter().map(|s| s.to_lowercase()).collect()
    }

    #[test]
    fn accepts_single_dataset_select() {
        let v = validate("SELECT a, b FROM events WHERE a > 1", &allowed(&["events"]), 1).unwrap();
        assert_eq!(v.datasets, vec!["events".to_string()]);
    }

    #[test]
    fn case_insensitive_table_match() {
        let v = validate("SELECT * FROM Events", &allowed(&["events"]), 1).unwrap();
        assert_eq!(v.datasets, vec!["events".to_string()]);
    }

    #[test]
    fn strips_trailing_semicolon() {
        let v = validate("SELECT 1 FROM events;", &allowed(&["events"]), 1).unwrap();
        assert_eq!(v.sql, "SELECT 1 FROM events");
    }

    #[test]
    fn allows_cte_over_single_dataset() {
        let sql = "WITH t AS (SELECT * FROM events) SELECT count(*) FROM t";
        let v = validate(sql, &allowed(&["events"]), 1).unwrap();
        assert_eq!(v.datasets, vec!["events".to_string()]);
    }

    #[test]
    fn allows_tableless_select() {
        let v = validate("SELECT 1 + 1", &allowed(&["events"]), 1).unwrap();
        assert!(v.datasets.is_empty());
    }

    #[test]
    fn rejects_unknown_table() {
        let err = validate("SELECT * FROM secrets", &allowed(&["events"]), 1).unwrap_err();
        assert!(matches!(err, AppError::InvalidValue(_)));
    }

    #[test]
    fn rejects_second_dataset_join() {
        let err = validate(
            "SELECT * FROM events e JOIN other o ON e.id = o.id",
            &allowed(&["events", "other"]),
            1,
        )
        .unwrap_err();
        assert!(matches!(err, AppError::InvalidValue(_)));
    }

    #[test]
    fn allows_two_datasets_when_limit_raised() {
        let v = validate(
            "SELECT * FROM events e JOIN other o ON e.id = o.id",
            &allowed(&["events", "other"]),
            2,
        )
        .unwrap();
        assert_eq!(v.datasets.len(), 2);
    }

    #[test]
    fn rejects_non_select() {
        let err = validate("DELETE FROM events", &allowed(&["events"]), 1).unwrap_err();
        assert!(matches!(err, AppError::InvalidValue(_)));
    }

    #[test]
    fn rejects_multiple_statements() {
        let err = validate("SELECT 1 FROM events; SELECT 2 FROM events", &allowed(&["events"]), 1)
            .unwrap_err();
        assert!(matches!(err, AppError::InvalidValue(_)));
    }

    #[test]
    fn rejects_file_table_function() {
        let err = validate("SELECT * FROM read_parquet('/etc/passwd')", &allowed(&["events"]), 1)
            .unwrap_err();
        assert!(matches!(err, AppError::InvalidValue(_)));
    }

    #[test]
    fn rejects_file_scalar_function() {
        let err = validate(
            "SELECT read_text('/etc/passwd') FROM events",
            &allowed(&["events"]),
            1,
        )
        .unwrap_err();
        assert!(matches!(err, AppError::InvalidValue(_)));
    }

    #[test]
    fn rejects_empty_sql() {
        let err = validate("   ", &allowed(&["events"]), 1).unwrap_err();
        assert!(matches!(err, AppError::InvalidValue(_)));
    }

    fn maps(
        tables: &[(&str, &str)],
        columns: &[(&str, &str)],
    ) -> (HashMap<String, String>, HashMap<String, String>) {
        let t = tables
            .iter()
            .map(|(k, v)| (k.to_string(), v.to_string()))
            .collect();
        let c = columns
            .iter()
            .map(|(k, v)| (k.to_string(), v.to_string()))
            .collect();
        (t, c)
    }

    #[test]
    fn canonicalizes_mixed_case_column_and_table() {
        let (t, c) = maps(
            &[("accidents", "accidents")],
            &[("state", "State"), ("id", "ID")],
        );
        let out = canonicalize_identifiers(
            "SELECT state, COUNT(*) AS n FROM Accidents GROUP BY STATE ORDER BY n DESC",
            &t,
            &c,
        );
        // Column refs become quoted canonical names; the table name is
        // quoted canonical; the alias `n` is left untouched.
        assert!(out.contains("\"State\""), "got: {out}");
        assert!(out.contains("FROM \"accidents\""), "got: {out}");
        assert!(out.contains("AS n"), "got: {out}");
        assert!(!out.contains("\"n\""), "alias must not be quoted: {out}");
    }

    #[test]
    fn canonicalizes_qualified_column() {
        let (t, c) = maps(&[("accidents", "accidents")], &[("state", "State")]);
        let out = canonicalize_identifiers("SELECT a.state FROM accidents AS a", &t, &c);
        // The column part is canonicalized; the table alias `a` is not a
        // registered table, so it is left alone.
        assert!(out.contains("a.\"State\""), "got: {out}");
    }

    #[test]
    fn leaves_unknown_identifiers_untouched() {
        let (t, c) = maps(&[("events", "events")], &[("id", "id")]);
        let out = canonicalize_identifiers("SELECT foo, bar FROM events", &t, &c);
        assert!(out.contains("foo"), "got: {out}");
        assert!(out.contains("bar"), "got: {out}");
        assert!(!out.contains("\"foo\""), "got: {out}");
    }

    #[test]
    fn returns_input_unchanged_on_parse_error() {
        let (t, c) = maps(&[], &[]);
        let garbage = "SELECT FROM WHERE";
        assert_eq!(canonicalize_identifiers(garbage, &t, &c), garbage);
    }
}