fix(read-only): allow REPLACE()/INSERT() scalar functions in queries

crates/dbx-sql/src/query_execution_sql.rs

@@ -255,11 +255,65 @@ fn is_safe_oracle_explain_dml_source(sql: &str) -> bool {
     ["INSERT", "UPDATE", "DELETE", "MERGE"].iter().any(|keyword| starts_with_keyword(&source, keyword))
 }
 
+/// Write verbs that mark a read-leading statement as a write, for example a
+/// data-modifying CTE (`WITH x AS (DELETE FROM t RETURNING *) SELECT * FROM x`).
+const DANGEROUS_SQL_KEYWORDS: &[&str] =
+    &["drop", "delete", "truncate", "alter", "update", "merge", "replace", "insert", "create"];
+
+/// Write verbs that are also scalar function names, so `REPLACE(col, 'a', 'b')`
+/// and `INSERT(str, pos, len, new)` are ordinary parts of a read-only query.
+///
+/// Only these two verbs are exempted when they are called with parentheses.
+/// `update` stays dangerous even then: MySQL accepts a parenthesized table
+/// reference (`UPDATE (t) SET c = 1`, verified on MySQL 8.4), while
+/// `REPLACE (`/`INSERT (` are rejected there as statements, so a parenthesized
+/// call can never hide a write for the exempted verbs.
+const WRITE_VERBS_WITH_SCALAR_FUNCTION_FORMS: &[&str] = &["replace", "insert"];
+
 pub fn contains_dangerous_sql_keyword(sql: &str) -> bool {
     let source = strip_sql_comments_and_literals(sql).to_lowercase();
-    ["drop", "delete", "truncate", "alter", "update", "merge", "replace", "insert", "create"]
-        .iter()
-        .any(|keyword| contains_word(&source, keyword))
+    DANGEROUS_SQL_KEYWORDS.iter().any(|keyword| contains_dangerous_sql_verb(&source, keyword))
+}
+
+/// Match a write verb as a whole word. A verb called with parentheses is a
+/// scalar function for [`WRITE_VERBS_WITH_SCALAR_FUNCTION_FORMS`] (`SELECT
+/// REPLACE(name, 'a', 'b') FROM users` must stay read-only), including when the
+/// dialect allows whitespace before the parenthesis.
+fn contains_dangerous_sql_verb(source: &str, keyword: &str) -> bool {
+    let bytes = source.as_bytes();
+    let keyword_bytes = keyword.as_bytes();
+    if keyword_bytes.is_empty() || bytes.len() < keyword_bytes.len() {
+        return false;
+    }
+    let allows_function_form = WRITE_VERBS_WITH_SCALAR_FUNCTION_FORMS.contains(&keyword);
+
+    for idx in 0..=bytes.len() - keyword_bytes.len() {
+        if &bytes[idx..idx + keyword_bytes.len()] != keyword_bytes {
+            continue;
+        }
+        if is_identifier_byte(idx.checked_sub(1).and_then(|i| bytes.get(i)).copied()) {
+            continue;
+        }
+        let rest = &bytes[idx + keyword_bytes.len()..];
+        match rest.first().copied() {
+            None => return true,
+            Some(b'(') if allows_function_form => continue,
+            Some(byte) if is_identifier_byte(Some(byte)) => continue,
+            Some(byte) => {
+                if allows_function_form && byte.is_ascii_whitespace() && starts_with_parenthesis(rest) {
+                    continue;
+                }
+                return true;
+            }
+        }
+    }
+    false
+}
+
+/// True when the first non-whitespace byte is `(` (SQL Server style `REPLACE (a, b, c)`).
+fn starts_with_parenthesis(rest: &[u8]) -> bool {
+    let offset = rest.iter().take_while(|byte| byte.is_ascii_whitespace()).count();
+    rest.get(offset) == Some(&b'(')
 }
 
 /// Keywords that start a read-only SQL statement.
@@ -1744,6 +1798,55 @@ mod tests {
         assert!(!contains_dangerous_sql_keyword("SELECT inserted FROM t"));
     }
 
+    #[test]
+    fn contains_dangerous_sql_keyword_ignores_scalar_functions_named_like_writes() {
+        // #9978: REPLACE()/INSERT() are scalar functions, not statements.
+        assert!(!contains_dangerous_sql_keyword("SELECT REPLACE(name, 'a', 'b') FROM users"));
+        assert!(!contains_dangerous_sql_keyword("SELECT REPLACE (name, 'a', 'b') FROM users"));
+        assert!(!contains_dangerous_sql_keyword("SELECT INSERT('Quadratic', 3, 4, 'What')"));
+        assert!(!contains_dangerous_sql_keyword("SELECT dropped, inserted FROM t"));
+        assert!(contains_dangerous_sql_keyword("REPLACE INTO users VALUES (1)"));
+        assert!(contains_dangerous_sql_keyword("REPLACE users SET name = 'x'"));
+        assert!(contains_dangerous_sql_keyword("INSERT INTO users VALUES (1)"));
+        // `UPDATE (t)` is a real write: MySQL accepts a parenthesized table reference.
+        assert!(contains_dangerous_sql_keyword("UPDATE (users) SET name = 'x'"));
+    }
+
+    #[test]
+    fn is_write_sql_allows_mysql_json_table_query_with_replace_function() {
+        // #9978: a JSON_TABLE query using REPLACE() must not be treated as a write,
+        // otherwise read-only connections ask for write permission before running it.
+        let sql = "with tmp as (\n  select '张三,李四,王五' as `names`\n)\nSELECT jt.name\nFROM tmp t\nJOIN JSON_TABLE(\n    CONCAT('[\"',REPLACE(t.`names`,',','\",\"'),'\"]'),\n    '$[*]' COLUMNS(name VARCHAR(50) PATH '$')\n) jt";
+        assert!(!is_write_sql_for_database(sql, DatabaseType::Mysql), "JSON_TABLE + REPLACE() must stay read-only");
+        assert!(!is_write_sql_for_database("SELECT REPLACE(name, 'a', 'b') FROM users", DatabaseType::Mysql));
+        assert!(!is_write_sql_for_database("SELECT INSERT('Quadratic', 3, 4, 'What')", DatabaseType::Mysql));
+        assert!(!is_write_sql_for_database("SELECT REPLACE (name, 'a', 'b') FROM users", DatabaseType::SqlServer));
+        assert!(!is_write_sql_for_database("SELECT replace(name, 'a', 'b') FROM users", DatabaseType::Postgres));
+        assert!(!is_write_sql(sql));
+    }
+
+    #[test]
+    fn is_write_sql_still_blocks_writes_using_function_like_verbs() {
+        assert!(is_write_sql_for_database("REPLACE INTO users VALUES (1)", DatabaseType::Mysql));
+        assert!(is_write_sql_for_database("REPLACE users SET name = 'x'", DatabaseType::Mysql));
+        assert!(is_write_sql_for_database("INSERT INTO users VALUES (1)", DatabaseType::Mysql));
+        // MySQL accepts a parenthesized table reference, so `UPDATE (` is a write.
+        assert!(is_write_sql_for_database("UPDATE (users) SET name = 'x'", DatabaseType::Mysql));
+        assert!(is_write_sql_for_database(
+            "WITH x AS (SELECT 1 AS n) UPDATE (users) SET name = 'x'",
+            DatabaseType::Mysql
+        ));
+        // Data-modifying CTEs keep being detected.
+        assert!(is_write_sql_for_database(
+            "WITH x AS (INSERT INTO users VALUES (1) RETURNING *) SELECT * FROM x",
+            DatabaseType::Postgres
+        ));
+        assert!(is_write_sql_for_database(
+            "WITH x AS (DELETE FROM users RETURNING *) SELECT * FROM x",
+            DatabaseType::Postgres
+        ));
+    }
+
     #[test]
     fn contains_dangerous_sql_keyword_ignores_in_string_literals() {
         assert!(!contains_dangerous_sql_keyword("SELECT 'DROP TABLE users' FROM t"));