[client-v2, jdbc-v2] SQLUtils.enquoteLiteral / enquoteIdentifier do not escape backslashes, corrupting or breaking SQL

Start with client-v2/src/main/java/com/clickhouse/client/api/sql/SQLUtils.java and compare enquoteLiteral and enquoteIdentifier with escapeSingleQuotes. Run client-v2/src/test/java/com/clickhouse/client/api/sql/SQLUtilsTest.java and jdbc-v2/.../EnquoteBackslashTest.java using the provided Maven command; done means literals and identifiers preserve embedded and trailing backslashes, and metadata patterns no longer fail.

Description

com.clickhouse.client.api.sql.SQLUtils.enquoteLiteral(String) escapes only the single quote, by doubling it:

// client-v2/src/main/java/com/clickhouse/client/api/sql/SQLUtils.java:14-19
public static String enquoteLiteral(String str) {
    if (str == null) { throw new IllegalArgumentException("Input string cannot be null"); }
    return "'" + str.replace("'", "''") + "'";
}

ClickHouse treats the backslash as an escape character inside single-quoted strings, so a value containing a backslash is either silently corrupted (\t becomes a TAB) or breaks the statement (a value ending in \ escapes the closing quote → Code: 62 ... Single quoted string is not closed (SYNTAX_ERROR)).

The same defect exists in enquoteIdentifier (SQLUtils.java:30-38), which only doubles " — ClickHouse also honours backslash escapes inside double-quoted identifiers.

Note the inconsistency inside the very same class: SQLUtils.escapeSingleQuotes (line 136) does get it right —

public static String escapeSingleQuotes(String x) {
    return x.replace("\\", "\\\\").replace("'", "\\'");
}

so PreparedStatementImpl.encodeObject (which uses escapeSingleQuotes) is safe, while enquoteLiteral is not. There are two escaping paths and only one of them is correct.

Affected surfaces

1. java.sql.Statement.enquoteLiteral(String) — jdbc-v2/.../StatementImpl.java:508 delegates straight to SQLUtils.enquoteLiteral. This is a standard JDBC 4.3 API that callers are told to use to build safe SQL.
2. java.sql.Statement.enquoteNCharLiteral(String) — StatementImpl.java:527, same delegation.
3. java.sql.Statement.enquoteIdentifier(String, boolean) — StatementImpl.java:513.
4. DatabaseMetaData.getColumns(...) — jdbc-v2/.../metadata/DatabaseMetaDataImpl.java:1101-1103 builds its system.columns query with SQLUtils.enquoteLiteral on the caller-supplied schemaPattern / tableNamePattern / columnNamePattern. No API misuse is needed here: a pattern containing a backslash — which is the JDBC-standard escape character for _ and % in metadata patterns — makes the driver's own internal query fail with a syntax error.

Existing coverage (client-v2/src/test/java/com/clickhouse/client/api/sql/SQLUtilsTest.java and jdbc-v2/.../StatementTest.testEnquoteLiteral) exercises only quote characters, so the gap is not caught.

ClickHouse server version

26.7.3.19 (official build), reached over HTTP at localhost:8123. Verified against a running server, not code analysis alone.

Reproduction

jdbc-v2/src/test/java/com/clickhouse/jdbc/EnquoteBackslashTest.java:

package com.clickhouse.jdbc;

import org.testng.Assert;
import org.testng.annotations.Test;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class EnquoteBackslashTest {

    private static final String URL = "jdbc:ch:http://localhost:8123/default";

    private Connection conn() throws SQLException {
        Properties p = new Properties();
        p.setProperty("user", "default");
        p.setProperty("password", "");
        return new ConnectionImpl(URL, p);
    }

    @Test
    public void silentCorruption() throws Exception {
        try (Connection c = conn(); Statement stmt = c.createStatement()) {
            String value = "path like C:\\temp x";   // one real backslash
            String quoted = stmt.enquoteLiteral(value);
            try (ResultSet rs = stmt.executeQuery("SELECT " + quoted + " AS v")) {
                Assert.assertTrue(rs.next());
                Assert.assertEquals(rs.getString("v"), value);
            }
        }
    }

    @Test
    public void brokenStatement() throws Exception {
        try (Connection c = conn(); Statement stmt = c.createStatement()) {
            String value = "ends with backslash\\";
            try (ResultSet rs = stmt.executeQuery("SELECT " + stmt.enquoteLiteral(value))) {
                Assert.assertTrue(rs.next());
                Assert.assertEquals(rs.getString(1), value);
            }
        }
    }

    @Test
    public void identifierCorruption() throws Exception {
        try (Connection c = conn(); Statement stmt = c.createStatement()) {
            String ident = "col\\tname";             // backslash + 't'
            try (ResultSet rs = stmt.executeQuery("SELECT 1 AS " + stmt.enquoteIdentifier(ident, true))) {
                Assert.assertTrue(rs.next());
                Assert.assertEquals(rs.getMetaData().getColumnLabel(1), ident);
            }
        }
    }

    @Test
    public void metadataPatternBroken() throws Exception {
        try (Connection c = conn()) {
            try (ResultSet rs = c.getMetaData().getColumns(null, "default", "tbl\\", "%")) {
                while (rs.next()) { }
            }
        }
    }
}

Run with:

mvn -pl jdbc-v2 test -Dtest=EnquoteBackslashTest

Expected

All four pass: the literal round-trips unchanged, the identifier keeps its backslash, and getColumns returns an (empty) result set.

Actual — all four fail

Tests run: 4, Failures: 4, Errors: 0, Skipped: 0

silentCorruption:
  expected [path like C:\temp x] but found [path like C:<TAB>emp x]
  (the \t was consumed as a TAB escape; length() returns 18 instead of 19)

brokenStatement:
  java.sql.SQLException: Code: 62. DB::Exception: Single quoted string is not closed:
  Syntax error: failed at position 8 ('ends with backslash\'): 'ends with backslash\'.
  (SYNTAX_ERROR) (version 26.7.3.19 (official build))

identifierCorruption:
  expected [col\tname] but found [col<TAB>name]

metadataPatternBroken:
  java.sql.SQLException: Code: 62. DB::Exception: Single quoted string is not closed:
  Syntax error: failed at position 2827 (' ORDER BY TABLE_SCHEM, TABLE_NAME, ORDINAL_POSITION)
  (SYNTAX_ERROR) (version 26.7.3.19 (official build))

(<TAB> above is a literal 0x09 byte in the real output.)

Suggested fix

Escape the backslash before the quote in client-v2/src/main/java/com/clickhouse/client/api/sql/SQLUtils.java:

• enquoteLiteral (line 14): escape \ to \\ first, then handle '. Reusing the already-correct escapeSingleQuotes (line 136) would collapse the two escaping paths into one and keep the class self-consistent.
• enquoteIdentifier (line 30): likewise escape \ to \\ before doubling ".

Worth extending SQLUtilsTest's data providers with backslash cases (embedded \t, trailing \, \\) so the gap stays closed.

Link

Same class of bug reported for clickhouse-connect: https://github.com/ClickHouse/clickhouse-connect/issues/975 (SQLAlchemy DDL rendered COMMENT / DEFAULT literals through a generic string type that only doubles quotes, leaving backslashes unescaped).