Experiment on parsing backslash escapes in a more convenient way #10922

src/IO/ReadHelpers.cpp

@@ -283,7 +283,9 @@ static void parseComplexEscapeSequence(Vector & s, ReadBuffer & buf)
     if (buf.eof())
         throw Exception("Cannot parse escape sequence", ErrorCodes::CANNOT_PARSE_ESCAPE_SEQUENCE);
 
-    if (*buf.position() == 'x')
+    char char_after_backslash = *buf.position();
+
+    if (char_after_backslash == 'x')
     {
         ++buf.position();
         /// escape sequence of the form \xAA
@@ -291,7 +293,7 @@ static void parseComplexEscapeSequence(Vector & s, ReadBuffer & buf)
         readPODBinary(hex_code, buf);
         s.push_back(unhex2(hex_code));
     }
-    else if (*buf.position() == 'N')
+    else if (char_after_backslash == 'N')
     {
         /// Support for NULLs: \N sequence must be parsed as empty string.
         ++buf.position();
@@ -299,7 +301,15 @@ static void parseComplexEscapeSequence(Vector & s, ReadBuffer & buf)
     else
     {
         /// The usual escape sequence of a single character.
-        s.push_back(parseEscapeSequence(*buf.position()));
+        char decoded_char = parseEscapeSequence(char_after_backslash);
+
+        /// For convenience using LIKE and regular expressions,
+        /// we leave backslash when user write something like 'Hello 100\%':
+        /// it is parsed like Hello 100\% instead of Hello 100%
+        if (decoded_char != '\\' && !isControlASCII(decoded_char))
+            s.push_back('\\');
+
+        s.push_back(decoded_char);
         ++buf.position();
     }
 }

src/IO/tests/CMakeLists.txt

@@ -37,9 +37,6 @@ target_link_libraries (parse_int_perf2 PRIVATE clickhouse_common_io)
 add_executable (read_write_int read_write_int.cpp)
 target_link_libraries (read_write_int PRIVATE clickhouse_common_io)
 
-add_executable (mempbrk mempbrk.cpp)
-target_link_libraries (mempbrk PRIVATE clickhouse_common_io)
-
 add_executable (o_direct_and_dirty_pages o_direct_and_dirty_pages.cpp)
 target_link_libraries (o_direct_and_dirty_pages PRIVATE clickhouse_common_io)
 

src/IO/tests/mempbrk.cpp

@@ -1,90 +0,0 @@
-#include <string>
-#include <iostream>
-#include <iomanip>
-
-#include <Common/Stopwatch.h>
-
-#include <Core/Types.h>
-#include <IO/ReadHelpers.h>
-#include <IO/WriteHelpers.h>
-#include <IO/ReadBufferFromFileDescriptor.h>
-#include <IO/WriteBufferFromFileDescriptor.h>
-
-#include <common/find_symbols.h>
-
-namespace DB
-{
-namespace ErrorCodes
-{
-    extern const int CANNOT_PARSE_ESCAPE_SEQUENCE;
-}
-}
-
-
-namespace test
-{
-static void readEscapedString(DB::String & s, DB::ReadBuffer & buf)
-    {
-        s = "";
-        while (!buf.eof())
-        {
-            const char * next_pos = find_first_symbols<'\b', '\f', '\n', '\r', '\t', '\0', '\\'>(buf.position(), buf.buffer().end());
-
-            s.append(buf.position(), next_pos - buf.position());
-            buf.position() += next_pos - buf.position();
-
-            if (!buf.hasPendingData())
-                continue;
-
-            if (*buf.position() == '\t' || *buf.position() == '\n')
-                return;
-
-            if (*buf.position() == '\\')
-            {
-                ++buf.position();
-                if (buf.eof())
-                    throw DB::Exception("Cannot parse escape sequence", DB::ErrorCodes::CANNOT_PARSE_ESCAPE_SEQUENCE);
-                s += DB::parseEscapeSequence(*buf.position());
-                ++buf.position();
-            }
-        }
-    }
-}
-
-
-int main(int, char **)
-{
-    try
-    {
-        DB::ReadBufferFromFileDescriptor in(STDIN_FILENO);
-//        DB::WriteBufferFromFileDescriptor out(STDOUT_FILENO);
-        std::string s;
-        size_t rows = 0;
-
-        Stopwatch watch;
-
-        while (!in.eof())
-        {
-            test::readEscapedString(s, in);
-            in.ignore();
-
-            ++rows;
-
-/*            DB::writeEscapedString(s, out);
-            DB::writeChar('\n', out);*/
-        }
-
-        watch.stop();
-        std::cerr << std::fixed << std::setprecision(2)
-            << "Read " << rows << " rows (" << in.count() / 1000000.0 << " MB) in " << watch.elapsedSeconds() << " sec., "
-            << rows / watch.elapsedSeconds() << " rows/sec. (" << in.count() / watch.elapsedSeconds() / 1000000 << " MB/s.)"
-            << std::endl;
-    }
-    catch (const DB::Exception & e)
-    {
-        std::cerr << e.what() << ", " << e.displayText() << std::endl;
-        return 1;
-    }
-
-    return 0;
-}

tests/queries/0_stateless/01284_escape_sequences_php_mysql_style.reference

@@ -0,0 +1,3 @@
+a\\_\\c\\l\\i\\c\\k\\h\\o\\u\\s	a\\_\\c\\l\\i\\c\\k\\h\\o\\u\\s\\e
+1	0	1	1
+1	1	0	0	0

tests/queries/0_stateless/01284_escape_sequences_php_mysql_style.sql

@@ -0,0 +1,6 @@
+SELECT 'a\_\c\l\i\c\k\h\o\u\s\e', 'a\\_\\c\\l\\i\\c\\k\\h\\o\\u\\s\\e';
+select 'aXb' like 'a_b', 'aXb' like 'a\_b', 'a_b' like 'a\_b', 'a_b' like 'a\\_b';
+SELECT match('Hello', '\w+'), match('Hello', '\\w+'), match('Hello', '\\\w+'), match('Hello', '\w\+'), match('Hello', 'w+');
+
+SELECT match('Hello', '\He\l\l\o'); -- { serverError 427 }
+SELECT match('Hello', '\H\e\l\l\o'); -- { serverError 427 }