MWL#36: Add a mysqlbinlog option to change the used database.

Add rewrite_db() member to the Table_map_log_event class.
Each RBR-event in binary log is preceded by a Table_map event
containing a (db_id, db_name) pair. The rewrite_db(new_name)
function replaces db_name by new_name in a buffer containing
Table_map event read from the binary log.

sql/log_event.cc

@@ -8005,6 +8005,100 @@ Table_map_log_event::~Table_map_log_event()
   my_free(m_memory, MYF(MY_ALLOW_ZERO_PTR));
 }
 
+
+#ifdef MYSQL_CLIENT
+/*
+  Reset db name. This function assumes that temp_buf member contains event
+  representation taken from a binary log. It resets m_dbnam and m_dblen and
+  rewrites temp_buf with new db name.
+  On success returns 0, on failure return non-zero value.
+*/
+int Table_map_log_event::rewrite_db(
+  const char* new_db,
+  size_t new_len,
+  const Format_description_log_event* desc)
+{
+  DBUG_ENTER("Table_map_log_event::rewrite_db");
+  DBUG_ASSERT(temp_buf);
+
+  uint header_len= min(desc->common_header_len,
+                       LOG_EVENT_MINIMAL_HEADER_LEN) + TABLE_MAP_HEADER_LEN;
+  int len_diff;
+
+  if (!(len_diff= new_len - m_dblen))
+  {
+    memcpy((void*) (temp_buf + header_len + 1), new_db, m_dblen + 1);
+    memcpy((void*) m_dbnam, new_db, m_dblen + 1);
+    DBUG_RETURN(0);
+  }
+
+  // Create new temp_buf
+  ulong event_cur_len= uint4korr(temp_buf + EVENT_LEN_OFFSET);
+  ulong event_new_len= event_cur_len + len_diff;
+  char* new_temp_buf= (char*) my_malloc(event_new_len, MYF(MY_WME));
+
+  if (!new_temp_buf)
+  {
+    sql_print_error("Table_map_log_event::rewrite_dbname: "
+      "failed to allocate new temp_buf (%d bytes required)", event_new_len);
+    DBUG_RETURN(-1);
+  }
+
+  // Rewrite temp_buf
+  char* ptr= new_temp_buf;
+  ulong cnt= 0;
+
+  // Copy header and change event length
+  memcpy(ptr, temp_buf, header_len);
+  int4store(ptr + EVENT_LEN_OFFSET, event_new_len);
+  ptr += header_len;
+  cnt += header_len;
+
+  // Write new db name length and new name
+  *ptr++ = new_len;
+  memcpy(ptr, new_db, new_len + 1);
+  ptr += new_len + 1;
+  cnt += m_dblen + 2;
+
+  // Copy rest part
+  memcpy(ptr, temp_buf + cnt, event_cur_len - cnt);
+
+  // Reregister temp buf
+  free_temp_buf();
+  register_temp_buf(new_temp_buf);
+
+  // Reset m_dbnam and m_dblen members
+  m_dblen= new_len;
+
+  // m_dbnam resides in m_memory together with m_tblnam and m_coltype
+  uchar* memory= m_memory;
+  char const* tblnam= m_tblnam;
+  uchar* coltype= m_coltype;
+
+  m_memory= (uchar*) my_multi_malloc(MYF(MY_WME),
+                                     &m_dbnam, (uint) m_dblen + 1,
+                                     &m_tblnam, (uint) m_tbllen + 1,
+                                     &m_coltype, (uint) m_colcnt,
+                                     NullS);
+
+  if (!m_memory)
+  {
+    sql_print_error("Table_map_log_event::rewrite_dbname: "
+      "failed to allocate new m_memory (%d + %d + %d bytes required)",
+      m_dblen + 1, m_tbllen + 1, m_colcnt);
+    DBUG_RETURN(-1);
+  }
+
+  memcpy((void*)m_dbnam, new_db, m_dblen + 1);
+  memcpy((void*)m_tblnam, tblnam, m_tbllen + 1);
+  memcpy(m_coltype, coltype, m_colcnt);
+
+  my_free(memory, MYF(MY_WME));
+  DBUG_RETURN(0);
+}
+#endif /* MYSQL_CLIENT */
+
+
 /*
   Return value is an error code, one of:
 

sql/log_event.h

@@ -3310,6 +3310,8 @@ public:
   ulong get_table_id() const        { return m_table_id; }
   const char *get_table_name() const { return m_tblnam; }
   const char *get_db_name() const    { return m_dbnam; }
+  int rewrite_db(const char* new_name, size_t new_name_len,
+                 const Format_description_log_event*);
 #endif
 
   virtual Log_event_type get_type_code() { return TABLE_MAP_EVENT; }