Internal Structures
There are a number of internal structures within the scripting element of MariaDB Proxy. The primary structure is proxy and this provides an interface to the many common structures used throughout the script, such as connection lists and configured backend servers. Other structures, such as the incoming packet from the client and result sets are only available within the context of one of the scriptable functions.
| Attribute | Description |
|---|---|
connection
| A structure containing the active client connections. For a list of attributes, see proxy.connection.
|
servers
| A structure containing the list of configured backend servers. For a list of attributes, see proxy.global.backends.
|
queries
| A structure containing the queue of queries that will be sent to the server during a single client query. For a list of attributes, see proxy.queries.
|
PROXY_VERSION
| The version number of MariaDB Proxy, encoded in hex. You can use this to check that the version number supports a particular option from within the Lua script. Note that the value is encoded as a hex value, so to check the version is at least 0.5.1 you compare against 0x00501. |
proxy.connection
The proxy.connection object is read only, and provides information about the current connection, and is split into a client and server tables. This enables you to examine information about both the incoming client connections to the proxy (client), and to the backend servers (server).
| Attribute | Description |
|---|---|
client.default_db
| Default database requested by the client |
client.username
| User name used to authenticate |
client.scrambled_password
| The scrambled version of the password used to authenticate |
client.dst.name
| The combined address:port of the Proxy port used by this client (should match the --proxy-address configuration parameter)
|
client.dst.address
| The IP address of the of the Proxy port used by this client |
client.dst.port
| The port number of the of the Proxy port used by this client |
client.src.name
| The combined address:port of the client (originating) TCP/IP endpoint
|
client.src.address
| The IP address of the client (originating) TCP/IP port |
client.src.port
| The port of the client (originating) TCP/IP endpoint |
server.scramble_buffer
| The scramble buffer used to scramble the password |
server.mysqld_version
| The MariaDB version number of the server |
server.thread_id
| The ID of the thread handling the connection to the current server |
server.dst.name
| The combined address:port for the backend server for the current connection (i.e. the connection to the MariaDB server)
|
server.dst.address
| The address for the backend server |
server.dst.port
| The port for the backend server |
server.src.name
| The combined address:port for the TCP/IP endpoint used by the Proxy to connect to the backend server
|
server.src.address
| The address of the endpoint for the proxy-side connection to the MariaDB server |
server.src.port
| The port of the endpoint for the proxy-side connection to the MariaDB server |
proxy.global.backends
The proxy.global.backends table is partially writable and contains an array of all the configured backend servers and the server metadata (IP address, status, etc.). You can determine the array index of the current connection using proxy.connection['backend_ndx'] which is the index into this table of the backend server being used by the active connection.
The attributes for each entry within the proxy.global.backends table are shown in this table.
| Attribute | Description |
|---|---|
dst.name
| The combined address:port of the backend server.
|
dst.address
| The IP address of the backend server. |
dst.port
| The port of the backend server. |
connected_clients
| The number of clients currently connected. |
state
| The status of the backend server. See Backend State/Type Constants. |
type
| The type of the backend server. You can use this to identify whether the backed was configured as a standard read/write backend, or a read-only backend. You can compare this value to the proxy.BACKEND_TYPE_RW and proxy.BACKEND_TYPE_RO. |
proxy.queries
The proxy.queries object is a queue representing the list of queries to be sent to the server. The queue is not populated automatically, but if you do not explicitly populate the queue, queries are passed on to the backend server verbatim. Also, if you do not populate the query queue by hand, the read_query_result() function is not triggered.
The following methods are supported for populating the proxy.queries object.
| Function | Description |
|---|---|
append(id,packet,[options])
| Appends a query to the end of the query queue. The id is an integer identifier that you can use to recognize the query results when they are returned by the server. The packet should be a properly formatted query packet. The optional options should be a table containing the options specific to this packet.
|
prepend(id,packet)
| Prepends a query to the query queue. The id is an identifier that you can use to recognize the query results when they are returned by the server. The packet should be a properly formatted query packet.
|
reset()
| Empties the query queue. |
len()
| Returns the number of query packets in the queue. |
For example, you could append a query packet to the proxy.queries queue by using the append():
proxy.queries:append(1,packet)
The optional third argument to append() should contain the options for the packet. To have access to the result set through the read_query_result() function, set the resultset_is_needed flag to true:
proxy.queries:append( 1, packet, { resultset_is_needed = true } )
If that flag is false (the default), proxy will:
- Send the result set to the client as soon as it is received
- Reduce memory usage (because the result set is not stored internally for processing)
- Reduce latency of returning results to the client
- Pass data from server to client unaltered
The default mode is therefore quicker and useful if you only want to monitor the queries sent, and the basic statistics.
To perform any kind of manipulation on the returned data, you must set the flag to true, which will:
- Store the result set so that it can be processed.
- Enable modification of the result set before it is returned to the client.
- Enable you to discard the result set instead of returning it to the client.
proxy.response
The proxy.response structure is used when you want to return your own MariaDB response, instead of forwarding a packet that you have received a backend server. The structure holds the response type information, an optional error message, and the result set (rows/columns) to return.
| Attribute | Description |
|---|---|
type
| The type of the response. The type must be either MYSQLD_PACKET_OK or MYSQLD_PACKET_ERR. If the MYSQLD_PACKET_ERR, you should set the value of the mysql.response.errmsg with a suitable error message.
|
errmsg
| A string containing the error message that will be returned to the client. |
resultset
| A structure containing the result set information (columns and rows), identical to what would be returned when returning a results from a SELECT query. |
When using proxy.response you either set proxy.response.type to proxy.MYSQLD_PACKET_OK and then build resultset to contain the results to return, or set proxy.response.type to proxy.MYSQLD_PACKET_ERR and set the proxy.response.errmsg to a string with the error message. To send the completed result set or error message, you should return the proxy.PROXY_SEND_RESULT to trigger the return of the packet information.
An example of this can be seen in the tutorial-resultset.lua script within the MariaDB Proxy package:
if string.lower(command) == 'show' and string.lower(option) == 'querycounter' then
---
-- proxy.PROXY_SEND_RESULT requires
--
-- proxy.response.type to be either
-- * proxy.MYSQLD_PACKET_OK or
-- * proxy.MYSQLD_PACKET_ERR
--
-- for proxy.MYSQLD_PACKET_OK you need a resultset
-- * fields
-- * rows
--
-- for proxy.MYSQLD_PACKET_ERR
-- * errmsg
proxy.response.type = proxy.MYSQLD_PACKET_OK
proxy.response.resultset = {
fields = {
{ type = proxy.MYSQL_TYPE_LONG, name = 'global_query_counter', },
{ type = proxy.MYSQL_TYPE_LONG, name = 'query_counter', },
},
rows = {
{ proxy.global.query_counter, query_counter }
}
}
-- we have our result, send it back
return proxy.PROXY_SEND_RESULT elseif string.lower(command) == 'show' and string.lower(option) == 'myerror' then
proxy.response.type = proxy.MYSQLD_PACKET_ERR
proxy.response.errmsg = 'my first error'
return proxy.PROXY_SEND_RESULT
proxy.response.resultset
The proxy.response.resultset structure should be populated with the rows and columns of data to return. The structure contains the information about the entire result set, with the individual elements of the data shown in the following table.
| Attribute | Description |
|---|---|
fields
| The definition of the columns being returned. This should be a dictionary structure with the type specifying the MariaDB data type, and the name specifying the column name. Columns should be listed in the order of the column data that will be returned.
|
flags
| A number of flags related to the result set. Valid flags include auto_commit (whether an automatic commit was triggered), no_good_index_used (the query executed without using an appropriate index), and no_index_used (the query executed without using any index).
|
rows
| The actual row data. The information should be returned as an array of arrays. Each inner array should contain the column data, with the outer array making up the entire result set. |
warning_count
| The number of warnings for this result set. |
affected_rows
| The number of rows affected by the original statement. |
insert_id
| The last insert ID for an auto-incremented column in a table. |
query_status
| The status of the query operation. You can use the MYSQLD_PACKET_OK or MYSQLD_PACKET_ERR constants to populate this parameter. |
For an example showing how to use this structure, see proxy.response.
Proxy Return State Constants
The following constants are used internally by the proxy to specify the response to send to the client or server. All constants are exposed as values within the main proxy table.
| Constant | Description |
|---|---|
PROXY_SEND_QUERY
| Causes the proxy to send the current contents of the queries queue to the server. |
PROXY_SEND_RESULT
| Causes the proxy to send a result set back to the client. |
PROXY_IGNORE_RESULT
| Causes the proxy to drop the result set (nothing is returned to the client). |
As constants, these entities are available without qualification in the Lua scripts. For example, at the end of the read_query_result() you might return PROXY_IGNORE_RESULT:
return proxy.PROXY_IGNORE_RESULT
Packet State Constants
The following states describe the status of a network packet. These items are entries within the main proxy table.
| Constant | Description |
|---|---|
MYSQLD_PACKET_OK
| The packet is OK |
MYSQLD_PACKET_ERR
| The packet contains error information |
MYSQLD_PACKET_RAW
| The packet contains raw data |
Backend State/Type Constants
The following constants are used either to define the status or type of the backend MariaDB server to which the proxy is connected. These items are entries within the main proxy table.
| Constant | Description |
|---|---|
BACKEND_STATE_UNKNOWN
| The current status is unknown |
BACKEND_STATE_UP
| The backend is known to be up (available) |
BACKEND_STATE_DOWN
| The backend is known to be down (unavailable) |
BACKEND_TYPE_UNKNOWN
| Backend type is unknown |
BACKEND_TYPE_RW
| Backend is available for read/write |
BACKEND_TYPE_RO
| Backend is available only for read-only use |
Server Command Constants
The following values are used in the packets exchanged between the client and server to identify the information in the rest of the packet. These items are entries within the main proxy table. The packet type is defined as the first character in the sent packet. For example, when intercepting packets from the client to edit or monitor a query, you would check that the first byte of the packet was of type proxy.COM_QUERY.
| Constant | Description |
|---|---|
COM_SLEEP
| Sleep |
COM_QUIT
| Quit |
COM_INIT_DB
| Initialize database |
COM_QUERY
| Query |
COM_FIELD_LIST
| Field List |
COM_CREATE_DB
| Create database |
COM_DROP_DB
| Drop database |
COM_REFRESH
| Refresh |
COM_SHUTDOWN
| Shutdown |
COM_STATISTICS
| Statistics |
COM_PROCESS_INFO
| Process List |
COM_CONNECT
| Connect |
COM_PROCESS_KILL
| Kill |
COM_DEBUG
| Debug |
COM_PING
| Ping |
COM_TIME
| Time |
COM_DELAYED_INSERT
| Delayed insert |
COM_CHANGE_USER
| Change user |
COM_BINLOG_DUMP
| Binlog dump |
COM_TABLE_DUMP
| Table dump |
COM_CONNECT_OUT
| Connect out |
COM_REGISTER_SLAVE
| Register slave |
COM_STMT_PREPARE
| Prepare server-side statement |
COM_STMT_EXECUTE
| Execute server-side statement |
COM_STMT_SEND_LONG_DATA
| Long data |
COM_STMT_CLOSE
| Close server-side statement |
COM_STMT_RESET
| Reset statement |
COM_SET_OPTION
| Set option |
COM_STMT_FETCH
| Fetch statement |
COM_DAEMON
| Daemon (MySQL 5.1 only) |
COM_ERROR
| Error |
MySQL Type Constants
These constants are used to identify the field types in the query result data returned to clients from the result of a query. These items are entries within the main proxy table.