Logs for mysqlnd_azure plugin

This patch is added for print some running information of mysqlnd_azure to a local file. Current status: Under developing.

New Added Configuration

`mysqlnd_azure.logfilePath`

Name	mysqlnd_azure.logfilePath
Comment	Filename that you want your log writes to.
Type	String
Accepted Value	String length <= 255, legal filename string
Default	mysqlnd_azure_runtime.log
Dynamic	NO
Note	1. This variable was inited at PHP Module Init (MINIT) period, and immutable at runtime. a call of `ini_set('mysqlnd_azure.logLevel', '$VAL');` would fail. 2. Filename length cannot exceed the file system's restriction(255), otherwise system will use the default filename and throw a warning "Given logfile name too long, redirected to default: mysqlnd_azure_runtime.log"

`mysqlnd_azure.logLevel`

Name	mysqlnd_azure.logLevel
Comment	The verbose level of log we generate.
Type	Enumeration
Accepted Value	[ 0 \| 1 \| 2 \| 3 ]
Default	0 (OFF)
Dynamic	Yes
Note	1. When the current `mysqlnd_azure.logLevel > 0`, change logLevel at runtime will be logged.

Loglevel supported

we support 3 level of logs for user:

[DEBUG]:
1. source code path(inside which function);
2. connection information(except password);
3. verbose running status (e.g. customer given redirected server information directly... )
[INFO]:
1. connection fallback when mysqlnd_azure.enableRedirection=preferred with details (cannot get redirection info from OK packet/ try connect using redirect information failed , ...);
2. cache operations
[ERROR]:
1. any operation may cause customer see connection break (e.x. original conn/ redirected_conn established failed, ... and connection fall back when mysqlnd_azure.enableRedirection = ON)

[SYSTM] maked log rows for Azure mysqlnd Log Module itself, when current mysqlnd_azure.logLevel > 0, any operation related to log system itself will be logged. For example, if someone call ini_set('mysqlnd_azure.logLevel', '2'); at runtime, there may appear a log like
2020-03-27 09:09:05 [SYSTM] mysqlnd_azure.logLevel changed: 3 -> 2

Level value relationship to level logged

0: No log written
1: [SYSTM] + [ERROR]
2: [SYSTM] + [ERROR] + [INFO]
3: [SYSTM] + [ERROR] + [INFO] + [DEBUG]

Configuration Example:

You can add to section [mysqlnd_azure] in file php.ini

[mysqlnd_azure]
mysqlnd_azure.enableRedirect = 2
mysqlnd_azure.logfilePath = "test.log"
mysqlnd_azure.logLevel = 3

phpinfo() / php -i

After successfully configured, try php -i, there will be var:val pairs listed below mysqlnd_azure section, like:

mysqlnd_azure

mysqlnd_azure => enableRedirect
enableRedirect => preferred
logfilePath => santotest.log
logLevel => 3

What the logs would be (example)

After turned on the option mentioned before, you will see something like :

2020-03-13 11:00:13 [ERROR] Connection cannot established with given information, please check the server availability, or your parameters given
 2020-03-13 11:00:54 [DEBUG] mysqlnd_azure.c: mysqlnd_azure::connect()
 2020-03-13 11:00:54 [DEBUG] mysqlnd_azure.enableRedirect: PREFERRD
 2020-03-13 11:00:54 [INFO ] SSL not enabled, and mysqlnd_zaure.enableRedirect if PREFERRED, connection will go through gateway.
 2020-03-13 11:00:54 [DEBUG] mysqlnd_azure.c: mysqlnd_azure::connect()
 2020-03-13 11:00:54 [INFO ] No cache found
 2020-03-13 11:00:54 [DBEUG] mysqlnd_azure.c: mysqlnd_azure_data::connect()
 2020-03-13 11:00:54 [DEBUG] Connection Information: host=127.0.0.1 user=santo db=test port=3306 flags=131072 persistent=1 state=0
 2020-03-13 11:00:54 [ERROR] Connection cannot established with given information, please check the server availability, or your parameters given
 2020-03-13 11:00:54 [DEBUG] mysqlnd_azure.c: mysqlnd_azure::connect()
 2020-03-13 11:00:54 [INFO ] No cache found
 2020-03-13 11:00:54 [DBEUG] mysqlnd_azure.c: mysqlnd_azure_data::connect()
 2020-03-13 11:00:54 [DEBUG] Connection Information: host=santo.mysql.database.azure.com user=test@santo db= port=3306 flags=131072 persistent=1 state=0
 2020-03-13 11:00:54 [DEBUG] Classical connection OK, try to get REDIRECTION information
 2020-03-13 11:00:54 [DEBUG] mysqlnd_azure.c: get_redirect_info()
 2020-03-13 11:00:54 [DEBUG] Successfully get redirection information, try to connect with redirection connection
 2020-03-13 11:00:54 [DEBUG] mysqlnd_azure.c: set_redirect_client_options()
 2020-03-13 11:00:55 [DEBUG] Redirect conntion established.
 2020-03-13 11:00:55 [DEBUG] Prepare the context of new connection
 2020-03-13 11:00:55 [DEBUG] mysqlnd_azure.c: mysqlnd_azure::connect()
 2020-03-13 11:00:55 [DEBUG] mysqlnd_azure.enableRedirect: PREFERRD
 2020-03-13 11:00:55 [INFO ] SSL not enabled, and mysqlnd_zaure.enableRedirect if PREFERRED, connection will go through gateway.

microsoft / mysqlnd_azure

Add AZURE_LOG() to log plugin runtime information #11