From 5018dd610974ec3a732b0573961138a14f086b04 Mon Sep 17 00:00:00 2001
From: Adriano dos Santos Fernandes <adrianosf@gmail.com>
Date: Mon, 3 May 2021 11:19:14 -0300
Subject: [PATCH] Improvement #6786 - Add session time zone to system context.

---
 doc/sql.extensions/README.context_variables2 |  2 ++
 doc/sql.extensions/README.time_zone.md       | 15 +++++++++++++++
 src/jrd/SysFunction.cpp                      |  7 +++++++
 3 files changed, 24 insertions(+)

diff --git a/doc/sql.extensions/README.context_variables2 b/doc/sql.extensions/README.context_variables2
index 1421baa370..5ef0fff719 100644
--- a/doc/sql.extensions/README.context_variables2
+++ b/doc/sql.extensions/README.context_variables2
@@ -131,6 +131,8 @@ Usage:
    EXT_CONN_POOL_ACTIVE_COUNT   | Count of active connections, associated with pool
                                 |
    EXT_CONN_POOL_LIFETIME       | Idle connection lifetime, in seconds
+                                |
+   SESSION_TIMEZONE             | Current session time zone.
 
 Notes:
    To prevent DoS attacks against Firebird Server you are not allowed to have
diff --git a/doc/sql.extensions/README.time_zone.md b/doc/sql.extensions/README.time_zone.md
index ed6f7927ff..5480cb1536 100644
--- a/doc/sql.extensions/README.time_zone.md
+++ b/doc/sql.extensions/README.time_zone.md
@@ -329,6 +329,21 @@ select localtimestamp
   from rdb$database;
 ```
 
+### `SESSION_TIMEZONE` context variable
+
+`RDB$GET_CONTEXT('SYSTEM', 'SESSION_TIMEZONE')` could be used to obtain the session current time zone.
+
+#### Examples
+
+```
+set time zone 'america/sao_paulo';
+select rdb$get_context('SYSTEM', 'SESSION_TIMEZONE') from rdb$database;
+-- Result: America/Sao_Paulo
+
+set time zone '-3:00';
+-- Result: -03:00
+```
+
 # Changes in `CURRENT_TIME` and `CURRENT_TIMESTAMP`
 
 In version 4.0, `CURRENT_TIME` and `CURRENT_TIMESTAMP` are changed to return `TIME WITH TIME ZONE` and `TIMESTAMP WITH TIME ZONE` (with time zone set to the session time zone), different than previous versions, that returned the types without time zone.
diff --git a/src/jrd/SysFunction.cpp b/src/jrd/SysFunction.cpp
index a2f93bc48f..1edfc45383 100644
--- a/src/jrd/SysFunction.cpp
+++ b/src/jrd/SysFunction.cpp
@@ -384,6 +384,7 @@ const char
 	SESSION_IDLE_TIMEOUT[] = "SESSION_IDLE_TIMEOUT",
 	STATEMENT_TIMEOUT[] = "STATEMENT_TIMEOUT",
 	EFFECTIVE_USER_NAME[] = "EFFECTIVE_USER",
+	SESSION_TIMEZONE[] = "SESSION_TIMEZONE",
 	// SYSTEM namespace: transaction wise items
 	TRANSACTION_ID_NAME[] = "TRANSACTION_ID",
 	ISOLATION_LEVEL_NAME[] = "ISOLATION_LEVEL",
@@ -4331,6 +4332,12 @@ dsc* evlGetContext(thread_db* tdbb, const SysFunction*, const NestValueArray& ar
 				return NULL;
 			resultStr = user.c_str();
 		}
+		else if (nameStr == SESSION_TIMEZONE)
+		{
+			char timeZoneBuffer[TimeZoneUtil::MAX_SIZE];
+			TimeZoneUtil::format(timeZoneBuffer, sizeof(timeZoneBuffer), attachment->att_current_timezone);
+			resultStr = timeZoneBuffer;
+		}
 		else
 		{
 			// "Context variable %s is not found in namespace %s"