Fix for bug #6266 "Invalid DATETIME value is not handled properly".

In server we assume that datetime values stored in MYSQL_TIME struct
are normalized (and year is not greater than 9999), so we should 
perform range checks in all places then we convert something to
MYSQL_TIME. 


include/my_time.h:
  Added one more argument to set_zero_time() function to make it more 
  convinient.
  Added comment clarifying why MAX_DATE_STRING_REP_LENGTH value is 30.
include/mysql_time.h:
  Documented MySQL's internal assumptions for members of MYSQL_TIME
  structure.
libmysql/libmysql.c:
  It does not make sense to set MYSQL_TIME::time_type twice in case of 
  errors.
mysql-test/r/type_datetime.result:
  Added test for bug #6266 "Invalid DATETIME value not handled properly".
mysql-test/t/type_datetime.test:
  Added test for bug #6266 "Invalid DATETIME value not handled properly".
sql-common/my_time.c:
  str_to_datetime(): Added missing check for too big year values.
  set_zero_time(): added time_type argument, since MYSQL_TIMESTAMP_NONE
    is not the value that we want in most cases.
sql/field.cc:
  Field_datetime::store_time():
    clarified why we don't perform any range checks here.
sql/item.cc:
  Item_param::set_time():
   Added comment describing this method and range checking for TIME
   values.
sql/sql_prepare.cc:
  Removed comments about range checking for TIME values in prepared 
  statements, which are no longer true.
  set_zero_time() has one more argument now.
tests/client_test.c:
  Added test for bug #6266 "Invalid DATETIME value not handled properly"

2 files changed, 15 insertions, 2 deletions

diff --git a/include/my_time.h b/include/my_time.h
index dab17904b2d..94701e159c4 100644
--- a/include/my_time.h
+++ b/include/my_time.h
@@ -58,14 +58,15 @@ void init_time(void);
 my_time_t 
 my_system_gmt_sec(const MYSQL_TIME *t, long *my_timezone, bool *in_dst_time_gap);
 
-void set_zero_time(MYSQL_TIME *tm);
+void set_zero_time(MYSQL_TIME *tm, enum enum_mysql_timestamp_type time_type);
 
 /*
   Required buffer length for my_time_to_str, my_date_to_str,
   my_datetime_to_str and TIME_to_string functions. Note, that the
   caller is still responsible to check that given TIME structure
   has values in valid ranges, otherwise size of the buffer could
-  be not enough.
+  be not enough. We also rely on the fact that even wrong values
+  sent using binary protocol fit in this buffer.
 */
 #define MAX_DATE_STRING_REP_LENGTH 30
 
diff --git a/include/mysql_time.h b/include/mysql_time.h
index ec67d60dea5..5f4fc12c005 100644
--- a/include/mysql_time.h
+++ b/include/mysql_time.h
@@ -33,6 +33,18 @@ enum enum_mysql_timestamp_type
 };
 
 
+/*
+  Structure which is used to represent datetime values inside MySQL.
+
+  We assume that values in this structure are normalized, i.e. year <= 9999,
+  month <= 12, day <= 31, hour <= 23, hour <= 59, hour <= 59. Many functions
+  in server such as my_system_gmt_sec() or make_time() family of functions
+  rely on this (actually now usage of make_*() family relies on a bit weaker
+  restriction). Also functions that produce MYSQL_TIME as result ensure this.
+  There is one exception to this rule though if this structure holds time
+  value (time_type == MYSQL_TIMESTAMP_TIME) days and hour member can hold
+  bigger values.
+*/
 typedef struct st_mysql_time
 {
   unsigned int  year, month, day, hour, minute, second;