MDEV-9319 ALTER from a bigger to a smaller blob type truncates too much data

mysql-test/r/ctype_utf8.result

@@ -5804,5 +5804,21 @@ c0	c1	c2	c3	c4
 2012-06-11 15:18:24	2012-06-11 15:18:24	2012-06-11 15:18:24	2012-06-11 15:18:24	2012-06-11 15:18:24
 DROP TABLE t2, t1;
 #
+# MDEV-9319 ALTER from a bigger to a smaller blob type truncates too much data
+#
+SET NAMES utf8;
+CREATE TABLE t1 (a TEXT CHARACTER SET utf8);
+INSERT INTO t1 VALUES (REPEAT('Ａ',100));
+SELECT OCTET_LENGTH(a) FROM t1;
+OCTET_LENGTH(a)
+300
+ALTER TABLE t1 MODIFY a TINYTEXT CHARACTER SET utf8;
+Warnings:
+Warning	1265	Data truncated for column 'a' at row 1
+SELECT OCTET_LENGTH(a),a FROM t1;
+OCTET_LENGTH(a)	a
+255	ＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡＡ
+DROP TABLE t1;
+#
 # End of 5.5 tests
 #

mysql-test/r/ctype_utf8mb4.result

@@ -2606,6 +2606,22 @@ Warning	1292	Truncated incorrect INTEGER value: 'a'
 DROP TABLE t1;
 # End of test for Bug#13581962,Bug#14096619
 #
+# MDEV-9319 ALTER from a bigger to a smaller blob type truncates too much data
+#
+SET NAMES utf8mb4;
+CREATE TABLE t1 (a TEXT CHARACTER SET utf8mb4);
+INSERT INTO t1 VALUES (REPEAT('😎',100));
+SELECT OCTET_LENGTH(a) FROM t1;
+OCTET_LENGTH(a)
+400
+ALTER TABLE t1 MODIFY a TINYTEXT CHARACTER SET utf8mb4;
+Warnings:
+Warning	1265	Data truncated for column 'a' at row 1
+SELECT OCTET_LENGTH(a),a FROM t1;
+OCTET_LENGTH(a)	a
+252	😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎😎
+DROP TABLE t1;
+#
 # End of 5.5 tests
 #
 #

mysql-test/r/myisam-blob.result

@@ -29,9 +29,11 @@ select length(data) from t1;
 length(data)
 18874368
 alter table t1 modify data blob;
+Warnings:
+Warning	1265	Data truncated for column 'data' at row 1
 select length(data) from t1;
 length(data)
-0
+65535
 drop table t1;
 CREATE TABLE t1 (data BLOB) ENGINE=myisam;
 INSERT INTO t1 (data) VALUES (NULL);

mysql-test/r/type_blob.result

@@ -1000,9 +1000,42 @@ COUNT(*)
 DROP FUNCTION f1;
 DROP TABLE t1;
 End of 5.1 tests
+#
+# Start of 5.5 tests
+#
 CREATE TABLE t1 ( f1 blob, f2 blob );
 INSERT INTO t1 VALUES ('','');
 SELECT f1,f2,"found row" FROM t1 WHERE f1 = f2 ;
 f1	f2	found row
 		found row
 DROP TABLE t1;
+#
+# MDEV-9319 ALTER from a bigger to a smaller blob type truncates too much data
+#
+CREATE TABLE t1 (a MEDIUMBLOB);
+INSERT INTO t1 VALUES (REPEAT(0x61,128000));
+SELECT LENGTH(a) FROM t1;
+LENGTH(a)
+128000
+ALTER TABLE t1 MODIFY a BLOB;
+Warnings:
+Warning	1265	Data truncated for column 'a' at row 1
+SELECT LENGTH(a) FROM t1;
+LENGTH(a)
+65535
+DROP TABLE t1;
+CREATE TABLE t1 (a BLOB);
+INSERT INTO t1 VALUES (REPEAT(0x61,65000));
+SELECT LENGTH(a) FROM t1;
+LENGTH(a)
+65000
+ALTER TABLE t1 MODIFY a TINYBLOB;
+Warnings:
+Warning	1265	Data truncated for column 'a' at row 1
+SELECT LENGTH(a) FROM t1;
+LENGTH(a)
+255
+DROP TABLE t1;
+#
+# End of 5.5 tests
+#

mysql-test/t/ctype_utf8.test

@@ -1648,6 +1648,17 @@ SHOW CREATE TABLE t2;
 SELECT * FROM t2;
 DROP TABLE t2, t1;
 
+--echo #
+--echo # MDEV-9319 ALTER from a bigger to a smaller blob type truncates too much data
+--echo #
+SET NAMES utf8;
+CREATE TABLE t1 (a TEXT CHARACTER SET utf8);
+INSERT INTO t1 VALUES (REPEAT('Ａ',100));
+SELECT OCTET_LENGTH(a) FROM t1;
+ALTER TABLE t1 MODIFY a TINYTEXT CHARACTER SET utf8;
+SELECT OCTET_LENGTH(a),a FROM t1;
+DROP TABLE t1;
+
 --echo #
 --echo # End of 5.5 tests
 --echo #

mysql-test/t/ctype_utf8mb4.test

@@ -1826,6 +1826,18 @@ DROP TABLE t1;
 
 --echo # End of test for Bug#13581962,Bug#14096619
 
+--echo #
+--echo # MDEV-9319 ALTER from a bigger to a smaller blob type truncates too much data
+--echo #
+SET NAMES utf8mb4;
+CREATE TABLE t1 (a TEXT CHARACTER SET utf8mb4);
+INSERT INTO t1 VALUES (REPEAT('😎',100));
+SELECT OCTET_LENGTH(a) FROM t1;
+ALTER TABLE t1 MODIFY a TINYTEXT CHARACTER SET utf8mb4;
+SELECT OCTET_LENGTH(a),a FROM t1;
+DROP TABLE t1;
+
+
 --echo #
 --echo # End of 5.5 tests
 --echo #

mysql-test/t/type_blob.test

@@ -643,6 +643,10 @@ DROP TABLE t1;
 
 --echo End of 5.1 tests
 
+--echo #
+--echo # Start of 5.5 tests
+--echo #
+
 #
 # Problem when comparing blobs #778901
 #
@@ -651,3 +655,24 @@ CREATE TABLE t1 ( f1 blob, f2 blob );
 INSERT INTO t1 VALUES ('','');
 SELECT f1,f2,"found row" FROM t1 WHERE f1 = f2 ;
 DROP TABLE t1;
+
+--echo #
+--echo # MDEV-9319 ALTER from a bigger to a smaller blob type truncates too much data
+--echo #
+CREATE TABLE t1 (a MEDIUMBLOB);
+INSERT INTO t1 VALUES (REPEAT(0x61,128000));
+SELECT LENGTH(a) FROM t1;
+ALTER TABLE t1 MODIFY a BLOB;
+SELECT LENGTH(a) FROM t1;
+DROP TABLE t1;
+
+CREATE TABLE t1 (a BLOB);
+INSERT INTO t1 VALUES (REPEAT(0x61,65000));
+SELECT LENGTH(a) FROM t1;
+ALTER TABLE t1 MODIFY a TINYBLOB;
+SELECT LENGTH(a) FROM t1;
+DROP TABLE t1;
+
+--echo #
+--echo # End of 5.5 tests
+--echo #

sql/field.cc

@@ -7068,6 +7068,35 @@ uint32 Field_blob::get_length(const uchar *pos, uint packlength_arg)
 }
 
 
+/**
+  Copy a value from another BLOB field of the same character set.
+  This method is used by Copy_field, e.g. during ALTER TABLE.
+*/
+int Field_blob::copy_value(Field_blob *from)
+{
+  DBUG_ASSERT(field_charset == from->charset());
+  int rc= 0;
+  uint32 length= from->get_length();
+  uchar *data;
+  from->get_ptr(&data);
+  if (packlength < from->packlength)
+  {
+    int well_formed_errors;
+    set_if_smaller(length, Field_blob::max_data_length());
+    length= field_charset->cset->well_formed_len(field_charset,
+                                                 (const char *) data,
+                                                 (const char *) data + length,
+                                                 length, &well_formed_errors);
+    rc= report_if_important_data((const char *) data + length,
+                                 (const char *) data + from->get_length(),
+                                 true);
+  }
+  store_length(length);
+  bmove(ptr + packlength, (uchar*) &data, sizeof(char*));
+  return rc;
+}
+
+
 int Field_blob::store(const char *from,uint length,CHARSET_INFO *cs)
 {
   ASSERT_COLUMN_MARKED_FOR_WRITE_OR_COMPUTED;

sql/field.h

@@ -1830,6 +1830,11 @@ protected:
   */
   String value;
   
+  void store_length(uchar *i_ptr, uint i_packlength, uint32 i_number);
+  inline void store_length(uint32 number)
+  {
+    store_length(ptr, packlength, number);
+  }
 public:
   Field_blob(uchar *ptr_arg, uchar *null_ptr_arg, uchar null_bit_arg,
 	     enum utype unireg_check_arg, const char *field_name_arg,
@@ -1902,11 +1907,6 @@ public:
   int reset(void) { bzero(ptr, packlength+sizeof(uchar*)); return 0; }
   void reset_fields() { bzero((uchar*) &value,sizeof(value)); }
   uint32 get_field_buffer_size(void) { return value.alloced_length(); }
-  void store_length(uchar *i_ptr, uint i_packlength, uint32 i_number);
-  inline void store_length(uint32 number)
-  {
-    store_length(ptr, packlength, number);
-  }
   inline uint32 get_length(uint row_offset= 0)
   { return get_length(ptr+row_offset, this->packlength); }
   uint32 get_length(const uchar *ptr, uint packlength);
@@ -1935,6 +1935,7 @@ public:
   {
     set_ptr_offset(0, length, data);
   }
+  int copy_value(Field_blob *from);
   uint get_key_image(uchar *buff,uint length, imagetype type);
   void set_key_image(const uchar *buff,uint length);
   void sql_type(String &str) const;

sql/field_conv.cc

@@ -332,9 +332,7 @@ static void do_copy_next_number(Copy_field *copy)
 
 static void do_copy_blob(Copy_field *copy)
 {
-  ulong length=((Field_blob*) copy->from_field)->get_length();
-  ((Field_blob*) copy->to_field)->store_length(length);
-  memcpy(copy->to_ptr, copy->from_ptr, sizeof(char*));
+  ((Field_blob*) copy->to_field)->copy_value(((Field_blob*) copy->from_field));
 }
 
 static void do_conv_blob(Copy_field *copy)
@@ -709,13 +707,8 @@ Copy_field::get_copy_func(Field *to,Field *from)
     if (!(from->flags & BLOB_FLAG) || from->charset() != to->charset())
       return do_conv_blob;
     if (from_length != to_length)
-    {
-      // Correct pointer to point at char pointer
-      to_ptr+=   to_length - to->table->s->blob_ptr_size;
-      from_ptr+= from_length- from->table->s->blob_ptr_size;
       return do_copy_blob;
   }
-  }
   else
   {
     if (to->real_type() == MYSQL_TYPE_BIT ||