MDEV-4513 Valgrind warnings (Conditional jump or move depends on uninitialised...

MDEV-4513 Valgrind warnings (Conditional jump or move depends on uninitialised value) in inflate on UNCOMPRESS

mysql-test/r/func_compress.result

@@ -147,3 +147,11 @@ DROP TABLE t1;
 #
 # End of 5.3 tests
 #
+SELECT UNCOMPRESS(CAST(0 AS BINARY(5)));
+UNCOMPRESS(CAST(0 AS BINARY(5)))
+NULL
+Warnings:
+Warning	1259	ZLIB: Input data corrupted
+#
+# End of 5.5 tests
+#

mysql-test/t/func_compress.test

@@ -136,3 +136,12 @@ DROP TABLE t1;
 --echo #
 --echo # End of 5.3 tests
 --echo #
+
+#
+# MDEV-4513 Valgrind warnings (Conditional jump or move depends on uninitialised value) in inflate on UNCOMPRESS
+#
+SELECT UNCOMPRESS(CAST(0 AS BINARY(5)));
+
+--echo #
+--echo # End of 5.5 tests
+--echo #

sql/item_strfunc.cc

@@ -3720,7 +3720,7 @@ String *Item_func_uncompress::val_str(String *str)
     goto err;
 
   if ((err= uncompress((Byte*)buffer.ptr(), &new_size,
-		       ((const Bytef*)res->ptr())+4,res->length())) == Z_OK)
+		       ((const Bytef*)res->ptr())+4,res->length()-4)) == Z_OK)
   {
     buffer.length((uint32) new_size);
     return &buffer;