Description:
Hi,
I'm developing some MySQL-related libraries on Fedora 22 Workstation.
My database server running on its own machine uses the following packages:
community-mysql.x86_64 5.6.24-3.fc22
community-mysql-common.x86_64 5.6.24-3.fc22
community-mysql-errmsg.x86_64 5.6.24-3.fc22
community-mysql-server.x86_64 5.6.24-3.fc22
My database client running on its own machine too uses the following packages:
community-mysql.x86_64 5.6.24-3.fc22
community-mysql-common.x86_64 5.6.24-3.fc22
community-mysql-devel.x86_64 5.6.24-3.fc22
community-mysql-libs.x86_64 5.6.24-3.fc22
The problem I'm encountering is in the use of the mysql_stmt_fetch_column() function.
According to its documentation, this function should be able to fetch the value of a column
in pieces. Therefore, one of my library test cases is to make sure that the fetching of a
column by chunks works correctly. My test table contains two rows. The value of the TEXT
column in the first row is "The quick brown fox jumps over the lazy dog near the bank of the
river." and the second row contains "ODBC C data types indicate the data type of C buffers
used to store data in the application.". When the mysql_stmt_fetch_column() function fetches
the value of the TEXT column, the first chunk is OK but the succeeding chunks have the
incorrect values.
I have also verified that if I fetch the whole column in one go, the resulting value is OK.
However, fetching in chunks is still desired because if the column so happens to be in the
megabytes or even gigabytes in size, fetching in one go is not effective use of memory.
I'm supplying a test program (testprog.cpp) in how to repeat which illustrates this problem.
The test program was compiled using the following command line:
g++ -L/usr/lib64/mysql -lmysqlclient -m64 -o testprog -std=c++14 testprog.cpp
This is the contents of the output file (testprog.txt) of the test program:
File: testprog.txt
0000 : 54 68 65 20 71 75 69 63-6B 20 62 72 6F 77 6E 20 : The quick brown
0010 : D8 CE 3E 7C FF 7F 00 00-D7 CE 3E 7C FF 7F 00 00 : ..>|......>|....
0020 : E0 CE 3E 7C FF 7F 00 00-54 CF 3E 7C FF 7F 00 00 : ..>|....T.>|....
0030 : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................
0040 : 00 00 00 00 00 00 00 - : .......
Note from the above hex dump that the first 16 bytes are correct but the rest are not.
Regards,
Leo
How to repeat:
Compile and run this test program (testprog.cpp):
NOTE: Replace the parameters of mysql_real_connect() function according to your test environment.
#include <cassert>
#include <cstring>
#include <fstream>
#include <mysql/mysql.h>
int main()
{
auto res1 = mysql_library_init(0, nullptr, nullptr);
assert(res1 == 0);
MYSQL mysql;
mysql_init(&mysql);
auto res2 = mysql_options(&mysql, MYSQL_SET_CHARSET_NAME, "utf8");
assert(res2 == 0);
auto res3 = mysql_real_connect(&mysql, "host/ip", "user", "password", "database", 0, nullptr, 0);
assert(res3 != nullptr);
auto mysql_stmt = mysql_stmt_init(&mysql);
assert(mysql_stmt != nullptr);
auto res4 = mysql_stmt_prepare(mysql_stmt, "SELECT aclob FROM testtbl LIMIT 1", 25);
assert(res4 == 0);
auto res5 = mysql_stmt_execute(mysql_stmt);
assert(res5 == 0);
MYSQL_BIND mysql_bind1[1];
char buffer1[1];
unsigned long length1;
my_bool is_null1;
std::memset(mysql_bind1, 0, sizeof(mysql_bind1));
mysql_bind1[0].buffer_type = MYSQL_TYPE_STRING;
mysql_bind1[0].buffer = buffer1;
mysql_bind1[0].buffer_length = 0;
mysql_bind1[0].length = &length1;
mysql_bind1[0].is_null = &is_null1;
mysql_bind1[0].is_unsigned = 0;
mysql_bind1[0].error = nullptr;
auto res6 = mysql_stmt_bind_result(mysql_stmt, mysql_bind1);
assert(res6 == 0);
auto res7 = mysql_stmt_fetch(mysql_stmt);
assert(res7 == MYSQL_DATA_TRUNCATED);
std::fstream file("testprog.txt", std::ios_base::out|std::ios_base::trunc|std::ios_base::binary);
assert(file.is_open());
MYSQL_BIND mysql_bind2[1];
char buffer2[16];
unsigned long length2;
my_bool is_null2;
std::memset(mysql_bind2, 0, sizeof(mysql_bind2));
mysql_bind2[0].buffer_type = MYSQL_TYPE_STRING;
mysql_bind2[0].buffer = buffer2;
mysql_bind2[0].buffer_length = sizeof(buffer2);
mysql_bind2[0].length = &length2;
mysql_bind2[0].is_null = &is_null2;
mysql_bind2[0].is_unsigned = 0;
mysql_bind2[0].error = nullptr;
for (unsigned long offset = 0; offset < length1; offset += length2)
{
auto res8 = mysql_stmt_fetch_column(mysql_stmt, mysql_bind2, 0, offset);
assert(res8 == 0);
file.write(buffer2, length2);
assert(!file.fail());
}
file.close();
mysql_stmt_free_result(mysql_stmt);
mysql_stmt_close(mysql_stmt);
mysql_close(&mysql);
mysql_library_end();
return 0;
}
Suggested fix:
Fix mysql_stmt_fetch_column() function such that the correct data is transferred to the receiving buffer on succeeding calls to the function.
Description: Hi, I'm developing some MySQL-related libraries on Fedora 22 Workstation. My database server running on its own machine uses the following packages: community-mysql.x86_64 5.6.24-3.fc22 community-mysql-common.x86_64 5.6.24-3.fc22 community-mysql-errmsg.x86_64 5.6.24-3.fc22 community-mysql-server.x86_64 5.6.24-3.fc22 My database client running on its own machine too uses the following packages: community-mysql.x86_64 5.6.24-3.fc22 community-mysql-common.x86_64 5.6.24-3.fc22 community-mysql-devel.x86_64 5.6.24-3.fc22 community-mysql-libs.x86_64 5.6.24-3.fc22 The problem I'm encountering is in the use of the mysql_stmt_fetch_column() function. According to its documentation, this function should be able to fetch the value of a column in pieces. Therefore, one of my library test cases is to make sure that the fetching of a column by chunks works correctly. My test table contains two rows. The value of the TEXT column in the first row is "The quick brown fox jumps over the lazy dog near the bank of the river." and the second row contains "ODBC C data types indicate the data type of C buffers used to store data in the application.". When the mysql_stmt_fetch_column() function fetches the value of the TEXT column, the first chunk is OK but the succeeding chunks have the incorrect values. I have also verified that if I fetch the whole column in one go, the resulting value is OK. However, fetching in chunks is still desired because if the column so happens to be in the megabytes or even gigabytes in size, fetching in one go is not effective use of memory. I'm supplying a test program (testprog.cpp) in how to repeat which illustrates this problem. The test program was compiled using the following command line: g++ -L/usr/lib64/mysql -lmysqlclient -m64 -o testprog -std=c++14 testprog.cpp This is the contents of the output file (testprog.txt) of the test program: File: testprog.txt 0000 : 54 68 65 20 71 75 69 63-6B 20 62 72 6F 77 6E 20 : The quick brown 0010 : D8 CE 3E 7C FF 7F 00 00-D7 CE 3E 7C FF 7F 00 00 : ..>|......>|.... 0020 : E0 CE 3E 7C FF 7F 00 00-54 CF 3E 7C FF 7F 00 00 : ..>|....T.>|.... 0030 : 00 00 00 00 00 00 00 00-00 00 00 00 00 00 00 00 : ................ 0040 : 00 00 00 00 00 00 00 - : ....... Note from the above hex dump that the first 16 bytes are correct but the rest are not. Regards, Leo How to repeat: Compile and run this test program (testprog.cpp): NOTE: Replace the parameters of mysql_real_connect() function according to your test environment. #include <cassert> #include <cstring> #include <fstream> #include <mysql/mysql.h> int main() { auto res1 = mysql_library_init(0, nullptr, nullptr); assert(res1 == 0); MYSQL mysql; mysql_init(&mysql); auto res2 = mysql_options(&mysql, MYSQL_SET_CHARSET_NAME, "utf8"); assert(res2 == 0); auto res3 = mysql_real_connect(&mysql, "host/ip", "user", "password", "database", 0, nullptr, 0); assert(res3 != nullptr); auto mysql_stmt = mysql_stmt_init(&mysql); assert(mysql_stmt != nullptr); auto res4 = mysql_stmt_prepare(mysql_stmt, "SELECT aclob FROM testtbl LIMIT 1", 25); assert(res4 == 0); auto res5 = mysql_stmt_execute(mysql_stmt); assert(res5 == 0); MYSQL_BIND mysql_bind1[1]; char buffer1[1]; unsigned long length1; my_bool is_null1; std::memset(mysql_bind1, 0, sizeof(mysql_bind1)); mysql_bind1[0].buffer_type = MYSQL_TYPE_STRING; mysql_bind1[0].buffer = buffer1; mysql_bind1[0].buffer_length = 0; mysql_bind1[0].length = &length1; mysql_bind1[0].is_null = &is_null1; mysql_bind1[0].is_unsigned = 0; mysql_bind1[0].error = nullptr; auto res6 = mysql_stmt_bind_result(mysql_stmt, mysql_bind1); assert(res6 == 0); auto res7 = mysql_stmt_fetch(mysql_stmt); assert(res7 == MYSQL_DATA_TRUNCATED); std::fstream file("testprog.txt", std::ios_base::out|std::ios_base::trunc|std::ios_base::binary); assert(file.is_open()); MYSQL_BIND mysql_bind2[1]; char buffer2[16]; unsigned long length2; my_bool is_null2; std::memset(mysql_bind2, 0, sizeof(mysql_bind2)); mysql_bind2[0].buffer_type = MYSQL_TYPE_STRING; mysql_bind2[0].buffer = buffer2; mysql_bind2[0].buffer_length = sizeof(buffer2); mysql_bind2[0].length = &length2; mysql_bind2[0].is_null = &is_null2; mysql_bind2[0].is_unsigned = 0; mysql_bind2[0].error = nullptr; for (unsigned long offset = 0; offset < length1; offset += length2) { auto res8 = mysql_stmt_fetch_column(mysql_stmt, mysql_bind2, 0, offset); assert(res8 == 0); file.write(buffer2, length2); assert(!file.fail()); } file.close(); mysql_stmt_free_result(mysql_stmt); mysql_stmt_close(mysql_stmt); mysql_close(&mysql); mysql_library_end(); return 0; } Suggested fix: Fix mysql_stmt_fetch_column() function such that the correct data is transferred to the receiving buffer on succeeding calls to the function.