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Re: libpq bug? - Mailing list pgsql-general

From	patrick keshishian
Subject	Re: libpq bug?
Date	December 29, 2018 10:37:55
Msg-id	CAN0yQBr=+vfOZxrtGbLMeeb-cT4uDrTvAadFcKOr6pXQ7exx9A@mail.gmail.com Whole thread Raw
In response to	Re: libpq bug? (Igor Korot <ikorot01@gmail.com>)
Responses	Re: libpq bug? (Igor Korot <ikorot01@gmail.com>)
List	pgsql-general

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On Fri, Dec 28, 2018 at 5:40 PM Igor Korot <ikorot01@gmail.com> wrote:

Hi, Patrick,

Here is my new code:

int PostgresDatabase::GetTableOwner (const std::wstring &schemaName,
const std::wstring &tableName, std::wstring &owner,
std::vector<std::wstring> &errorMsg)
{
int result = 0;
std::wstring query = L"SELECT u.usename FROM pg_class c, pg_user
u, pg_namespace n WHERE n.oid = c.relnamespace AND u.usesysid =
c.relowner AND n.nspname = $1 AND relname = $2";
char *values[2];
values[0] = NULL, values[1] = NULL;
int charlength1 = schemaName.length() * sizeof( wchar_t ),
charlength2 = tableName.length() * sizeof( wchar_t );
values[0] = new char[schemaName.length() * sizeof( wchar_t ) + 1];
values[1] = new char[tableName.length() * sizeof( wchar_t ) + 1];
memset( values[0], '\0', schemaName.length() * sizeof( wchar_t ) + 1 );
memset( values[1], '\0', tableName.length() * sizeof( wchar_t ) + 1 );
strcpy( values[0], m_pimpl->m_myconv.to_bytes( schemaName.c_str()
).c_str() );
strcpy( values[1], m_pimpl->m_myconv.to_bytes( tableName.c_str()
).c_str() );
int len1 = (int) schemaName.length() * sizeof( wchar_t );
int len2 = (int) tableName.length() * sizeof( wchar_t );
int length[2] = { len1, len2 };
int formats[2] = { 1, 1 };
PGresult *res = PQexecParams( m_db, m_pimpl->m_myconv.to_bytes(
query.c_str() ).c_str(), 2, NULL, values, length, formats, 1 );
ExecStatusType status = PQresultStatus( res );
if( status != PGRES_COMMAND_OK && status != PGRES_TUPLES_OK )
{
result = 1;
std::wstring err = m_pimpl->m_myconv.from_bytes(
PQerrorMessage( m_db ) );
errorMsg.push_back( L"Error executing query: " + err );
PQclear( res );
}
else
{
owner = m_pimpl->m_myconv.from_bytes( PQgetvalue( res, 0, 0 ) );
}
return result;
}

The charlength2 variable contains the value of 8 and I'm still getting
the same error.

I was hoping someone more versed in C++ would jump in to answer your question. I haven't used C++ in at least a decade.

You need to convert the wchar_t data that wstring stores into UTF-8. Personally, I would use iconv (common enough).

I assume the PostgresDatabase class is your own (?) I would add a helper function to do the conversion. Here is a very rough template for you to adapt if you think it helps you.

#include <err.h>

#include <stdlib.h>

#include <string.h>

#include <iostream>

#include <string>

#include <iconv.h>

class PGDB {

public:

// your stuff ...

iconv_t ic;

PGDB(void) {

setlocale(LC_CTYPE, "");

ic = iconv_open("UTF-8", "wchar_t");

if ((iconv_t)-1 == ic)

errx(1, "iconv_open");

}

~PGDB() {

iconv_close(ic);

}

// caller should free()

char *wchar2utf8(std::wstring const &ws) {

char *in, *buf, *out;

size_t bufsz, inbytes, outbytes;

in = (char *)ws.data();

inbytes = ws.length() * sizeof(wchar_t);

outbytes = inbytes;

bufsz = inbytes + 1; // XXX check for overflow

buf = (char *)calloc(bufsz, 1);

if (NULL == buf)

err(1, NULL); // or throw something

out = buf;

if ((size_t)-1 == iconv(ic, &in, &inbytes, &out, &outbytes))

errx(1, "iconv"); // or throw ...

// TODO ensure inbytes is 0 (meaning all input consumed)

return buf;

}

};

// demo using above PGDB class/code

int main(int argc, char *argv[])

{

char *str;

size_t i, n;

std::wstring tab;

PGDB pg;

tab = L"ºabcß";

str = pg.wchar2utf8(tab);

n = strlen(str);

for (i = 0; i < n; ++i) {

printf("%02hhx ", str[i]);

}

printf("\n");

printf("->%s<-\n", str);

free(str);

return 0;

}

So in GetTableOwner() you'd call wchar2utf8() for the input wstring data and you don't do the new/memset/strcpy. Just remember to free() the returned utf8 string pointers after call to PQexecParams().

cheers,

--patrick

Any idea?

Thank you.

On Fri, Dec 28, 2018 at 5:40 PM patrick keshishian <pkeshish@gmail.com> wrote:
>
> On Fri, Dec 28, 2018 at 3:07 PM Igor Korot <ikorot01@gmail.com> wrote:
>>
>> Hi,
>>
>> On Fri, Dec 28, 2018 at 4:51 PM patrick keshishian <pkeshish@gmail.com> wrote:
>> >
>> >
>> > On Fri, Dec 28, 2018 at 2:00 PM Igor Korot <ikorot01@gmail.com> wrote:
>> >>
>> >> Hi, ALL,
>> >> Following code:
>> >>
>> >> int PostgresDatabase::GetTableOwner (const std::wstring &schemaName,
>> >> const std::wstring &tableName, std::wstring &owner,
>> >> std::vector<std::wstring> &errorMsg)
>> >> {
>> >> int result = 0;
>> >> std::wstring query = L"SELECT u.usename FROM pg_class c, pg_user
>> >> u, pg_namespace n WHERE n.oid = c.relnamespace AND u.usesysid =
>> >> c.relowner AND n.nspname = $1 AND relname = $2";
>> >> char *values[2];
>> >> values[0] = NULL, values[1] = NULL;
>> >> values[0] = new char[schemaName.length() + 1];
>> >> values[1] = new char[tableName.length() + 1];
>> >> memset( values[0], '\0', schemaName.length() + 1 );
>> >> memset( values[1], '\0', tableName.length() + 1 );
>> >> strcpy( values[0], m_pimpl->m_myconv.to_bytes( schemaName.c_str()
>> >> ).c_str() );
>> >> strcpy( values[1], m_pimpl->m_myconv.to_bytes( tableName.c_str()
>> >> ).c_str() );
>> >> int len1 = (int) schemaName.length();
>> >> int len2 = (int) tableName.length();
>> >> int length[2] = { len1, len2 };
>> >> int formats[2] = { 1, 1 };
>> >> PGresult *res = PQexecParams( m_db, m_pimpl->m_myconv.to_bytes(
>> >> query.c_str() ).c_str(), 2, NULL, values, length, formats, 1 );
>> >> ExecStatusType status = PQresultStatus( res );
>> >> if( status != PGRES_COMMAND_OK && status != PGRES_TUPLES_OK )
>> >> {
>> >> result = 1;
>> >> std::wstring err = m_pimpl->m_myconv.from_bytes(
>> >> PQerrorMessage( m_db ) );
>> >> errorMsg.push_back( L"Error executing query: " + err );
>> >> PQclear( res );
>> >> }
>> >> else
>> >> {
>> >> owner = m_pimpl->m_myconv.from_bytes( PQgetvalue( res, 0, 0 ) );
>> >> }
>> >> return result;
>> >> }
>> >>
>> >> when ran with the call of
>> >>
>> >> GetTableOwner( "public", "abcß", owner, errorMsg );
>> >>
>> >> returns:
>> >>
>> >> ERROR: Invalid byte sequence for encoding UTF8.
>> >>
>> >> Does this mean I found the bug in the library?
>> >
>> >
>> > The bug is in your C++ code. "abcß" as tableName.lenght() (wstring) returns 4 (as in four characters) not number of bytes required to represent the intended string: 61 62 63 c3 9f
>> > Since the last character is a 2 bytes in length. Therefore, your call to PQexecParams() specifies a shorter length and hence an invalid UTF-8 sequence.
>> >
>> > Furthermore, your value[] array allocation is in error since wstring::length returns number of characters, not number of bytes. so you will end up with buffer-overflows.
>>
>> So I should use
>> https://stackoverflow.com/questions/9278723/how-can-i-get-the-byte-size-of-stdwstring
>> in both places?
>
>
> size() also returns 4. If you multiply it with sizeof(wchar_t) you will end up with maximum buffers size necessary to hold the string (minus terminating \0), but not the correct length you are after. I am unsure of the "correct" C++ solution.
>
> Sorry,
> --patrick
>
>
>>
>> Thank you.
>>
>> >
>> > HTH,
>> > --patrick
>> >
>> >
>> >>
>> >> Any idea what I can do?
>> >>
>> >> Thank you.
>> >>

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Re: libpq bug? - Mailing list pgsql-general

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