I have a connection from a postgres client (Windows 7) to a remote Postgres server (Ubuntu) - Postgres version 9.5.
The postgres client is a c-program using embedded sql (libecpg.dll).
When I pull the network cable after the connection is established, I get:
Unhandled exception at 0x1000bca0 in ...exe: 0xC0000005: Access violation reading location 0x00000000
In the debugger call stack, the last 4 entries are for
libecpg.dll: libecpg.dll!100047f7(),
libecpg.dll!100041fd(),
libecpg.dll!10008bc8(),
libecpg.dll!10008431(), ....
Did further research:
The access violation occurs in function fmtstr() because the parameter value is NULL
static void
fmtstr(char *value, int leftjust, int minlen, int maxwidth, int pointflag, PrintfTarget *target)
{
int padlen,
vallen; /* amount to pad */
/*
* If a maxwidth (precision) is specified, we must not fetch more bytes
* than that.
*/
if (pointflag)
vallen = pg_strnlen(value, maxwidth);
else
vallen = strlen(value); // value == NULL
...
The parameter value is filled from a va_arg() call in function dopr():
static void dopr(PrintfTarget *target, const char *format, va_list args)
...
case 's':
if (!have_star)
{
if (pointflag)
precision = accum;
else
fieldwidth = accum;
}
if (have_dollar)
strvalue = argvalues[fmtpos].cptr;
else
strvalue = va_arg(args, char *);
fmtstr(strvalue, leftjust, fieldwidth, precision, pointflag,
target);
break;
...
The access violation only occurs if I pull the network cable but not if I deactivate the network.
In function ecpg_execute():
if (stmt->statement_type == ECPGst_execute) {
...
}
else
{
if (stmt->nparams == 0)
{
**stmt->results** = PQexec(stmt->connection->connection, stmt->command);
ecpg_log("ecpg_execute on line %d: using PQexec\n", stmt->lineno);
}
else
{
stmt->results = PQexecParams(stmt->connection->connection, stmt->command, stmt->nparams, NULL, (const char *const *) stmt->paramvalues, NULL, NULL, 0);
...
}
When pulling the network cable stmt->results is not NULL
When deactivating the network stmt->results is NULL
