@ -77,7 +77,7 @@ psprintf(const char *fmt,...)
* pvsnprintf * pvsnprintf
* *
* Attempt to format text data under the control of fmt ( an sprintf - style * Attempt to format text data under the control of fmt ( an sprintf - style
* format string ) and insert it into buf ( which has length len , len > 0 ) . * format string ) and insert it into buf ( which has length len ) .
* *
* If successful , return the number of bytes emitted , not counting the * If successful , return the number of bytes emitted , not counting the
* trailing zero byte . This will always be strictly less than len . * trailing zero byte . This will always be strictly less than len .
@ -89,14 +89,11 @@ psprintf(const char *fmt,...)
* Other error cases do not return , but exit via elog ( ERROR ) or exit ( ) . * Other error cases do not return , but exit via elog ( ERROR ) or exit ( ) .
* Hence , this shouldn ' t be used inside libpq . * Hence , this shouldn ' t be used inside libpq .
* *
* This function exists mainly to centralize our workarounds for
* non - C99 - compliant vsnprintf implementations . Generally , any call that
* pays any attention to the return value should go through here rather
* than calling snprintf or vsnprintf directly .
*
* Note that the semantics of the return value are not exactly C99 ' s . * Note that the semantics of the return value are not exactly C99 ' s .
* First , we don ' t promise that the estimated buffer size is exactly right ; * First , we don ' t promise that the estimated buffer size is exactly right ;
* callers must be prepared to loop multiple times to get the right size . * callers must be prepared to loop multiple times to get the right size .
* ( Given a C99 - compliant vsnprintf , that won ' t happen , but it is rumored
* that some implementations don ' t always return the same value . . . )
* Second , we return the recommended buffer size , not one less than that ; * Second , we return the recommended buffer size , not one less than that ;
* this lets overflow concerns be handled here rather than in the callers . * this lets overflow concerns be handled here rather than in the callers .
*/ */
@ -105,28 +102,10 @@ pvsnprintf(char *buf, size_t len, const char *fmt, va_list args)
{ {
int nprinted ; int nprinted ;
Assert ( len > 0 ) ;
errno = 0 ;
/*
* Assert check here is to catch buggy vsnprintf that overruns the
* specified buffer length . Solaris 7 in 64 - bit mode is an example of a
* platform with such a bug .
*/
# ifdef USE_ASSERT_CHECKING
buf [ len - 1 ] = ' \0 ' ;
# endif
nprinted = vsnprintf ( buf , len , fmt , args ) ; nprinted = vsnprintf ( buf , len , fmt , args ) ;
Assert ( buf [ len - 1 ] = = ' \0 ' ) ; /* We assume failure means the fmt is bogus, hence hard failure is OK */
if ( unlikely ( nprinted < 0 ) )
/*
* If vsnprintf reports an error other than ENOMEM , fail . The possible
* causes of this are not user - facing errors , so elog should be enough .
*/
if ( nprinted < 0 & & errno ! = 0 & & errno ! = ENOMEM )
{ {
# ifndef FRONTEND # ifndef FRONTEND
elog ( ERROR , " vsnprintf failed: %m " ) ; elog ( ERROR , " vsnprintf failed: %m " ) ;
@ -136,42 +115,21 @@ pvsnprintf(char *buf, size_t len, const char *fmt, va_list args)
# endif # endif
} }
/*
if ( ( size_t ) nprinted < len )
* Note : some versions of vsnprintf return the number of chars actually
* stored , not the total space needed as C99 specifies . And at least one
* returns - 1 on failure . Be conservative about believing whether the
* print worked .
*/
if ( nprinted > = 0 & & ( size_t ) nprinted < len - 1 )
{ {
/* Success. Note nprinted does not include trailing null. */ /* Success. Note nprinted does not include trailing null. */
return ( size_t ) nprinted ; return ( size_t ) nprinted ;
} }
if ( nprinted > = 0 & & ( size_t ) nprinted > len )
{
/*
* This appears to be a C99 - compliant vsnprintf , so believe its
* estimate of the required space . ( If it ' s wrong , the logic will
* still work , but we may loop multiple times . ) Note that the space
* needed should be only nprinted + 1 bytes , but we ' d better allocate
* one more than that so that the test above will succeed next time .
*
* In the corner case where the required space just barely overflows ,
* fall through so that we ' ll error out below ( possibly after
* looping ) .
*/
if ( ( size_t ) nprinted < = MaxAllocSize - 2 )
return nprinted + 2 ;
}
/*
/*
* Buffer overrun , and we don ' t know how much space is needed . Estimate * We assume a C99 - compliant vsnprintf , so believe its estimate of the
* twice the previous buffer size , but not more than MaxAllocSize ; if we * required space , and add one for the trailing null . ( If it ' s wrong , the
* are already at MaxAllocSize , choke . Note we use this palloc - oriented * logic will still work , but we may loop multiple times . )
* overflow limit even when in frontend . *
* Choke if the required space would exceed MaxAllocSize . Note we use
* this palloc - oriented overflow limit even when in frontend .
*/ */
if ( len > = MaxAllocSize ) if ( unlikely ( ( size_t ) nprinted > MaxAllocSize - 1 ) )
{ {
# ifndef FRONTEND # ifndef FRONTEND
ereport ( ERROR , ereport ( ERROR ,
@ -183,8 +141,5 @@ pvsnprintf(char *buf, size_t len, const char *fmt, va_list args)
# endif # endif
} }
if ( len > = MaxAllocSize / 2 ) return nprinted + 1 ;
return MaxAllocSize ;
return len * 2 ;
} }
Tom Lane
7 years ago