On Fri. 14 May 2022 at 20:04, Max Staudt <max@xxxxxxxxx> wrote:
> On Fri, 13 May 2022 11:38:31 +0900
> Vincent Mailhol <vincent.mailhol@xxxxxxxxx> wrote:
> > > +/* Compare buffer to string length, then compare buffer to fixed
> > > string.
> > > + * This ensures two things:
> > > + * - It flags cases where the fixed string is only the start of
> > > the
> > > + * buffer, rather than exactly all of it.
> > > + * - It avoids byte comparisons in case the length doesn't match.
> > > + *
> > > + * strncmp() cannot be used here because it accepts the following
> > > wrong case:
> > > + * strncmp("CAN ER", "CAN ERROR", 6);
> >
> > What about:
> > strncmp("CAN ER", "CAN ERROR", 7);
> > ?
>
> NAK, because this may overread the buffer by one byte (the NUL byte).
> I am comparing naked bytes, not NUL-terminated strings.
Right, I missed the fact that the first argument was not Null terminated.
Your example is misleading: "CAN ER" is a string literal which is NULL
terminated, it doesn't reflect the use case.
My suggestion: first rename the function to reflect the feature it
brings. For example: elm327_rxbuff_cmp(). Naming it as if it was a
library is also misleading.
Also make it return bool.
For example, I would write it like in this fashion:
/*
* elm327_rxfuff_cmp - compare received buffer against expected error message
* @rxbuff: received buffer. Not NUL-terminated.
* @rxbuff_len: size of @rxbuff.
* @err_msg: error message against which we compare. Must be NUL-terminated.
*
* This function flags cases where the @rxbuff is only the start of @err_msg
* rather than exactly all of it.
*/
static inline bool elm327_rxbuff_cmp(const u8 *rxbuff, size_t
rxbuff_len, const char *err_msg)
{
size_t err_len = strlen(err_msg);
return (rxbuff_len == err_len) && !memcmp(rxbuff, err_msg, rxbuff_len);
}
Naming the arguments instead of using generic terms such as buffer and
string make it easier to follow what you are doing. The important
message is that @rxbuff is not terminated. With this information, it
becomes clear that the string functions can not be used in
replacement, no need to explicitly tell it.
[...]
Other answers are OK.
