On Sun, 3 May 2020, Noel Duffy via fpc-pascal wrote:
Using fpc 3.0.4 on Fedora 30.
I've just started using the StrToHostAddr6 function in the sockets unit
to parse IPv6 addresses. I've found a couple of issues with it.
1. Even if address parsing fails, StrToHostAddr6 doesn't return an
all-zero result in the in6_addr return value. The documentation states
that it does, but my tests show it doesn't.
I fixed that.
The problem is that the StrToHostAddr6 function doesn't set its return
value until the end of the function. If a parse error occurs
mid-function, it zeroes the record in which it's writing the result but
exits without setting the function return value. What gets returned
depends on what's on the stack.
I could have sworn that fpc would detect a function exiting without
setting a return value, but clearly 3.0.4 doesn't.
It checks if the result is assigned. This is done;
But it does not check this for every exit, as far as I know it never has.
2. The second problem is that a colon-separated string containing
hexadecimal values of any length will be parsed and treated as valid by
StrToHostAddr6. E.g, it will parse a string like
"fe80ca2f1::906e:9d2f:a520:4172". The sample program produces this
output for this string:
"fe80ca2f1::906e:9d2f:a520:4172" ->
A2-F1-00-00-00-00-00-00-90-6E-9D-2F-A5-20-41-72-
For the part before the first colon, it has discarded all but the last
two bytes, A2 and F1. But it should not have accepted this string at
all. There can be only four characters between the colons.
If you send a patch for this, I'll apply it.
Neither of these are difficult to fix. But I am curious to know why the
compiler lets a function return without setting a return value and
doesn't at least issue a warning. I know it does in some cases, because
I've often seen the message "Function result doesn't appear to be set".
But maybe that's only if you never set the result, as opposed to setting
it only for some paths through the code.
Exactly.
Michael.
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