Re: pgsql: Make cancel request keys longer

On 09/04/2025 13:28, Heikki Linnakangas wrote:
> On 09/04/2025 12:39, Peter Eisentraut wrote:
>> On 09.04.25 10:53, Heikki Linnakangas wrote:
>>> On 08/04/2025 22:41, Heikki Linnakangas wrote:
>>>> On 08/04/2025 20:06, Peter Eisentraut wrote:
>>>>> While I was looking at this, I suggest to make the first argument 
>>>>> void *.  This is consistent for passing binary data.
>>>>
>>>> Ok, sure.
>>>
>>> On second thoughts, -1 on that. 'void *' is appropriate for functions 
>>> like libc's read() or pq_sendbytes(), where the buffer can point to 
>>> anything. In other words, the caller is expected to have a pointer 
>>> like 'foobar *', and it gets cast to 'void *' when you call the 
>>> function. That's not the case with the cancellation key. The 
>>> cancellation key is just an array of bytes, the caller is expected to 
>>> pass an array of bytes, not a struct.
>>>
>>> The right precedent for that are e.g. SCRAM functions in scram- 
>>> common.h, for example. They use "const uint8 *" for the hashes.
>>>
>>> I'll switch to "const uint *" everywhere that deals with cancel keys. 
>>> There are a few more variables elsewhere in the backend and in libpq.
>>
>> I was having the same second thoughts overnight.  I agree with your 
>> conclusion.
> 
> Here's a patch to change cancellation keys to "uint8 *". I did the same 
> for a few other places, namely the new scram_client_key_binary and 
> scram_server_key_binary fields in pg_conn, and a few libpq functions 
> that started to give compiler warnings after that. There probably would 
> be more code that could be changed to follow this convention, but I 
> didn't look hard. What do you think?
> 
> I'm on the edge with the pg_b64_encode/decode functions, whether they 
> should work on "uint8 *" or "void *". On one hand, you do base64 
> encoding on a byte array, which would support "uint8 *". But on the 
> other hand, you might use it for encoding things with more structure, 
> which would support "void *". I went with "void *", mostly out of 
> convenience as many of the SCRAM functions that currently use 
> pg_b64_encode/decode, use "char *" to represent byte arrays. But 
> arguably those should be changed to use "uint8 *" too.

I went around looking a bit more anyway. Here's a patch to change more 
places to use 'uint8' for byte arrays, in SCRAM and MD5 salts and 
digests and such. It's a bit of code churn, but I think it improves 
readability. Especially the SCRAM code sometimes deals with 
base64-encoded string representations of digests and sometimes with 
decoded byte arrays, and it's helpful to use different datatypes for them.

-- 
Heikki Linnakangas
Neon (https://neon.tech)