Re: Can no longer receive short ASN1 messages

Do you have a reproducer available?

I tried this quickly with the following code (need to link it statically
since I'm hacking into internal interfaces)

#include <stdlib.h>
#include <stdio.h>
#include <openssl/bio.h>
#include <openssl/buffer.h>
#include "internal/asn1.h"

unsigned char msgbuf[] = { 1, 2, 0, 1 };


int main(int argc, char **argv)
{
    BIO *in = BIO_new_mem_buf(msgbuf, 4);
    BUF_MEM *membuf = NULL;

    asn1_d2i_read_bio(in, &membuf);
}

If you step through it with gdb, you can see that the returned BUF_MEM
contains the data in the message buffer, with no hangs.

Best
Neil


On Mon, Mar 9, 2026 at 4:49 PM 'Sands, Daniel N.' via openssl-users <
[email protected]> wrote:

> As of 3.5.x, after an issue having something to do with headers, I can no
> longer receive messages of less than 8 bytes.  As an example, if I only
> need to send a status code as a response, I will send 1 tag byte, 1 length
> byte, and possibly 1 byte indicating an integer status code.  Since this is
> a TCP socket, I keep the socket open for further communication.  The
> receiving side now insists on receiving at least HEADER_SIZE bytes (8)
> before it will do anything, so now both sides are at a stalemate—the
> receiver still waiting for its message, and the sender waiting for further
> communication from the sender.
>
>
>
> I saw in issue 21777 why this was done, but the strategy is not working
> for short messages.  I suggest an alternate strategy where you add a “need”
> variable, which is the very least amount of bytes necessary to decode the
> next part, and want will be some value higher than that.  If “want” bytes
> can be read, awesome.  If it’s stalled between “want” and “need” then just
> go ahead and process it.  If it’s less than “need”, then, and only then, do
> you continue the loop.  Obviously, “need” would only start at 2, since the
> smallest legal DER encoding is 2 bytes (the NULL type).  It would expand if
> the tag or length turn out to be multiple bytes.
>
>
>
> Anyway, is there a workaround for this, other than reducing HEADER_SIZE
> and recompiling, or attaching non-sequitur data just to reach the 8-byte
> minimum?
>
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