AcornSSL parameter error

I’ve just had my first go at using AcornSSL directly (usually I let AcornHTTP do all the work so this is new to me).

I can create a socket, but when I try to use setsockopt to set the host name, I get “Parameter error (code 22)”. I’ve trimmed it down to the minimal code to make it fail:

#include <stdio.h>
#include "sys/types.h"
#include "sys/socket.h"

extern int __swi(0x50f80) tls_socket(int, int, int); // AcornSSL_Creat
extern int __swi(0x50f8b) tls_setsockopt(int, int, int, void *, int); // AcornSSL_Setsockopt

void connect_socket(char *host)
{
    int sock = tls_socket(AF_INET, SOCK_STREAM, 0);
    tls_setsockopt(sock, SOL_SOCKET, 0x11e0, host, 4); // 11e0 is SO_ACORNSSL_HOSTNAME.
    // Then I'll do an AcornSSL_Connect, but we're not getting this far.
}

int main(void)
{
    connect_socket("www.example.com");
    return 0;
}

What am I doing wrong here? I imagine that I’ve overlooked something simple, as usual :)

I’ve never tried this, but isn’t the last argument to setsockopt the size of the preceding value (host)? It won’t be the size of the pointer, but the thing it’s pointing to.

The docs say to use 4.

optval = pointer to the expected name of the host name
optlen = 4, the size of a string pointer

I did try strlen(host) but got the same error.

It’s based on mbedTLS, so maybe their documentation will be helpful. https://os.mbed.com/docs/mbed-os/v6.15/apis/tlssocket.html https://os.mbed.com/docs/mbed-os/v6.15/mbed-os-api-doxy/class_t_l_s_socket.html

Perhaps the socket has to be connected to the host before passing it to setsockopt?

R3 = pointer to buffer for option value
R4 = size of option value buffer

R4 should be the length of the thing R3 points to, which I’m assuming is a string.

It’s not the best documentation!

R4 should be the length of the thing R3 points to

I don’t mean to be argumentative, but are you sure? Side note: It’s a real pity that so many different things return the same error code.

Perhaps the socket has to be connected to the host before passing it to setsockopt?

Per the docs (my emphasis): “A session can be configured by calling the Getsockopt or Setsockopt SWIs (after Creat or CreateSession, and before Connect) to alter parameters relating to this specific session.”

Are you in a position to re-build the module from source? You could put some different error codes in, temporarily, to narrow down exactly where the error’s coming from.

(That code for the length check is odd. I’d have expected it to be checking for a pointer to a const char * pointing at the string, but that’s not the case, either. I’d say it’s a bug.)

Are you in a position to re-build the module from source? You could put some different error codes in, temporarily, to narrow down exactly where the error’s coming from.

I was thinking about that, but decided that asking the question would be easier :)

I’d say it’s a bug.

If so, it’s probably an old bug that’s had to be retained for API compatibility.

What am I doing wrong here?

I think you’re trying to be too smart and inlining with extern int __swi(0x50f8b) tls_setsockopt(int, int, int, void *, int);

Take a look at the first bullet point in the section In-line SWI Functions in the Acorn C/C++ manual, then count how many arguments your tls_setsockopt has. That final int is pushed on the stack per the APCS, when the SWI expects it in R4. Swap to _swix and all will be fine.

The docs say to use 4.

Yes, the optval is a pointer to a string, therefore optlen is the size of a pointer to a string, which is 4 currently.

AHA! Thanks :)

Next is to figure out why I’m getting a handshake error, but that can keep until later. (Edit: Resolved).