SDL/src/audio/SDL_audiodev.c

/*
  Simple DirectMedia Layer
  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>

  This software is provided 'as-is', without any express or implied
  warranty.  In no event will the authors be held liable for any damages
  arising from the use of this software.

  Permission is granted to anyone to use this software for any purpose,
  including commercial applications, and to alter it and redistribute it
  freely, subject to the following restrictions:

  1. The origin of this software must not be misrepresented; you must not
     claim that you wrote the original software. If you use this software
     in a product, an acknowledgment in the product documentation would be
     appreciated but is not required.
  2. Altered source versions must be plainly marked as such, and must not be
     misrepresented as being the original software.
  3. This notice may not be removed or altered from any source distribution.
*/
#include "SDL_internal.h"

// Get the name of the audio device we use for output

#if defined(SDL_AUDIO_DRIVER_NETBSD) || defined(SDL_AUDIO_DRIVER_OSS)

#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h> // For close()

#include "SDL_audiodev_c.h"

#ifndef SDL_PATH_DEV_DSP
#if defined(SDL_PLATFORM_NETBSD) || defined(SDL_PLATFORM_OPENBSD)
#define SDL_PATH_DEV_DSP "/dev/audio"
#else
#define SDL_PATH_DEV_DSP "/dev/dsp"
#endif
#endif
#ifndef SDL_PATH_DEV_DSP24
#define SDL_PATH_DEV_DSP24 "/dev/sound/dsp"
#endif
#ifndef SDL_PATH_DEV_AUDIO
#define SDL_PATH_DEV_AUDIO "/dev/audio"
#endif

static void test_device(const bool recording, const char *fname, int flags, bool (*test)(int fd))
{
    struct stat sb;
    const int audio_fd = open(fname, flags | O_CLOEXEC, 0);
    if (audio_fd >= 0) {
        if ((fstat(audio_fd, &sb) == 0) && (S_ISCHR(sb.st_mode))) {
            const bool okay = test(audio_fd);
            close(audio_fd);
            if (okay) {
                static size_t dummyhandle = 0;
                dummyhandle++;
                SDL_assert(dummyhandle != 0);

                /* Note that spec is NULL; while we are opening the device
                 * endpoint here, the endpoint does not provide any mix format
                 * information,  making this information inaccessible at
                 * enumeration time
                 */
                SDL_AddAudioDevice(recording, fname, NULL, (void *)(uintptr_t)dummyhandle);
            }
        } else {
            close(audio_fd);
        }
    }
}

static bool test_stub(int fd)
{
    return true;
}

static void SDL_EnumUnixAudioDevices_Internal(const bool recording, const bool classic, bool (*test)(int))
{
    const int flags = recording ? OPEN_FLAGS_INPUT : OPEN_FLAGS_OUTPUT;
    const char *audiodev;
    char audiopath[1024];

    if (!test) {
        test = test_stub;
    }

    // Figure out what our audio device is
    audiodev = SDL_getenv("AUDIODEV");
    if (!audiodev) {
        if (classic) {
            audiodev = SDL_PATH_DEV_AUDIO;
        } else {
            struct stat sb;

            // Added support for /dev/sound/\* in Linux 2.4
            if (((stat("/dev/sound", &sb) == 0) && S_ISDIR(sb.st_mode)) && ((stat(SDL_PATH_DEV_DSP24, &sb) == 0) && S_ISCHR(sb.st_mode))) {
                audiodev = SDL_PATH_DEV_DSP24;
            } else {
                audiodev = SDL_PATH_DEV_DSP;
            }
        }
    }
    test_device(recording, audiodev, flags, test);

    if (SDL_strlen(audiodev) < (sizeof(audiopath) - 3)) {
        int instance = 0;
        while (instance <= 64) {
            (void)SDL_snprintf(audiopath, SDL_arraysize(audiopath),
                               "%s%d", audiodev, instance);
            instance++;
            test_device(recording, audiopath, flags, test);
        }
    }
}

void SDL_EnumUnixAudioDevices(const bool classic, bool (*test)(int))
{
    SDL_EnumUnixAudioDevices_Internal(true, classic, test);
    SDL_EnumUnixAudioDevices_Internal(false, classic, test);
}

#endif // Audio device selection