WASI preview1 experiment in D

gistfile1.txt

// this describes how to call a WASI function like fd_write

module core.wasi.preview1;

version(WebAssembly):
extern(C): // disable D mangling

import ldc.attributes;

static assert(byte.alignof == 1);
static assert(ubyte.alignof == 1);
static assert(short.alignof == 2);
static assert(ushort.alignof == 2);
static assert(int.alignof == 4);
static assert(uint.alignof == 4);
static assert(long.alignof == 8);
static assert(ulong.alignof == 8);

alias __wasi_size_t = uint;
alias __wasi_filesize_t = ulong;
alias __wasi_timestamp_t = ulong;
alias __wasi_clockid_t = uint;


enum uint __WASI_CLOCKID_REALTIME = 0;
enum uint __WASI_CLOCKID_MONOTONIC = 1;
enum uint __WASI_CLOCKID_PROCESS_CPUTIME_ID = 2;
enum uint __WASI_CLOCKID_THREAD_CPUTIME_ID  = 3;

alias __wasi_errno_t = ushort;

enum ushort __WASI_ERRNO_SUCCESS = 0;
enum ushort __WASI_ERRNO_2BIG = 1;
enum ushort __WASI_ERRNO_ACCES = 2;
enum ushort __WASI_ERRNO_ADDRINUSE = 3;
enum ushort __WASI_ERRNO_ADDRNOTAVAIL = 4;
enum ushort __WASI_ERRNO_AFNOSUPPORT = 5;
enum ushort __WASI_ERRNO_AGAIN = 6;
enum ushort __WASI_ERRNO_ALREADY = 7;
enum ushort __WASI_ERRNO_BADF = 8;
enum ushort __WASI_ERRNO_BADMSG = 9;
enum ushort __WASI_ERRNO_BUSY = 10;
enum ushort __WASI_ERRNO_CANCELED = 11;
enum ushort __WASI_ERRNO_CHILD = 12;
enum ushort __WASI_ERRNO_CONNABORTED = 13;
enum ushort __WASI_ERRNO_CONNREFUSED = 14;
enum ushort __WASI_ERRNO_CONNRESET = 15;
enum ushort __WASI_ERRNO_DEADLK = 16;
enum ushort __WASI_ERRNO_DESTADDRREQ = 17;
enum ushort __WASI_ERRNO_DOM = 18;
enum ushort __WASI_ERRNO_DQUOT = 19;
enum ushort __WASI_ERRNO_EXIST = 20;
enum ushort __WASI_ERRNO_FAULT = 21;
enum ushort __WASI_ERRNO_FBIG = 22;
enum ushort __WASI_ERRNO_HOSTUNREACH = 23;
enum ushort __WASI_ERRNO_IDRM = 24;
enum ushort __WASI_ERRNO_ILSEQ = 25;
enum ushort __WASI_ERRNO_INPROGRESS = 26;
enum ushort __WASI_ERRNO_INTR = 27;
enum ushort __WASI_ERRNO_INVAL = 28;
enum ushort __WASI_ERRNO_IO = 29;
enum ushort __WASI_ERRNO_ISCONN = 30;
enum ushort __WASI_ERRNO_ISDIR = 31;
enum ushort __WASI_ERRNO_LOOP = 32;
enum ushort __WASI_ERRNO_MFILE = 33;
enum ushort __WASI_ERRNO_MLINK = 34;
enum ushort __WASI_ERRNO_MSGSIZE = 35;
enum ushort __WASI_ERRNO_MULTIHOP = 36;
enum ushort __WASI_ERRNO_NAMETOOLONG = 37;
enum ushort __WASI_ERRNO_NETDOWN = 38;
enum ushort __WASI_ERRNO_NETRESET = 39;
enum ushort __WASI_ERRNO_NETUNREACH = 40;
enum ushort __WASI_ERRNO_NFILE = 41;
enum ushort __WASI_ERRNO_NOBUFS = 42;
enum ushort __WASI_ERRNO_NODEV = 43;
enum ushort __WASI_ERRNO_NOENT = 44;
enum ushort __WASI_ERRNO_NOEXEC = 45;
enum ushort __WASI_ERRNO_NOLCK = 46;
enum ushort __WASI_ERRNO_NOLINK = 47;
enum ushort __WASI_ERRNO_NOMEM = 48;
enum ushort __WASI_ERRNO_NOMSG = 49;
enum ushort __WASI_ERRNO_NOPROTOOPT = 50;
enum ushort __WASI_ERRNO_NOSPC = 51;
enum ushort __WASI_ERRNO_NOSYS = 52;
enum ushort __WASI_ERRNO_NOTCONN = 53;
enum ushort __WASI_ERRNO_NOTDIR = 54;
enum ushort __WASI_ERRNO_NOTEMPTY = 55;
enum ushort __WASI_ERRNO_NOTRECOVERABLE = 56;
enum ushort __WASI_ERRNO_NOTSOCK = 57;
enum ushort __WASI_ERRNO_NOTSUP = 58;
enum ushort __WASI_ERRNO_NOTTY = 59;
enum ushort __WASI_ERRNO_NXIO = 60;
enum ushort __WASI_ERRNO_OVERFLOW = 61;
enum ushort __WASI_ERRNO_OWNERDEAD = 62;
enum ushort __WASI_ERRNO_PERM = 63;
enum ushort __WASI_ERRNO_PIPE = 64;
enum ushort __WASI_ERRNO_PROTO = 65;
enum ushort __WASI_ERRNO_PROTONOSUPPORT = 66;
enum ushort __WASI_ERRNO_PROTOTYPE = 67;
enum ushort __WASI_ERRNO_RANGE = 68;
enum ushort __WASI_ERRNO_ROFS = 69;
enum ushort __WASI_ERRNO_SPIPE = 70;
enum ushort __WASI_ERRNO_SRCH = 71;
enum ushort __WASI_ERRNO_STALE = 72;
enum ushort __WASI_ERRNO_TIMEDOUT = 73;
enum ushort __WASI_ERRNO_TXTBSY = 74;
enum ushort __WASI_ERRNO_XDEV = 75;
enum ushort __WASI_ERRNO_NOTCAPABLE = 76;



alias __wasi_rights_t = ulong;

enum ulong __WASI_RIGHTS_FD_DATASYNC = 1;
enum ulong __WASI_RIGHTS_FD_READ = 2;
enum ulong __WASI_RIGHTS_FD_SEEK = 4;
enum ulong __WASI_RIGHTS_FD_FDSTAT_SET_FLAGS = 8;
enum ulong __WASI_RIGHTS_FD_SYNC = 16;
enum ulong __WASI_RIGHTS_FD_TELL = 32;
enum ulong __WASI_RIGHTS_FD_WRITE = 64;
enum ulong __WASI_RIGHTS_FD_ADVISE = 128;
enum ulong __WASI_RIGHTS_FD_ALLOCATE = 256;
enum ulong __WASI_RIGHTS_PATH_CREATE_DIRECTORY = 512;
enum ulong __WASI_RIGHTS_PATH_CREATE_FILE = 1024;
enum ulong __WASI_RIGHTS_PATH_LINK_SOURCE = 2048;
enum ulong __WASI_RIGHTS_PATH_LINK_TARGET = 4096;
enum ulong __WASI_RIGHTS_PATH_OPEN = 8192;
enum ulong __WASI_RIGHTS_FD_READDIR = 16384;
enum ulong __WASI_RIGHTS_PATH_READLINK = 32768;
enum ulong __WASI_RIGHTS_PATH_RENAME_SOURCE = 65536;
enum ulong __WASI_RIGHTS_PATH_RENAME_TARGET = 131072;
enum ulong __WASI_RIGHTS_PATH_FILESTAT_GET = 262144;
enum ulong __WASI_RIGHTS_PATH_FILESTAT_SET_SIZE = 524288;
enum ulong __WASI_RIGHTS_PATH_FILESTAT_SET_TIMES = 1048576;
enum ulong __WASI_RIGHTS_FD_FILESTAT_GET = 2097152;
enum ulong __WASI_RIGHTS_FD_FILESTAT_SET_SIZE = 4194304;
enum ulong __WASI_RIGHTS_FD_FILESTAT_SET_TIMES = 8388608;
enum ulong __WASI_RIGHTS_PATH_SYMLINK = 16777216;
enum ulong __WASI_RIGHTS_PATH_REMOVE_DIRECTORY = 33554432;
enum ulong __WASI_RIGHTS_PATH_UNLINK_FILE = 67108864;
enum ulong __WASI_RIGHTS_POLL_FD_READWRITE = 134217728;
enum ulong __WASI_RIGHTS_SOCK_SHUTDOWN = 268435456;

alias __wasi_fd_t = uint;

struct __wasi_iovec_t 
{
    /**
     * The address of the buffer to be filled.
     */
    ubyte* buf;

    /**
     * The length of the buffer to be filled.
     */
    __wasi_size_t buf_len;

}

struct __wasi_ciovec_t 
{
    /**
     * The address of the buffer to be written.
     */
    const(ubyte)* buf;

    /**
     * The length of the buffer to be written.
     */
    __wasi_size_t buf_len;
}

alias __wasi_filedelta_t = long;
alias __wasi_whence_t = ubyte;

enum ubyte __WASI_WHENCE_SET = 0;
enum ubyte __WASI_WHENCE_CUR = 1;
enum ubyte __WASI_WHENCE_END = 2;

alias __wasi_dircookie_t = ulong;
alias __wasi_dirnamlen_t = uint;
alias __wasi_inode_t = ulong;

@llvmAttr("wasm-import-module", "wasi_snapshot_preview1") 
__wasi_errno_t fd_write(__wasi_fd_t fd, const(__wasi_ciovec_t)* iovs, size_t iovs_len, __wasi_size_t *nwritten);

Note that not all WASM runtime implement preview1 in the same way, but it seems to be on its way.