mmSyncRead

fn mmSyncRead(file: File, memory: []u8, offset: u64) File.ReadPositionalError!void {
    if (is_windows) {
        var i: usize = 0;
        while (true) {
            const buf = memory[i..];
            if (buf.len == 0) break;
            const n = try readFilePositionalWindows(file, buf, offset + i);
            if (n == 0) {
                @memset(memory[i..], 0);
                break;
            }
            i += n;
        }
    } else if (native_os == .wasi and !builtin.link_libc) {
        var i: usize = 0;
        const syscall: Syscall = try .start();
        while (true) {
            const buf = memory[i..];
            if (buf.len == 0) {
                syscall.finish();
                break;
            }
            var n: usize = undefined;
            const vec: std.os.wasi.iovec_t = .{ .base = buf.ptr, .len = buf.len };
            switch (std.os.wasi.fd_pread(file.handle, (&vec)[0..1], 1, offset + i, &n)) {
                .SUCCESS => {
                    if (n == 0) {
                        syscall.finish();
                        @memset(memory[i..], 0);
                        break;
                    }
                    i += n;
                    try syscall.checkCancel();
                    continue;
                },
                .INTR, .TIMEDOUT => {
                    try syscall.checkCancel();
                    continue;
                },
                .NOTCONN => |err| return syscall.errnoBug(err), // not a socket
                .CONNRESET => |err| return syscall.errnoBug(err), // not a socket
                .BADF => |err| return syscall.errnoBug(err), // use after free
                .INVAL => |err| return syscall.errnoBug(err),
                .FAULT => |err| return syscall.errnoBug(err), // segmentation fault
                .AGAIN => |err| return syscall.errnoBug(err),
                .IO => return syscall.fail(error.InputOutput),
                .ISDIR => return syscall.fail(error.IsDir),
                .NOBUFS => return syscall.fail(error.SystemResources),
                .NOMEM => return syscall.fail(error.SystemResources),
                .NXIO => return syscall.fail(error.Unseekable),
                .SPIPE => return syscall.fail(error.Unseekable),
                .OVERFLOW => return syscall.fail(error.Unseekable),
                .NOTCAPABLE => return syscall.fail(error.AccessDenied),
                else => |err| return syscall.unexpectedErrno(err),
            }
        }
    } else {
        var i: usize = 0;
        const syscall: Syscall = try .start();
        while (true) {
            const buf = memory[i..];
            if (buf.len == 0) {
                syscall.finish();
                break;
            }
            const rc = pread_sym(file.handle, buf.ptr, buf.len, @intCast(offset + i));
            switch (posix.errno(rc)) {
                .SUCCESS => {
                    const n: usize = @intCast(rc);
                    if (n == 0) {
                        syscall.finish();
                        @memset(memory[i..], 0);
                        break;
                    }
                    i += n;
                    try syscall.checkCancel();
                    continue;
                },
                .INTR, .TIMEDOUT => {
                    try syscall.checkCancel();
                    continue;
                },
                .NXIO => return syscall.fail(error.Unseekable),
                .SPIPE => return syscall.fail(error.Unseekable),
                .OVERFLOW => return syscall.fail(error.Unseekable),
                .NOBUFS => return syscall.fail(error.SystemResources),
                .NOMEM => return syscall.fail(error.SystemResources),
                .AGAIN => return syscall.fail(error.WouldBlock),
                .IO => return syscall.fail(error.InputOutput),
                .ISDIR => return syscall.fail(error.IsDir),
                .NOTCONN => |err| return syscall.errnoBug(err), // not a socket
                .CONNRESET => |err| return syscall.errnoBug(err), // not a socket
                .INVAL => |err| return syscall.errnoBug(err),
                .FAULT => |err| return syscall.errnoBug(err),
                .BADF => |err| return syscall.errnoBug(err), // use after free
                else => |err| return syscall.unexpectedErrno(err),
            }
        }
    }
}