Function lseek_END [src]

Repositions read/write file offset relative to the end.

Prototype

pub fn lseek_END(fd: fd_t, offset: i64) SeekError!void

Parameters

fd: fd_toffset: i64

Possible Errors

AccessDenied

In WASI, this error may occur when the file descriptor does not hold the required rights to seek on it.

Unexpected UnexpectedError

The Operating System returned an undocumented error code.

This error is in theory not possible, but it would be better to handle this error than to invoke undefined behavior.

When this error code is observed, it usually means the Zig Standard Library needs a small patch to add the error code to the error set for the respective function.

Unseekable

Source

  pub fn lseek_END(fd: fd_t, offset: i64) SeekError!void {
    if (native_os == .linux and !builtin.link_libc and @sizeOf(usize) == 4) {
        var result: u64 = undefined;
        switch (errno(system.llseek(fd, @bitCast(offset), &result, SEEK.END))) {
            .SUCCESS => return,
            .BADF => unreachable, // always a race condition
            .INVAL => return error.Unseekable,
            .OVERFLOW => return error.Unseekable,
            .SPIPE => return error.Unseekable,
            .NXIO => return error.Unseekable,
            else => |err| return unexpectedErrno(err),
        }
    }
    if (native_os == .windows) {
        return windows.SetFilePointerEx_END(fd, offset);
    }
    if (native_os == .wasi and !builtin.link_libc) {
        var new_offset: wasi.filesize_t = undefined;
        switch (wasi.fd_seek(fd, offset, .END, &new_offset)) {
            .SUCCESS => return,
            .BADF => unreachable, // always a race condition
            .INVAL => return error.Unseekable,
            .OVERFLOW => return error.Unseekable,
            .SPIPE => return error.Unseekable,
            .NXIO => return error.Unseekable,
            .NOTCAPABLE => return error.AccessDenied,
            else => |err| return unexpectedErrno(err),
        }
    }
    const lseek_sym = if (lfs64_abi) system.lseek64 else system.lseek;
    switch (errno(lseek_sym(fd, @bitCast(offset), SEEK.END))) {
        .SUCCESS => return,
        .BADF => unreachable, // always a race condition
        .INVAL => return error.Unseekable,
        .OVERFLOW => return error.Unseekable,
        .SPIPE => return error.Unseekable,
        .NXIO => return error.Unseekable,
        else => |err| return unexpectedErrno(err),
    }
}  