Function readv [src]

Number of bytes read is returned. Upon reading end-of-file, zero is returned. For POSIX systems, if fd is opened in non blocking mode, the function will return error.WouldBlock when EAGAIN is received. On Windows, if the application has a global event loop enabled, I/O Completion Ports are used to perform the I/O. error.WouldBlock is not possible on Windows. This operation is non-atomic on the following systems: Windows On these systems, the read races with concurrent writes to the same file descriptor. This function assumes that all vectors, including zero-length vectors, have a pointer within the address space of the application.

Prototype

pub fn readv(fd: fd_t, iov: []const iovec) ReadError!usize

Parameters

fd: fd_tiov: []const iovec

Possible Errors

AccessDenied

In WASI, this error occurs when the file descriptor does not hold the required rights to read from it.

BrokenPipe

Canceled

reading a timerfd with CANCEL_ON_SET will lead to this error when the clock goes through a discontinuous change

ConnectionResetByPeer

ConnectionTimedOut

InputOutput

IsDir

LockViolation

Unable to read file due to lock.

NotOpenForReading

OperationAborted

ProcessNotFound

This error occurs in Linux if the process to be read from no longer exists.

SocketNotConnected

SystemResources

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.

WouldBlock

This error occurs when no global event loop is configured, and reading from the file descriptor would block.

Source

  pub fn readv(fd: fd_t, iov: []const iovec) ReadError!usize {
    if (native_os == .windows) {
        // TODO improve this to use ReadFileScatter
        if (iov.len == 0) return 0;
        const first = iov[0];
        return read(fd, first.base[0..first.len]);
    }
    if (native_os == .wasi and !builtin.link_libc) {
        var nread: usize = undefined;
        switch (wasi.fd_read(fd, iov.ptr, iov.len, &nread)) {
            .SUCCESS => return nread,
            .INTR => unreachable,
            .INVAL => unreachable,
            .FAULT => unreachable,
            .AGAIN => unreachable, // currently not support in WASI
            .BADF => return error.NotOpenForReading, // can be a race condition
            .IO => return error.InputOutput,
            .ISDIR => return error.IsDir,
            .NOBUFS => return error.SystemResources,
            .NOMEM => return error.SystemResources,
            .NOTCONN => return error.SocketNotConnected,
            .CONNRESET => return error.ConnectionResetByPeer,
            .TIMEDOUT => return error.ConnectionTimedOut,
            .NOTCAPABLE => return error.AccessDenied,
            else => |err| return unexpectedErrno(err),
        }
    }

    while (true) {
        const rc = system.readv(fd, iov.ptr, @min(iov.len, IOV_MAX));
        switch (errno(rc)) {
            .SUCCESS => return @intCast(rc),
            .INTR => continue,
            .INVAL => unreachable,
            .FAULT => unreachable,
            .NOENT => return error.ProcessNotFound,
            .AGAIN => return error.WouldBlock,
            .BADF => return error.NotOpenForReading, // can be a race condition
            .IO => return error.InputOutput,
            .ISDIR => return error.IsDir,
            .NOBUFS => return error.SystemResources,
            .NOMEM => return error.SystemResources,
            .NOTCONN => return error.SocketNotConnected,
            .CONNRESET => return error.ConnectionResetByPeer,
            .TIMEDOUT => return error.ConnectionTimedOut,
            else => |err| return unexpectedErrno(err),
        }
    }
}  