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# zx_stream_readv_at

## Summary

Read data from a stream at the given offset.

## Declaration

```c
#include <zircon/syscalls.h>

zx_status_t zx_stream_readv_at(zx_handle_t handle,
                               uint32_t options,
                               zx_off_t offset,
                               zx_iovec_t* vectors,
                               size_t num_vectors,
                               size_t* actual);
```

## Description

`zx_stream_readv_at()` attempts to read bytes from the stream, starting at the
given *offset*, into the buffers specified by *vectors* and *num_vectors*. If
successful, the number of bytes actually read are return via *actual*.

If the given *offset* is beyond the end of the stream, `zx_stream_readv_at()`
will succeed in reading zero bytes.

If a NULL *actual* is passed in, it will be ignored.

Does not advance the seek offset of the stream.

If the contents of *vectors* change during this operation, if any of the buffers
overlap, or if any of the buffers overlap *vectors*, the behavior is unspecified.

*options* is reserved for future use and must be 0.

## Rights

*handle* must be of type **ZX_OBJ_TYPE_STREAM** and have **ZX_RIGHT_READ**.

## Return value

`zx_stream_readv_at()` returns **ZX_OK** on success, and writes into
*actual* (if non-NULL) the exact number of bytes read.

## Errors

**ZX_ERR_BAD_HANDLE**  *handle* is not a valid handle.

**ZX_ERR_WRONG_TYPE**   *handle* is not a stream handle.

**ZX_ERR_ACCESS_DENIED**  *handle* does not have the **ZX_RIGHT_READ** right.

**ZX_ERR_INVALID_ARGS**  vectors is an invalid `zx_iovec_t` or *options* is
nonzero.

**ZX_ERR_NOT_FOUND**  the *vectors* address, or an address specified within
*vectors* does not map to address in address space.

**ZX_ERR_BAD_STATE**  the underlying data source cannot be read.

## See also

 - [`zx_stream_create()`]
 - [`zx_stream_readv()`]
 - [`zx_stream_seek()`]
 - [`zx_stream_writev()`]
 - [`zx_stream_writev_at()`]

[`zx_stream_create()`]: stream_create.md
[`zx_stream_readv()`]: stream_readv.md
[`zx_stream_seek()`]: stream_seek.md
[`zx_stream_writev()`]: stream_writev.md
[`zx_stream_writev_at()`]: stream_writev_at.md