class ZeroCopyInputStream

Obtains a chunk of data from the stream.

Preconditions:

* "size" and "data" are not NULL.

Postconditions:

* If the returned value is false, there is no more data to return or

an error occurred. All errors are permanent.

* Otherwise, "size" points to the actual number of bytes read and "data"

points to a pointer to a buffer containing these bytes.

* Ownership of this buffer remains with the stream, and the buffer

remains valid only until some other method of the stream is called

or the stream is destroyed.

* It is legal for the returned buffer to have zero size, as long

as repeatedly calling Next() eventually yields a buffer with non-zero

size.

Backs up a number of bytes, so that the next call to Next() returns

data again that was already returned by the last call to Next(). This

is useful when writing procedures that are only supposed to read up

to a certain point in the input, then return. If Next() returns a

buffer that goes beyond what you wanted to read, you can use BackUp()

to return to the point where you intended to finish.

Preconditions:

* The last method called must have been Next().

* count must be less than or equal to the size of the last buffer

returned by Next().

Postconditions:

* The last "count" bytes of the last buffer returned by Next() will be

pushed back into the stream. Subsequent calls to Next() will return

the same data again before producing new data.

Skips `count` number of bytes.

Returns true on success, or false if some input error occurred, or `count`

exceeds the end of the stream. This function may skip up to `count - 1`

bytes in case of failure.

Preconditions:

* `count` is non-negative.

Returns the total number of bytes read since this object was created.

Read the next `count` bytes and append it to the given Cord.

In the case of a read error, the method reads as much data as possible into

the cord before returning false. The default implementation iterates over

the buffers and appends up to `count` bytes of data into `cord` using the

`absl::CordBuffer` API.

Some streams may implement this in a way that avoids copying by sharing or

reference counting existing data managed by the stream implementation.