You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: stream.rs
    path of file: ./repos/flac/src
    
    the code of the file until where you have to start completion: use metadata;
use frame;
use subframe;

use metadata::{Metadata, StreamInfo};
use frame::frame_parser;
use utility::{
  ErrorKind, ByteStream, ReadStream, Sample, SampleSize, StreamProducer,
  many_metadata,
};

use std::io;
use std::usize;
use std::fs::File;

/// FLAC stream that decodes and hold file information.
pub struct Stream<P: StreamProducer> {
  info: StreamInfo,
  metadata: Vec<Metadata>,
  producer: P,
}

/// Alias for a FLAC stream produced from `Read`.
pub type StreamReader<R>  = Stream<ReadStream<R>>;

/// Alias for a FLAC stream produced from a byte stream buffer.
pub type StreamBuffer<'a> = Stream<ByteS
    
  fn next(&mut self) -> Option<Self::Item> {
    if self.sample_index == self.block_size {
      let buffer = &mut self.buffer;

      if let Some(block_size) = self.stream.next_frame(buffer) {
        self.sample_index = 0;
        self.block_size   = block_size;
      } else {
        return None;
      }
    }

    let channels = self.stream.info.channels as usize;
    let index    = self.sample_index + (self.channel * self.block_size);
    let sample   = unsafe { *self.buffer.get_unchecked(index) };

    self.channel += 1;

    // Reset current channel
    if self.channel == channels {
      self.channel       = 0;
      self.sample_index += 1;
      self.samples_left -= 1;
    }

    S::to_normal(sample)
  }