After reading this write up you should be able to understand how to create programs that use the io package to stream data for IO. This writeup shows how to use the io.Reader and io.Writer interfaces to implement streaming IO in your program. The following is a simple example that uses a string reader, created with strings.NewReader(string), to stream byte values from a string source: This loop will continue until the method returns an io.EOF error. Method Read is designed to be called within a loop where, with each iteration, it reads a chunk of data from the source and places it into buffer p. Streaming data directly from a reader is easy.

Nevertheless, before using a reader, consult its documentation. Fortunately, readers from the standard library follow sensible approaches that make it easy to stream. Lastly, a call to Read() that returns n=0 and err=nil does not mean EOF as the next call to Read() may return more data.Īs you can see, properly reading a stream directly from a reader can be tricky.

In that case, any subsequent reads must return n=0, err=io.EOF. However, depending on implementation, a reader may choose to return a non-zero n and err = nil at the end of stream. When a Read() exhausts available data, a reader may return a non-zero n and err=io.EOF.Depending on your use, you may choose to keep the bytes in p or retry. For instance, reading from a TCP socket that is abruptly closed. Upon error, Read() may still return n bytes in buffer p.After a Read() call, n may be less then len(p).Read() will read up to len(p) into p, when possible.The behavior of a reader will depend on its implementation, however there are a few rules, from the io.Reader doc that you should be aware of when consuming directly from a reader: Reading Rules (added)Īfter a Reddit feedback, I have decided to add this section about reading that may be helpful. If the source has exhausted its content, Read should return io.EOF. Implementation of the Read() method should return the number of bytes read or an error if one occurred. For a type to function as a reader, it must implement method Read(p byte) from interface io.Reader (shown below): type Reader interface

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