Why does io.Copy sometimes lose lines when reading from a socket?

Solution 1:

bufio.Reader implements buffering for an io.Reader object. What does this mean? If you use a bufio.Reader to read from an io.Reader source, it may read more data from its source (and buffer it) than what you read directly from the bufio.Reader itself.

This means if you use a bufio.Reader to read from the sock first, and then you use io.Copy(), there may be some data already read from sock and sitting in the bufio.Reader's internal buffer, which io.Copy() will not see and will not copy.

You shouldn't mix those 2 on the same io.Reader source. If you must, then be sure to first drain the bufio.Reader's buffer, then proceed to copy from sock like this:

// First drain the buffer:
n, err := io.Copy(os.Stdout, rdr)
// Handle error

// Then proceed with the socket:
n, err = io.Copy(os.Stdout, sock)
// Handle error

Why does io.Copy sometimes lose lines when reading from a socket?

Solution 1:

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