The Go FuncCloser Pattern: A Solution for Closing Inner io.Readers

2023/08/18

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The article discusses the Go FuncCloser pattern, which is a solution for handling inner io.Readers that do not offer a way to close themselves. One example of this issue is with the bufio.Reader type. The author provides a code snippet that opens a file, peeks at the first 512 bytes to detect the mime type, and then returns an io.ReadCloser to read and close the file. However, this code does not compile because bufio.Reader does not implement the io.Closer interface. To fix this issue, the author introduces the FuncCloser pattern, which allows adding a custom Close() error function to an io.Reader, effectively turning it into an io.ReadCloser. The article also demonstrates how to implement more complex closing behavior using a closure. The author suggests that this pattern can also be useful for io.Writer/io.WriteCloser. This solution provides a way for developers to properly close inner io.Readers and avoid resource leaks in their code.