blakesmith/ar

Golang ar archive file library

ar's Issues

Satisfy io.Writer interface when using io.Copy returns io.ErrShortWrite

When writing unaligned files, and the Writer Write function returns n+n2, err it simply panics when writing to a bytes.Buffer with io.Copy.

I have created a testcase:

xor-gate@9e954ed

See:

• https://github.com/golang/go/blob/8c190e58541493c580590a77fccfee87d174e5d4/src/io/io.go#L401
• peterebden@5ee5116

Support chunked file writing

This is really a superset of #4.

Currently,

ar/writer.go

Lines 93 to 96 in 809d437

	if len(b)%2 == 1 { // data size must be aligned to an even byte
	n2, _ := aw.w.Write([]byte{'\n'})
	return n+n2, err
	}

essentially closes the file after each call to Write, which means you can't use the API to write a file one piece at a time (e.g. with io.Copy, or dumping out from a stream),

It should only write that footer when aw.nb == 0.

In my opinion, the best way to handle this would be to follow the example of archive/tar and don't write the file footer until either the next call to WriteHeader() or Close(). Of course that would require introduction of a Close method, which would be a breaking API change.

When given a ReaderAt, support returning a SectionReader

Returning []bytes means that tools using this library need to have enough memory available to store the data they're reading, even if the algorithms they're applying to that data would work just as well on a stream with constant memory requirements.

It would be helpful to be able to retrieve not just a file's contents, but a SectionReader that would let those contents be read directly from the underlying storage at a later time, when a seekable backing store is available.

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I'm willing to do the work to implement this myself; this issue is provided as a vehicle for discussion, to ensure that the concept is acceptable before I go writing code.