add missing 'done' in write_request

[ottigeda]

DataSink::done was not assigned in write_request.
Therefore it was not possible to call "done" in an content provider.
I expected that should be the way to go, in case of failure to provide the content.
As an example, this could happen because the file to provide has vanished from disk in mean time.
I tried to implement it the same way as in other places, I hope it makes sense to you ?

[yhirose]

@ottigeda, thank you for your contribution! The code looks almost good to me. Could you handle the following two things? Then, I'll merge it. Thanks!

1. Change data_sink.is_writable implementation as below

    data_sink.is_writable = [&](void) {
      return strm.is_writable() && written_length >= 0;
    };

2. Apply the same change to the following section

cpp-httplib/httplib.h

Lines 4138 to 4160 in ba685db

	#ifdef CPPHTTPLIB_ZLIB_SUPPORT
	if (compress_) {
	if (content_provider) {
	size_t offset = 0;
	DataSink data_sink;
	data_sink.write = [&](const char *data, size_t data_len) {
	req.body.append(data, data_len);
	offset += data_len;
	};
	data_sink.is_writable = [&](void) { return true; };
	while (offset < content_length) {
	content_provider(offset, content_length - offset, data_sink);
	}
	} else {
	req.body = body;
	}
	if (!detail::compress(req.body)) { return nullptr; }
	req.headers.emplace("Content-Encoding", "gzip");
	} else
	#endif

[ottigeda]

Is it that, what you wanted to have in addition ?

[yhirose]

@ottigeda, thanks for the update. I have been pondering over this change, and came to remember that done is only used for stopping chunked transfer data stream. This is not for canceling or aborting the streaming process.

So instead of implementing done method in this case. I have rather added 'boolean return value' to ContentProvider type for this purpose. If we want to cancel the streaming process, the functor should return false. It actually corresponds to the behavior of ContentReceiver.

This is a breaking change to the ContentProvider interface. But it's necessary for the API consistency.

Sorry that I couldn't use your changes. But thank you very much for bringing this matter!

[ottigeda]

No problem, your alternative solution is perfectly fine with me. Thanks a lot!