Chunked responses in libevent2

I am trying to do a chunked response (of large files) in libevent this way::

evhttp_send_reply_start(request, HTTP_OK, "OK");

int fd = open("filename", O_RDONLY);
size_t fileSize = <get_file_size>;
struct evbuffer *databuff = NULL;
for (off_t offset = 0;offset < fileSize;)
{
    databuff = evbuffer_new();

    size_t bytesLeft = fileSize - offset;
    size_t bytesToRead = bytesLeft > MAX_READ_SIZE ? MAX_READ_SIZE : bytesLeft;

    evbuffer_add_file(databuff, fd, offset, bytesToRead);
    offset += bytesToRead;

    evhttp_send_reply_chunk(request, databuff); // send it
    evbuffer_free(databuff);                    // destroy it
}

evhttp_send_reply_end(request);

fclose(fptr);

Problem is with this I have a feeling the add_file is asynchronous so the 3rd or so evhttp_send_reply_chunk gives me an error (or something similar):

[warn] evhttp_send_chain Closed(45): Bad file descriptor

I set MAX_READ_SIZE to be 8 to actually test out chunked transfer enc开发者_如何转开发oding.

I noticed there was a evhttp_request_set_chunked_cb (struct evhttp_request *, void(*cb)(struct evhttp_request *, void *)) method I could use but could not find any examples on how to use.

For instance, how could I pass an argument to the callback? The argument seems to be the same argument that was passed to the request handler which is not what I want, because I want to create an object that holds the file descriptor and the file offset I am sending out.

Appreciate all help.

Thanks in advance Sri

The libevent v2 documentation doesn't say that it's async, but it does say that it closes the file descriptor which your code doesn't account for.

I believe you need to move int fd = open("filename", O_RDONLY); inside your loop.

you can also test the chunk handling outside of your file code by just building a string buffer from scratch.

aside from that, (and the last line which should be fclose(fp); your example looks correct

Nice Nice mate. Thanks for that. I just realised that the only reason I wanted to chunked transfers were to avoid buffer reads. But since evbuffer_add_file already uses sendfile (if it finds it) this is not really an issue.

So I removed the loop completely and tried. But the contents are still not being sent. but atleast this time I dont have the bad file descriptor error (you are right - this was due to the file being closed - a check of file handles confirmed this!).