net.websocket.frames: Additionally return partial frame if there is one

mod_websocket: Continue to process data already in the buffer after an error occurs Previously any error, or even a normal websocket close frame, would return early, leaving potentially entire frames in the buffer unprocessed and then discarded. This change stops processing new data, but returns an existing processed data up to the point of the error/close.

mod_websocket: Enforce stanza size limit and close stream

mod_websocket: Add separate limit for frame buffer size

mod_websocket: handle full frame buffer and raise stream error

mod_websocket: Switch partial frame buffering to util.dbuffer This improves performance and enforces stanza size limits earlier in the pipeline.

net.websocket.frames: Allow all methods to work on non-string objects Instead of using the string library, use methods from the passed object, which are assumed to be equivalent. This provides compatibility with objects from util.ringbuffer and util.dbuffer, for example.

util.dbuffer: Simplify test case An earlier theory involved the bug being related to collapsing multiple items, so it exercised that too. Also correct the comment, it referred to the space in "hello world" in an earlier version before the test string was changed to "foobar", which was what was tested in a REPL

util.dbuffer: Fix :sub() not working with partially-consumed chunks (thanks Zash for test case) This also appears to fix some bugs with chunk-encoded streams in net.http.parser.

util.dbuffer: dynamic string buffer Similar to util.ringbuffer (and shares almost identical API). Differences: - size limit is optional and dynamic - does not allocate a fixed buffer of max_size bytes - focus on simply storing references to existing string objects where possible, avoiding unnecessary allocations - references are still stored in a ring buffer to enable use as a fast FIFO Optional second parameter to new() provides the number of ring buffer segments. On Lua 5.2 on my laptop, a segment is ~19 bytes. If the ring buffer fills up, the next write will compact all strings into a single item.