Preparations for WebSockets #2040
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Introduce a new callback StreamHandler that replaces all other content-serving mechanisms, if set. The handler is not called in response to HEAD or CONNECT requests, or when following a redirect. In conjunction with a response handler, it provides a minimal interface to implement a WebSocket client.
Add a function to streams for obtaining the maximum size that may be passed to read() without blocking. read() may return fewer bytes including none.
Refactor detail::random_string() to output random bytes in addition to random alphanumeric strings, and change the interface to fill a buffer given a char pointer and length, instead of returning a string. Rename the new function to random_bytes(). Add an overload random_string() that implements the old behavior on top of random_bytes().
Add an overload for detail::select_read() that accepts two FDs and reports readability via two boolean out parameters. This is required to implement interruptible reads. Both overloads build on top of a common implementation that optimizes to the same assembly for the common, single FD case.
- random_bytes() - random_string() - select_read() - set_nonblocking()
Similarly to client stream handlers, setting a handler on the response replaces all other content-serving mechanisms. No connection-, content-, or ranges-related headers are added. This provides a minimal interface to implement a WebSocket server.
By passing -1 in sec, the timeout becomes infinite. This is only valid for the 2 FD version.
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This PR lays the groundwork for an upcoming implementation of WebSockets. It makes the following changes:
StreamHandler. If set, it replaces all other content-serving mechanisms and – in conjunction with a response handler – provides a minimal interface to implement a WebSocket client. TheResponsestruct gained aset_stream_handler()function to accomplish the same server-side.nonblocking_read_size()which returns a size that is guaranteed to not blockread()calls.read()may return fewer bytes including none at all.Add timeout setters, to allow other protocol implementations to set more appropriate timeouts in stream handlers.random_bytes(): Refactorrandom_string()intorandom_bytes(). This will be used to generate the masking key for WebSockets.select_read(): Add a two FD version ofselect_read()with support for infinite timeouts. This change is critical to implement bidirectional communication. The WebSockets implementation will use this to interrupt reads when a message is added to the send queue. Branching on the non-type template parameter ensures the common, single FD case isn't pessimized.httplib.{h,cc}.I'm aware of #1103 and while I liked it initially, IMHO, it falls short of its goal of supporting protocol switching generically. The stream handler mechanism doesn't bill itself as anything but another way to handle the body of an HTTP response. It's meant as a low-level, advanced feature that doesn't have to be exposed in the high-level API. (Protocol switching isn't limited to
GETrequests.)I've happily taken some inspiration from it, though. (Thanks, @PixlRainbow!)
Checklist:
std::function<bool(Stream&)>withStreamHandler?CPPHTTPLIB_USE_POLLwhere applicable.