- naive circular queue, described in the article "A Scalable, Portable, and Memory-Efficient Lock-Free FIFO Queue" by Ruslan Nikolaev: https://drops.dagstuhl.de/opus/volltexte/2019/11335/pdf/LIPIcs-DISC-2019-28.pdf - circular queue, proposed by Valentin Bartenev in the "Unit router application IPC" design draft
This is required due to lack of a graceful shutdown: there is a small gap between the runtime's memory pool release and router process's exit. Thus, a worker thread may start processing a request between these two operations, which may result in an http fields hash access and subsequent crash. To simplify issue reproduction, it makes sense to add a 2 sec sleep before exit() in nxt_runtime_exit().
The setuid/setgid syscalls requires root capabilities but if the kernel supports unprivileged user namespace then the child process has the full set of capabilities in the new namespace, then we can allow setting "user" and "group" in such cases (this is a common security use case). Tests were added to ensure user gets meaningful error messages for uid/gid mapping misconfigurations.
Name and value in each header are 0-terminated, so additional 2 bytes should be allocated for them. There were several attempts to add these 2 bytes to headers in language modules, but some modules weren't updated. Also, adding these 2 bytes is specific to the implementation which may be changed later, so extending this mechanics to modules may cause errors.
This field was intended for MIME type lookup by file extension when serving static files, but this use case is too narrow; only a fraction of requests targets static content, and the URI presumably isn't rewritten. Moreover, current implementation uses the entire filename for MIME type lookup if the file has no extension. Instead of extracting filenames and extensions when parsing requests, it's easier to obtain them right before serving static content; this behavior is already implemented. Thus, we can drop excessive logic from parser.
In theory, all space characters in request target must be encoded; however, some clients may violate the specification. For the sake of interoperability, Unit supports unencoded space characters. Previously, if there was a space character before the extension or arguments parts, those parts weren't recognized. Also, quoted symbols and complex target weren't detected after a space character.