Worker protocol

Workers start as php -d disable_functions=<list> worker.php <mode> <entry>, where <mode> is how the entry runs: callable for -mode worker and prefork, script for -mode legacy. The gateway gets <list> once from php worker.php probe, a JSON object that also names what -mode prefork needs and this PHP lacks (pcntl_fork, pcntl_waitpid, posix_kill), and echoes a line the gateway wrote on its stdin. The gateway stops there when the command cannot run, fails, does not run worker.php, or does not pass stdin through to PHP, saying which. Later, if as many workers as -workers end before any request was answered, it stops too, instead of replacing them forever. With -mode prefork, the master starts as php -d disable_functions=<list> worker.php <mode> <entry> <socket> <workers>, and each forked worker speaks the protocol on its connection to <socket> instead of stdin and stdout. With -project-root, --project-root=<dir> comes last, and the worker sets PROJECT_ROOT before it loads the entry.

A frame is a 4-byte big-endian length followed by JSON. After booting, the worker sends the frame {"ready":true,"pid":<pid>}. Then, for each request, the gateway sends a frame on stdin, with a new random boundary, followed by the raw request body, and the worker answers on stdout with the raw body, the boundary, and a frame:

gateway → worker   {"boundary":"--warmphp-<random>","id":"<request id>","server":{...CGI vars...},"body_size":<n>,"fields":[[name,value]],"files":[{field,name,type,tmp_name,error,size}]}<n body bytes>
worker  → gateway  <body bytes>--warmphp-<random>{"status":200,"headers":["Content-Type: text/html"],"metrics":{"ms":23.9,"cpu_ms":6.2,"memory_kb":2840},"exit":false}

Output outside a request, such as boot messages, goes to stderr, so it never mixes with a body. Around each request the worker writes \x01start <id> <pid> and \x01end <id> to stderr, each on a line of its own: they come through the pipe in order with PHP's own lines, which is how the gateway ties those lines to the request. The gateway rejects a frame whose length is absurd (any printable byte read as a length is), answers 502 and replaces the worker.

Metric units match the log field reference: ms and cpu_ms are milliseconds; memory_kb is KiB despite its field name. Body and frame lengths are bytes.