Function test_subdaemons

lightningd/lightningd.c:441–504

~ Check we can run them, and check their versions */

/*~ Check we can run them, and check their versions */
void test_subdaemons(const struct lightningd *ld)
{
	size_t i;

	/*~ CCAN's ARRAY_SIZE() should always be used on defined arrays like
	 * the subdaemons array above.  You can calculate the number of
	 * elements it has using `sizeof(subdaemons)/sizeof(subdaemons[0])`
	 * but if `subdaemons` were refactored into a pointer (eg. to make
	 * it a dynamic array) that would erroneously evaluate to `1`.
	 *
	 * ARRAY_SIZE will cause a compiler error if the argument is actually
	 * a pointer, not an array. */
	for (i = 0; i < ARRAY_SIZE(subdaemons); i++) {
		/*~ CCAN's path module uses tal, so wants a context to
		 * allocate from.  We have a magic convenience context
		 * `tmpctx` for temporary allocations like this.
		 *
		 * Because all our daemons at their core are of form `while
		 * (!stopped) handle_events();` (an event loop pattern), we
		 * can free `tmpctx` in that top-level loop after each event
		 * is handled.
		 */
		int outfd;
		const char *dpath = subdaemon_path(tmpctx, ld, subdaemons[i]);
		const char *verstring;
		/*~ CCAN's pipecmd module is like popen for grownups: it
		 * takes pointers to fill in stdin, stdout and stderr file
		 * descriptors if desired, and the remainder of arguments
		 * are the command and its argument. */
		pid_t pid = pipecmd(NULL, &outfd, &outfd,
				    dpath, "--version", NULL);

		/*~ Our logging system: spam goes in at log_debug level, but
		 * logging is mainly added by developer necessity and removed
		 * by developer/user complaints.  The only strong convention
		 * is that log_broken() is used for "should never happen".
		 *
		 * Note, however, that logging takes care to preserve the
		 * global `errno` which is set above. */
		log_debug(ld->log, "testing %s", dpath);

		/*~ ccan/err is a wrapper around BSD's err.h, which defines
		 * the convenience functions err() (error with message
		 * followed by a string based on errno) and errx() (same,x
		 * but no errno string). */
		if (pid == -1)
			err(EXITCODE_SUBDAEMON_FAIL, "Could not run %s", dpath);

		/*~ CCAN's grab_file module contains a routine to read into a
		 * tallocated buffer until EOF (with nul appended!) */
		verstring = grab_fd_str(tmpctx, outfd);
		/*~ Like many CCAN modules, it set errno on failure, which
		 * err (ccan/err, but usually just the BSD <err.h>) prints */
		if (!verstring)
			err(1, "Could not get output from %s", dpath);
		/*~ strstarts is from CCAN/str. */
		if (!strstarts(verstring, version())
		    || verstring[strlen(version())] != '\n')