Terrible hack for preloading custom readline functions

fzf_readline.c

/* gcc -Wall -fPIC -shared -o fzf_readline.so fzf_readline.c -ldl */

/* a much nastier version of https://github.com/lincheney/rl_custom_function,
 * but works with readline in Debian/Ubuntu
 */

#define _GNU_SOURCE

#include <stdlib.h>
#include <stdio.h>
#include <readline/readline.h>
#include <readline/history.h>
#include <dlfcn.h>

int init_done=0;
char *(*origfn)(const char*);

static rl_command_func_t *get_custom() {
	void *lib=dlopen("/usr/lib/librl_custom_complete.so", RTLD_LAZY);

	if(!lib) {
		fprintf(stderr, "couldn't open custom func lib\n");
		return NULL;
	}

	rl_command_func_t *func = dlsym(lib, "rl_custom_function");

	if(!func) {
		fprintf(stderr, "couldn't find func\n");
	}

	return func;
}

char *readline (const char *prompt) {
	printf("In our own readline\n");
	if (init_done)
		return (*origfn)(prompt);

	printf("doing init\n");
	origfn = dlsym(RTLD_NEXT, "readline");
	if (!origfn) {
		fprintf(stderr, "couldn't resolve original readline(), aborting\n");
		exit(255);
	}
	rl_command_func_t *custom = get_custom();
	if (custom) {
		int (*addfun)(const char *, rl_command_func_t *);
		addfun=dlsym(RTLD_NEXT, "rl_add_funmap_entry");
		if(!addfun) {
			fprintf(stderr, "couldn't resolve rl_add_funmap_entry()\n");
		} else {
			int res=(*addfun)("rl_custom_complete", custom);
			printf("add_funmap_entry returned %u\n",res);
		}
	}

	init_done=1;

	return (*origfn)(prompt);
}