finit/libink/client.c

/* libink — synchronous client-side D-Bus calls.
 *
 * Pairs with server.c / connection.c on the receiving end.  The
 * intent is for short-lived CLI tools (initctl) and tests to use
 * libink as their D-Bus client rather than reimplementing the
 * wire format.
 *
 * Copyright (c) 2026  Joachim Wiberg <troglobit@gmail.com>
 * SPDX-License-Identifier: MIT
 */

#include <errno.h>
#include <poll.h>
#include <stdarg.h>
#include <stdlib.h>
#include <string.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

#include "internal.h"

struct link_client {
	int          fd;
	uint32_t     next_serial;
	link_reply_t reply;		/* most recent reply view (points into rxbuf) */
	/* Distinct from "reply.type == 0": LINK_MSG_INVALID is 0, which
	 * is a wire-valid (if malformed) type, so we need an out-of-band
	 * "have we ever produced a reply?" flag. */
	int          have_reply;
	/* Re-use the server-side rx buffer size for incoming replies.
	 * Replies to our methods are bounded by the same per-message
	 * sanity cap as everything else. */
	uint8_t      rxbuf[LINK_RX_BUF_SIZE];
	size_t       rxlen;
};

link_client_t *link_client_open(const char *path)
{
	struct sockaddr_un sun = { .sun_family = AF_UNIX };
	link_client_t *c;
	int            fd;

	if (!path || strlen(path) >= sizeof(sun.sun_path))
		return NULL;
	memcpy(sun.sun_path, path, strlen(path) + 1);

	fd = socket(AF_UNIX, SOCK_STREAM, 0);
	if (fd < 0)
		return NULL;
	if (connect(fd, (struct sockaddr *)&sun, sizeof(sun)) < 0) {
		close(fd);
		return NULL;
	}
	if (__auth_client(fd, geteuid()) < 0) {
		close(fd);
		return NULL;
	}

	c = calloc(1, sizeof(*c));
	if (!c) {
		close(fd);
		return NULL;
	}
	c->fd          = fd;
	c->next_serial = 1;
	return c;
}

void link_client_close(link_client_t *c)
{
	if (!c)
		return;
	if (c->fd >= 0)
		close(c->fd);
	free(c);
}

/* read_full / send_all live in libink/io.c. */
#define read_full(fd, buf, len)  __io_read_full ((fd), (buf), (len))
#define send_all(fd, buf, len)   __io_write_all((fd), (buf), (len))

#define ALIGN_UP(x, n) (((x) + (n) - 1) & ~((size_t)((n) - 1)))

/* Read one complete D-Bus message: the 16-byte fixed header tells
 * us fields_len + body_len, so we then issue exactly one more read
 * for the remainder.  Both lengths are bounded against rxbuf before
 * arithmetic so a malformed wire u32 can't wrap into a near-4-GiB
 * read. */
static int read_one(link_client_t *c, struct link_msg *msg)
{
	uint32_t body_len, fields_len, body_off, total;
	ssize_t  consumed;

	memset(msg, 0, sizeof(*msg));

	if (read_full(c->fd, c->rxbuf, 16) < 0)
		return -1;
	if (c->rxbuf[0] != 'l')
		return -1;

	body_len   = (uint32_t)c->rxbuf[4]
		   | ((uint32_t)c->rxbuf[5] << 8)
		   | ((uint32_t)c->rxbuf[6] << 16)
		   | ((uint32_t)c->rxbuf[7] << 24);
	fields_len = (uint32_t)c->rxbuf[12]
		   | ((uint32_t)c->rxbuf[13] << 8)
		   | ((uint32_t)c->rxbuf[14] << 16)
		   | ((uint32_t)c->rxbuf[15] << 24);

	/* Bound the wire-supplied lengths before any arithmetic on
	 * them.  Without this, fields_len = 0xFFFFFFF0 would wrap
	 * 16u + fields_len to near zero, bypass the total < rxbuf
	 * check, and trigger an out-of-bounds read. */
	if (fields_len > sizeof(c->rxbuf) || body_len > sizeof(c->rxbuf))
		return -1;

	body_off = (uint32_t)ALIGN_UP(16u + fields_len, 8u);
	total    = body_off + body_len;
	if (total > sizeof(c->rxbuf) || total < 16)
		return -1;

	if (read_full(c->fd, c->rxbuf + 16, total - 16) < 0)
		return -1;
	c->rxlen = total;

	consumed = __msg_parse(c->rxbuf, c->rxlen, msg);
	if (consumed <= 0)
		return -1;
	return 0;
}

static void publish_reply(link_client_t *c, const struct link_msg *m)
{
	c->reply.type       = m->type;
	c->reply.signature  = m->signature;
	c->reply.error_name = m->error_name;
	c->reply.path       = m->path;
	c->reply.interface  = m->interface;
	c->reply.member     = m->member;
	c->reply.body       = m->body_avail ? m->body : NULL;
	c->reply.body_len   = m->body_avail;
	c->have_reply       = 1;
}

/* The reply view in c->reply points into c->rxbuf and is invalidated
 * the moment we touch that buffer again -- clear it at every entry,
 * even on the bad-args path, so link_client_reply() cannot return
 * stale dangling pointers from a previous call. */
static void clear_reply(link_client_t *c)
{
	if (!c)
		return;
	memset(&c->reply, 0, sizeof(c->reply));
	c->have_reply = 0;
}

/* Wait up to timeout_ms (-1 = forever) for one full inbound frame
 * and publish it.  Returns 0 on success, 1 on timeout, -1 on error. */
static int read_and_publish(link_client_t *c, int timeout_ms)
{
	struct link_msg msg;

	if (timeout_ms >= 0) {
		struct pollfd pfd = { .fd = c->fd, .events = POLLIN };
		int rc;

		do {
			rc = poll(&pfd, 1, timeout_ms);
		} while (rc < 0 && errno == EINTR);
		if (rc < 0)
			return -1;
		if (rc == 0)
			return 1;
	}

	if (read_one(c, &msg) < 0)
		return -1;
	publish_reply(c, &msg);
	return 0;
}

int link_client_call(link_client_t *c,
		     const char *obj_path,
		     const char *interface,
		     const char *member,
		     const char *signature,
		     const uint8_t *body, size_t body_len)
{
	/* Generous: Manager1 headers fit in ~150 B, but the buffer is
	 * shared with whatever future callers throw at us, and an
	 * overflow only manifests as a silent LINK_CALL_FAIL via
	 * __msg_build_method_call returning -1.  1 KiB on stack
	 * is cheap insurance. */
	uint8_t  hdr[1024];
	ssize_t  hlen;
	uint32_t serial;

	clear_reply(c);
	if (!c || c->fd < 0 || !obj_path || !member)
		return LINK_CALL_FAIL;

	serial = c->next_serial++;
	hlen = __msg_build_method_call(hdr, sizeof(hdr), serial,
					   obj_path, interface, member,
					   signature, (uint32_t)body_len);
	if (hlen < 0)
		return LINK_CALL_FAIL;

	if (send_all(c->fd, hdr, (size_t)hlen) < 0)
		return LINK_CALL_FAIL;
	if (body_len > 0 && send_all(c->fd, body, body_len) < 0)
		return LINK_CALL_FAIL;

	if (read_and_publish(c, -1) != 0)
		return LINK_CALL_FAIL;

	if (c->reply.type == LINK_MSG_METHOD_RETURN)
		return LINK_CALL_OK;
	if (c->reply.type == LINK_MSG_ERROR)
		return LINK_CALL_ERROR;
	return LINK_CALL_FAIL;
}

const link_reply_t *link_client_reply(link_client_t *c)
{
	if (!c || !c->have_reply)
		return NULL;
	return &c->reply;
}

/* Marshal varargs into `body` (capacity `cap`) according to `sig`.
 * Returns the marshalled length on success, -1 on overflow or
 * unsupported type code. */
static ssize_t marshal_va(uint8_t *body, size_t cap,
			  const char *sig, va_list ap)
{
	link_writer_t w;
	const char   *s;

	link_writer_init(&w, body, cap);
	for (s = sig; *s; s++) {
		switch (*s) {
		case 'y':
			link_w_byte(&w, (uint8_t)va_arg(ap, int));
			break;
		case 'b':
			link_w_bool(&w, va_arg(ap, int));
			break;
		case 'u':
			link_w_u32(&w, va_arg(ap, uint32_t));
			break;
		case 's':
			link_w_string(&w, va_arg(ap, const char *));
			break;
		case 'o':
			link_w_path(&w, va_arg(ap, const char *));
			break;
		default:
			return -1;
		}
	}
	return link_writer_finish(&w);
}

int link_client_call_v(link_client_t *c,
		       const char *obj_path,
		       const char *interface,
		       const char *member,
		       const char *signature, ...)
{
	uint8_t body[1024];
	ssize_t body_len = 0;

	if (signature && *signature) {
		va_list ap;

		va_start(ap, signature);
		body_len = marshal_va(body, sizeof(body), signature, ap);
		va_end(ap);
		if (body_len < 0)
			return LINK_CALL_FAIL;
	}

	return link_client_call(c, obj_path, interface, member,
				signature, body, (size_t)body_len);
}

int link_client_wait(link_client_t *c, int timeout_ms)
{
	clear_reply(c);
	if (!c || c->fd < 0)
		return -1;
	return read_and_publish(c, timeout_ms);
}