tor/src/feature/hs/hs_pirprocess.c

/**
 * \file hs_pirprocess.c
 * \brief Handle hidden service PIR helper processes.
 **/

#include "core/or/or.h"

#include "feature/hs/hs_pirprocess.h"

#define SUBPROCESS_PRIVATE
#include "lib/process/env.h"
#include "lib/process/subprocess.h"
#include "lib/evloop/compat_libevent.h"

#include <event2/event.h>

#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif

typedef enum {
    PIRPROCESS_READSTATE_HEADER,
    PIRPROCESS_READSTATE_BODY
} PIRProcessReadState;

struct pir_process_st {
    process_handle_t *process;
    buf_t *stdin_buf;
    struct event *stdin_ev;
    struct event *stdout_ev;
    struct event *stderr_ev;
    char *loglabel;
    pir_process_msghandler_t msghandler;
    PIRProcessReadState readstate;
    size_t readoff, readleft;
    unsigned char hdrbuf[PIRPROCESS_HDR_SIZE];
    char *bodybuf;
};

/* This is called when the pir process has output for us. */
static void
pirprocess_stdoutcb(evutil_socket_t fd, short what, void *arg)
{
    pir_process_t handle = (pir_process_t)arg;

    if (!(what & EV_READ)) {
        /* Not sure why we're here */
        return;
    }

    if (handle->readstate == PIRPROCESS_READSTATE_HEADER) {
        int res = read(fd, handle->hdrbuf + handle->readoff, handle->readleft);
        if (res <= 0) return;
        handle->readoff += res;
        handle->readleft -= res;
        if (handle->readleft == 0) {
            handle->readleft = ntohl(*(uint32_t*)
                    (handle->hdrbuf+PIRPROCESS_HDR_SIZE-4));
            tor_free(handle->bodybuf);
            if (handle->readleft > 0) {
                handle->bodybuf = tor_malloc(handle->readleft+1);
                handle->bodybuf[handle->readleft] = '\0';
                handle->readoff = 0;
                handle->readstate = PIRPROCESS_READSTATE_BODY;
            } else {
                (handle->msghandler)(handle->hdrbuf, NULL, 0);
                handle->readoff = 0;
                handle->readleft = PIRPROCESS_HDR_SIZE;
                handle->readstate = PIRPROCESS_READSTATE_HEADER;
            }
        }
    } else if (handle->readstate == PIRPROCESS_READSTATE_BODY) {
        int res = read(fd, handle->bodybuf + handle->readoff,
                        handle->readleft);
        if (res <= 0) return;
        handle->readoff += res;
        handle->readleft -= res;
        if (handle->readleft == 0) {
            /* Reading is complete */
            (handle->msghandler)(handle->hdrbuf, handle->bodybuf,
                handle->readoff);

            /* Prepare for the next output from the PIR server */
            tor_free(handle->bodybuf);
            handle->readoff = 0;
            handle->readleft = PIRPROCESS_HDR_SIZE;
            handle->readstate = PIRPROCESS_READSTATE_HEADER;
        }
    }
}

/* This is called when the pir process is ready to read from its stdin. */
static void
pirprocess_stdincb(evutil_socket_t fd, short what, void *arg)
{
    pir_process_t handle = (pir_process_t)arg;
    int res;
    size_t bufsize = buf_datalen(handle->stdin_buf);
    char *netbuf = NULL;

    if (!(what & EV_WRITE)) {
        /* Not sure why we're here */
        log_info(LD_DIRSERV,"PIRSERVER bailing");
        return;
    }

    if (bufsize == 0) {
        log_err(LD_DIRSERV,"PIRSERVER trying to write 0-length buffer");
        return;
    }

    netbuf = tor_malloc(bufsize);
    if (netbuf == NULL) {
        log_err(LD_DIRSERV,"PIRSERVER failed to allocate buffer");
        return;
    }

    /* One might think that just calling buf_flush_to_socket would be
     * the thing to do, but that function ends up calling sendto()
     * instead of write(), which doesn't work on pipes.  So we do it
     * more manually.  Using a bufferevent may be another option. */
    buf_peek(handle->stdin_buf, netbuf, bufsize);
    res = write(fd, netbuf, bufsize);
    tor_free(netbuf);
    if (res < 0 && (errno == EAGAIN || errno == EWOULDBLOCK)) {
        /* Try writing again later */
        event_add(handle->stdin_ev, NULL);
        return;
    }
    if (res <= 0) {
        /* Stop trying to write. */
        return;
    }
    buf_drain(handle->stdin_buf, res);
    bufsize -= res;

    if (bufsize > 0) {
        /* There's more to write */
        event_add(handle->stdin_ev, NULL);
    }
}

/* This is called when the pir process writes something to its stderr. */
static void
pirprocess_stderrcb(evutil_socket_t fd, short what, void *arg)
{
    pir_process_t handle = (pir_process_t)arg;

    if (!(what & EV_READ)) {
        /* Not sure why we're here */
        return;
    }

    char buf[1000];
    int res = read(fd, buf, sizeof(buf)-1);
    if (res <= 0) return;
    buf[res] = '\0';
    log_info(LD_DIRSERV,"%s %s", handle->loglabel, escaped(buf));
}

void
hs_pirprocess_close(pir_process_t *handlep)
{
    pir_process_t handle;

    if (!handlep) return;

    if (!*handlep) return;

    handle = *handlep;

    if (handle->stdin_buf) {
        buf_free(handle->stdin_buf);
    }
    if (handle->stdin_ev) {
        event_free(handle->stdin_ev);
    }
    if (handle->stdout_ev) {
        event_free(handle->stdout_ev);
    }
    if (handle->stderr_ev) {
        event_free(handle->stderr_ev);
    }
    if (handle->process) {
        tor_process_handle_destroy(handle->process, 1);
    }
    if (handle->loglabel) {
        tor_free(handle->loglabel);
    }
    if (handle->bodybuf) {
        tor_free(handle->bodybuf);
    }
    tor_free(handle);
    *handlep = NULL;
}

void
hs_pirprocess_poke(const char *path, const char *loglabel,
    pir_process_msghandler_t msghandler, pir_process_t *handlep)
{
    int res;
    smartlist_t *env_vars = get_current_process_environment_variables();
    const char *argv[2];
    process_environment_t *env;
    pir_process_t handle;

    if (!handlep) return;

    if (*handlep) {
        handle = *handlep;

        if (handle->process &&
                handle->process->status == PROCESS_STATUS_RUNNING) {
            /* The PIR process appears to be open */
            return;
        }
    }

    /* Close everything we've got and start over */
    hs_pirprocess_close(handlep);

    if (!path) {
        /* We don't have a configured PIR server */
        return;
    }

    *handlep = tor_malloc_zero(sizeof(struct pir_process_st));
    handle = *handlep;

    /* Start the process */

    argv[0] = path;
    argv[1] = NULL;

    env = process_environment_make(env_vars);

    res = tor_spawn_background(path, argv, env, &(handle->process));

    SMARTLIST_FOREACH(env_vars, void *, x, tor_free(x));
    smartlist_free(env_vars);

    if (res != PROCESS_STATUS_RUNNING) {
        /* Launch failure */
        hs_pirprocess_close(handlep);
        return;
    }

    handle->loglabel = tor_strdup(loglabel);
    handle->msghandler = msghandler;

    /* Create a libevent event to listen to the PIR process' responses. */
    handle->stdout_ev = event_new(tor_libevent_get_base(),
        handle->process->stdout_pipe, EV_READ|EV_PERSIST,
        pirprocess_stdoutcb, handle);
    event_add(handle->stdout_ev, NULL);

    /* And one to listen to the PIR server's stderr. */
    handle->stderr_ev = event_new(tor_libevent_get_base(),
        handle->process->stderr_pipe, EV_READ|EV_PERSIST,
        pirprocess_stderrcb, handle);
    event_add(handle->stderr_ev, NULL);

    /* And one for writability to the pir process' stdin, but don't add
     * it just yet.  Also create the buffer it will use. */
    handle->stdin_buf = buf_new();
    handle->stdin_ev = event_new(tor_libevent_get_base(),
        handle->process->stdin_pipe, EV_WRITE, pirprocess_stdincb,
        handle);

    handle->readstate = PIRPROCESS_READSTATE_HEADER;
    handle->readoff = 0;
    handle->readleft = PIRPROCESS_HDR_SIZE;
    handle->bodybuf = NULL;
}

int
hs_pirprocess_send(pir_process_t handle, const unsigned char *buf,
    size_t len)
{
    if (handle->process == NULL ||
            handle->process->status != PROCESS_STATUS_RUNNING) {
        /* We don't have a process to talk to */
        return -1;
    }

    /* Write the data to the stdin buffer */
    if (len > 0) {
        buf_add(handle->stdin_buf, (const char *)buf, len);
        event_add(handle->stdin_ev, NULL);
    }
    return len;
}