#include "cache.h"
#include "pkt-line.h"
#include <signal.h>
#include <sys/wait.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>

static const char daemon_usage[] = "git-daemon [--inetd | --port=n]";

static int upload(char *dir, int dirlen)
{
        if (chdir(dir) < 0)
                return -1;
        chdir(".git");

        /*
         * Security on the cheap.
         *
         * We want a readable HEAD, usable "objects" directory, and 
         * a "git-daemon-export-ok" flag that says that the other side
         * is ok with us doing this.
         */
        if (access("git-daemon-export-ok", F_OK) ||
            access("objects/00", X_OK) ||
            access("HEAD", R_OK))
                return -1;

        /*
         * We'll ignore SIGTERM from now on, we have a
         * good client.
         */
        signal(SIGTERM, SIG_IGN);

        /* git-upload-pack only ever reads stuff, so this is safe */
        execlp("git-upload-pack", "git-upload-pack", ".", NULL);
        return -1;
}

static int execute(void)
{
        static char line[1000];
        int len;

        len = packet_read_line(0, line, sizeof(line));

        if (len && line[len-1] == '\n')
                line[--len] = 0;

        if (!strncmp("git-upload-pack /", line, 17))
                return upload(line + 16, len - 16);

        fprintf(stderr, "got bad connection '%s'\n", line);
        return -1;
}


/*
 * We count spawned/reaped separately, just to avoid any
 * races when updating them from signals. The SIGCHLD handler
 * will only update children_reaped, and the fork logic will
 * only update children_spawned.
 *
 * MAX_CHILDREN should be a power-of-two to make the modulus
 * operation cheap. It should also be at least twice
 * the maximum number of connections we will ever allow.
 */
#define MAX_CHILDREN 128

static int max_connections = 25;

/* These are updated by the signal handler */
static volatile unsigned int children_reaped = 0;
pid_t dead_child[MAX_CHILDREN];

/* These are updated by the main loop */
static unsigned int children_spawned = 0;
static unsigned int children_deleted = 0;

struct child {
        pid_t pid;
        int addrlen;
        struct sockaddr_in address;
} live_child[MAX_CHILDREN];

static void add_child(int idx, pid_t pid, struct sockaddr_in *addr, int addrlen)
{
        live_child[idx].pid = pid;
        live_child[idx].addrlen = addrlen;
        live_child[idx].address = *addr;
}

/*
 * Walk from "deleted" to "spawned", and remove child "pid".
 *
 * We move everything up by one, since the new "deleted" will
 * be one higher.
 */
static void remove_child(pid_t pid, unsigned deleted, unsigned spawned)
{
        struct child n;

        deleted %= MAX_CHILDREN;
        spawned %= MAX_CHILDREN;
        if (live_child[deleted].pid == pid) {
                live_child[deleted].pid = -1;
                return;
        }
        n = live_child[deleted];
        for (;;) {
                struct child m;
                deleted = (deleted + 1) % MAX_CHILDREN;
                if (deleted == spawned)
                        die("could not find dead child %d\n", pid);
                m = live_child[deleted];
                live_child[deleted] = n;
                if (m.pid == pid)
                        return;
                n = m;
        }
}

/*
 * This gets called if the number of connections grows
 * past "max_connections".
 *
 * We _should_ start off by searching for connections
 * from the same IP, and if there is some address wth
 * multiple connections, we should kill that first.
 *
 * As it is, we just "randomly" kill 25% of the connections,
 * and our pseudo-random generator sucks too. I have no
 * shame.
 *
 * Really, this is just a place-holder for a _real_ algorithm.
 */
static void kill_some_children(int signo, unsigned start, unsigned stop)
{
        start %= MAX_CHILDREN;
        stop %= MAX_CHILDREN;
        while (start != stop) {
                if (!(start & 3))
                        kill(live_child[start].pid, signo);
                start = (start + 1) % MAX_CHILDREN;
        }
}

static void check_max_connections(void)
{
        for (;;) {
                int active;
                unsigned spawned, reaped, deleted;

                spawned = children_spawned;
                reaped = children_reaped;
                deleted = children_deleted;

                while (deleted < reaped) {
                        pid_t pid = dead_child[deleted % MAX_CHILDREN];
                        remove_child(pid, deleted, spawned);
                        deleted++;
                }
                children_deleted = deleted;

                active = spawned - deleted;
                if (active <= max_connections)
                        break;

                /* Kill some unstarted connections with SIGTERM */
                kill_some_children(SIGTERM, deleted, spawned);
                if (active <= max_connections << 1)
                        break;

                /* If the SIGTERM thing isn't helping use SIGKILL */
                kill_some_children(SIGKILL, deleted, spawned);
                sleep(1);
        }
}

static void handle(int incoming, struct sockaddr_in *addr, int addrlen)
{
        pid_t pid = fork();

        if (pid) {
                unsigned idx;

                close(incoming);
                if (pid < 0)
                        return;

                idx = children_spawned % MAX_CHILDREN;
                children_spawned++;
                add_child(idx, pid, addr, addrlen);

                check_max_connections();
                return;
        }

        dup2(incoming, 0);
        dup2(incoming, 1);
        close(incoming);
        exit(execute());
}

static void child_handler(int signo)
{
        for (;;) {
                pid_t pid = waitpid(-1, NULL, WNOHANG);

                if (pid > 0) {
                        unsigned reaped = children_reaped;
                        dead_child[reaped % MAX_CHILDREN] = pid;
                        children_reaped = reaped + 1;
                        continue;
                }
                break;
        }
}

static int serve(int port)
{
        int sockfd;
        struct sockaddr_in addr;

        signal(SIGCHLD, child_handler);
        sockfd = socket(PF_INET, SOCK_STREAM, IPPROTO_IP);
        if (sockfd < 0)
                die("unable to open socket (%s)", strerror(errno));
        memset(&addr, 0, sizeof(addr));
        addr.sin_port = htons(port);
        addr.sin_family = AF_INET;
        if (bind(sockfd, (void *)&addr, sizeof(addr)) < 0)
                die("unable to bind to port %d (%s)", port, strerror(errno));
        if (listen(sockfd, 5) < 0)
                die("unable to listen to port %d (%s)", port, strerror(errno));

        for (;;) {
                struct sockaddr_in in;
                socklen_t addrlen = sizeof(in);
                int incoming = accept(sockfd, (void *)&in, &addrlen);

                if (incoming < 0) {
                        switch (errno) {
                        case EAGAIN:
                        case EINTR:
                        case ECONNABORTED:
                                continue;
                        default:
                                die("accept returned %s", strerror(errno));
                        }
                }
                handle(incoming, &in, addrlen);
        }
}

int main(int argc, char **argv)
{
        int port = DEFAULT_GIT_PORT;
        int inetd_mode = 0;
        int i;

        for (i = 1; i < argc; i++) {
                char *arg = argv[i];

                if (!strncmp(arg, "--port=", 7)) {
                        char *end;
                        unsigned long n;
                        n = strtoul(arg+7, &end, 0);
                        if (arg[7] && !*end) {
                                port = n;
                                continue;
                        }
                }

                if (!strcmp(arg, "--inetd")) {
                        inetd_mode = 1;
                        continue;
                }

                usage(daemon_usage);
        }

        if (inetd_mode)
                return execute();

        return serve(port);
}