/*
 * Replacement for a missing getaddrinfo.
 *
 * This is an implementation of getaddrinfo for systems that don't have one so
 * that networking code can use a consistant interface without #ifdef.  It is
 * a fairly minimal implementation, with the following limitations:
 *
 *   - IPv4 support only.  IPv6 is not supported.
 *   - AI_ADDRCONFIG is ignored.
 *   - Not thread-safe due to gethostbyname and getservbyname.
 *   - SOCK_DGRAM and SOCK_STREAM only.
 *   - Multiple possible socket types only generate one addrinfo struct.
 *   - Protocol hints aren't used correctly.
 *
 * The last four issues could probably be easily remedied, but haven't been
 * needed to date.  Adding IPv6 support isn't worth it; systems with IPv6
 * support should already support getaddrinfo natively.
 *
 * The canonical version of this file is maintained in the rra-c-util package,
 * which can be found at <http://www.eyrie.org/~eagle/software/rra-c-util/>.
 *
 * Written by Russ Allbery <eagle@eyrie.org>
 *
 * The authors hereby relinquish any claim to any copyright that they may have
 * in this work, whether granted under contract or by operation of law or
 * international treaty, and hereby commit to the public, at large, that they
 * shall not, at any time in the future, seek to enforce any copyright in this
 * work against any person or entity, or prevent any person or entity from
 * copying, publishing, distributing or creating derivative works of this
 * work.
 */

#include <config.h>
#include <portable/system.h>
#include <portable/socket.h>

#include <errno.h>

/* We need access to h_errno to map errors from gethostbyname. */
#if !HAVE_DECL_H_ERRNO
extern int h_errno;
#endif

/*
 * The netdb constants, which aren't always defined (particularly if h_errno
 * isn't declared).  We also make sure that a few of the less-used ones are
 * defined so that we can deal with them in case statements.
 */
#ifndef HOST_NOT_FOUND
# define HOST_NOT_FOUND 1
# define TRY_AGAIN      2
# define NO_RECOVERY    3
# define NO_DATA        4
#endif
#ifndef NETDB_INTERNAL
# define NETDB_INTERNAL -1
#endif

/*
 * If we're running the test suite, rename the functions to avoid conflicts
 * with the system version.  Note that we don't rename the structures and
 * constants, but that should be okay (except possibly for gai_strerror).
 */
#if TESTING
# undef gai_strerror
# undef freeaddrinfo
# undef getaddrinfo
# define gai_strerror test_gai_strerror
# define freeaddrinfo test_freeaddrinfo
# define getaddrinfo  test_getaddrinfo
const char *test_gai_strerror(int);
void test_freeaddrinfo(struct addrinfo *);
int test_getaddrinfo(const char *, const char *, const struct addrinfo *,
                     struct addrinfo **);
#endif

/*
 * If the native platform doesn't support AI_NUMERICSERV or AI_NUMERICHOST,
 * pick some other values for them.
 */
#if TESTING
# if AI_NUMERICSERV == 0
#  undef AI_NUMERICSERV
#  define AI_NUMERICSERV 0x0080
# endif
# if AI_NUMERICHOST == 0
#  undef AI_NUMERICHOST
#  define AI_NUMERICHOST 0x0100
# endif
#endif

/*
 * Value representing all of the hint flags set.  Linux uses flags up to
 * 0x0400, so be sure not to break when testing on that platform.
 */
#if TESTING
# ifdef HAVE_GETADDRINFO
#  define AI_INTERNAL_ALL 0x04ff
# else
#  define AI_INTERNAL_ALL 0x01ff
# endif
#else
# define AI_INTERNAL_ALL 0x007f
#endif

/* Table of strings corresponding to the EAI_* error codes. */
static const char * const gai_errors[] = {
    "Host name lookup failure",         /*  1 EAI_AGAIN */
    "Invalid flag value",               /*  2 EAI_BADFLAGS */
    "Unknown server error",             /*  3 EAI_FAIL */
    "Unsupported address family",       /*  4 EAI_FAMILY */
    "Memory allocation failure",        /*  5 EAI_MEMORY */
    "Host unknown or not given",        /*  6 EAI_NONAME */
    "Service not supported for socket", /*  7 EAI_SERVICE */
    "Unsupported socket type",          /*  8 EAI_SOCKTYPE */
    "System error",                     /*  9 EAI_SYSTEM */
    "Supplied buffer too small",        /* 10 EAI_OVERFLOW */
};

/* Macro to set the len attribute of sockaddr_in. */
#if HAVE_STRUCT_SOCKADDR_SA_LEN
# define sin_set_length(s) ((s)->sin_len  = sizeof(struct sockaddr_in))
#else
# define sin_set_length(s) /* empty */
#endif

/*
 * Used for iterating through arrays.  ARRAY_SIZE returns the number of
 * elements in the array (useful for a < upper bound in a for loop).
 */
#define ARRAY_SIZE(array) (sizeof(array) / sizeof((array)[0]))


/*
 * Return a constant string for a given EAI_* error code or a string
 * indicating an unknown error.
 */
const char *
gai_strerror(int ecode)
{
    if (ecode < 1 || (size_t) ecode > ARRAY_SIZE(gai_errors))
        return "Unknown error";
    else
        return gai_errors[ecode - 1];
}


/*
 * Free a linked list of addrinfo structs.
 */
void
freeaddrinfo(struct addrinfo *ai)
{
    struct addrinfo *next;

    while (ai != NULL) {
        next = ai->ai_next;
        free(ai->ai_addr);
        free(ai->ai_canonname);
        free(ai);
        ai = next;
    }
}


/*
 * Convert a numeric service string to a number with error checking, returning
 * true if the number was parsed correctly and false otherwise.  Stores the
 * converted number in the second argument.  Equivalent to calling strtol, but
 * with the base always fixed at 10, with checking of errno, ensuring that all
 * of the string is consumed, and checking that the resulting number is
 * positive.
 */
static bool
convert_service(const char *string, long *result)
{
    char *end;

    if (*string == '\0')
        return false;
    errno = 0;
    *result = strtol(string, &end, 10);
    if (errno != 0 || *end != '\0' || *result < 0)
        return false;
    return true;
}


/*
 * Allocate a new addrinfo struct, setting some defaults given that this
 * implementation is IPv4 only.  Also allocates an attached sockaddr_in and
 * zeroes it, per the requirement for getaddrinfo.  Takes the socktype,
 * canonical name (which is copied if not NULL), address, and port.  Returns
 * NULL on a memory allocation failure.
 */
static struct addrinfo *
gai_addrinfo_new(int socktype, const char *canonical, struct in_addr addr,
                 unsigned short port)
{
    struct addrinfo *ai;
    struct sockaddr_in *sin;

    ai = malloc(sizeof(*ai));
    if (ai == NULL)
        return NULL;
    sin = calloc(1, sizeof(struct sockaddr_in));
    if (sin == NULL) {
        free(ai);
        return NULL;
    }
    ai->ai_addr = (struct sockaddr *) sin;
    ai->ai_next = NULL;
    if (canonical == NULL)
        ai->ai_canonname = NULL;
    else {
        ai->ai_canonname = strdup(canonical);
        if (ai->ai_canonname == NULL) {
            freeaddrinfo(ai);
            return NULL;
        }
    }
    ai->ai_flags = 0;
    ai->ai_family = AF_INET;
    ai->ai_socktype = socktype;
    ai->ai_protocol = (socktype == SOCK_DGRAM) ? IPPROTO_UDP : IPPROTO_TCP;
    ai->ai_addrlen = sizeof(struct sockaddr_in);
    sin->sin_family = AF_INET;
    sin->sin_addr = addr;
    sin->sin_port = htons(port);
    sin_set_length(sin);
    return ai;
}


/*
 * Look up a service.  Takes the service name (which may be numeric), the hint
 * flags, a pointer to the socket type (used to determine whether TCP or UDP
 * services are of interest and, if 0, is filled in with the result of
 * getservbyname if the service was not numeric), and a pointer to the
 * addrinfo struct to fill in.  Returns 0 on success or an EAI_* error on
 * failure.
 */
static int
gai_service(const char *servname, int flags, int *type, unsigned short *port)
{
    struct servent *servent;
    const char *protocol;
    long value;

    if (convert_service(servname, &value)) {
        if (value > (1L << 16) - 1)
            return EAI_SERVICE;
        *port = value;
    } else {
        if (flags & AI_NUMERICSERV)
            return EAI_NONAME;
        if (*type != 0)
            protocol = (*type == SOCK_DGRAM) ? "udp" : "tcp";
        else
            protocol = NULL;

        /*
         * We really technically should be generating an addrinfo struct for
         * each possible protocol unless type is set, but this works well
         * enough for what I need this for.
         */
        servent = getservbyname(servname, protocol);
        if (servent == NULL)
            return EAI_NONAME;
        if (strcmp(servent->s_proto, "udp") == 0)
            *type = SOCK_DGRAM;
        else if (strcmp(servent->s_proto, "tcp") == 0)
            *type = SOCK_STREAM;
        else
            return EAI_SERVICE;
        *port = htons(servent->s_port);
    }
    return 0;
}


/*
 * Look up a host and fill in a linked list of addrinfo structs with the
 * results, one per IP address of the returned host.  Takes the name or IP
 * address of the host as a string, the lookup flags, the type of socket (to
 * fill into the addrinfo structs), the port (likewise), and a pointer to
 * where the head of the linked list should be put.  Returns 0 on success or
 * the appropriate EAI_* error.
 */
static int
gai_lookup(const char *nodename, int flags, int socktype, unsigned short port,
           struct addrinfo **res)
{
    struct addrinfo *ai, *first, *prev;
    struct in_addr addr;
    struct hostent *host;
    const char *canonical;
    int i;

    if (inet_aton(nodename, &addr)) {
        canonical = (flags & AI_CANONNAME) ? nodename : NULL;
        ai = gai_addrinfo_new(socktype, canonical, addr, port);
        if (ai == NULL)
            return EAI_MEMORY;
        *res = ai;
        return 0;
    } else {
        if (flags & AI_NUMERICHOST)
            return EAI_NONAME;
        host = gethostbyname(nodename);
        if (host == NULL)
            switch (h_errno) {
            case HOST_NOT_FOUND:
                return EAI_NONAME;
            case TRY_AGAIN:
            case NO_DATA:
                return EAI_AGAIN;
            case NO_RECOVERY:
                return EAI_FAIL;
            case NETDB_INTERNAL:
            default:
                return EAI_SYSTEM;
            }
        if (host->h_addr_list[0] == NULL)
            return EAI_FAIL;
        canonical = (flags & AI_CANONNAME)
            ? ((host->h_name != NULL) ? host->h_name : nodename)
            : NULL;
        first = NULL;
        prev = NULL;
        for (i = 0; host->h_addr_list[i] != NULL; i++) {
            if (host->h_length != sizeof(addr)) {
                freeaddrinfo(first);
                return EAI_FAIL;
            }
            memcpy(&addr, host->h_addr_list[i], sizeof(addr));
            ai = gai_addrinfo_new(socktype, canonical, addr, port);
            if (ai == NULL) {
                freeaddrinfo(first);
                return EAI_MEMORY;
            }
            if (first == NULL) {
                first = ai;
                prev = ai;
            } else {
                prev->ai_next = ai;
                prev = ai;
            }
        }
        *res = first;
        return 0;
    }
}


/*
 * The actual getaddrinfo implementation.
 */
int
getaddrinfo(const char *nodename, const char *servname,
            const struct addrinfo *hints, struct addrinfo **res)
{
    struct addrinfo *ai;
    struct in_addr addr;
    int flags, socktype, status;
    unsigned short port;

    /* Take the hints into account and check them for validity. */
    if (hints != NULL) {
        flags = hints->ai_flags;
        socktype = hints->ai_socktype;
        if ((flags & AI_INTERNAL_ALL) != flags)
            return EAI_BADFLAGS;
        if (hints->ai_family != AF_UNSPEC && hints->ai_family != AF_INET)
            return EAI_FAMILY;
        if (socktype != 0 && socktype != SOCK_STREAM && socktype != SOCK_DGRAM)
            return EAI_SOCKTYPE;

        /* EAI_SOCKTYPE isn't quite right, but there isn't anything better. */
        if (hints->ai_protocol != 0) {
            int protocol = hints->ai_protocol;
            if (protocol != IPPROTO_TCP && protocol != IPPROTO_UDP)
                return EAI_SOCKTYPE;
        }
    } else {
        flags = 0;
        socktype = 0;
    }

    /*
     * See what we're doing.  If nodename is null, either AI_PASSIVE is set or
     * we're getting information for connecting to a service on the loopback
     * address.  Otherwise, we're getting information for connecting to a
     * remote system.
     */
    if (servname == NULL)
        port = 0;
    else {
        status = gai_service(servname, flags, &socktype, &port);
        if (status != 0)
            return status;
    }
    if (nodename != NULL)
        return gai_lookup(nodename, flags, socktype, port, res);
    else {
        if (servname == NULL)
            return EAI_NONAME;
        if ((flags & AI_PASSIVE) == AI_PASSIVE)
            addr.s_addr = INADDR_ANY;
        else
            addr.s_addr = htonl(0x7f000001UL);
        ai = gai_addrinfo_new(socktype, NULL, addr, port);
        if (ai == NULL)
            return EAI_MEMORY;
        *res = ai;
        return 0;
    }
}