getaddrinfo_a(3) - Linux manual page (original) (raw)

getaddrinfoa(3) Library Functions Manual getaddrinfoa(3)

NAME top

   getaddrinfo_a, gai_suspend, gai_error, gai_cancel - asynchronous
   network address and service translation

LIBRARY top

   Asynchronous name lookup library (_libanl_, _-lanl_)

SYNOPSIS top

   **#define _GNU_SOURCE** /* See feature_test_macros(7) */
   **#include <netdb.h>**

   **int getaddrinfo_a(int** _mode_**, struct gaicb ***_list_**[restrict],**
                     **int** _n_**, struct sigevent *restrict** _sevp_**);**
   **int gai_suspend(const struct gaicb *const** _list_**[], int** _n_**,**
                     **const struct timespec ***_timeout_**);**

   **int gai_error(struct gaicb ***_req_**);**
   **int gai_cancel(struct gaicb ***_req_**);**

DESCRIPTION top

   The **getaddrinfo_a**() function performs the same task as
   [getaddrinfo(3)](../man3/getaddrinfo.3.html), but allows multiple name look-ups to be performed
   asynchronously, with optional notification on completion of look-
   up operations.

   The _mode_ argument has one of the following values:

   **GAI_WAIT**
          Perform the look-ups synchronously.  The call blocks until
          the look-ups have completed.

   **GAI_NOWAIT**
          Perform the look-ups asynchronously.  The call returns
          immediately, and the requests are resolved in the
          background.  See the discussion of the _sevp_ argument below.

   The array _list_ specifies the look-up requests to process.  The _n_
   argument specifies the number of elements in _list_.  The requested
   look-up operations are started in parallel.  NULL elements in _list_
   are ignored.  Each request is described by a _gaicb_ structure,
   defined as follows:

       struct gaicb {
           const char            *ar_name;
           const char            *ar_service;
           const struct addrinfo *ar_request;
           struct addrinfo       *ar_result;
       };

   The elements of this structure correspond to the arguments of
   [getaddrinfo(3)](../man3/getaddrinfo.3.html).  Thus, _arname_ corresponds to the _node_ argument
   and _arservice_ to the _service_ argument, identifying an Internet
   host and a service.  The _arrequest_ element corresponds to the
   _hints_ argument, specifying the criteria for selecting the returned
   socket address structures.  Finally, _arresult_ corresponds to the
   _res_ argument; you do not need to initialize this element, it will
   be automatically set when the request is resolved.  The _addrinfo_
   structure referenced by the last two elements is described in
   [getaddrinfo(3)](../man3/getaddrinfo.3.html).

   When _mode_ is specified as **GAI_NOWAIT**, notifications about resolved
   requests can be obtained by employing the _sigevent_ structure
   pointed to by the _sevp_ argument.  For the definition and general
   details of this structure, see [sigevent(3type)](../man3/sigevent.3type.html).  The
   _sevp->sigevnotify_ field can have the following values:

   **SIGEV_NONE**
          Don't provide any notification.

   **SIGEV_SIGNAL**
          When a look-up completes, generate the signal _sigevsigno_
          for the process.  See [sigevent(3type)](../man3/sigevent.3type.html) for general details.
          The _sicode_ field of the _siginfot_ structure will be set to
          **SI_ASYNCNL**.

   **SIGEV_THREAD**
          When a look-up completes, invoke _sigevnotifyfunction_ as
          if it were the start function of a new thread.  See
          [sigevent(3type)](../man3/sigevent.3type.html) for details.

   For **SIGEV_SIGNAL** and **SIGEV_THREAD**, it may be useful to point
   _sevp->sigevvalue.sivalptr_ to _list_.

   The **gai_suspend**() function suspends execution of the calling
   thread, waiting for the completion of one or more requests in the
   array _list_.  The _n_ argument specifies the size of the array _list_.
   The call blocks until one of the following occurs:

   •  One or more of the operations in _list_ completes.

   •  The call is interrupted by a signal that is caught.

   •  The time interval specified in _timeout_ elapses.  This argument
      specifies a timeout in seconds plus nanoseconds (see
      [nanosleep(2)](../man2/nanosleep.2.html) for details of the _timespec_ structure).  If
      _timeout_ is NULL, then the call blocks indefinitely (until one
      of the events above occurs).

   No explicit indication of which request was completed is given;
   you must determine which request(s) have completed by iterating
   with **gai_error**() over the list of requests.

   The **gai_error**() function returns the status of the request _req_:
   either **EAI_INPROGRESS** if the request was not completed yet, 0 if
   it was handled successfully, or an error code if the request could
   not be resolved.

   The **gai_cancel**() function cancels the request _req_.  If the request
   has been canceled successfully, the error status of the request
   will be set to **EAI_CANCELED** and normal asynchronous notification
   will be performed.  The request cannot be canceled if it is
   currently being processed; in that case, it will be handled as if
   **gai_cancel**() has never been called.  If _req_ is NULL, an attempt is
   made to cancel all outstanding requests that the process has made.

RETURN VALUE top

   The **getaddrinfo_a**() function returns 0 if all of the requests have
   been enqueued successfully, or one of the following nonzero error
   codes:

   **EAI_AGAIN**
          The resources necessary to enqueue the look-up requests
          were not available.  The application may check the error
          status of each request to determine which ones failed.

   **EAI_MEMORY**
          Out of memory.

   **EAI_SYSTEM**
          _mode_ is invalid.

   The **gai_suspend**() function returns 0 if at least one of the listed
   requests has been completed.  Otherwise, it returns one of the
   following nonzero error codes:

   **EAI_AGAIN**
          The given timeout expired before any of the requests could
          be completed.

   **EAI_ALLDONE**
          There were no actual requests given to the function.

   **EAI_INTR**
          A signal has interrupted the function.  Note that this
          interruption might have been caused by signal notification
          of some completed look-up request.

   The **gai_error**() function can return **EAI_INPROGRESS** for an
   unfinished look-up request, 0 for a successfully completed look-up
   (as described above), one of the error codes that could be
   returned by [getaddrinfo(3)](../man3/getaddrinfo.3.html), or the error code **EAI_CANCELED** if the
   request has been canceled explicitly before it could be finished.

   The **gai_cancel**() function can return one of these values:

   **EAI_CANCELED**
          The request has been canceled successfully.

   **EAI_NOTCANCELED**
          The request has not been canceled.

   **EAI_ALLDONE**
          The request has already completed.

   The [gai_strerror(3)](../man3/gai%5Fstrerror.3.html) function translates these error codes to a
   human readable string, suitable for error reporting.

ATTRIBUTES top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌──────────────────────────────────────┬───────────────┬─────────┐
   │ **Interface** │ **Attribute** │ **Value** │
   ├──────────────────────────────────────┼───────────────┼─────────┤
   │ **getaddrinfo_a**(), **gai_suspend**(),      │ Thread safety │ MT-Safe │
   │ **gai_error**(), **gai_cancel**()            │               │         │
   └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS top

   GNU.

HISTORY top

   glibc 2.2.3.

   The interface of **getaddrinfo_a**() was modeled after the
   [lio_listio(3)](../man3/lio%5Flistio.3.html) interface.

EXAMPLES top

   Two examples are provided: a simple example that resolves several
   requests in parallel synchronously, and a complex example showing
   some of the asynchronous capabilities.

Synchronous example The program below simply resolves several hostnames in parallel, giving a speed-up compared to resolving the hostnames sequentially using getaddrinfo(3). The program might be used like this:

       $ **./a.out mirrors.kernel.org enoent.linuxfoundation.org gnu.org**
       mirrors.kernel.org: 139.178.88.99
       enoent.linuxfoundation.org: Name or service not known
       gnu.org: 209.51.188.116

   Here is the program source code

   #define _GNU_SOURCE
   #include <err.h>
   #include <netdb.h>
   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>

   #define MALLOC(n, type)  ((type *) reallocarray(NULL, n, sizeof(type)))

   int
   main(int argc, char *argv[])
   {
       int ret;
       struct gaicb *reqs[argc - 1];
       char host[NI_MAXHOST];
       struct addrinfo *res;

       if (argc < 2) {
           fprintf(stderr, "Usage: %s HOST...\n", argv[0]);
           exit(EXIT_FAILURE);
       }

       for (size_t i = 0; i < argc - 1; i++) {
           reqs[i] = MALLOC(1, struct gaicb);
           if (reqs[i] == NULL)
               err(EXIT_FAILURE, "malloc");

           memset(reqs[i], 0, sizeof(*reqs[0]));
           reqs[i]->ar_name = argv[i + 1];
       }

       ret = getaddrinfo_a(GAI_WAIT, reqs, argc - 1, NULL);
       if (ret != 0) {
           fprintf(stderr, "getaddrinfo_a() failed: %s\n",
                   gai_strerror(ret));
           exit(EXIT_FAILURE);
       }

       for (size_t i = 0; i < argc - 1; i++) {
           printf("%s: ", reqs[i]->ar_name);
           ret = gai_error(reqs[i]);
           if (ret == 0) {
               res = reqs[i]->ar_result;

               ret = getnameinfo(res->ai_addr, res->ai_addrlen,
                                 host, sizeof(host),
                                 NULL, 0, NI_NUMERICHOST);
               if (ret != 0) {
                   fprintf(stderr, "getnameinfo() failed: %s\n",
                           gai_strerror(ret));
                   exit(EXIT_FAILURE);
               }
               puts(host);

           } else {
               puts(gai_strerror(ret));
           }
       }
       exit(EXIT_SUCCESS);
   }

Asynchronous example This example shows a simple interactive getaddrinfo_a() front-end. The notification facility is not demonstrated.

   An example session might look like this:

       $ **./a.out**
       > a mirrors.kernel.org enoent.linuxfoundation.org gnu.org
       > c 2
       [2] gnu.org: Request not canceled
       > w 0 1
       [00] mirrors.kernel.org: Finished
       > l
       [00] mirrors.kernel.org: 139.178.88.99
       [01] enoent.linuxfoundation.org: Processing request in progress
       [02] gnu.org: 209.51.188.116
       > l
       [00] mirrors.kernel.org: 139.178.88.99
       [01] enoent.linuxfoundation.org: Name or service not known
       [02] gnu.org: 209.51.188.116

   The program source is as follows:

   #define _GNU_SOURCE
   #include <assert.h>
   #include <err.h>
   #include <netdb.h>
   #include <stdio.h>
   #include <stdlib.h>
   #include <string.h>

   #define CALLOC(n, type)  ((type *) calloc(n, sizeof(type)))

   #define REALLOCF(ptr, n, type)                                          \
   ({                                                                      \
       static_assert(__builtin_types_compatible_p(typeof(ptr), type *));   \
                                                                           \
       (type *) reallocarrayf(ptr, n, sizeof(type));                       \
   })

   static struct gaicb **reqs = NULL;
   static size_t nreqs = 0;

   static inline void *
   reallocarrayf(void *p, size_t n, size_t size)
   {
       void  *q;

       q = reallocarray(p, n, size);
       if (q == NULL && n != 0 && size != 0)
           free(p);
       return q;
   }

   static char *
   getcmd(void)
   {
       static char buf[256];

       fputs("> ", stdout); fflush(stdout);
       if (fgets(buf, sizeof(buf), stdin) == NULL)
           return NULL;

       if (buf[strlen(buf) - 1] == '\n')
           buf[strlen(buf) - 1] = 0;

       return buf;
   }

   /* Add requests for specified hostnames. */
   static void
   add_requests(void)
   {
       size_t nreqs_base = nreqs;
       char *host;
       int ret;

       while ((host = strtok(NULL, " "))) {
           nreqs++;
           reqs = REALLOCF(reqs, nreqs, struct gaicb *);
           if (reqs == NULL)
               err(EXIT_FAILURE, "reallocf");

           reqs[nreqs - 1] = CALLOC(1, struct gaicb);
           if (reqs[nreqs - 1] == NULL)
               err(EXIT_FAILURE, "calloc");

           reqs[nreqs - 1]->ar_name = strdup(host);
       }

       /* Queue nreqs_base..nreqs requests. */

       ret = getaddrinfo_a(GAI_NOWAIT, &reqs[nreqs_base],
                           nreqs - nreqs_base, NULL);
       if (ret) {
           fprintf(stderr, "getaddrinfo_a() failed: %s\n",
                   gai_strerror(ret));
           exit(EXIT_FAILURE);
       }
   }

   /* Wait until at least one of specified requests completes. */
   static void
   wait_requests(void)
   {
       char *id;
       int ret;
       size_t n;
       struct gaicb const **wait_reqs;

       wait_reqs = CALLOC(nreqs, const struct gaicb *);
       if (wait_reqs == NULL)
           err(EXIT_FAILURE, "calloc");

                   /* NULL elements are ignored by gai_suspend(). */

       while ((id = strtok(NULL, " ")) != NULL) {
           n = atoi(id);

           if (n >= nreqs) {
               printf("Bad request number: %s\n", id);
               return;
           }

           wait_reqs[n] = reqs[n];
       }

       ret = gai_suspend(wait_reqs, nreqs, NULL);
       if (ret) {
           printf("gai_suspend(): %s\n", gai_strerror(ret));
           return;
       }

       for (size_t i = 0; i < nreqs; i++) {
           if (wait_reqs[i] == NULL)
               continue;

           ret = gai_error(reqs[i]);
           if (ret == EAI_INPROGRESS)
               continue;

           printf("[%02zu] %s: %s\n", i, reqs[i]->ar_name,
                  ret == 0 ? "Finished" : gai_strerror(ret));
       }
   }

   /* Cancel specified requests. */
   static void
   cancel_requests(void)
   {
       char *id;
       int ret;
       size_t n;

       while ((id = strtok(NULL, " ")) != NULL) {
           n = atoi(id);

           if (n >= nreqs) {
               printf("Bad request number: %s\n", id);
               return;
           }

           ret = gai_cancel(reqs[n]);
           printf("[%s] %s: %s\n", id, reqs[atoi(id)]->ar_name,
                  gai_strerror(ret));
       }
   }

   /* List all requests. */
   static void
   list_requests(void)
   {
       int ret;
       char host[NI_MAXHOST];
       struct addrinfo *res;

       for (size_t i = 0; i < nreqs; i++) {
           printf("[%02zu] %s: ", i, reqs[i]->ar_name);
           ret = gai_error(reqs[i]);

           if (!ret) {
               res = reqs[i]->ar_result;

               ret = getnameinfo(res->ai_addr, res->ai_addrlen,
                                 host, sizeof(host),
                                 NULL, 0, NI_NUMERICHOST);
               if (ret) {
                   fprintf(stderr, "getnameinfo() failed: %s\n",
                           gai_strerror(ret));
                   exit(EXIT_FAILURE);
               }
               puts(host);
           } else {
               puts(gai_strerror(ret));
           }
       }
   }

   int
   main(void)
   {
       char *cmdline;
       char *cmd;

       while ((cmdline = getcmd()) != NULL) {
           cmd = strtok(cmdline, " ");

           if (cmd == NULL) {
               list_requests();
           } else {
               switch (cmd[0]) {
               case 'a':
                   add_requests();
                   break;
               case 'w':
                   wait_requests();
                   break;
               case 'c':
                   cancel_requests();
                   break;
               case 'l':
                   list_requests();
                   break;
               default:
                   fprintf(stderr, "Bad command: %c\n", cmd[0]);
                   break;
               }
           }
       }
       exit(EXIT_SUCCESS);
   }

SEE ALSO top

   [getaddrinfo(3)](../man3/getaddrinfo.3.html), [inet(3)](../man3/inet.3.html), [lio_listio(3)](../man3/lio%5Flistio.3.html), [hostname(7)](../man7/hostname.7.html), [ip(7)](../man7/ip.7.html),
   [sigevent(3type)](../man3/sigevent.3type.html)

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Linux man-pages 6.10 2024-11-17 getaddrinfoa(3)

Pages that refer to this page:getaddrinfo(3), sigevent(3type), strtok(3)