## GResolver

GResolver — Asynchronous and cancellable DNS resolver

## Synopsis

    #include <gio/gio.h>

                        GResolver;
    GResolver *         g_resolver_get_default              (void);
    void                g_resolver_set_default              (GResolver *resolver);
    GList *             g_resolver_lookup_by_name           (GResolver *resolver,
                                                             const gchar *hostname,
                                                             GCancellable *cancellable,
                                                             GError **error);
    void                g_resolver_lookup_by_name_async     (GResolver *resolver,
                                                             const gchar *hostname,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);
    GList *             g_resolver_lookup_by_name_finish    (GResolver *resolver,
                                                             GAsyncResult *result,
                                                             GError **error);
    void                g_resolver_free_addresses           (GList *addresses);
    gchar *             g_resolver_lookup_by_address        (GResolver *resolver,
                                                             GInetAddress *address,
                                                             GCancellable *cancellable,
                                                             GError **error);
    void                g_resolver_lookup_by_address_async  (GResolver *resolver,
                                                             GInetAddress *address,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);
    gchar *             g_resolver_lookup_by_address_finish (GResolver *resolver,
                                                             GAsyncResult *result,
                                                             GError **error);
    GList *             g_resolver_lookup_service           (GResolver *resolver,
                                                             const gchar *service,
                                                             const gchar *protocol,
                                                             const gchar *domain,
                                                             GCancellable *cancellable,
                                                             GError **error);
    void                g_resolver_lookup_service_async     (GResolver *resolver,
                                                             const gchar *service,
                                                             const gchar *protocol,
                                                             const gchar *domain,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);
    GList *             g_resolver_lookup_service_finish    (GResolver *resolver,
                                                             GAsyncResult *result,
                                                             GError **error);
    void                g_resolver_free_targets             (GList *targets);

    #define             G_RESOLVER_ERROR
    enum                GResolverError;

## Object Hierarchy

      GObject
       +----GResolver

      GEnum
       +----GResolverError

## Signals

      "reload"                                         : Run Last

## Description

GResolver provides cancellable synchronous and asynchronous DNS resolution, for hostnames (`g_resolver_lookup_by_address()`, `g_resolver_lookup_by_name()` and their async variants) and SRV (service) records (`g_resolver_lookup_service()`).

GNetworkAddress and GNetworkService provide wrappers around GResolver functionality that also implement GSocketConnectable, making it easy to connect to a remote host/service.

## Details

### GResolver

    typedef struct _GResolver GResolver;

The object that handles DNS resolution. Use `g_resolver_get_default()` to get the default resolver.

### g_resolver_get_default ()

    GResolver *         g_resolver_get_default              (void);

Gets the default GResolver. You should unref it when you are done with it. GResolver may use its reference count as a hint about how many threads/processes, etc it should allocate for concurrent DNS resolutions.

Returns : | the default GResolver. [transfer full]

Since 2.22

### g_resolver_set_default ()

    void                g_resolver_set_default              (GResolver *resolver);

Sets `resolver` to be the application's default resolver (reffing `resolver`, and unreffing the previous default resolver, if any). Future calls to `g_resolver_get_default()` will return this resolver.

This can be used if an application wants to perform any sort of DNS caching or "pinning"; it can implement its own GResolver that calls the original default resolver for DNS operations, and implements its own cache policies on top of that, and then set itself as the default resolver for all later code to use.

`resolver` : | the new default GResolver

Since 2.22

### g_resolver_lookup_by_name ()

    GList *             g_resolver_lookup_by_name           (GResolver *resolver,
                                                             const gchar *hostname,
                                                             GCancellable *cancellable,
                                                             GError **error);

Synchronously resolves `hostname` to determine its associated IP address(es). `hostname` may be an ASCII-only or UTF-8 hostname, or the textual form of an IP address (in which case this just becomes a wrapper around `g_inet_address_new_from_string()`).

On success, `g_resolver_lookup_by_name()` will return a GList of GInetAddress, sorted in order of preference and guaranteed to not contain duplicates. That is, if using the result to connect to `hostname`, you should attempt to connect to the first address first, then the second if the first fails, etc. If you are using the result to listen on a socket, it is appropriate to add each result using e.g. `g_socket_listener_add_address()`.

If the DNS resolution fails, `error` (if non-`NULL`) will be set to a value from GResolverError.

If `cancellable` is non-`NULL`, it can be used to cancel the operation, in which case `error` (if non-`NULL`) will be set to `G_IO_ERROR_CANCELLED`.

If you are planning to connect to a socket on the resolved IP address, it may be easier to create a GNetworkAddress and use its GSocketConnectable interface.

`resolver` : | a GResolver
`hostname` : | the hostname to look up
`cancellable` : | a GCancellable, or `NULL`. [allow-none]
`error` : | return location for a GError, or `NULL`
Returns : | a GList of GInetAddress, or `NULL` on error. You must unref each of the addresses and free the list when you are done with it. (You can use `g_resolver_free_addresses()` to do this.). [element-type GInetAddress][transfer full]

Since 2.22

### g_resolver_lookup_by_name_async ()

    void                g_resolver_lookup_by_name_async     (GResolver *resolver,
                                                             const gchar *hostname,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);

Begins asynchronously resolving `hostname` to determine its associated IP address(es), and eventually calls `callback`, which must call `g_resolver_lookup_by_name_finish()` to get the result. See `g_resolver_lookup_by_name()` for more details.

`resolver` : | a GResolver
`hostname` : | the hostname to look up the address of
`cancellable` : | a GCancellable, or `NULL`. [allow-none]
`callback` : | callback to call after resolution completes. [scope async]
`user_data` : | data for `callback`. [closure]

Since 2.22

### g_resolver_lookup_by_name_finish ()

    GList *             g_resolver_lookup_by_name_finish    (GResolver *resolver,
                                                             GAsyncResult *result,
                                                             GError **error);

Retrieves the result of a call to `g_resolver_lookup_by_name_async()`.

If the DNS resolution failed, `error` (if non-`NULL`) will be set to a value from GResolverError. If the operation was cancelled, `error` will be set to `G_IO_ERROR_CANCELLED`.

`resolver` : | a GResolver
`result` : | the result passed to your GAsyncReadyCallback
`error` : | return location for a GError, or `NULL`
Returns : | a GList of GInetAddress, or `NULL` on error. See `g_resolver_lookup_by_name()` for more details. [element-type GInetAddress][transfer full]

Since 2.22

### g_resolver_free_addresses ()

    void                g_resolver_free_addresses           (GList *addresses);

Frees `addresses` (which should be the return value from `g_resolver_lookup_by_name()` or `g_resolver_lookup_by_name_finish()`). (This is a convenience method; you can also simply free the results by hand.)

`addresses` : | a GList of GInetAddress

Since 2.22

### g_resolver_lookup_by_address ()

    gchar *             g_resolver_lookup_by_address        (GResolver *resolver,
                                                             GInetAddress *address,
                                                             GCancellable *cancellable,
                                                             GError **error);

Synchronously reverse-resolves `address` to determine its associated hostname.

If the DNS resolution fails, `error` (if non-`NULL`) will be set to a value from GResolverError.

If `cancellable` is non-`NULL`, it can be used to cancel the operation, in which case `error` (if non-`NULL`) will be set to `G_IO_ERROR_CANCELLED`.

`resolver` : | a GResolver
`address` : | the address to reverse-resolve
`cancellable` : | a GCancellable, or `NULL`. [allow-none]
`error` : | return location for a GError, or `NULL`
Returns : | a hostname (either ASCII-only, or in ASCII-encoded form), or `NULL` on error.

Since 2.22

### g_resolver_lookup_by_address_async ()

    void                g_resolver_lookup_by_address_async  (GResolver *resolver,
                                                             GInetAddress *address,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);

Begins asynchronously reverse-resolving `address` to determine its associated hostname, and eventually calls `callback`, which must call `g_resolver_lookup_by_address_finish()` to get the final result.

`resolver` : | a GResolver
`address` : | the address to reverse-resolve
`cancellable` : | a GCancellable, or `NULL`. [allow-none]
`callback` : | callback to call after resolution completes. [scope async]
`user_data` : | data for `callback`. [closure]

Since 2.22

### g_resolver_lookup_by_address_finish ()

    gchar *             g_resolver_lookup_by_address_finish (GResolver *resolver,
                                                             GAsyncResult *result,
                                                             GError **error);

Retrieves the result of a previous call to `g_resolver_lookup_by_address_async()`.

If the DNS resolution failed, `error` (if non-`NULL`) will be set to a value from GResolverError. If the operation was cancelled, `error` will be set to `G_IO_ERROR_CANCELLED`.

`resolver` : | a GResolver
`result` : | the result passed to your GAsyncReadyCallback
`error` : | return location for a GError, or `NULL`
Returns : | a hostname (either ASCII-only, or in ASCII-encoded form), or `NULL` on error.

Since 2.22

### g_resolver_lookup_service ()

    GList *             g_resolver_lookup_service           (GResolver *resolver,
                                                             const gchar *service,
                                                             const gchar *protocol,
                                                             const gchar *domain,
                                                             GCancellable *cancellable,
                                                             GError **error);

Synchronously performs a DNS SRV lookup for the given `service` and `protocol` in the given `domain` and returns an array of GSrvTarget. `domain` may be an ASCII-only or UTF-8 hostname. Note also that the `service` and `protocol` arguments do not include the leading underscore that appears in the actual DNS entry.

On success, `g_resolver_lookup_service()` will return a GList of GSrvTarget, sorted in order of preference. (That is, you should attempt to connect to the first target first, then the second if the first fails, etc.)

If the DNS resolution fails, `error` (if non-`NULL`) will be set to a value from GResolverError.

If `cancellable` is non-`NULL`, it can be used to cancel the operation, in which case `error` (if non-`NULL`) will be set to `G_IO_ERROR_CANCELLED`.

If you are planning to connect to the service, it is usually easier to create a GNetworkService and use its GSocketConnectable interface.

`resolver` : | a GResolver
`service` : | the service type to look up (eg, "ldap")
`protocol` : | the networking protocol to use for `service` (eg, "tcp")
`domain` : | the DNS domain to look up the service in
`cancellable` : | a GCancellable, or `NULL`. [allow-none]
`error` : | return location for a GError, or `NULL`
Returns : | a GList of GSrvTarget, or `NULL` on error. You must free each of the targets and the list when you are done with it. (You can use `g_resolver_free_targets()` to do this.). [element-type GSrvTarget][transfer full]

Since 2.22

### g_resolver_lookup_service_async ()

    void                g_resolver_lookup_service_async     (GResolver *resolver,
                                                             const gchar *service,
                                                             const gchar *protocol,
                                                             const gchar *domain,
                                                             GCancellable *cancellable,
                                                             GAsyncReadyCallback callback,
                                                             gpointer user_data);

Begins asynchronously performing a DNS SRV lookup for the given `service` and `protocol` in the given `domain`, and eventually calls `callback`, which must call `g_resolver_lookup_service_finish()` to get the final result. See `g_resolver_lookup_service()` for more details.

`resolver` : | a GResolver
`service` : | the service type to look up (eg, "ldap")
`protocol` : | the networking protocol to use for `service` (eg, "tcp")
`domain` : | the DNS domain to look up the service in
`cancellable` : | a GCancellable, or `NULL`. [allow-none]
`callback` : | callback to call after resolution completes. [scope async]
`user_data` : | data for `callback`. [closure]

Since 2.22

### g_resolver_lookup_service_finish ()

    GList *             g_resolver_lookup_service_finish    (GResolver *resolver,
                                                             GAsyncResult *result,
                                                             GError **error);

Retrieves the result of a previous call to `g_resolver_lookup_service_async()`.

If the DNS resolution failed, `error` (if non-`NULL`) will be set to a value from GResolverError. If the operation was cancelled, `error` will be set to `G_IO_ERROR_CANCELLED`.

`resolver` : | a GResolver
`result` : | the result passed to your GAsyncReadyCallback
`error` : | return location for a GError, or `NULL`
Returns : | a GList of GSrvTarget, or `NULL` on error. See `g_resolver_lookup_service()` for more details. [element-type GSrvTarget][transfer full]

Since 2.22

### g_resolver_free_targets ()

    void                g_resolver_free_targets             (GList *targets);

Frees `targets` (which should be the return value from `g_resolver_lookup_service()` or `g_resolver_lookup_service_finish()`). (This is a convenience method; you can also simply free the results by hand.)

`targets` : | a GList of GSrvTarget

Since 2.22

### G_RESOLVER_ERROR

    #define G_RESOLVER_ERROR (g_resolver_error_quark ())

Error domain for GResolver. Errors in this domain will be from the GResolverError enumeration. See GError for more information on error domains.

### enum GResolverError

    typedef enum {
      G_RESOLVER_ERROR_NOT_FOUND,
      G_RESOLVER_ERROR_TEMPORARY_FAILURE,
      G_RESOLVER_ERROR_INTERNAL
    } GResolverError;

An error code used with `G_RESOLVER_ERROR` in a GError returned from a GResolver routine.

`G_RESOLVER_ERROR_NOT_FOUND` | the requested name/address/service was not found
`G_RESOLVER_ERROR_TEMPORARY_FAILURE` | the requested information could not be looked up due to a network error or similar problem
`G_RESOLVER_ERROR_INTERNAL` | unknown error

Since 2.22

## Signal Details

### The `"reload"` signal

    void                user_function                      (GResolver *resolver,
                                                            gpointer   user_data)      : Run Last

Emitted when the resolver notices that the system resolver configuration has changed.

`resolver` : | a GResolver
`user_data` : | user data set when the signal handler was connected.