Throw h_errno specific exceptions after res_query errors.

cbits/hs_resolv.h

@@ -9,6 +9,10 @@
 # include <netinet/in.h>
 #endif
 
+#if defined(HAVE_DECL_H_ERRNO)
+# include <netdb.h>
+#endif
+
 #if defined(HAVE_ARPA_NAMESER_H)
 # include <arpa/nameser.h>
 #endif
@@ -30,6 +34,18 @@
 # error broken invariant
 #endif
 
+/* Macro to calculate error code returned by hs_get_h_errno */
+#define __HS_GET_H_ERRNO(h_errno)    \
+  switch(h_errno)                    \
+  {                                  \
+    case HOST_NOT_FOUND: return 1;   \
+    case NO_DATA:        return 2;   \
+    case NO_RECOVERY:    return 3;   \
+    case TRY_AGAIN:      return 4;   \
+    case 0:              return 0;   \
+    default:             return -1;  \
+  }
+
 #if USE_RES_NQUERY
 
 inline static int
@@ -86,7 +102,22 @@ hs_res_close(struct __res_state *s)
   res_nclose(s);
 }
 
+inline static int
+hs_get_h_errno(struct __res_state *s)
+{
+#if defined(HAVE_DECL_H_ERRNO)
+#if defined(HAVE_STRUCT___RES_STATE_RES_H_ERRNO)
+  assert(s);
+  __HS_GET_H_ERRNO(s->res_h_errno)
+#else
+  __HS_GET_H_ERRNO(h_errno)
+#endif
 #else
+  return -1;
+#endif
+}
+
+#else  /* USE_RES_NQUERY */
 
 /* use non-reentrant API */
 
@@ -139,6 +170,16 @@ hs_res_close(void *s)
 {
 }
 
+inline static int
+hs_get_h_errno(void *s)
+{
+#if defined(HAVE_DECL_H_ERRNO)
+  __HS_GET_H_ERRNO(h_errno)
+#else
+  return -1;
 #endif
+}
+
+#endif /* USE_RES_NQUERY */
 
 #endif /* HS_RESOLV_H */

configure.ac

@@ -34,6 +34,10 @@ AC_CHECK_DECLS([res_query, res_nquery], [], [], [[
 #include <resolv.h>
 ]])
 
+AC_CHECK_DECLS([h_errno], [], [], [[
+#include <netdb.h>
+]])
+
 dnl ----------------------------------------------------------------------------
 
 RESOLV_SEARCH_LIBS([res_query],[res_query(0,0,0,0,0)],[resolv bind],[EXTRA_LIBS="$EXTRA_LIBS $ac_lib"],[
@@ -67,6 +71,17 @@ USE_RES_NQUERY=0
 AC_MSG_WARN([could not figure out which C library contains res_nquery(3)])
 ])
 
+AC_CHECK_MEMBERS([struct __res_state.res_h_errno],[],[],[[
+#include <sys/types.h>
+#ifdef HAVE_NETINET_IN_H
+# include <netinet/in.h>
+#endif
+#ifdef HAVE_ARPA_NAMESER_H
+# include <arpa/nameser.h>
+#endif
+#include <resolv.h>
+]])
+
 else
 
 AC_MSG_WARN([could not determine sizeof(struct __res_state)])

src/Network/DNS.hs

@@ -98,18 +98,35 @@ import           Compat
 import           Network.DNS.FFI
 import           Network.DNS.Message
 
--- | Exception thrown in case of errors while encoding or decoding into a 'Msg'.
+-- | Exception thrown in case of errors while resolving or encoding/decoding into a 'Msg'.
 --
 -- @since 0.1.1.0
-data DnsException = DnsEncodeException
-                  | DnsDecodeException
-                  deriving (Show, Typeable)
+data DnsException
+  = DnsEncodeException
+  | DnsDecodeException
+  | DnsHostNotFound
+      -- ^ No such domain (authoritative)
+      --
+      -- @since 0.2.0.0
+  | DnsNoData
+      -- ^ No record for requested type
+      --
+      -- @since 0.2.0.0
+  | DnsNoRecovery
+      -- ^ Non recoverable errors, REFUSED, NOTIMP
+      --
+      -- @since 0.2.0.0
+  | DnsTryAgain
+      -- ^ No such domain (non-authoritative) or SERVERFAIL
+      --
+      -- @since 0.2.0.0
+  deriving (Show, Typeable)
 
 instance Exception DnsException
 
 -- | Send a query via @res_query(3)@ and decode its response into a 'Msg'
 --
--- Throws 'DnsException' in case of encoding or decoding errors. May throw other IO exceptions in case of network errors.
+-- Throws 'DnsException' in case of resolving or encoding/decoding errors. May throw other IO exceptions in case of network errors.
 --
 -- === Example
 --
@@ -158,7 +175,13 @@ queryRaw (Class cls) (Name name) qtype = withCResState $ \stptr -> do
                 unless (errno == eOK) $
                     throwErrno "res_query"
 
-                fail "res_query(3) failed"
+                h_errno <- c_get_h_errno stptr
+                case h_errno of
+                    1 -> throwIO DnsHostNotFound
+                    2 -> throwIO DnsNoData
+                    3 -> throwIO DnsNoRecovery
+                    4 -> throwIO DnsTryAgain
+                    _ -> fail "res_query(3) failed"
 
             BS.packCStringLen (resptr, fromIntegral reslen)
 

src/Network/DNS/FFI.hs

@@ -81,3 +81,6 @@ foreign import capi safe "hs_resolv.h hs_res_mkquery" c_res_mkquery :: Ptr CResS
 
 -- void hs_res_close(void *);
 foreign import capi safe "hs_resolv.h hs_res_close" c_res_close :: Ptr CResState -> IO ()
+
+-- void *hs_get_h_errno(void *);
+foreign import capi unsafe "hs_resolv.h hs_get_h_errno" c_get_h_errno :: Ptr CResState -> IO CInt