net: set DNSError.IsTemorary from addrinfoErrno errors

DNSErrors that are created via addrinfoErrno(...) currently do not
have the "IsTemporary" set. However the addrinfoErrno type itself
has the Temporary() property.

This PR sets DNSError.IsTemporary to the addrinfoErrno.Temporary
value. This is useful to e.g. detect if a DNSError is of type
EAI_AGAIN (which is currently not possible AFAICT).

src/net/cgo_unix.go

@@ -106,15 +106,17 @@ func cgoLookupServicePort(hints *C.struct_addrinfo, network, service string) (po
 	var res *C.struct_addrinfo
 	gerrno, err := C.getaddrinfo(nil, (*C.char)(unsafe.Pointer(&cservice[0])), hints, &res)
 	if gerrno != 0 {
+		isTemporary := false
 		switch gerrno {
 		case C.EAI_SYSTEM:
 			if err == nil { // see golang.org/issue/6232
 				err = syscall.EMFILE
 			}
 		default:
 			err = addrinfoErrno(gerrno)
+			isTemporary = addrinfoErrno(gerrno).Temporary()
 		}
-		return 0, &DNSError{Err: err.Error(), Name: network + "/" + service}
+		return 0, &DNSError{Err: err.Error(), Name: network + "/" + service, IsTemporary: isTemporary}
 	}
 	defer C.freeaddrinfo(res)
 
@@ -159,6 +161,7 @@ func cgoLookupIPCNAME(network, name string) (addrs []IPAddr, cname string, err e
 	gerrno, err := C.getaddrinfo((*C.char)(unsafe.Pointer(&h[0])), nil, &hints, &res)
 	if gerrno != 0 {
 		isErrorNoSuchHost := false
+		isTemporary := false
 		switch gerrno {
 		case C.EAI_SYSTEM:
 			if err == nil {
@@ -176,9 +179,10 @@ func cgoLookupIPCNAME(network, name string) (addrs []IPAddr, cname string, err e
 			isErrorNoSuchHost = true
 		default:
 			err = addrinfoErrno(gerrno)
+			isTemporary = addrinfoErrno(gerrno).Temporary()
 		}
 
-		return nil, "", &DNSError{Err: err.Error(), Name: name, IsNotFound: isErrorNoSuchHost}
+		return nil, "", &DNSError{Err: err.Error(), Name: name, IsNotFound: isErrorNoSuchHost, IsTemporary: isTemporary}
 	}
 	defer C.freeaddrinfo(res)
 
@@ -299,15 +303,17 @@ func cgoLookupAddrPTR(addr string, sa *C.struct_sockaddr, salen C.socklen_t) (na
 		}
 	}
 	if gerrno != 0 {
+		isTemporary := false
 		switch gerrno {
 		case C.EAI_SYSTEM:
 			if err == nil { // see golang.org/issue/6232
 				err = syscall.EMFILE
 			}
 		default:
 			err = addrinfoErrno(gerrno)
+			isTemporary = addrinfoErrno(gerrno).Temporary()
 		}
-		return nil, &DNSError{Err: err.Error(), Name: addr}
+		return nil, &DNSError{Err: err.Error(), Name: addr, IsTemporary: isTemporary}
 	}
 	for i := 0; i < len(b); i++ {
 		if b[i] == 0 {