Better handling of server error response

Show FAIL status if the address is listed at the provider
Show ERR status if an error occured during the lookup

README.md

@@ -23,19 +23,24 @@ go build
 
 ## Execute
 
+```sh
 ./dnsbl-check -i 1.2.3.4 -p providers
+```
 
 ## Output
 
 The program returns every result in a new line, fields are separated by TAB character `\t`.
 
-The line starts with the status: `OK` or `ERR`
+The line starts with the status: `OK` or `FAIL` or `ERR`
+- `OK` returned if no listing found for the address
+- `FAIL` returned if listing found for the address
+- `ERR` returned if the address lookup failed
 Second field is the address
 Third field is the provider
-Fourth field is filled only if the address listed at the provider. If no reason returned from te provider, the `unknown reason` text will be shown.
-
+Fourth field is filled only if the statis is either `FAIL` or `ERR`. If the status is `FAIL` and no reason returned from te provider, the `unknown reason` text will be shown. If the status is `ERR` the error message will be shown here.
 
 ```
-OK	45.95.168.196	zen.spamhaus.org
-ERR	45.95.168.196	dnsbl-1.uceprotect.net	IP 45.95.168.196 is UCEPROTECT-Level 1 listed. See http://www.uceprotect.net/rblcheck.php?ipr=45.95.168.196
+OK	127.0.0.2	dyn.rbl.polspam.pl
+FAIL	127.0.0.2	bl.spamcop.net	Blocked - see https://www.spamcop.net/bl.shtml?127.0.0.2
+ERR	127.0.0.2	spam.dnsbl.anonmails.de	lookup 2.0.0.127.spam.dnsbl.anonmails.de on 127.0.0.53:53: server misbehaving
 ```

main.go

@@ -58,23 +58,24 @@ type LookupResult struct {
 	Address       string
 	Reason        string
 	Provider      DNSBLProvider
+	Error         error
 }
 
 func lookup(address string, provider DNSBLProvider) LookupResult {
 	isListed, err := provider.IsBlacklisted(address)
 	if err != nil {
-		fmt.Println(err)
-		os.Exit(1)
+		return LookupResult{
+			Provider: provider,
+			Address:  address,
+			Error:    err,
+		}
 	}
 
 	if isListed {
 		desc, err := provider.GetReason(address)
 
-		if err != nil {
-			fmt.Println("ERROR", err.Error())
-		}
-
 		return LookupResult{
+			Error:         err,
 			Address:       address,
 			IsBlacklisted: true,
 			Provider:      provider,
@@ -164,6 +165,10 @@ func getProviders(fn string) ([]string, error) {
 }
 
 func processLookupResult(result LookupResult) {
+	if result.Error != nil {
+		fmt.Println(fmt.Sprintf("ERR\t%s\t%s\t%s", result.Address, result.Provider.GetName(), result.Error))
+		return
+	}
 	if result.IsBlacklisted {
 		var reason string
 
@@ -173,7 +178,7 @@ func processLookupResult(result LookupResult) {
 			reason = result.Reason
 		}
 
-		fmt.Println(fmt.Sprintf("ERR\t%s\t%s\t%s", result.Address, result.Provider.GetName(), reason))
+		fmt.Println(fmt.Sprintf("FAIL\t%s\t%s\t%s", result.Address, result.Provider.GetName(), reason))
 	} else {
 		fmt.Println(fmt.Sprintf("OK\t%s\t%s", result.Address, result.Provider.GetName()))
 	}
@@ -187,7 +192,7 @@ func main() {
 	list, err := getProviders(*domainsFile)
 
 	if err != nil {
-		fmt.Println("Error reading domains")
+		fmt.Fprintln(os.Stderr, "Error reading domains")
 		os.Exit(1)
 	}