Pull request: 4865-refactor-dns-handlers

Updates #4865.

Squashed commit of the following:

commit b874088ee72dfd0cae5f4102fac87e1f26245ddf
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Sep 2 14:01:52 2022 +0300

    dnsforward: imp code, docs

commit a1b95fda58b777a54e7dcd57f0c419200f8fdc15
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Thu Sep 1 19:37:45 2022 +0300

    all: refactor dns handler; opt

internal/filtering/dnsrewrite.go

@@ -34,8 +34,8 @@ func (d *DNSFilter) processDNSRewrites(dnsr []*rules.NetworkRule) (res Result) {
 			}}
 
 			return Result{
-				Reason:    RewrittenRule,
 				Rules:     rules,
+				Reason:    RewrittenRule,
 				CanonName: dr.NewCNAME,
 			}
 		}
@@ -60,16 +60,16 @@ func (d *DNSFilter) processDNSRewrites(dnsr []*rules.NetworkRule) (res Result) {
 			}
 
 			return Result{
-				Reason:           RewrittenRule,
-				Rules:            rules,
 				DNSRewriteResult: dnsrr,
+				Rules:            rules,
+				Reason:           RewrittenRule,
 			}
 		}
 	}
 
 	return Result{
-		Reason:           RewrittenRule,
-		Rules:            rules,
 		DNSRewriteResult: dnsrr,
+		Rules:            rules,
+		Reason:           RewrittenRule,
 	}
 }

internal/filtering/filtering.go

@@ -390,18 +390,8 @@ type ResultRule struct {
 // TODO(a.garipov): Clarify relationships between fields.  Perhaps
 // replace with a sum type or an interface?
 type Result struct {
-	// IsFiltered is true if the request is filtered.
-	IsFiltered bool `json:",omitempty"`
-
-	// Reason is the reason for blocking or unblocking the request.
-	Reason Reason `json:",omitempty"`
-
-	// Rules are applied rules.  If Rules are not empty, each rule is not nil.
-	Rules []*ResultRule `json:",omitempty"`
-
-	// IPList is the lookup rewrite result.  It is empty unless Reason is set to
-	// Rewritten.
-	IPList []net.IP `json:",omitempty"`
+	// DNSRewriteResult is the $dnsrewrite filter rule result.
+	DNSRewriteResult *DNSRewriteResult `json:",omitempty"`
 
 	// CanonName is the CNAME value from the lookup rewrite result.  It is empty
 	// unless Reason is set to Rewritten or RewrittenRule.
@@ -411,8 +401,18 @@ type Result struct {
 	// Reason is set to FilteredBlockedService.
 	ServiceName string `json:",omitempty"`
 
-	// DNSRewriteResult is the $dnsrewrite filter rule result.
-	DNSRewriteResult *DNSRewriteResult `json:",omitempty"`
+	// IPList is the lookup rewrite result.  It is empty unless Reason is set to
+	// Rewritten.
+	IPList []net.IP `json:",omitempty"`
+
+	// Rules are applied rules.  If Rules are not empty, each rule is not nil.
+	Rules []*ResultRule `json:",omitempty"`
+
+	// Reason is the reason for blocking or unblocking the request.
+	Reason Reason `json:",omitempty"`
+
+	// IsFiltered is true if the request is filtered.
+	IsFiltered bool `json:",omitempty"`
 }
 
 // Matched returns true if any match at all was found regardless of
@@ -874,9 +874,9 @@ func makeResult(matchedRules []rules.Rule, reason Reason) (res Result) {
 	}
 
 	return Result{
-		IsFiltered: reason == FilteredBlockList,
-		Reason:     reason,
 		Rules:      resRules,
+		Reason:     reason,
+		IsFiltered: reason == FilteredBlockList,
 	}
 }
 

internal/filtering/safebrowsing.go

@@ -325,12 +325,12 @@ func (d *DNSFilter) checkSafeBrowsing(
 	}
 
 	res = Result{
-		IsFiltered: true,
-		Reason:     FilteredSafeBrowsing,
 		Rules: []*ResultRule{{
 			Text:         "adguard-malware-shavar",
 			FilterListID: SafeBrowsingListID,
 		}},
+		Reason:     FilteredSafeBrowsing,
+		IsFiltered: true,
 	}
 
 	return check(sctx, res, d.safeBrowsingUpstream)
@@ -359,12 +359,12 @@ func (d *DNSFilter) checkParental(
 	}
 
 	res = Result{
-		IsFiltered: true,
-		Reason:     FilteredParental,
 		Rules: []*ResultRule{{
 			Text:         "parental CATEGORY_BLACKLISTED",
 			FilterListID: ParentalListID,
 		}},
+		Reason:     FilteredParental,
+		IsFiltered: true,
 	}
 
 	return check(sctx, res, d.parentalUpstream)

internal/filtering/safesearch.go

@@ -98,11 +98,11 @@ func (d *DNSFilter) checkSafeSearch(
 	}
 
 	res = Result{
-		IsFiltered: true,
-		Reason:     FilteredSafeSearch,
 		Rules: []*ResultRule{{
 			FilterListID: SafeSearchListID,
 		}},
+		Reason:     FilteredSafeSearch,
+		IsFiltered: true,
 	}
 
 	if ip := net.ParseIP(safeHost); ip != nil {