Pull request: all: fix lint and naming issues

Merge in DNS/adguard-home from 2276-fix-lint to master

Updates #2276.

Squashed commit of the following:

commit 433f44cc7b674a20ed60a9d29466ba888b3ef66e
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Mon Dec 7 14:14:28 2020 +0300

    querylog: improve code and documentation

commit 851df97d2a87de5e7180a502055ee6f1a6defdca
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Dec 4 20:36:32 2020 +0300

    all: fix lint and naming issues

internal/querylog/searchcriteria.go

@@ -0,0 +1,155 @@
+package querylog
+
+import (
+	"strings"
+
+	"github.com/AdguardTeam/AdGuardHome/internal/dnsfilter"
+)
+
+type criteriaType int
+
+const (
+	ctDomainOrClient  criteriaType = iota // domain name or client IP address
+	ctFilteringStatus                     // filtering status
+)
+
+const (
+	filteringStatusAll      = "all"
+	filteringStatusFiltered = "filtered" // all kinds of filtering
+
+	filteringStatusBlocked             = "blocked"              // blocked or blocked services
+	filteringStatusBlockedService      = "blocked_services"     // blocked
+	filteringStatusBlockedSafebrowsing = "blocked_safebrowsing" // blocked by safebrowsing
+	filteringStatusBlockedParental     = "blocked_parental"     // blocked by parental control
+	filteringStatusWhitelisted         = "whitelisted"          // whitelisted
+	filteringStatusRewritten           = "rewritten"            // all kinds of rewrites
+	filteringStatusSafeSearch          = "safe_search"          // enforced safe search
+	filteringStatusProcessed           = "processed"            // not blocked, not white-listed entries
+)
+
+// filteringStatusValues -- array with all possible filteringStatus values
+var filteringStatusValues = []string{
+	filteringStatusAll, filteringStatusFiltered, filteringStatusBlocked,
+	filteringStatusBlockedService, filteringStatusBlockedSafebrowsing, filteringStatusBlockedParental,
+	filteringStatusWhitelisted, filteringStatusRewritten, filteringStatusSafeSearch,
+	filteringStatusProcessed,
+}
+
+// searchCriteria - every search request may contain a list of different search criteria
+// we use each of them to match the query
+type searchCriteria struct {
+	criteriaType criteriaType // type of the criteria
+	strict       bool         // should we strictly match (equality) or not (indexOf)
+	value        string       // search criteria value
+}
+
+// quickMatch - quickly checks if the log entry matches this search criteria
+// the reason is to do it as quickly as possible without de-serializing the entry
+func (c *searchCriteria) quickMatch(line string) bool {
+	// note that we do this only for a limited set of criteria
+
+	switch c.criteriaType {
+	case ctDomainOrClient:
+		return c.quickMatchJSONValue(line, "QH") ||
+			c.quickMatchJSONValue(line, "IP")
+	default:
+		return true
+	}
+}
+
+// quickMatchJSONValue - helper used by quickMatch
+func (c *searchCriteria) quickMatchJSONValue(line, propertyName string) bool {
+	val := readJSONValue(line, propertyName)
+	if len(val) == 0 {
+		return false
+	}
+	val = strings.ToLower(val)
+	searchVal := strings.ToLower(c.value)
+
+	if c.strict && searchVal == val {
+		return true
+	}
+	if !c.strict && strings.Contains(val, searchVal) {
+		return true
+	}
+
+	return false
+}
+
+// match - checks if the log entry matches this search criteria
+func (c *searchCriteria) match(entry *logEntry) bool {
+	switch c.criteriaType {
+	case ctDomainOrClient:
+		return c.ctDomainOrClientCase(entry)
+	case ctFilteringStatus:
+		return c.ctFilteringStatusCase(entry.Result)
+	}
+
+	return false
+}
+
+func (c *searchCriteria) ctDomainOrClientCase(entry *logEntry) bool {
+	qhost := strings.ToLower(entry.QHost)
+	searchVal := strings.ToLower(c.value)
+	if c.strict && qhost == searchVal {
+		return true
+	}
+	if !c.strict && strings.Contains(qhost, searchVal) {
+		return true
+	}
+
+	if c.strict && entry.IP == c.value {
+		return true
+	}
+	if !c.strict && strings.Contains(entry.IP, c.value) {
+		return true
+	}
+	return false
+}
+
+func (c *searchCriteria) ctFilteringStatusCase(res dnsfilter.Result) bool {
+	switch c.value {
+	case filteringStatusAll:
+		return true
+
+	case filteringStatusFiltered:
+		return res.IsFiltered ||
+			res.Reason.In(
+				dnsfilter.NotFilteredWhiteList,
+				dnsfilter.ReasonRewrite,
+				dnsfilter.RewriteEtcHosts,
+			)
+
+	case filteringStatusBlocked:
+		return res.IsFiltered &&
+			res.Reason.In(dnsfilter.FilteredBlackList, dnsfilter.FilteredBlockedService)
+
+	case filteringStatusBlockedService:
+		return res.IsFiltered && res.Reason == dnsfilter.FilteredBlockedService
+
+	case filteringStatusBlockedParental:
+		return res.IsFiltered && res.Reason == dnsfilter.FilteredParental
+
+	case filteringStatusBlockedSafebrowsing:
+		return res.IsFiltered && res.Reason == dnsfilter.FilteredSafeBrowsing
+
+	case filteringStatusWhitelisted:
+		return res.Reason == dnsfilter.NotFilteredWhiteList
+
+	case filteringStatusRewritten:
+		return res.Reason.In(dnsfilter.ReasonRewrite, dnsfilter.RewriteEtcHosts)
+
+	case filteringStatusSafeSearch:
+		return res.IsFiltered && res.Reason == dnsfilter.FilteredSafeSearch
+
+	case filteringStatusProcessed:
+		return !res.Reason.In(
+			dnsfilter.FilteredBlackList,
+			dnsfilter.FilteredBlockedService,
+			dnsfilter.NotFilteredWhiteList,
+		)
+
+	default:
+		return false
+	}
+}