1 files changed, 53 insertions, 0 deletions
diff --git a/internal/blocklist/blocklist.go b/internal/blocklist/blocklist.go
new file mode 100644
index 0000000..34a456d
--- /dev/null
+++ b/internal/blocklist/blocklist.go
@@ -0,0 +1,53 @@
+package blocklist
+
+import (
+	"bufio"
+	"os"
+	"strings"
+)
+
+type Blocklist struct {
+	domains map[string]struct{}
+}
+
+func Load(path string) (*Blocklist, error) {
+	bl := &Blocklist{domains: make(map[string]struct{})}
+	f, err := os.Open(path)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return bl, nil
+		}
+		return nil, err
+	}
+	defer f.Close()
+
+	sc := bufio.NewScanner(f)
+	for sc.Scan() {
+		line := strings.TrimSpace(sc.Text())
+		if line == "" || line[0] == '#' {
+			continue
+		}
+		line = strings.ToLower(line)
+		line = strings.TrimSuffix(line, ".")
+		bl.domains[line] = struct{}{}
+	}
+	return bl, sc.Err()
+}
+
+func (bl *Blocklist) Blocked(qname string) bool {
+	qname = strings.ToLower(qname)
+	qname = strings.TrimSuffix(qname, ".")
+
+	if _, ok := bl.domains[qname]; ok {
+		return true
+	}
+
+	for i := 0; i < len(qname); i++ {
+		if qname[i] == '.' {
+			if _, ok := bl.domains[qname[i+1:]]; ok {
+				return true
+			}
+		}
+	}
+	return false
+}