fix(nntpd): support open-ended NNTP ranges in XOVER/OVER

parseRange split the spec on '-' and required BOTH bounds to parse as
integers. For a valid open-ended range like '5-' (RFC 3977 6.2.3 / RFC 2980
XOVER: article 5 through the last) strconv.ParseInt('') fails, so parseRange
returned (0, 0) and handleOver asked the backend for articles in [0, 0] —
zero rows. '-10' (first..10) was likewise broken.

Treat an empty bound as the extreme (low 0 / high MaxInt64) while still
returning an empty range for genuinely malformed specs. Add table-driven
tests for the open-ended and malformed forms.

internal/news/nntpd/range_test.go

@@ -1,6 +1,9 @@
 package nntpd
 
-import "testing"
+import (
+	"math"
+	"testing"
+)
 
 func TestParseRangeSingleArticle(t *testing.T) {
 	low, high := parseRange("5")
@@ -8,3 +11,27 @@ func TestParseRangeSingleArticle(t *testing.T) {
 		t.Fatalf(`parseRange("5") = %d, %d; want 5, 5`, low, high)
 	}
 }
+
+func TestParseRange(t *testing.T) {
+	// spec -> (low, high). Empty bounds mean the extreme; malformed -> (0, 0).
+	cases := []struct {
+		spec string
+		low  int64
+		high int64
+	}{
+		{"5", 5, 5},
+		{"5-10", 5, 10},
+		{"5-", 5, math.MaxInt64},
+		{"-10", 0, 10},
+		{"", 0, math.MaxInt64},
+		{"abc", 0, 0},
+		{"5-abc", 0, 0},
+		{"abc-10", 0, 0},
+	}
+	for _, c := range cases {
+		low, high := parseRange(c.spec)
+		if low != c.low || high != c.high {
+			t.Errorf("parseRange(%q) = %d, %d; want %d, %d", c.spec, low, high, c.low, c.high)
+		}
+	}
+}

internal/news/nntpd/server.go

@@ -165,27 +165,35 @@ func (s *Server) Process(nc net.Conn) {
 	}
 }
 
+// parseRange parses an NNTP article range spec (RFC 3977 §6.2.3 / RFC 2980).
+// An empty bound means "the extreme": "5-" is article 5 through the last
+// article, "-10" is the first article through 10, "5-10" is 5..10, "5" is the
+// single article 5, and "" is all articles. A genuinely malformed bound yields
+// an empty range (0, 0).
 func parseRange(spec string) (low, high int64) {
 	if spec == "" {
 		return 0, math.MaxInt64
 	}
-	parts := strings.Split(spec, "-")
-	if len(parts) == 1 {
-		h, err := strconv.ParseInt(parts[0], 10, 64)
+	parts := strings.SplitN(spec, "-", 2)
+	low, high = 0, math.MaxInt64
+	if parts[0] != "" {
+		v, err := strconv.ParseInt(parts[0], 10, 64)
 		if err != nil {
-			return 0, 0 // malformed — empty range instead of all articles
+			return 0, 0 // malformed low bound — empty range
 		}
-		return h, h
+		low = v
 	}
-	l, err := strconv.ParseInt(parts[0], 10, 64)
-	if err != nil {
-		return 0, 0 // malformed — empty range
+	if len(parts) == 1 { // single article, e.g. "5"
+		return low, low
 	}
-	h, err := strconv.ParseInt(parts[1], 10, 64)
-	if err != nil {
-		return 0, 0 // malformed — empty range
+	if parts[1] != "" {
+		v, err := strconv.ParseInt(parts[1], 10, 64)
+		if err != nil {
+			return 0, 0 // malformed high bound — empty range
+		}
+		high = v
 	}
-	return l, h
+	return low, high
 }
 
 func handleOver(args []string, s *session, c *textproto.Conn) error {