cmd/geth: era-download logic fix (#32081)

Downloading from a range was failing because it would return and error
early with an error misinterpreting "start-end".

---------

Co-authored-by: shantichanal <158101918+shantichanal@users.noreply.github.com>
Co-authored-by: Gary Rong <garyrong0905@gmail.com>

cmd/geth/chaincmd.go

@@ -765,15 +765,8 @@ func downloadEra(ctx *cli.Context) error {
 }
 
 func parseRange(s string) (start uint64, end uint64, ok bool) {
-	if m, _ := regexp.MatchString("[0-9]+", s); m {
+	log.Info("Parsing block range", "input", s)
-		start, err := strconv.ParseUint(s, 10, 64)
+	if m, _ := regexp.MatchString("^[0-9]+-[0-9]+$", s); m {
-		if err != nil {
-			return 0, 0, false
-		}
-		end = start
-		return start, end, true
-	}
-	if m, _ := regexp.MatchString("[0-9]+-[0-9]+", s); m {
 		s1, s2, _ := strings.Cut(s, "-")
 		start, err := strconv.ParseUint(s1, 10, 64)
 		if err != nil {
@@ -783,6 +776,19 @@ func parseRange(s string) (start uint64, end uint64, ok bool) {
 		if err != nil {
 			return 0, 0, false
 		}
+		if start > end {
+			return 0, 0, false
+		}
+		log.Info("Parsing block range", "start", start, "end", end)
+		return start, end, true
+	}
+	if m, _ := regexp.MatchString("^[0-9]+$", s); m {
+		start, err := strconv.ParseUint(s, 10, 64)
+		if err != nil {
+			return 0, 0, false
+		}
+		end = start
+		log.Info("Parsing single block range", "block", start)
 		return start, end, true
 	}
 	return 0, 0, false

cmd/geth/chaincmd_test.go

@@ -0,0 +1,98 @@
+// Copyright 2025 The go-ethereum Authors
+// This file is part of go-ethereum.
+//
+// go-ethereum is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// go-ethereum is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with go-ethereum. If not, see <http://www.gnu.org/licenses/>.
+
+package main
+
+import "testing"
+
+func TestParseRange(t *testing.T) {
+	var cases = []struct {
+		input    string
+		valid    bool
+		expStart uint64
+		expEnd   uint64
+	}{
+		{
+			input:    "0",
+			valid:    true,
+			expStart: 0,
+			expEnd:   0,
+		},
+		{
+			input:    "500",
+			valid:    true,
+			expStart: 500,
+			expEnd:   500,
+		},
+		{
+			input:    "-1",
+			valid:    false,
+			expStart: 0,
+			expEnd:   0,
+		},
+		{
+			input:    "1-1",
+			valid:    true,
+			expStart: 1,
+			expEnd:   1,
+		},
+		{
+			input:    "0-1",
+			valid:    true,
+			expStart: 0,
+			expEnd:   1,
+		},
+		{
+			input:    "1-0",
+			valid:    false,
+			expStart: 0,
+			expEnd:   0,
+		},
+		{
+			input:    "1-1000",
+			valid:    true,
+			expStart: 1,
+			expEnd:   1000,
+		},
+		{
+			input:    "1-1-",
+			valid:    false,
+			expStart: 0,
+			expEnd:   0,
+		},
+		{
+			input:    "-1-1",
+			valid:    false,
+			expStart: 0,
+			expEnd:   0,
+		},
+	}
+	for _, c := range cases {
+		start, end, valid := parseRange(c.input)
+		if valid != c.valid {
+			t.Errorf("Unexpected result, want: %t, got: %t", c.valid, valid)
+			continue
+		}
+		if valid {
+			if c.expStart != start {
+				t.Errorf("Unexpected start, want: %d, got: %d", c.expStart, start)
+			}
+			if c.expEnd != end {
+				t.Errorf("Unexpected end, want: %d, got: %d", c.expEnd, end)
+			}
+		}
+	}
+}