TODO.md

@@ -33,6 +33,9 @@ tested.
 
 # Completed Steps
 
+- 2026-10-27: `make asupdate` stops with an error when the download of `as.csv`
+  breaks off. The generator used to retry the failed read forever. A record that
+  does not parse is still logged and skipped (closes #177)
 - 2026-10-27: `make asupdate` runs the new `script/asupdate`. It replaces the AS
   list built into RouteWatch only when the generator succeeds and finds at least
   one AS. A failed download used to replace the list with an empty file. The

cmd/asinfo-gen/main.go

@@ -85,7 +85,8 @@ func main() {
 // parseCSV reads as.csv from r and returns its ASes, with the handle and the
 // description as the file spells them. A header whose first columns are not
 // the AS number, the handle and the description is an error. A record that
-// does not parse is logged and skipped. A file left with no AS is an error.
+// does not parse is logged and skipped. A read that fails, such as on a broken
+// download, is an error. A file left with no AS is an error.
 func parseCSV(r io.Reader) ([]ASInfo, error) {
 	reader := csv.NewReader(r)
 
@@ -109,12 +110,18 @@ func parseCSV(r io.Reader) ([]ASInfo, error) {
 			break
 		}
 
-		if err != nil {
+		if _, ok := errors.AsType[*csv.ParseError](err); ok {
 			log.Printf("Error reading CSV record: %v", err)
 
 			continue
 		}
 
+		// Any other error comes from the download, such as a broken
+		// connection. Every later read returns it again.
+		if err != nil {
+			return nil, fmt.Errorf("read CSV record: %w", err)
+		}
+
 		asn, err := strconv.Atoi(record[0])
 		if err != nil {
 			log.Printf("Invalid ASN %q: %v", record[0], err)

cmd/asinfo-gen/main_test.go

@@ -2,11 +2,18 @@ package main
 
 import (
 	"errors"
+	"io"
 	"slices"
 	"strings"
 	"testing"
+	"testing/iotest"
+	"time"
 )
 
+// parseTimeLimit is how long a test waits for parseCSV to return before it
+// fails.
+const parseTimeLimit = 2 * time.Second
+
 // TestParseCSVReadsTodaysLayout parses an as.csv with the country code column
 // that the source added after the description. It expects each AS with its
 // handle and description spelled exactly as in the file, accents included.
@@ -71,3 +78,65 @@ func TestParseCSVRejectsAFileWithNoASes(t *testing.T) {
 		}
 	}
 }
+
+// TestParseCSVSkipsARecordThatDoesNotParse parses an as.csv with a record
+// that has too few fields between two valid records. It expects both valid
+// ASes and no error, so that one bad record does not stop make asupdate.
+func TestParseCSVSkipsARecordThatDoesNotParse(t *testing.T) {
+	t.Parallel()
+
+	const asCSV = "asn,handle,description,country-code\n" +
+		"1,LVLT-1,Level 3 Parent LLC,US\n" +
+		"2,UDEL-DCN\n" +
+		"3,MIT-GATEWAYS,Massachusetts Institute of Technology,US\n"
+
+	got, err := parseCSV(strings.NewReader(asCSV))
+	if err != nil {
+		t.Fatalf("parseCSV: %v", err)
+	}
+
+	want := []ASInfo{
+		{ASN: 1, Handle: "LVLT-1", Description: "Level 3 Parent LLC"},
+		{
+			ASN:         3,
+			Handle:      "MIT-GATEWAYS",
+			Description: "Massachusetts Institute of Technology",
+		},
+	}
+
+	if !slices.Equal(got, want) {
+		t.Errorf("parseCSV = %+v, want %+v", got, want)
+	}
+}
+
+// TestParseCSVStopsWhenTheDownloadBreaksOff parses an as.csv whose download
+// breaks off after the first record. From then on every read fails, as on a
+// broken connection. It expects parseCSV to return that error, so that make
+// asupdate keeps the old list.
+func TestParseCSVStopsWhenTheDownloadBreaksOff(t *testing.T) {
+	t.Parallel()
+
+	const asCSV = "asn,handle,description,country-code\n" +
+		"1,LVLT-1,Level 3 Parent LLC,US\n"
+
+	download := io.MultiReader(
+		strings.NewReader(asCSV), iotest.ErrReader(io.ErrUnexpectedEOF))
+
+	// parseCSV runs on its own goroutine, so that a parseCSV that never
+	// returns fails the test instead of hanging it.
+	parsed := make(chan error, 1)
+
+	go func() {
+		_, err := parseCSV(download)
+		parsed <- err
+	}()
+
+	select {
+	case err := <-parsed:
+		if !errors.Is(err, io.ErrUnexpectedEOF) {
+			t.Errorf("parseCSV = %v, want %v", err, io.ErrUnexpectedEOF)
+		}
+	case <-time.After(parseTimeLimit):
+		t.Fatalf("parseCSV did not return within %v", parseTimeLimit)
+	}
+}