downloader: different sync strategy

eth/downloader/downloader_test.go

@@ -20,6 +20,7 @@ import (
 	"errors"
 	"fmt"
 	"math/big"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"testing"
@@ -1479,3 +1480,78 @@ func (ftp *floodingTestPeer) RequestHeadersByNumber(from uint64, count, skip int
 	}
 	return nil
 }
+
+func TestRemoteHeaderRequestSpan(t *testing.T) {
+	testCases := []struct {
+		remoteHeight uint64
+		localHeight  uint64
+		expected     []int
+	}{
+		// Remote is way higher. We should ask for the remote head and go backwards
+		{1500, 1000,
+			[]int{1323, 1339, 1355, 1371, 1387, 1403, 1419, 1435, 1451, 1467, 1483, 1499},
+		},
+		{15000, 13006,
+			[]int{14823, 14839, 14855, 14871, 14887, 14903, 14919, 14935, 14951, 14967, 14983, 14999},
+		},
+		//Remote is pretty close to us. We don't have to fetch as many
+		{1200, 1150,
+			[]int{1149, 1154, 1159, 1164, 1169, 1174, 1179, 1184, 1189, 1194, 1199},
+		},
+		// Remote is equal to us (so on a fork with higher td)
+		// We should get the closest couple of ancestors
+		{1500, 1500,
+			[]int{1497, 1499},
+		},
+		// We're higher than the remote! Odd
+		{1000, 1500,
+			[]int{997, 999},
+		},
+		// Check some weird edgecases that it behaves somewhat rationally
+		{0, 1500,
+			[]int{0, 2},
+		},
+		{6000000, 0,
+			[]int{5999823, 5999839, 5999855, 5999871, 5999887, 5999903, 5999919, 5999935, 5999951, 5999967, 5999983, 5999999},
+		},
+		{0, 0,
+			[]int{0, 2},
+		},
+	}
+	reqs := func(from, count, span int) []int {
+		var r []int
+		num := from
+		for len(r) < count {
+			r = append(r, num)
+			num += span + 1
+		}
+		return r
+	}
+	for i, tt := range testCases {
+		from, count, span, max := calculateRequestSpan(tt.remoteHeight, tt.localHeight)
+		data := reqs(int(from), count, span)
+
+		if max != uint64(data[len(data)-1]) {
+			t.Errorf("test %d: wrong last value %d != %d", i, data[len(data)-1], max)
+		}
+		failed := false
+		if len(data) != len(tt.expected) {
+			failed = true
+			t.Errorf("test %d: length wrong, expected %d got %d", i, len(tt.expected), len(data))
+		} else {
+			for j, n := range data {
+				if n != tt.expected[j] {
+					failed = true
+					break
+				}
+			}
+		}
+		if failed {
+			res := strings.Replace(fmt.Sprint(data), " ", ",", -1)
+			exp := strings.Replace(fmt.Sprint(tt.expected), " ", ",", -1)
+			fmt.Printf("got: %v\n", res)
+			fmt.Printf("exp: %v\n", exp)
+			t.Errorf("test %d: wrong values", i)
+		}
+	}
+}