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util/slicesx: add package for generic slice functions, use

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Now that we're using rand.Shuffle in a few locations, create a generic
shuffle function and use it instead. While we're at it, move the
interleaveSlices function to the same package for use.

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: I0b00920e5b3eea846b6cedc30bd34d978a049fd3
This commit is contained in:
Andrew Dunham
2023-03-03 13:15:56 -05:00
parent 88c7d19d54
commit 73fa7dd7af
9 changed files with 121 additions and 46 deletions
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18
net/dnscache/dnscache.go
View File

@@ -24,6 +24,7 @@ import (
"tailscale.com/types/logger"
"tailscale.com/util/cloudenv"
"tailscale.com/util/singleflight"
"tailscale.com/util/slicesx"
)
var zaddr netip.Addr
@@ -577,7 +578,7 @@ func (dc *dialCall) raceDial(ctx context.Context, ips []netip.Addr) (net.Conn, e
iv4 = append(iv4, ip)
}
}
ips = interleaveSlices(iv6, iv4)
ips = slicesx.Interleave(iv6, iv4)
go func() {
for i, ip := range ips {
@@ -636,21 +637,6 @@ func (dc *dialCall) raceDial(ctx context.Context, ips []netip.Addr) (net.Conn, e
}
}
// interleaveSlices combines two slices of the form [a, b, c] and [x, y, z]
// into a slice with elements interleaved; i.e. [a, x, b, y, c, z].
func interleaveSlices[T any](a, b []T) []T {
var (
i int
ret = make([]T, 0, len(a)+len(b))
)
for i = 0; i < len(a) && i < len(b); i++ {
ret = append(ret, a[i], b[i])
}
ret = append(ret, a[i:]...)
ret = append(ret, b[i:]...)
return ret
}
func v4addrs(aa []netip.Addr) (ret []netip.Addr) {
for _, a := range aa {
a = a.Unmap()

24
net/dnscache/dnscache_test.go
View File

@@ -141,30 +141,6 @@ func TestResolverAllHostStaticResult(t *testing.T) {
}
}
func TestInterleaveSlices(t *testing.T) {
testCases := []struct {
name string
a, b []int
want []int
}{
{name: "equal", a: []int{1, 3, 5}, b: []int{2, 4, 6}, want: []int{1, 2, 3, 4, 5, 6}},
{name: "short_b", a: []int{1, 3, 5}, b: []int{2, 4}, want: []int{1, 2, 3, 4, 5}},
{name: "short_a", a: []int{1, 3}, b: []int{2, 4, 6}, want: []int{1, 2, 3, 4, 6}},
{name: "len_1", a: []int{1}, b: []int{2, 4, 6}, want: []int{1, 2, 4, 6}},
{name: "nil_a", a: nil, b: []int{2, 4, 6}, want: []int{2, 4, 6}},
{name: "nil_all", a: nil, b: nil, want: []int{}},
}
for _, tc := range testCases {
t.Run(tc.name, func(t *testing.T) {
merged := interleaveSlices(tc.a, tc.b)
if !reflect.DeepEqual(merged, tc.want) {
t.Errorf("got %v; want %v", merged, tc.want)
}
})
}
}
func TestShouldTryBootstrap(t *testing.T) {
oldDebug := debug
t.Cleanup(func() { debug = oldDebug })

8
net/dnsfallback/dnsfallback.go
View File

@@ -14,7 +14,6 @@ import (
"errors"
"fmt"
"log"
"math/rand"
"net"
"net/http"
"net/netip"
@@ -31,6 +30,7 @@ import (
"tailscale.com/syncs"
"tailscale.com/tailcfg"
"tailscale.com/types/logger"
"tailscale.com/util/slicesx"
)
func Lookup(ctx context.Context, host string) ([]netip.Addr, error) {
@@ -56,8 +56,8 @@ func Lookup(ctx context.Context, host string) ([]netip.Addr, error) {
}
}
}
rand.Shuffle(len(cands4), func(i, j int) { cands4[i], cands4[j] = cands4[j], cands4[i] })
rand.Shuffle(len(cands6), func(i, j int) { cands6[i], cands6[j] = cands6[j], cands6[i] })
slicesx.Shuffle(cands4)
slicesx.Shuffle(cands6)
const maxCands = 6
var cands []nameIP // up to maxCands alternating v4/v6 as long as we have both
@@ -87,7 +87,7 @@ func Lookup(ctx context.Context, host string) ([]netip.Addr, error) {
continue
}
if ips := dm[host]; len(ips) > 0 {
rand.Shuffle(len(ips), func(i, j int) { ips[i], ips[j] = ips[j], ips[i] })
slicesx.Shuffle(ips)
logf("bootstrapDNS(%q, %q) for %q = %v", cand.dnsName, cand.ip, host, ips)
return ips, nil
}