osbase/net/dns/forward: add DNS forward handler
This adds a DNS server handler for forwarding queries to upstream DNS
resolvers, with a built-in cache. The implementation is partially based
on CoreDNS. The proxy, cache and up packages are only lightly modified.
The forward package itself however is mostly new code. Unlike CoreDNS,
it supports changing upstreams at runtime, and has integrated caching
and answer order randomization.
Some improvements over CoreDNS:
- Concurrent identical queries only result in one upstream query.
- In case of errors, Extended DNS Errors are added to replies.
- Very large replies are not stored in the cache to avoid using too much
memory.
Change-Id: I42294ae4997d621a6e55c98e46a04874eab75c99
Reviewed-on: https://review.monogon.dev/c/monogon/+/3258
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
Tested-by: Jenkins CI
diff --git a/osbase/net/dns/forward/up/up_test.go b/osbase/net/dns/forward/up/up_test.go
new file mode 100644
index 0000000..0d0f928
--- /dev/null
+++ b/osbase/net/dns/forward/up/up_test.go
@@ -0,0 +1,42 @@
+package up
+
+// Taken and modified from CoreDNS, under Apache 2.0.
+
+import (
+ "sync"
+ "sync/atomic"
+ "testing"
+ "time"
+)
+
+func TestUp(t *testing.T) {
+ pr := New()
+ wg := sync.WaitGroup{}
+ hits := int32(0)
+
+ upfunc := func() error {
+ atomic.AddInt32(&hits, 1)
+ // Sleep tiny amount so that our other pr.Do() calls hit the lock.
+ time.Sleep(3 * time.Millisecond)
+ wg.Done()
+ return nil
+ }
+
+ pr.Start(5 * time.Millisecond)
+ defer pr.Stop()
+
+ // These functions AddInt32 to the same hits variable, but we only want to
+ // wait when upfunc finishes, as that only calls Done() on the waitgroup.
+ upfuncNoWg := func() error { atomic.AddInt32(&hits, 1); return nil }
+ wg.Add(1)
+ pr.Do(upfunc)
+ pr.Do(upfuncNoWg)
+ pr.Do(upfuncNoWg)
+
+ wg.Wait()
+
+ h := atomic.LoadInt32(&hits)
+ if h != 1 {
+ t.Errorf("Expected hits to be %d, got %d", 1, h)
+ }
+}