diff options
author | Brad Fitzpatrick <bradfitz@golang.org> | 2014-04-17 13:28:40 -0700 |
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committer | Brad Fitzpatrick <bradfitz@golang.org> | 2014-04-17 13:28:40 -0700 |
commit | c45392bae0332e1407c4468ee35a5176651b03fa (patch) | |
tree | ebaed86deb3a963e919a51c334781f8d72e53c76 | |
parent | 576318c7bd9c1deeb5877df65dc26aeb53999ee2 (diff) | |
download | go-c45392bae0332e1407c4468ee35a5176651b03fa.tar.gz go-c45392bae0332e1407c4468ee35a5176651b03fa.zip |
net: fix probabilities in DNS SRV shuffleByWeight
Patch from msolo. Just moving it to a CL.
The test fails before and passes with the fix.
Fixes #7098
LGTM=msolo, rsc
R=rsc, iant, msolo
CC=golang-codereviews
https://golang.org/cl/88900044
-rw-r--r-- | src/pkg/net/dnsclient.go | 4 | ||||
-rw-r--r-- | src/pkg/net/dnsclient_test.go | 69 |
2 files changed, 71 insertions, 2 deletions
diff --git a/src/pkg/net/dnsclient.go b/src/pkg/net/dnsclient.go index 01db437294..9bffa11f91 100644 --- a/src/pkg/net/dnsclient.go +++ b/src/pkg/net/dnsclient.go @@ -191,10 +191,10 @@ func (addrs byPriorityWeight) shuffleByWeight() { } for sum > 0 && len(addrs) > 1 { s := 0 - n := rand.Intn(sum + 1) + n := rand.Intn(sum) for i := range addrs { s += int(addrs[i].Weight) - if s >= n { + if s > n { if i > 0 { t := addrs[i] copy(addrs[1:i+1], addrs[0:i]) diff --git a/src/pkg/net/dnsclient_test.go b/src/pkg/net/dnsclient_test.go new file mode 100644 index 0000000000..435eb35506 --- /dev/null +++ b/src/pkg/net/dnsclient_test.go @@ -0,0 +1,69 @@ +// Copyright 2014 The Go Authors. All rights reserved. +// Use of this source code is governed by a BSD-style +// license that can be found in the LICENSE file. + +package net + +import ( + "math/rand" + "testing" +) + +func checkDistribution(t *testing.T, data []*SRV, margin float64) { + sum := 0 + for _, srv := range data { + sum += int(srv.Weight) + } + + results := make(map[string]int) + + count := 1000 + for j := 0; j < count; j++ { + d := make([]*SRV, len(data)) + copy(d, data) + byPriorityWeight(d).shuffleByWeight() + key := d[0].Target + results[key] = results[key] + 1 + } + + actual := results[data[0].Target] + expected := float64(count) * float64(data[0].Weight) / float64(sum) + diff := float64(actual) - expected + t.Logf("actual: %v diff: %v e: %v m: %v", actual, diff, expected, margin) + if diff < 0 { + diff = -diff + } + if diff > (expected * margin) { + t.Errorf("missed target weight: expected %v, %v", expected, actual) + } +} + +func testUniformity(t *testing.T, size int, margin float64) { + rand.Seed(1) + data := make([]*SRV, size) + for i := 0; i < size; i++ { + data[i] = &SRV{Target: string('a' + i), Weight: 1} + } + checkDistribution(t, data, margin) +} + +func TestUniformity(t *testing.T) { + testUniformity(t, 2, 0.05) + testUniformity(t, 3, 0.10) + testUniformity(t, 10, 0.20) + testWeighting(t, 0.05) +} + +func testWeighting(t *testing.T, margin float64) { + rand.Seed(1) + data := []*SRV{ + {Target: "a", Weight: 60}, + {Target: "b", Weight: 30}, + {Target: "c", Weight: 10}, + } + checkDistribution(t, data, margin) +} + +func TestWeighting(t *testing.T) { + testWeighting(t, 0.05) +} |