fault: new package for fault injection

Doesn't do much.

Change-Id: Iab038564a753611a8bc8f44f33a57dbfe96d76e0

pkg/fault/fault.go

@@ -0,0 +1,59 @@
+/*
+Copyright 2014 The Camlistore Authors
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// Package fault handles fault injection for testing.
+package fault
+
+import (
+	"errors"
+	"math/rand"
+	"os"
+	"strconv"
+	"strings"
+)
+
+var fakeErr = errors.New("fake injected error for testing")
+
+// An Injector reports whether fake errors should be returned.
+type Injector struct {
+	failPercent int
+}
+
+// NewInjector returns a new fault injector with the given name.  The
+// environment variable "FAULT_" + capital(name) + "_FAIL_PERCENT"
+// controls the percentage of requests that fail. If undefined or
+// zero, no requests fail.
+func NewInjector(name string) *Injector {
+	var failPercent, _ = strconv.Atoi(os.Getenv("FAULT_" + strings.ToUpper(name) + "_FAIL_PERCENT"))
+	return &Injector{
+		failPercent: failPercent,
+	}
+}
+
+// ShouldFail reports whether a fake error should be returned.
+func (in *Injector) ShouldFail() bool {
+	return in.failPercent > 0 && in.failPercent > rand.Intn(100)
+}
+
+// FailErr checks ShouldFail and, if true, assigns a fake error to err
+// and returns true.
+func (in *Injector) FailErr(err *error) bool {
+	if !in.ShouldFail() {
+		return false
+	}
+	*err = fakeErr
+	return true
+}