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go/src/infra/libs/infra_util/errors.go

Index: go/src/infra/libs/infra_util/errors.go
diff --git a/go/src/infra/libs/infra_util/errors.go b/go/src/infra/libs/infra_util/errors.go
new file mode 100644
index 0000000000000000000000000000000000000000..9676978745dc3eca4976d31d605ee2fc2f86d972
--- /dev/null
+++ b/go/src/infra/libs/infra_util/errors.go
@@ -0,0 +1,71 @@
+// Copyright 2014 The Chromium 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 infra_util
+
+import (
+	"bytes"
+	"fmt"
+	"sync"
+)
+
+type MultiError []error
+
+func FanOutIn(hint int, producer func(chan<- func() error)) error {
+	funcChan := make(chan func() error, hint)
+	errChan := make(chan error)
+	go func() {
+		go func() {
+			defer close(funcChan)
+			producer(funcChan)
+		}()
+		grp := sync.WaitGroup{}
+		for f := range funcChan {
+			grp.Add(1)
+			f := f
+			go func() { defer grp.Done(); errChan <- f() }()
+		}
+		go func() { defer close(errChan); grp.Wait() }()
+	}()
+	return MultiErrorFromChan(errChan)
+}
+
+func MultiErrorFromChan(in <-chan error) error {
+	ret := MultiError{}
+	for err := range in {
+		if err != nil {
+			ret = append(ret, err)
+		}
+	}
+	if len(ret) != 0 {
+		return &ret
+	}
+	return nil
+}
+
+func (m *MultiError) Error() string {
+	if m == nil {
+		return "ME[]"
+	}
+	buf := &bytes.Buffer{}
+	fmt.Fprintf(buf, "ME[")
+	first := true
+	for _, e := range *m {
+		if !first {
+			fmt.Fprint(buf, ",")
+		}
+		first = false
+		fmt.Fprintf(buf, "%#v", e.Error())
+	}
+	fmt.Fprintf(buf, "]")
+	return buf.String()
+}
+
+func (m *MultiError) ErrorStrings() StringSet {
+	ret := make(StringSet, len(*m))
+	for _, e := range *m {
+		ret.Add(e.Error())
+	}
+	return ret
+}