1// Copyright 2019, OpenCensus Authors
2//
3// Licensed under the Apache License, Version 2.0 (the "License");
4// you may not use this file except in compliance with the License.
5// You may obtain a copy of the License at
6//
7//     http://www.apache.org/licenses/LICENSE-2.0
8//
9// Unless required by applicable law or agreed to in writing, software
10// distributed under the License is distributed on an "AS IS" BASIS,
11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12// See the License for the specific language governing permissions and
13// limitations under the License.
14//
15
16package tag
17
18const (
19	// valueTTLNoPropagation prevents tag from propagating.
20	valueTTLNoPropagation = 0
21
22	// valueTTLUnlimitedPropagation allows tag to propagate without any limits on number of hops.
23	valueTTLUnlimitedPropagation = -1
24)
25
26// TTL is metadata that specifies number of hops a tag can propagate.
27// Details about TTL metadata is specified at https://github.com/census-instrumentation/opencensus-specs/blob/master/tags/TagMap.md#tagmetadata
28type TTL struct {
29	ttl int
30}
31
32var (
33	// TTLUnlimitedPropagation is TTL metadata that allows tag to propagate without any limits on number of hops.
34	TTLUnlimitedPropagation = TTL{ttl: valueTTLUnlimitedPropagation}
35
36	// TTLNoPropagation is TTL metadata that prevents tag from propagating.
37	TTLNoPropagation = TTL{ttl: valueTTLNoPropagation}
38)
39
40type metadatas struct {
41	ttl TTL
42}
43
44// Metadata applies metadatas specified by the function.
45type Metadata func(*metadatas)
46
47// WithTTL applies metadata with provided ttl.
48func WithTTL(ttl TTL) Metadata {
49	return func(m *metadatas) {
50		m.ttl = ttl
51	}
52}
53