1// Copyright 2018 Google LLC
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
15package bigquery
16
17import (
18	"math/rand"
19	"os"
20	"sync"
21	"time"
22)
23
24// Support for random values (typically job IDs and insert IDs).
25
26const alphanum = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"
27
28var (
29	rngMu sync.Mutex
30	rng   = rand.New(rand.NewSource(time.Now().UnixNano() ^ int64(os.Getpid())))
31)
32
33// For testing.
34var randomIDFn = randomID
35
36// As of August 2017, the BigQuery service uses 27 alphanumeric characters for
37// suffixes.
38const randomIDLen = 27
39
40func randomID() string {
41	// This is used for both job IDs and insert IDs.
42	var b [randomIDLen]byte
43	rngMu.Lock()
44	for i := 0; i < len(b); i++ {
45		b[i] = alphanum[rng.Intn(len(alphanum))]
46	}
47	rngMu.Unlock()
48	return string(b[:])
49}
50
51// Seed seeds this package's random number generator, used for generating job and
52// insert IDs. Use Seed to obtain repeatable, deterministic behavior from bigquery
53// clients. Seed should be called before any clients are created.
54func Seed(s int64) {
55	rng = rand.New(rand.NewSource(s))
56}
57