common: no more relying on math/rand.DefaultSource

Fixes https://github.com/tendermint/tmlibs/issues/99
Updates https://github.com/tendermint/tendermint/issues/973

Removed usages of math/rand.DefaultSource in favour of our
own source that's seeded with a completely random source
and is safe for use in concurrent in multiple goroutines.
Also extend some functionality that the stdlib exposes such as
* RandPerm
* RandIntn
* RandInt31
* RandInt63

Also added an integration test whose purpose is to be run as
a consistency check to ensure that our results never repeat
hence that our internal PRNG is uniquely seeded each time.
This integration test can be triggered by setting environment variable:
`TENDERMINT_INTEGRATION_TESTS=true`
for example
```shell
TENDERMINT_INTEGRATION_TESTS=true go test
```

common/bit_array.go

@@ -3,7 +3,6 @@ package common
 import (
 	"encoding/binary"
 	"fmt"
-	"math/rand"
 	"strings"
 	"sync"
 )
@@ -212,12 +211,12 @@ func (bA *BitArray) PickRandom() (int, bool) {
 	if length == 0 {
 		return 0, false
 	}
-	randElemStart := rand.Intn(length)
+	randElemStart := RandIntn(length)
 	for i := 0; i < length; i++ {
 		elemIdx := ((i + randElemStart) % length)
 		if elemIdx < length-1 {
 			if bA.Elems[elemIdx] > 0 {
-				randBitStart := rand.Intn(64)
+				randBitStart := RandIntn(64)
 				for j := 0; j < 64; j++ {
 					bitIdx := ((j + randBitStart) % 64)
 					if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {
@@ -232,7 +231,7 @@ func (bA *BitArray) PickRandom() (int, bool) {
 			if elemBits == 0 {
 				elemBits = 64
 			}
-			randBitStart := rand.Intn(elemBits)
+			randBitStart := RandIntn(elemBits)
 			for j := 0; j < elemBits; j++ {
 				bitIdx := ((j + randBitStart) % elemBits)
 				if (bA.Elems[elemIdx] & (uint64(1) << uint(bitIdx))) > 0 {

common/random.go

@@ -3,6 +3,7 @@ package common
 import (
 	crand "crypto/rand"
 	"math/rand"
+	"sync"
 	"time"
 )
 
@@ -10,6 +11,11 @@ const (
 	strChars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz" // 62 characters
 )
 
+var rng struct {
+	sync.Mutex
+	*rand.Rand
+}
+
 func init() {
 	b := cRandBytes(8)
 	var seed uint64
@@ -17,7 +23,7 @@ func init() {
 		seed |= uint64(b[i])
 		seed <<= 8
 	}
-	rand.Seed(int64(seed))
+	rng.Rand = rand.New(rand.NewSource(int64(seed)))
 }
 
 // Constructs an alphanumeric string of given length.
@@ -25,7 +31,7 @@ func RandStr(length int) string {
 	chars := []byte{}
 MAIN_LOOP:
 	for {
-		val := rand.Int63()
+		val := rng.Int63()
 		for i := 0; i < 10; i++ {
 			v := int(val & 0x3f) // rightmost 6 bits
 			if v >= 62 {         // only 62 characters in strChars
@@ -45,72 +51,98 @@ MAIN_LOOP:
 }
 
 func RandUint16() uint16 {
-	return uint16(rand.Uint32() & (1<<16 - 1))
+	return uint16(RandUint32() & (1<<16 - 1))
 }
 
 func RandUint32() uint32 {
-	return rand.Uint32()
+	rng.Lock()
+	u32 := rng.Uint32()
+	rng.Unlock()
+	return u32
 }
 
 func RandUint64() uint64 {
-	return uint64(rand.Uint32())<<32 + uint64(rand.Uint32())
+	return uint64(RandUint32())<<32 + uint64(RandUint32())
 }
 
 func RandUint() uint {
-	return uint(rand.Int())
+	rng.Lock()
+	i := rng.Int()
+	rng.Unlock()
+	return uint(i)
 }
 
 func RandInt16() int16 {
-	return int16(rand.Uint32() & (1<<16 - 1))
+	return int16(RandUint32() & (1<<16 - 1))
 }
 
 func RandInt32() int32 {
-	return int32(rand.Uint32())
+	return int32(RandUint32())
 }
 
 func RandInt64() int64 {
-	return int64(rand.Uint32())<<32 + int64(rand.Uint32())
+	return int64(RandUint64())
 }
 
 func RandInt() int {
-	return rand.Int()
+	rng.Lock()
+	i := rng.Int()
+	rng.Unlock()
+	return i
+}
+
+func RandInt31() int32 {
+	rng.Lock()
+	i31 := rng.Int31()
+	rng.Unlock()
+	return i31
+}
+
+func RandInt63() int64 {
+	rng.Lock()
+	i63 := rng.Int63()
+	rng.Unlock()
+	return i63
 }
 
 // Distributed pseudo-exponentially to test for various cases
 func RandUint16Exp() uint16 {
-	bits := rand.Uint32() % 16
+	bits := RandUint32() % 16
 	if bits == 0 {
 		return 0
 	}
 	n := uint16(1 << (bits - 1))
-	n += uint16(rand.Int31()) & ((1 << (bits - 1)) - 1)
+	n += uint16(RandInt31()) & ((1 << (bits - 1)) - 1)
 	return n
 }
 
 // Distributed pseudo-exponentially to test for various cases
 func RandUint32Exp() uint32 {
-	bits := rand.Uint32() % 32
+	bits := RandUint32() % 32
 	if bits == 0 {
 		return 0
 	}
 	n := uint32(1 << (bits - 1))
-	n += uint32(rand.Int31()) & ((1 << (bits - 1)) - 1)
+	n += uint32(RandInt31()) & ((1 << (bits - 1)) - 1)
 	return n
 }
 
 // Distributed pseudo-exponentially to test for various cases
 func RandUint64Exp() uint64 {
-	bits := rand.Uint32() % 64
+	bits := RandUint32() % 64
 	if bits == 0 {
 		return 0
 	}
 	n := uint64(1 << (bits - 1))
-	n += uint64(rand.Int63()) & ((1 << (bits - 1)) - 1)
+	n += uint64(RandInt63()) & ((1 << (bits - 1)) - 1)
 	return n
 }
 
 func RandFloat32() float32 {
-	return rand.Float32()
+	rng.Lock()
+	f32 := rng.Float32()
+	rng.Unlock()
+	return f32
 }
 
 func RandTime() time.Time {
@@ -118,11 +150,24 @@ func RandTime() time.Time {
 }
 
 func RandBytes(n int) []byte {
-	bs := make([]byte, n)
-	for i := 0; i < n; i++ {
-		bs[i] = byte(rand.Intn(256))
-	}
-	return bs
+	return cRandBytes(n)
+}
+
+// RandIntn returns, as an int, a non-negative pseudo-random number in [0, n).
+// It panics if n <= 0
+func RandIntn(n int) int {
+	rng.Lock()
+	i := rng.Intn(n)
+	rng.Unlock()
+	return i
+}
+
+// RandPerm returns a pseudo-random permutation of n integers in [0, n).
+func RandPerm(n int) []int {
+	rng.Lock()
+	perm := rng.Perm(n)
+	rng.Unlock()
+	return perm
 }
 
 // NOTE: This relies on the os's random number generator.

common/random_test.go

@@ -0,0 +1,108 @@
+package common_test
+
+import (
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/tendermint/tmlibs/common"
+)
+
+// It is essential that these tests run and never repeat their outputs
+// lest we've been pwned and the behavior of our randomness is controlled.
+// See Issues:
+//  * https://github.com/tendermint/tmlibs/issues/99
+//  * https://github.com/tendermint/tendermint/issues/973
+func TestUniqueRng(t *testing.T) {
+	if os.Getenv("TENDERMINT_INTEGRATION_TESTS") == "" {
+		t.Skipf("Can only be run as an integration test")
+	}
+
+	// The goal of this test is to invoke the
+	// Rand* tests externally with no repeating results, booted up.
+	// Any repeated results indicate that the seed is the same or that
+	// perhaps we are using math/rand directly.
+	tmpDir, err := ioutil.TempDir("", "rng-tests")
+	if err != nil {
+		t.Fatalf("Creating tempDir: %v", err)
+	}
+	defer os.RemoveAll(tmpDir)
+
+	outpath := filepath.Join(tmpDir, "main.go")
+	f, err := os.Create(outpath)
+	if err != nil {
+		t.Fatalf("Setting up %q err: %v", outpath, err)
+	}
+	f.Write([]byte(integrationTestProgram))
+	if err := f.Close(); err != nil {
+		t.Fatalf("Closing: %v", err)
+	}
+
+	outputs := make(map[string][]int)
+	for i := 0; i < 100; i++ {
+		cmd := exec.Command("go", "run", outpath)
+		bOutput, err := cmd.CombinedOutput()
+		if err != nil {
+			t.Errorf("Run #%d: err: %v output: %s", i, err, bOutput)
+			continue
+		}
+		output := string(bOutput)
+		runs, seen := outputs[output]
+		if seen {
+			t.Errorf("Run #%d's output was already seen in previous runs: %v", i, runs)
+		}
+		outputs[output] = append(outputs[output], i)
+	}
+}
+
+const integrationTestProgram = `
+package main
+
+import (
+  "encoding/json"
+  "fmt"
+  "math/rand"
+
+  "github.com/tendermint/tmlibs/common"
+)
+
+func main() {
+  // Set math/rand's Seed so that any direct invocations
+  // of math/rand will reveal themselves.
+  rand.Seed(1)
+  perm := common.RandPerm(10)
+  blob, _ := json.Marshal(perm)
+  fmt.Printf("perm: %s\n", blob)
+
+  fmt.Printf("randInt: %d\n", common.RandInt())
+  fmt.Printf("randUint: %d\n", common.RandUint())
+  fmt.Printf("randIntn: %d\n", common.RandIntn(97))
+  fmt.Printf("randInt31: %d\n", common.RandInt31())
+  fmt.Printf("randInt32: %d\n", common.RandInt32())
+  fmt.Printf("randInt63: %d\n", common.RandInt63())
+  fmt.Printf("randInt64: %d\n", common.RandInt64())
+  fmt.Printf("randUint32: %d\n", common.RandUint32())
+  fmt.Printf("randUint64: %d\n", common.RandUint64())
+  fmt.Printf("randUint16Exp: %d\n", common.RandUint16Exp())
+  fmt.Printf("randUint32Exp: %d\n", common.RandUint32Exp())
+  fmt.Printf("randUint64Exp: %d\n", common.RandUint64Exp())
+}`
+
+func TestRngConcurrencySafety(t *testing.T) {
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+
+			_ = common.RandUint64()
+			<-time.After(time.Millisecond * time.Duration(common.RandIntn(100)))
+			_ = common.RandPerm(3)
+		}()
+	}
+	wg.Wait()
+}