Use max 3 precision in displaying floats

When formating floats in `nomad node status`, use a maximum precision of
3.

api/nodes.go

@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/hashicorp/nomad/helper"
 	"github.com/hashicorp/nomad/nomad/structs"
 )
 
@@ -673,9 +674,9 @@ func (v *StatValue) String() string {
 	case v.StringVal != nil:
 		return *v.StringVal
 	case v.FloatNumeratorVal != nil:
-		str := strconv.FormatFloat(*v.FloatNumeratorVal, 'f', -1, 64)
+		str := helper.FormatFloat(*v.FloatNumeratorVal, 3)
 		if v.FloatDenominatorVal != nil {
-			str += " / " + strconv.FormatFloat(*v.FloatDenominatorVal, 'f', -1, 64)
+			str += " / " + helper.FormatFloat(*v.FloatDenominatorVal, 3)
 		}
 
 		if v.Unit != "" {

api/resources.go

@@ -172,7 +172,7 @@ type Attribute struct {
 func (a Attribute) String() string {
 	switch {
 	case a.FloatVal != nil:
-		str := strconv.FormatFloat(*a.FloatVal, 'f', -1, 64)
+		str := helper.FormatFloat(*a.FloatVal, 3)
 		if a.Unit != "" {
 			str += " " + a.Unit
 		}

helper/funcs.go

@@ -4,6 +4,8 @@ import (
 	"crypto/sha512"
 	"fmt"
 	"regexp"
+	"strconv"
+	"strings"
 	"time"
 
 	multierror "github.com/hashicorp/go-multierror"
@@ -344,3 +346,26 @@ func CheckHCLKeys(node ast.Node, valid []string) error {
 
 	return result
 }
+
+// FormatFloat converts the floating-point number f to a string,
+// after rounding it to the passed unit.
+//
+// Uses 'f' format (-ddd.dddddd, no exponent), and uses at most
+// maxPrec digits after the decimal point.
+func FormatFloat(f float64, maxPrec int) string {
+	v := strconv.FormatFloat(f, 'f', -1, 64)
+
+	idx := strings.LastIndex(v, ".")
+	if idx == -1 {
+		return v
+	}
+
+	sublen := idx + maxPrec + 1
+	if sublen > len(v) {
+		sublen = len(v)
+	}
+
+	return v[:sublen]
+
+	return v
+}

helper/funcs_test.go

@@ -4,6 +4,8 @@ import (
 	"reflect"
 	"sort"
 	"testing"
+
+	"github.com/stretchr/testify/require"
 )
 
 func TestSliceStringIsSubset(t *testing.T) {
@@ -87,3 +89,35 @@ func BenchmarkCleanEnvVar(b *testing.B) {
 		CleanEnvVar(in, replacement)
 	}
 }
+
+func TestFormatRoundedFloat(t *testing.T) {
+	cases := []struct {
+		input    float64
+		expected string
+	}{
+		{
+			1323,
+			"1323",
+		},
+		{
+			10.321,
+			"10.321",
+		},
+		{
+			100000.31324324,
+			"100000.313",
+		},
+		{
+			100000.3,
+			"100000.3",
+		},
+		{
+			0.7654321,
+			"0.765",
+		},
+	}
+
+	for _, c := range cases {
+		require.Equal(t, c.expected, FormatFloat(c.input, 3))
+	}
+}