plot: Ensure timestamp monotonicity

lib/plot.go

@@ -2,6 +2,7 @@ package vegeta
 
 import (
 	"encoding/json"
+	"fmt"
 	"html/template"
 	"io"
 	"math"
@@ -47,7 +48,7 @@ func newLabeledSeries(label func(*Result) string) *labeledSeries {
 	}
 }
 
-func (ls *labeledSeries) add(r *Result) {
+func (ls *labeledSeries) add(r *Result) (err error) {
 	label := ls.label(r)
 
 	ts, ok := ls.series[label]
@@ -64,7 +65,7 @@ func (ls *labeledSeries) add(r *Result) {
 	}
 
 	if ls.buf[p.seq] = p; p.seq != ls.seq {
-		return // buffer
+		return nil // buffer
 	} else if ls.seq == 0 {
 		ls.began = r.Timestamp // first point in attack
 	}
@@ -73,11 +74,16 @@ func (ls *labeledSeries) add(r *Result) {
 	for {
 		p, ok := ls.buf[ls.seq]
 		if !ok {
-			return
+			return nil
 		}
-
 		delete(ls.buf, ls.seq)
-		p.ts.add(p.seq, uint64(p.t.Sub(ls.began))/1e6, p.v) // timestamp in ms precision
+
+		// timestamp in ms precision
+		err = p.ts.add(uint64(p.t.Sub(ls.began))/1e6, p.v)
+		if err != nil {
+			return fmt.Errorf("point with sequence number %d in %v", p.seq, err)
+		}
+
 		ls.seq++
 	}
 }
@@ -94,13 +100,13 @@ func NewHTMLPlot(title string, threshold int, label func(*Result) string) *HTMLP
 }
 
 // Add adds the given Result to the HTMLPlot time series.
-func (p *HTMLPlot) Add(r *Result) {
+func (p *HTMLPlot) Add(r *Result) error {
 	s, ok := p.series[r.Attack]
 	if !ok {
 		s = newLabeledSeries(p.label)
 		p.series[r.Attack] = s
 	}
-	s.add(r)
+	return s.add(r)
 }
 
 // Close closes the HTML plot for writing.

lib/timeseries.go

@@ -1,15 +1,19 @@
 package vegeta
 
 import (
+	"errors"
 	"time"
 
 	tsz "github.com/dgryski/go-tsz"
 	"github.com/tsenart/vegeta/lib/lttb"
 )
 
+// An in-memory timeSeries of points with high compression of
+// both timestamps and values.  It's not safe for concurrent use.
 type timeSeries struct {
 	attack string
 	label  string
+	prev   uint64
 	data   *tsz.Series
 	len    int
 }
@@ -22,9 +26,18 @@ func newTimeSeries(attack, label string) *timeSeries {
 	}
 }
 
-func (ts *timeSeries) add(seq, t uint64, v float64) {
+var errMonotonicTimestamp = errors.New("timeseries: non monotonically increasing timestamp.")
+
+func (ts *timeSeries) add(t uint64, v float64) error {
+	if ts.prev > t {
+		return errMonotonicTimestamp
+	}
+
 	ts.data.Push(t, v)
+	ts.prev = t
 	ts.len++
+
+	return nil
 }
 
 func (ts *timeSeries) iter() lttb.Iter {

plot.go

@@ -92,7 +92,10 @@ decode:
 				}
 				return err
 			}
-			plot.Add(&r)
+
+			if err = plot.Add(&r); err != nil {
+				return err
+			}
 		}
 	}