report: Add -hist option for -type=json

Closes tsenart#394

README.md

@@ -363,6 +363,8 @@ Options:
   --type    Which report type to generate (text | json | hist[buckets]).
             [default: text]
 
+  --hist    Histogram buckets, e.g.: '[0,1ms,10ms]'
+
   --every   Write the report to --output at every given interval (e.g 100ms)
             The default of 0 means the report will only be written after
             all results have been processed. [default: 0]
@@ -434,6 +436,7 @@ The `Error Set` shows a unique set of errors returned by all issued requests. Th
     "99th": 3530000,
     "max": 3660505
   },
+  "hist": [0, 0, 10, 46, 44, 0],
   "bytes_in": {
     "total": 606700,
     "mean": 6067
@@ -457,6 +460,8 @@ The `Error Set` shows a unique set of errors returned by all issued requests. Th
 }
 ```
 
+If the `-hist` parameter is not present, the `hist` field is omitted.
+
 #### `report -type=hist`
 
 Computes and prints a text based histogram for the given buckets.

lib/histogram.go

@@ -1,6 +1,7 @@
 package vegeta
 
 import (
+	"encoding/json"
 	"fmt"
 	"strings"
 	"time"
@@ -35,6 +36,11 @@ func (h *Histogram) Add(r *Result) {
 	h.Counts[i]++
 }
 
+// MarshalJSON returns a JSON encoding of the list of counts.
+func (h *Histogram) MarshalJSON() ([]byte, error) {
+	return json.Marshal(h.Counts)
+}
+
 // Nth returns the nth bucket represented as a string.
 func (bs Buckets) Nth(i int) (left, right string) {
 	if i >= len(bs)-1 {

lib/metrics.go

@@ -12,6 +12,8 @@ import (
 type Metrics struct {
 	// Latencies holds computed request latency metrics.
 	Latencies LatencyMetrics `json:"latencies"`
+	// Histogram, only if requested
+	Histogram *Histogram `json:"hist,omitempty"`
 	// BytesIn holds computed incoming byte metrics.
 	BytesIn ByteMetrics `json:"bytes_in"`
 	// BytesOut holds computed outgoing byte metrics.
@@ -75,6 +77,10 @@ func (m *Metrics) Add(r *Result) {
 			m.Errors = append(m.Errors, r.Error)
 		}
 	}
+
+	if m.Histogram != nil {
+		m.Histogram.Add(r)
+	}
 }
 
 // Close implements the Close method of the Report interface by computing

report.go

@@ -40,6 +40,7 @@ func reportCmd() command {
 	typ := fs.String("type", "text", "Report type to generate [text, json, hist[buckets]]")
 	every := fs.Duration("every", 0, "Report interval")
 	output := fs.String("output", "stdout", "Output file")
+	hist := fs.String("hist", "", "Histogram buckets, e.g.: \"[0,1ms,10ms]\"")
 
 	fs.Usage = func() {
 		fmt.Fprintln(os.Stderr, reportUsage)
@@ -51,11 +52,11 @@ func reportCmd() command {
 		if len(files) == 0 {
 			files = append(files, "stdin")
 		}
-		return report(files, *typ, *output, *every)
+		return report(files, *typ, *output, *every, *hist)
 	}}
 }
 
-func report(files []string, typ, output string, every time.Duration) error {
+func report(files []string, typ, output string, every time.Duration, histStr string) error {
 	if len(typ) < 4 {
 		return fmt.Errorf("invalid report type: %s", typ)
 	}
@@ -85,6 +86,12 @@ func report(files []string, typ, output string, every time.Duration) error {
 		rep, report = vegeta.NewTextReporter(&m), &m
 	case "json":
 		var m vegeta.Metrics
+		if histStr != "" {
+			m.Histogram = &vegeta.Histogram{}
+			if err := m.Histogram.Buckets.UnmarshalText([]byte(histStr)); err != nil {
+				return err
+			}
+		}
 		rep, report = vegeta.NewJSONReporter(&m), &m
 	case "hist":
 		if len(typ) < 6 {