lib: use vu ctx instead of request ctx for pushing metrics

PushIfNotDone is intended to use with VU context instead of request
context. This is a bug in current code base, but it is not triggered due
to the bug in Go net/http. A request context can be in cancelled state
due to be cancelled or timeouted. PushIfNotDone won't see the difference
and will skip pushing metrics for timeouted requests.

Fixing it by passing VU context to PushIfNotDone instead of request ctx.

Fixes #1260

js/modules/k6/http/request_test.go

@@ -274,13 +274,13 @@ func TestRequestAndBatch(t *testing.T) {
 			`))
 			endTime := time.Now()
 			require.Error(t, err)
-			assert.Contains(t, err.Error(), "Client.Timeout exceeded while awaiting headers")
+			assert.Contains(t, err.Error(), "context deadline exceeded")
 			assert.WithinDuration(t, startTime.Add(1*time.Second), endTime, 2*time.Second)
 
 			logEntry := hook.LastEntry()
 			if assert.NotNil(t, logEntry) {
 				assert.Equal(t, logrus.WarnLevel, logEntry.Level)
-				assert.Contains(t, logEntry.Data["error"].(error).Error(), "Client.Timeout exceeded while awaiting headers")
+				assert.Contains(t, logEntry.Data["error"].(error).Error(), "context deadline exceeded")
 				assert.Equal(t, "Request Failed", logEntry.Message)
 			}
 		})

lib/netext/httpext/request.go

@@ -264,7 +264,7 @@ func MakeRequest(ctx context.Context, preq *ParsedHTTPRequest) (*Response, error
 		}
 	}
 
-	tracerTransport := newTransport(state, tags)
+	tracerTransport := newTransport(ctx, state, tags)
 	var transport http.RoundTripper = tracerTransport
 
 	if state.Options.HTTPDebug.String != "" {

lib/netext/httpext/transport.go

@@ -33,9 +33,10 @@ import (
 	"github.com/loadimpact/k6/stats"
 )
 
-// transport is an implemenation of http.RoundTripper that will measure and emit
+// transport is an implementation of http.RoundTripper that will measure and emit
 // different metrics for each roundtrip
 type transport struct {
+	ctx   context.Context
 	state *lib.State
 	tags  map[string]string
 
@@ -72,10 +73,12 @@ var _ http.RoundTripper = &transport{}
 // requests made through it and annotates and emits the recorded metric samples
 // through the state.Samples channel.
 func newTransport(
+	ctx context.Context,
 	state *lib.State,
 	tags map[string]string,
 ) *transport {
 	return &transport{
+		ctx:             ctx,
 		state:           state,
 		tags:            tags,
 		lastRequestLock: new(sync.Mutex),
@@ -147,7 +150,7 @@ func (t *transport) measureAndEmitMetrics(unfReq *unfinishedRequest) *finishedRe
 	}
 
 	trail.SaveSamples(stats.IntoSampleTags(&tags))
-	stats.PushIfNotDone(unfReq.ctx, t.state.Samples, trail)
+	stats.PushIfNotDone(t.ctx, t.state.Samples, trail)
 
 	return result
 }