Adds repeatContent filter (#1616)

`repeatContent` filter generates response of specified size from repeated text

Signed-off-by: Alexander Yastrebov <alexander.yastrebov@zalando.de>

docs/reference/filters.md

@@ -506,6 +506,21 @@ Example:
 * -> randomContent(42) -> <shunt>;
 ```
 
+## repeatContent
+
+Generate response of specified size from repeated text.
+
+Parameters:
+
+* text to repeat (string)
+* size of response in bytes (int)
+
+Example:
+
+```
+* -> repeatContent("I will not waste chalk. ", 1000) -> <shunt>;
+```
+
 ## latency
 
 Enable adding artificial latency

filters/builtin/builtin.go

@@ -127,6 +127,7 @@ func MakeRegistry() filters.Registry {
 		NewSetDynamicBackendUrl(),
 		NewOriginMarkerSpec(),
 		diag.NewRandom(),
+		diag.NewRepeat(),
 		diag.NewLatency(),
 		diag.NewBandwidth(),
 		diag.NewChunks(),

filters/diag/diag.go

@@ -12,6 +12,7 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"net/http"
+	"strconv"
 	"sync"
 	"time"
 
@@ -22,6 +23,7 @@ const defaultChunkSize = 512
 
 const (
 	RandomName           = "randomContent"
+	RepeatName           = "repeatContent"
 	LatencyName          = "latency"
 	ChunksName           = "chunks"
 	BandwidthName        = "bandwidth"
@@ -47,6 +49,16 @@ type random struct {
 	len  int64
 }
 
+type repeat struct {
+	bytes []byte
+	len   int64
+}
+
+type repeatReader struct {
+	bytes  []byte
+	offset int
+}
+
 type throttle struct {
 	typ       throttleType
 	chunkSize int
@@ -68,6 +80,15 @@ func kbps2bpms(kbps float64) float64 {
 //
 func NewRandom() filters.Spec { return &random{} }
 
+// NewRepeat creates a filter specification whose filter instances can be used
+// to respond to requests with a repeated text. It expects the text and
+// the byte length of the response body to be generated as arguments.
+// Eskip example:
+//
+// 	* -> repeatContent("x", 100) -> <shunt>;
+//
+func NewRepeat() filters.Spec { return &repeat{} }
+
 // NewLatency creates a filter specification whose filter instances can be used
 // to add additional latency to responses. It expects the latency in milliseconds
 // as an argument. It always adds this value in addition to the natural latency,
@@ -146,6 +167,59 @@ func (r *random) Request(ctx filters.FilterContext) {
 
 func (r *random) Response(ctx filters.FilterContext) {}
 
+func (r *repeat) Name() string { return RepeatName }
+
+func (r *repeat) CreateFilter(args []interface{}) (filters.Filter, error) {
+	if len(args) != 2 {
+		return nil, filters.ErrInvalidFilterParameters
+	}
+
+	text, ok := args[0].(string)
+	if !ok || text == "" {
+		return nil, filters.ErrInvalidFilterParameters
+	}
+
+	var len int64
+	switch v := args[1].(type) {
+	case float64:
+		len = int64(v)
+	case int:
+		len = int64(v)
+	case int64:
+		len = v
+	default:
+		return nil, filters.ErrInvalidFilterParameters
+	}
+	if len < 0 {
+		return nil, filters.ErrInvalidFilterParameters
+	}
+
+	return &repeat{[]byte(text), len}, nil
+}
+
+func (r *repeat) Request(ctx filters.FilterContext) {
+	ctx.Serve(&http.Response{
+		StatusCode: http.StatusOK,
+		Header:     http.Header{"Content-Length": []string{strconv.FormatInt(r.len, 10)}},
+		Body:       ioutil.NopCloser(io.LimitReader(&repeatReader{r.bytes, 0}, r.len)),
+	})
+}
+
+func (r *repeatReader) Read(p []byte) (int, error) {
+	n := copy(p, r.bytes[r.offset:])
+	if n < len(p) {
+		n += copy(p[n:], r.bytes[:r.offset])
+		for n < len(p) {
+			copy(p[n:], p[:n])
+			n *= 2
+		}
+	}
+	r.offset = (r.offset + len(p)) % len(r.bytes)
+	return len(p), nil
+}
+
+func (r *repeat) Response(ctx filters.FilterContext) {}
+
 func (t *throttle) Name() string {
 	switch t.typ {
 	case latency:

filters/diag/diag_test.go

@@ -6,6 +6,7 @@ import (
 	"io/ioutil"
 	"math/rand"
 	"net/http"
+	"strconv"
 	"testing"
 	"time"
 
@@ -212,6 +213,137 @@ func TestRandom(t *testing.T) {
 	}
 }
 
+func TestRepeat(t *testing.T) {
+	for _, ti := range []struct {
+		args     []interface{}
+		err      bool
+		expected string
+	}{{
+		args: []interface{}{},
+		err:  true,
+	}, {
+		args: []interface{}{1, "wrong types"},
+		err:  true,
+	}, {
+		args: []interface{}{"too few arguments"},
+		err:  true,
+	}, {
+		args: []interface{}{"too many arguments", 10.0, "extra"},
+		err:  true,
+	}, {
+		args: []interface{}{"length is not a number", "10"},
+		err:  true,
+	}, {
+		args: []interface{}{"", 10},
+		err:  true,
+	}, {
+		args: []interface{}{"negative length", -1},
+		err:  true,
+	}, {
+		args:     []interface{}{"zero length", 0},
+		expected: "",
+	}, {
+		args:     []interface{}{"1", 1},
+		expected: "1",
+	}, {
+		args:     []interface{}{"float", 2.0},
+		expected: "fl",
+	}, {
+		args:     []interface{}{"0123456789", 3},
+		expected: "012",
+	}, {
+		args:     []interface{}{"0123456789", 30},
+		expected: "012345678901234567890123456789",
+	}} {
+		repeat := NewRepeat()
+		_, err := repeat.CreateFilter(ti.args)
+		if ti.err {
+			if err == nil {
+				t.Errorf("expected error for %v", ti.args)
+			}
+			continue
+		} else {
+			if err != nil {
+				t.Errorf("unexpected error %v for %v", err, ti.args)
+				continue
+			}
+		}
+
+		p := proxytest.New(filters.Registry{RepeatName: repeat}, &eskip.Route{
+			Filters: []*eskip.Filter{{Name: RepeatName, Args: ti.args}},
+			Shunt:   true})
+		defer p.Close()
+
+		rsp, err := http.Get(p.URL)
+		if err != nil {
+			t.Fatal(err)
+		}
+		defer rsp.Body.Close()
+
+		if rsp.StatusCode != http.StatusOK {
+			t.Fatalf("request failed: %d", rsp.StatusCode)
+		}
+
+		b, err := ioutil.ReadAll(rsp.Body)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		got := string(b)
+		if got != ti.expected {
+			t.Errorf("result mismatch for %v", ti.args)
+		}
+
+		if rsp.Header.Get("Content-Length") != strconv.Itoa(len(ti.expected)) {
+			t.Error("content length mismatch")
+		}
+	}
+}
+
+func TestRepeatReader(t *testing.T) {
+	r := &repeatReader{[]byte("0123456789"), 0}
+
+	checkRead(t, r, 5, "01234")
+	checkRead(t, r, 5, "56789")
+	checkRead(t, r, 3, "012")
+	checkRead(t, r, 3, "345")
+	checkRead(t, r, 3, "678")
+	checkRead(t, r, 3, "901")
+	checkRead(t, r, 10, "2345678901")
+	checkRead(t, r, 8, "23456789")
+	checkRead(t, r, 15, "012345678901234")
+	checkRead(t, r, 25, "5678901234567890123456789")
+	checkRead(t, r, 1, "0")
+	checkRead(t, r, 2, "12")
+	checkRead(t, r, 3, "345")
+	checkRead(t, r, 4, "6789")
+	checkRead(t, r, 5, "01234")
+	checkRead(t, r, 6, "567890")
+	checkRead(t, r, 7, "1234567")
+	checkRead(t, r, 8, "89012345")
+	checkRead(t, r, 9, "678901234")
+	checkRead(t, r, 10, "5678901234")
+	checkRead(t, r, 11, "56789012345")
+	checkRead(t, r, 12, "678901234567")
+}
+
+func checkRead(t *testing.T, r io.Reader, n int, expected string) {
+	b := make([]byte, n)
+	m, err := r.Read(b)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+	if m != n {
+		t.Errorf("expected to read %d bytes, got %d", n, m)
+		return
+	}
+	s := string(b)
+	if s != expected {
+		t.Errorf("expected %s, got %s", expected, s)
+	}
+}
+
 func TestThrottleArgs(t *testing.T) {
 	for _, ti := range []struct {
 		msg  string