(upstream) toxic for http headers

README.md

@@ -411,6 +411,12 @@ Closes connection when transmitted data exceeded limit.
 
  - `bytes`: number of bytes it should transmit before connection is closed
 
+#### http_request_headers
+
+Modifies http request headers. This toxic only has effect when the direction equals `upstream`. The most common use case would be modifying the Host header when using reverse proxies.
+
+ - `headers`: a key value map with the headers to set.
+
 ### HTTP API
 
 All communication with the Toxiproxy daemon from the client happens through the

toxics/http_request_headers.go

@@ -0,0 +1,56 @@
+package toxics
+
+import (
+	"bufio"
+	"bytes"
+	"io"
+	"net/http"
+	"strings"
+
+	"github.com/Shopify/toxiproxy/stream"
+)
+
+// HttpToxic modifies requests headers (upstream) for http requests. Not to be used with direction = downstream
+type HttpToxic struct {
+	Headers map[string]string `json:"headers"`
+}
+
+func (t *HttpToxic) modifyRequest(request *http.Request) {
+	// Add all headers to request. Host is derived from the url if we dont set it explicitly.
+	for k, v := range t.Headers {
+		if strings.EqualFold("Host", k) {
+			request.Host = v
+		} else {
+			request.Header.Set(k, v)
+		}
+	}
+}
+
+func (t *HttpToxic) Pipe(stub *ToxicStub) {
+	buffer := bytes.NewBuffer(make([]byte, 0, 32*1024))
+	writer := stream.NewChanWriter(stub.Output)
+	reader := stream.NewChanReader(stub.Input)
+	reader.SetInterrupt(stub.Interrupt)
+	for {
+		tee := io.TeeReader(reader, buffer)
+		req, err := http.ReadRequest(bufio.NewReader(tee))
+		if err == stream.ErrInterrupted {
+			buffer.WriteTo(writer)
+			return
+		} else if err == io.EOF {
+			stub.Close()
+			return
+		}
+		if err != nil {
+			buffer.WriteTo(writer)
+		} else {
+			t.modifyRequest(req)
+			req.Write(writer)
+		}
+		buffer.Reset()
+	}
+}
+
+func init() {
+	Register("http_request_headers", new(HttpToxic))
+}

toxics/http_request_headers_test.go

@@ -0,0 +1,79 @@
+package toxics_test
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/Shopify/toxiproxy/toxics"
+)
+
+func echoRequestHeaders(w http.ResponseWriter, r *http.Request) {
+	headersMap := map[string]string{}
+
+	for k, v := range r.Header {
+		// headers can contain multiple elements. for the purposes of this test we pick the 1st
+		headersMap[k] = v[0]
+	}
+
+	mapAsJson, _ := json.Marshal(headersMap)
+	w.Write([]byte(mapAsJson))
+}
+
+func TestToxicAddsHTTPHeaders(t *testing.T) {
+	http.HandleFunc("/", echoRequestHeaders)
+
+	ln, err := net.Listen("tcp", "localhost:0")
+	if err != nil {
+		t.Fatal("Failed to create TCP server", err)
+	}
+
+	go http.Serve(ln, nil)
+	defer ln.Close()
+
+	proxy := NewTestProxy("test", ln.Addr().String())
+	proxy.Start()
+	defer proxy.Stop()
+
+	resp, err := http.Get("http://" + proxy.Listen)
+	if err != nil {
+		t.Error("Failed to connect to proxy", err)
+	}
+
+	body, err := ioutil.ReadAll(resp.Body)
+
+	AssertDoesNotContainHeader(t, string(body), "Foo", "Bar")
+	AssertDoesNotContainHeader(t, string(body), "Lorem", "Ipsum")
+
+	proxy.Toxics.AddToxicJson(ToxicToJson(t, "", "http_request_headers", "upstream", &toxics.HttpToxic{Headers: map[string]string{"Foo": "Bar", "Lorem": "Ipsum"}}))
+
+	resp, err = http.Get("http://" + proxy.Listen)
+	if err != nil {
+		t.Error("Failed to connect to proxy", err)
+	}
+
+	body, err = ioutil.ReadAll(resp.Body)
+
+	AssertContainsHeader(t, string(body), "Foo", "Bar")
+	AssertContainsHeader(t, string(body), "Lorem", "Ipsum")
+}
+
+func AssertDoesNotContainHeader(t *testing.T, body string, headerKey string, headerValue string) {
+	containsHeader := strings.Contains(string(body), fmt.Sprintf(`"%s":"%s"`, headerKey, headerValue))
+
+	if containsHeader {
+		t.Errorf("Unexpected header found. Header=%s", headerKey)
+	}
+}
+
+func AssertContainsHeader(t *testing.T, body string, headerKey string, headerValue string) {
+	containsHeader := strings.Contains(string(body), fmt.Sprintf(`"%s":"%s"`, headerKey, headerValue))
+
+	if !containsHeader {
+		t.Errorf("Expected header not found. Header=%s", headerKey)
+	}
+}