Fix request body handling

cassette/server_replay.go

@@ -7,6 +7,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"slices"
+	"strings"
 	"testing"
 )
 
@@ -39,6 +40,10 @@ func TestInteractionReplay(t *testing.T, handler http.Handler, interaction *Inte
 		t.Errorf("unexpected error getting interaction request: %v", err)
 	}
 
+	if len(req.Form) > 0 {
+		req.Body = io.NopCloser(strings.NewReader(req.Form.Encode()))
+	}
+
 	w := httptest.NewRecorder()
 	handler.ServeHTTP(w, req)
 

recorder/middleware.go

@@ -1,6 +1,8 @@
 package recorder
 
 import (
+	"bytes"
+	"io"
 	"net/http"
 	"net/http/httptest"
 )
@@ -9,8 +11,15 @@ import (
 func (rec *Recorder) Middleware(next http.Handler) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		ww := newPassthrough(w)
+
+		// Tee the body so it can be read by the next handler and by the recorder
+		body := &bytes.Buffer{}
+		r.Body = io.NopCloser(io.TeeReader(r.Body, body))
+
 		next.ServeHTTP(ww, r)
 
+		r.Body = io.NopCloser(body)
+
 		// On the server side, requests do not have Host and Scheme so it must be set
 		r.URL.Host = "go-vcr"
 		r.URL.Scheme = "http"