Add: request_body replace directive

modules/caddyhttp/requestbody/caddyfile.go

@@ -68,6 +68,12 @@ func parseCaddyfile(h httpcaddyfile.Helper) (caddyhttp.MiddlewareHandler, error)
 			}
 			rb.WriteTimeout = timeout
 
+		case "replace":
+			var replaceStr string
+			if !h.AllArgs(&replaceStr) {
+				return nil, h.ArgErr()
+			}
+			rb.Replace = replaceStr
 		default:
 			return nil, h.Errf("unrecognized request_body subdirective '%s'", h.Val())
 		}

modules/caddyhttp/requestbody/requestbody.go

@@ -17,6 +17,7 @@ package requestbody
 import (
 	"io"
 	"net/http"
+	"strings"
 	"time"
 
 	"go.uber.org/zap"
@@ -41,6 +42,8 @@ type RequestBody struct {
 	// EXPERIMENTAL. Subject to change/removal.
 	WriteTimeout time.Duration `json:"write_timeout,omitempty"`
 
+	Replace string `json:"replace,omitempty"`
+
 	logger *zap.Logger
 }
 
@@ -58,6 +61,14 @@ func (rb *RequestBody) Provision(ctx caddy.Context) error {
 }
 
 func (rb RequestBody) ServeHTTP(w http.ResponseWriter, r *http.Request, next caddyhttp.Handler) error {
+	if rb.Replace != "" {
+		err := r.Body.Close()
+		if err != nil {
+			return err
+		}
+		r.Body = io.NopCloser(strings.NewReader(rb.Replace))
+		r.ContentLength = int64(len(rb.Replace))
+	}
 	if r.Body == nil {
 		return next.ServeHTTP(w, r)
 	}