Fix a forwarding bug where the headers were modified in request events

Request events are intended to show the original unmodified client
input, but this was lost as forwarding mutated the raw headers.

Author: pimterry

src/rules/requests/request-handlers.ts

@@ -39,7 +39,8 @@ import {
     rawHeadersToObjectPreservingCase,
     flattenPairedRawHeaders,
     findRawHeader,
-    pairFlatRawHeaders
+    pairFlatRawHeaders,
+    findRawHeaderIndex
 } from '../../util/header-utils';
 import { streamToBuffer, asBuffer } from '../../util/buffer-utils';
 import {
@@ -437,12 +438,18 @@ export class PassThroughHandler extends PassThroughHandlerDefinition {
 
             const hostHeaderName = isH2Downstream ? ':authority' : 'host';
 
-            let hostHeader = findRawHeader(rawHeaders, hostHeaderName);
-            if (!hostHeader) {
+            let hostHeaderIndex = findRawHeaderIndex(rawHeaders, hostHeaderName);
+            let hostHeader: [string, string];
+
+            if (hostHeaderIndex === -1) {
                 // Should never happen really, but just in case:
                 hostHeader = [hostHeaderName, hostname!];
-                rawHeaders.unshift(hostHeader);
-            };
+                hostHeaderIndex = rawHeaders.length;
+            } else {
+                // Clone this - we don't want to modify the original headers, as they're used for events
+                hostHeader = _.clone(rawHeaders[hostHeaderIndex]);
+            }
+            rawHeaders[hostHeaderIndex] = hostHeader;
 
             if (updateHostHeader === undefined || updateHostHeader === true) {
                 // If updateHostHeader is true, or just not specified, match the new target
@@ -554,10 +561,11 @@ export class PassThroughHandler extends PassThroughHandlerDefinition {
                 rawHeaders = objectHeadersToRaw(headers);
             }
         } else if (this.beforeRequest) {
-            const completedRequest = await waitForCompletedRequest(clientReq);
-            const clientRawHeaders = completedRequest.rawHeaders;
+            const clientRawHeaders = rawHeaders;
             const clientHeaders = rawHeadersToObject(clientRawHeaders);
 
+            const completedRequest = await waitForCompletedRequest(clientReq);
+
             const modifiedReq = await this.beforeRequest({
                 ...completedRequest,
                 url: reqUrl, // May have been overwritten by forwarding

src/util/header-utils.ts

@@ -24,6 +24,9 @@ with. Those are:
 export const findRawHeader = (rawHeaders: RawHeaders, targetKey: string) =>
     rawHeaders.find(([key]) => key.toLowerCase() === targetKey);
 
+export const findRawHeaderIndex = (rawHeaders: RawHeaders, targetKey: string) =>
+    rawHeaders.findIndex(([key]) => key.toLowerCase() === targetKey);
+
 const findRawHeaders = (rawHeaders: RawHeaders, targetKey: string) =>
     rawHeaders.filter(([key]) => key.toLowerCase() === targetKey);