From 23b81ff81210a123311bd348405d4d5daebaac7b Mon Sep 17 00:00:00 2001
From: Anmol Sethi <hi@nhooyr.io>
Date: Wed, 20 Jan 2021 14:26:15 -0500
Subject: [PATCH] proxy.ts: Do not always rewrite redirects against the base
 path

This breaks --proxy-path-passthrough

However, we still need this when that code is disabled as many apps will
issue absolute redirects and expect the proxy to rewrite as appropriate.

e.g. Go's http.Redirect will rewrite relative redirects as absolute!
See https://golang.org/pkg/net/http/#Redirect
---
 src/node/proxy.ts            | 2 ++
 src/node/routes/pathProxy.ts | 6 ++++--
 2 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/node/proxy.ts b/src/node/proxy.ts
index da430f5b3a15..35fd5d81a4d0 100644
--- a/src/node/proxy.ts
+++ b/src/node/proxy.ts
@@ -9,6 +9,8 @@ proxy.on("error", (error, _, res) => {
 })
 
 // Intercept the response to rewrite absolute redirects against the base path.
+// Is disabled when the request has no base path which means --proxy-path-passthrough has
+// been enabled.
 proxy.on("proxyRes", (res, req) => {
   if (res.headers.location && res.headers.location.startsWith("/") && (req as any).base) {
     res.headers.location = (req as any).base + res.headers.location
diff --git a/src/node/routes/pathProxy.ts b/src/node/routes/pathProxy.ts
index 9554a006d290..6a6b9d29c23d 100644
--- a/src/node/routes/pathProxy.ts
+++ b/src/node/routes/pathProxy.ts
@@ -28,8 +28,10 @@ router.all("/(:port)(/*)?", (req, res) => {
     throw new HttpError("Unauthorized", HttpCode.Unauthorized)
   }
 
-  // Absolute redirects need to be based on the subpath when rewriting.
-  ;(req as any).base = `${req.baseUrl}/${req.params.port}`
+  if (!req.args["proxy-path-passthrough"]) {
+    // Absolute redirects need to be based on the subpath when rewriting.
+    ;(req as any).base = `${req.baseUrl}/${req.params.port}`
+  }
 
   proxy.web(req, res, {
     ignorePath: true,