From f5cf3fd33187b3fa29dc762075152435244fa8f2 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 da430f5b..35fd5d81 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 9554a006..6a6b9d29 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,