From 1b18e671a689b67bde20fdc7fb8cf1d6283e4ec9 Mon Sep 17 00:00:00 2001
From: Matt Kane <m@mk.gg>
Date: Fri, 4 Oct 2024 18:43:29 +0100
Subject: [PATCH] fix(netlify): support middleware rewrite (#413)

* fix(netlify): support middleware rewrite

* Changeset
---
 .changeset/fast-penguins-build.md |  5 +++++
 packages/netlify/src/index.ts     | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+)
 create mode 100644 .changeset/fast-penguins-build.md

diff --git a/.changeset/fast-penguins-build.md b/.changeset/fast-penguins-build.md
new file mode 100644
index 000000000..afdc8786c
--- /dev/null
+++ b/.changeset/fast-penguins-build.md
@@ -0,0 +1,5 @@
+---
+'@astrojs/netlify': patch
+---
+
+Fixes `context.rewrite` in edge middleware
diff --git a/packages/netlify/src/index.ts b/packages/netlify/src/index.ts
index feaa718bf..8ce19d51e 100644
--- a/packages/netlify/src/index.ts
+++ b/packages/netlify/src/index.ts
@@ -294,6 +294,25 @@ export default function netlifyIntegration(
 					params: {}
 				});
 				ctx.locals = { netlify: { context } }
+				// https://docs.netlify.com/edge-functions/api/#return-a-rewrite
+				ctx.rewrite = (target) => {
+					if(target instanceof Request) {
+						// We can only mutate headers, so if anything else is different, we need to fetch
+						// the target URL instead.
+						if(target.method !== request.method || target.body || target.url.origin !== request.url.origin) {
+							return fetch(target);
+						}
+						// We can't replace the headers object, so we need to delete all headers and set them again
+						request.headers.forEach((_value, key) => {
+							request.headers.delete(key);
+						});
+						target.headers.forEach((value, key) => {
+							request.headers.set(key, value);
+						});
+						return new URL(target.url);
+					}
+					return new URL(target, request.url);
+				};
 				const next = () => {
 					const { netlify, ...otherLocals } = ctx.locals;
 					request.headers.set("x-astro-locals", trySerializeLocals(otherLocals));