fix(middleware): compute client address (#12222)

* fix(middleware): compute client address

* add unit test

4 files changed, 53 insertions, 3 deletions

diff --git a/.changeset/slimy-kids-peel.md b/.changeset/slimy-kids-peel.md
new file mode 100644
index 000000000..706d01d47
--- /dev/null
+++ b/.changeset/slimy-kids-peel.md
@@ -0,0 +1,5 @@
+---
+'astro': patch
+---
+
+Fixes an issue where the edge middleware couldn't correctly compute the client IP address when calling `ctx.clientAddress()`
diff --git a/packages/astro/src/core/middleware/index.ts b/packages/astro/src/core/middleware/index.ts
index 2ca802126..a684d23c0 100644
--- a/packages/astro/src/core/middleware/index.ts
+++ b/packages/astro/src/core/middleware/index.ts
@@ -8,6 +8,7 @@ import {
 import { ASTRO_VERSION, clientAddressSymbol, clientLocalsSymbol } from '../constants.js';
 import { AstroCookies } from '../cookies/index.js';
 import { AstroError, AstroErrorData } from '../errors/index.js';
+import { getClientIpAddress } from '../routing/request.js';
 import { sequence } from './sequence.js';
 
 function defineMiddleware(fn: MiddlewareHandler) {
@@ -50,6 +51,7 @@ function createContext({
 	let preferredLocale: string | undefined = undefined;
 	let preferredLocaleList: string[] | undefined = undefined;
 	let currentLocale: string | undefined = undefined;
+	let clientIpAddress: string | undefined;
 	const url = new URL(request.url);
 	const route = url.pathname;
 
@@ -85,10 +87,14 @@ function createContext({
 		},
 		url,
 		get clientAddress() {
-			if (clientAddressSymbol in request) {
-				return Reflect.get(request, clientAddressSymbol) as string;
+			if (clientIpAddress) {
+				return clientIpAddress;
 			}
-			throw new AstroError(AstroErrorData.StaticClientAddressNotAvailable);
+			clientIpAddress = getClientIpAddress(request);
+			if (!clientIpAddress) {
+				throw new AstroError(AstroErrorData.StaticClientAddressNotAvailable);
+			}
+			return clientIpAddress;
 		},
 		get locals() {
 			let locals = Reflect.get(request, clientLocalsSymbol);
diff --git a/packages/astro/src/core/routing/request.ts b/packages/astro/src/core/routing/request.ts
new file mode 100644
index 000000000..f7e917a53
--- /dev/null
+++ b/packages/astro/src/core/routing/request.ts
@@ -0,0 +1,20 @@
+/**
+ * Utilities for extracting information from `Request`
+ */
+
+// Parses multiple header and returns first value if available.
+export function getFirstForwardedValue(multiValueHeader?: string | string[] | null) {
+	return multiValueHeader
+		?.toString()
+		?.split(',')
+		.map((e) => e.trim())?.[0];
+}
+
+/**
+ * Returns the first value associated to the `x-forwarded-for` header.
+ *
+ * @param {Request} request
+ */
+export function getClientIpAddress(request: Request): string | undefined {
+	return getFirstForwardedValue(request.headers.get('x-forwarded-for'));
+}
diff --git a/packages/astro/test/units/routing/api-context.test.js b/packages/astro/test/units/routing/api-context.test.js
new file mode 100644
index 000000000..1e955e50c
--- /dev/null
+++ b/packages/astro/test/units/routing/api-context.test.js
@@ -0,0 +1,19 @@
+import assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import { createContext } from '../../../dist/core/middleware/index.js';
+
+describe('createAPIContext', () => {
+	it('should return the clientAddress', () => {
+		const request = new Request('http://example.com', {
+			headers: {
+				'x-forwarded-for': '192.0.2.43, 172.16.58.3',
+			},
+		});
+
+		const context = createContext({
+			request,
+		});
+
+		assert.equal(context.clientAddress, '192.0.2.43');
+	});
+});