fix: suggest changes to cj/fix/chat-base-path

Makefile

@@ -6,7 +6,7 @@ BASE_PATH ?= /magic-base-path-placeholder
 
 $(CHAT_SOURCES_STAMP): $(CHAT_SOURCES)
 	@echo "Chat sources changed. Running build steps..."
-	cd chat && BASE_PATH=${BASE_PATH} bun run build
+	cd chat && NEXT_PUBLIC_BASE_PATH="${BASE_PATH}" bun run build
 	rm -rf lib/httpapi/chat && mkdir -p lib/httpapi/chat && touch lib/httpapi/chat/marker
 	cp -r chat/out/. lib/httpapi/chat/
 	touch $@

chat/next.config.ts

@@ -1,5 +1,8 @@
 import type { NextConfig } from "next";
-const basePath = process.env.BASE_PATH ?? "/chat";
+let basePath = process.env.NEXT_PUBLIC_BASE_PATH ?? "/chat";
+if (basePath.endsWith("/")) {
+  basePath = basePath.slice(0, -1);
+}
 
 const nextConfig: NextConfig = {
   // Enable static exports

chat/src/components/chat-provider.tsx

@@ -51,14 +51,20 @@ interface ChatContextValue {
 
 const ChatContext = createContext<ChatContextValue | undefined>(undefined);
 
-export function ChatProvider({ children }: PropsWithChildren) {
-  const [messages, setMessages] = useState<(Message | DraftMessage)[]>([]);
-  const [loading, setLoading] = useState<boolean>(false);
-  const [serverStatus, setServerStatus] = useState<ServerStatus>("unknown");
-  const eventSourceRef = useRef<EventSource | null>(null);
+const useAgentAPIUrl = (): string => {
   const searchParams = useSearchParams();
-  // NOTE(cian): We use '../../' here to construct the agent API URL relative
-  // to the current window location. Let's say the app is hosted on a subpath
+  const paramsUrl = searchParams.get("url");
+  if (paramsUrl) {
+    return paramsUrl;
+  }
+  const basePath = process.env.NEXT_PUBLIC_BASE_PATH;
+  if (!basePath) {
+    throw new Error(
+      "agentAPIUrl is not set. Please set the url query parameter to the URL of the AgentAPI or the NEXT_PUBLIC_BASE_PATH environment variable."
+    );
+  }
+  // NOTE(cian): We use '../' here to construct the agent API URL relative
+  // to the chat's location. Let's say the app is hosted on a subpath
   // `/@admin/workspace.agent/apps/ccw/`. When you visit this URL you get
   // redirected to `/@admin/workspace.agent/apps/ccw/chat/embed`. This serves
   // this React application, but it needs to know where the agent API is hosted.
@@ -67,8 +73,25 @@ export function ChatProvider({ children }: PropsWithChildren) {
   // `window.location.origin` but this assumes that the application owns the
   // entire origin.
   // See: https://github.com/coder/coder/issues/18779#issuecomment-3133290494 for more context.
-  const defaultAgentAPIURL = new URL("../../", window.location.href).toString();
-  const agentAPIUrl = searchParams.get("url") || defaultAgentAPIURL;
+  let chatURL: string = new URL(basePath, window.location.origin).toString();
+  // NOTE: trailing slashes and relative URLs are tricky.
+  // https://developer.mozilla.org/en-US/docs/Web/API/URL_API/Resolving_relative_references#current_directory_relative
+  if (!chatURL.endsWith("/")) {
+    chatURL += "/";
+  }
+  const agentAPIURL = new URL("..", chatURL).toString();
+  if (agentAPIURL.endsWith("/")) {
+    return agentAPIURL.slice(0, -1);
+  }
+  return agentAPIURL;
+};
+
+export function ChatProvider({ children }: PropsWithChildren) {
+  const [messages, setMessages] = useState<(Message | DraftMessage)[]>([]);
+  const [loading, setLoading] = useState<boolean>(false);
+  const [serverStatus, setServerStatus] = useState<ServerStatus>("unknown");
+  const eventSourceRef = useRef<EventSource | null>(null);
+  const agentAPIUrl = useAgentAPIUrl();
 
   // Set up SSE connection to the events endpoint
   useEffect(() => {

lib/httpapi/server.go

@@ -7,6 +7,7 @@ import (
 	"log/slog"
 	"net/http"
 	"net/url"
+	"strings"
 	"sync"
 	"time"
 
@@ -97,7 +98,7 @@ func NewServer(ctx context.Context, agentType mf.AgentType, process *termexec.Pr
 		agentio:      process,
 		agentType:    agentType,
 		emitter:      emitter,
-		chatBasePath: chatBasePath,
+		chatBasePath: strings.TrimSuffix(chatBasePath, "/"),
 	}
 
 	// Register API routes