fix: enable streaming for sonar-deep-research

src/index.test.ts

@@ -473,14 +473,35 @@ describe("Perplexity MCP Server", () => {
       const models = ["sonar-pro", "sonar-deep-research", "sonar-reasoning-pro"];
 
       for (const model of models) {
-        const mockResponse = {
-          choices: [{ message: { content: `Response from ${model}` } }],
-        };
-
-        global.fetch = vi.fn().mockResolvedValue({
-          ok: true,
-          json: async () => mockResponse,
-        } as Response);
+        if (model === "sonar-deep-research") {
+          // sonar-deep-research uses streaming, so provide an SSE mock
+          const sseData = [
+            `data: ${JSON.stringify({ choices: [{ delta: { content: "Response " } }] })}\n\n`,
+            `data: ${JSON.stringify({ choices: [{ delta: { content: `from ${model}` } }] })}\n\n`,
+            `data: [DONE]\n\n`,
+          ].join("");
+
+          const stream = new ReadableStream({
+            start(controller) {
+              controller.enqueue(new TextEncoder().encode(sseData));
+              controller.close();
+            },
+          });
+
+          global.fetch = vi.fn().mockResolvedValue({
+            ok: true,
+            body: stream,
+          } as unknown as Response);
+        } else {
+          const mockResponse = {
+            choices: [{ message: { content: `Response from ${model}` } }],
+          };
+
+          global.fetch = vi.fn().mockResolvedValue({
+            ok: true,
+            json: async () => mockResponse,
+          } as Response);
+        }
 
         const messages = [{ role: "user", content: "test" }];
         const result = await performChatCompletion(messages, model);

src/server.ts

@@ -60,6 +60,77 @@ export function stripThinkingTokens(content: string): string {
   return content.replace(/<think>[\s\S]*?<\/think>/g, '').trim();
 }
 
+export async function consumeSSEStream(response: Response): Promise<ChatCompletionResponse> {
+  const body = response.body;
+  if (!body) {
+    throw new Error("Response body is null");
+  }
+
+  const reader = (body as ReadableStream<Uint8Array>).getReader();
+  const decoder = new TextDecoder();
+
+  let contentParts: string[] = [];
+  let citations: string[] | undefined;
+  let usage: ChatCompletionResponse["usage"] | undefined;
+  let id: string | undefined;
+  let model: string | undefined;
+  let created: number | undefined;
+  let buffer = "";
+
+  while (true) {
+    const { done, value } = await reader.read();
+    if (done) break;
+
+    buffer += decoder.decode(value, { stream: true });
+
+    const lines = buffer.split("\n");
+    // Keep the last potentially incomplete line in the buffer
+    buffer = lines.pop() || "";
+
+    for (const line of lines) {
+      const trimmed = line.trim();
+      if (!trimmed || !trimmed.startsWith("data:")) continue;
+
+      const data = trimmed.slice("data:".length).trim();
+      if (data === "[DONE]") continue;
+
+      try {
+        const parsed = JSON.parse(data);
+
+        if (parsed.id) id = parsed.id;
+        if (parsed.model) model = parsed.model;
+        if (parsed.created) created = parsed.created;
+        if (parsed.citations) citations = parsed.citations;
+        if (parsed.usage) usage = parsed.usage;
+
+        const delta = parsed.choices?.[0]?.delta;
+        if (delta?.content) {
+          contentParts.push(delta.content);
+        }
+      } catch {
+        // Skip malformed JSON chunks (e.g. keep-alive pings)
+      }
+    }
+  }
+
+  const assembled: ChatCompletionResponse = {
+    choices: [
+      {
+        message: { content: contentParts.join("") },
+        finish_reason: "stop",
+        index: 0,
+      },
+    ],
+    ...(citations && { citations }),
+    ...(usage && { usage }),
+    ...(id && { id }),
+    ...(model && { model }),
+    ...(created && { created }),
+  };
+
+  return ChatCompletionResponseSchema.parse(assembled);
+}
+
 export async function performChatCompletion(
   messages: Message[],
   model: string = "sonar-pro",
@@ -74,10 +145,13 @@ export async function performChatCompletion(
   // Read timeout fresh each time to respect env var changes
   const TIMEOUT_MS = parseInt(process.env.PERPLEXITY_TIMEOUT_MS || "300000", 10);
 
+  const useStreaming = model === "sonar-deep-research";
+
   const url = new URL(`${PERPLEXITY_BASE_URL}/chat/completions`);
   const body: Record<string, unknown> = {
     model: model,
     messages: messages,
+    ...(useStreaming && { stream: true }),
     ...(options?.search_recency_filter && { search_recency_filter: options.search_recency_filter }),
     ...(options?.search_domain_filter && { search_domain_filter: options.search_domain_filter }),
     ...(options?.search_context_size && { web_search_options: { search_context_size: options.search_context_size } }),
@@ -125,8 +199,12 @@ export async function performChatCompletion(
 
   let data: ChatCompletionResponse;
   try {
-    const json = await response.json();
-    data = ChatCompletionResponseSchema.parse(json);
+    if (useStreaming) {
+      data = await consumeSSEStream(response);
+    } else {
+      const json = await response.json();
+      data = ChatCompletionResponseSchema.parse(json);
+    }
   } catch (error) {
     if (error instanceof z.ZodError) {
       const issues = error.issues;