fix: /v1/completions returns legacy text-completion format, not chat (#3571) (#3596)

src/app/api/v1/completions/route.ts

@@ -2,6 +2,7 @@ import { CORS_HEADERS } from "@/shared/utils/cors";
 import { buildClientRawRequest, handleChat } from "@/sse/handlers/chat";
 import { initTranslators } from "@omniroute/open-sse/translator/index.ts";
 import { createInjectionGuard } from "@/middleware/promptInjectionGuard";
+import { asTextCompletionResponse } from "./textCompletionTransform.ts";
 
 let initPromise = null;
 const injectionGuard = createInjectionGuard();
@@ -74,13 +75,18 @@ export async function POST(request: Request) {
           headers: request.headers,
           body: JSON.stringify(normalized),
         });
-        return await handleChat(newRequest, buildClientRawRequest(request, body));
+        // #3571 — translate the chat-pipeline response back to the legacy
+        // text-completion shape so OpenAI Completion clients (e.g. TabbyML) work.
+        return await asTextCompletionResponse(
+          await handleChat(newRequest, buildClientRawRequest(request, body))
+        );
       }
     }
   } catch (error) {
     console.error("[SECURITY] Prompt injection guard failed:", error);
   }
 
-  // Standard path: body already has messages[] (chat format)
-  return await handleChat(request);
+  // Standard path: body already has messages[] (chat format). Still emit the legacy
+  // text-completion shape — this is the /v1/completions contract (#3571).
+  return await asTextCompletionResponse(await handleChat(request));
 }

src/app/api/v1/completions/textCompletionTransform.ts

@@ -0,0 +1,122 @@
+/**
+ * #3571 — `/v1/completions` is the legacy OpenAI Completions API. OmniRoute routes
+ * it internally through the chat pipeline, which emits chat-shaped payloads
+ * (`chat.completion` / `chat.completion.chunk` with `choices[].message|delta.content`).
+ * Legacy Completion clients (e.g. TabbyML's `openai/completion` backend) require
+ * `choices[].text` and `object: "text_completion"`, and crash on the chat shape
+ * (`Error("missing field 'text'")`).
+ *
+ * These helpers translate a chat-shaped object/stream back to the legacy
+ * text-completion shape so the endpoint honours its OpenAI Completions contract.
+ */
+
+type AnyRec = Record<string, any>;
+
+function choiceText(choice: AnyRec): string {
+  if (!choice || typeof choice !== "object") return "";
+  // chat.completion → message.content; chat.completion.chunk → delta.content;
+  // already-text shape → text.
+  const text = choice.message?.content ?? choice.delta?.content ?? choice.text ?? "";
+  return typeof text === "string" ? text : "";
+}
+
+/**
+ * Convert a single chat.completion / chat.completion.chunk object into the legacy
+ * text-completion shape (`object: "text_completion"`, `choices[].text`).
+ * Non-object input and already-text_completion objects are returned unchanged.
+ */
+export function toTextCompletionObject(obj: AnyRec): AnyRec {
+  if (!obj || typeof obj !== "object" || !Array.isArray(obj.choices)) return obj;
+
+  const choices = obj.choices.map((c: AnyRec, i: number) => ({
+    text: choiceText(c),
+    index: typeof c?.index === "number" ? c.index : i,
+    logprobs: c?.logprobs ?? null,
+    finish_reason: c?.finish_reason ?? null,
+  }));
+
+  const out: AnyRec = {
+    id: obj.id,
+    object: "text_completion",
+    created: obj.created,
+    model: obj.model,
+    choices,
+  };
+  if (obj.usage) out.usage = obj.usage;
+  if (obj.system_fingerprint !== undefined) out.system_fingerprint = obj.system_fingerprint;
+  return out;
+}
+
+/**
+ * Transform the payload of a single SSE `data:` line. Returns the re-serialized
+ * text-completion JSON, `"[DONE]"` unchanged, or the original payload when it is
+ * not JSON we recognise.
+ */
+export function transformSseData(payload: string): string {
+  const trimmed = payload.trim();
+  if (trimmed === "" || trimmed === "[DONE]") return trimmed;
+  try {
+    return JSON.stringify(toTextCompletionObject(JSON.parse(trimmed)));
+  } catch {
+    return trimmed;
+  }
+}
+
+function transformLine(line: string): string {
+  if (!line.startsWith("data:")) return line;
+  const payload = line.slice("data:".length).replace(/^ /, "");
+  return "data: " + transformSseData(payload);
+}
+
+/**
+ * A line-oriented SSE TransformStream that rewrites each `data:` event from chat
+ * shape to text-completion shape, passing through blank separators and `[DONE]`.
+ */
+export function createTextCompletionStreamTransformer(): TransformStream<Uint8Array, Uint8Array> {
+  const decoder = new TextDecoder();
+  const encoder = new TextEncoder();
+  let buffer = "";
+  return new TransformStream<Uint8Array, Uint8Array>({
+    transform(chunk, controller) {
+      buffer += decoder.decode(chunk, { stream: true });
+      let idx: number;
+      while ((idx = buffer.indexOf("\n")) >= 0) {
+        const line = buffer.slice(0, idx);
+        buffer = buffer.slice(idx + 1);
+        controller.enqueue(encoder.encode(transformLine(line) + "\n"));
+      }
+    },
+    flush(controller) {
+      if (buffer.length > 0) controller.enqueue(encoder.encode(transformLine(buffer)));
+    },
+  });
+}
+
+/**
+ * Wrap a chat-pipeline Response so `/v1/completions` returns the legacy
+ * text-completion shape. Error responses and non-JSON/non-SSE bodies pass through.
+ */
+export async function asTextCompletionResponse(res: Response): Promise<Response> {
+  if (!res.ok) return res;
+  const contentType = res.headers.get("content-type") || "";
+
+  if (contentType.includes("text/event-stream") && res.body) {
+    return new Response(res.body.pipeThrough(createTextCompletionStreamTransformer()), {
+      status: res.status,
+      headers: res.headers,
+    });
+  }
+
+  if (contentType.includes("application/json")) {
+    const obj = await res.json().catch(() => null);
+    if (obj === null) return res;
+    const headers = new Headers(res.headers);
+    headers.delete("content-length"); // body length changed after re-serialization
+    return new Response(JSON.stringify(toTextCompletionObject(obj)), {
+      status: res.status,
+      headers,
+    });
+  }
+
+  return res;
+}