fix(deepseek): sanitize empty OpenAI-compat SSE fields

Strip dummy finish_reason/function_call payloads so downstream clients do not treat incomplete chunks as real tool calls.

Co-authored-by: Cursor <cursoragent@cursor.com>

deepseek-no-think-proxy.mjs

@@ -111,6 +111,90 @@ export function injectDeepseekThinkingDisabled(body) {
   };
 }
 
+function isEmptyFunctionCall(value) {
+  if (value == null) return true;
+  if (typeof value !== 'object' || Array.isArray(value)) return false;
+  const name = String(value.name ?? '').trim();
+  const args = String(value.arguments ?? '').trim();
+  return !name && !args;
+}
+
+export function sanitizeOpenAiCompatChatChunk(chunk) {
+  if (!chunk || typeof chunk !== 'object' || Array.isArray(chunk)) {
+    return { chunk, changed: false };
+  }
+  const next = { ...chunk };
+  let changed = false;
+  if (Array.isArray(chunk.choices)) {
+    next.choices = chunk.choices.map((choice) => {
+      if (!choice || typeof choice !== 'object') return choice;
+      const patched = { ...choice };
+      if (patched.finish_reason === '') {
+        patched.finish_reason = null;
+        changed = true;
+      }
+      const delta = patched.delta;
+      if (delta && typeof delta === 'object' && !Array.isArray(delta)) {
+        const nextDelta = { ...delta };
+        if (nextDelta.content === '') {
+          delete nextDelta.content;
+          changed = true;
+        }
+        if (nextDelta.reasoning_content === '') {
+          delete nextDelta.reasoning_content;
+          changed = true;
+        }
+        if (nextDelta.refusal === '') {
+          delete nextDelta.refusal;
+          changed = true;
+        }
+        if (nextDelta.extra_fields == null) {
+          delete nextDelta.extra_fields;
+          changed = true;
+        }
+        if (Array.isArray(nextDelta.tool_calls) && nextDelta.tool_calls.length === 0) {
+          delete nextDelta.tool_calls;
+          changed = true;
+        }
+        if (isEmptyFunctionCall(nextDelta.function_call)) {
+          delete nextDelta.function_call;
+          changed = true;
+        }
+        const hasPayload = Object.keys(nextDelta).some((key) => key !== 'role');
+        if (nextDelta.role && !hasPayload) {
+          delete nextDelta.role;
+          changed = true;
+        }
+        patched.delta = nextDelta;
+      }
+      return patched;
+    });
+  }
+  return { chunk: changed ? next : chunk, changed };
+}
+
+export function sanitizeOpenAiCompatSseText(text) {
+  const raw = String(text ?? '');
+  if (!raw) return { text: raw, changed: false };
+  let changed = false;
+  const lines = raw.split('\n');
+  const out = lines.map((line) => {
+    if (!line.startsWith('data:')) return line;
+    const payload = line.slice(5).trim();
+    if (!payload || payload === '[DONE]') return line;
+    try {
+      const parsed = JSON.parse(payload);
+      const result = sanitizeOpenAiCompatChatChunk(parsed);
+      if (!result.changed) return line;
+      changed = true;
+      return `data: ${JSON.stringify(result.chunk)}`;
+    } catch {
+      return line;
+    }
+  });
+  return { text: changed ? out.join('\n') : raw, changed };
+}
+
 function decodeJsonPointerToken(value) {
   return String(value ?? '').replace(/~1/g, '/').replace(/~0/g, '~');
 }
@@ -339,12 +423,34 @@ export function createDeepseekNoThinkProxy({
       res.end();
       return;
     }
+    const isSse = String(upstream.headers.get('content-type') ?? '')
+      .toLowerCase()
+      .includes('text/event-stream');
     const reader = upstream.body.getReader();
+    const decoder = new TextDecoder();
+    let sseCarry = '';
     try {
       while (true) {
         const { done, value } = await reader.read();
         if (done) break;
-        res.write(Buffer.from(value));
+        if (!isSse) {
+          res.write(Buffer.from(value));
+          continue;
+        }
+        sseCarry += decoder.decode(value, { stream: true });
+        const lines = sseCarry.split('\n');
+        sseCarry = lines.pop() ?? '';
+        for (const line of lines) {
+          const sanitized = sanitizeOpenAiCompatSseText(`${line}\n`);
+          res.write(sanitized.text);
+        }
+      }
+      if (isSse) {
+        sseCarry += decoder.decode();
+        if (sseCarry) {
+          const sanitized = sanitizeOpenAiCompatSseText(sseCarry);
+          res.write(sanitized.text);
+        }
       }
       res.end();
     } catch (err) {

deepseek-no-think-proxy.test.mjs

@@ -6,6 +6,7 @@ import {
   deepseekDisableThinkingEnabled,
   flattenLocalJsonSchemaRefs,
   injectDeepseekThinkingDisabled,
+  sanitizeOpenAiCompatSseText,
   isMoonshotApiUrl,
   moonshotToolSchemaCompatEnabled,
   resolveDeepseekNoThinkProxyBaseUrl,
@@ -24,6 +25,21 @@ test('injectDeepseekThinkingDisabled adds thinking.disabled when absent', () =>
   assert.equal(body.model, 'deepseek-v4-flash');
 });
 
+test('sanitizeOpenAiCompatSseText strips empty finish_reason and dummy function_call', () => {
+  const raw = [
+    'data: {"choices":[{"delta":{"role":"assistant","content":"","tool_calls":[],"function_call":null},"finish_reason":""}]}',
+    'data: {"choices":[{"delta":{"content":"四季分明","function_call":{"name":"","arguments":""}},"finish_reason":"stop"}]}',
+    'data: [DONE]',
+    '',
+  ].join('\n');
+  const { text, changed } = sanitizeOpenAiCompatSseText(raw);
+  assert.equal(changed, true);
+  assert.match(text, /"content":"四季分明"/);
+  assert.doesNotMatch(text, /"finish_reason":""/);
+  assert.doesNotMatch(text, /"function_call"/);
+  assert.match(text, /data: \[DONE\]/);
+});
+
 test('injectDeepseekThinkingDisabled overrides enabled thinking config', () => {
   const { body, injected } = injectDeepseekThinkingDisabled({
     model: 'deepseek-v4-pro',