bug: guard against empty choices in Fireworks AI stream chunks

src/providers/fireworks-ai/chatComplete.test.ts

@@ -0,0 +1,125 @@
+import { FireworksAIChatCompleteStreamChunkTransform } from './chatComplete';
+
+describe('FireworksAIChatCompleteStreamChunkTransform', () => {
+  it('transforms a normal stream chunk with choices', () => {
+    const input = JSON.stringify({
+      id: 'chatcmpl-123',
+      object: 'chat.completion.chunk',
+      created: 1700000000,
+      model: 'accounts/fireworks/models/llama-v3p1-405b-instruct',
+      choices: [
+        {
+          index: 0,
+          delta: { role: 'assistant', content: 'Hello' },
+          finish_reason: null,
+          logprobs: null,
+        },
+      ],
+      usage: null,
+    });
+
+    const result = FireworksAIChatCompleteStreamChunkTransform(
+      `data: ${input}`
+    );
+    const parsed = JSON.parse(result.replace('data: ', '').trim());
+
+    expect(parsed.id).toBe('chatcmpl-123');
+    expect(parsed.provider).toBe('fireworks-ai');
+    expect(parsed.choices).toHaveLength(1);
+    expect(parsed.choices[0].delta.content).toBe('Hello');
+    expect(parsed.choices[0].finish_reason).toBeNull();
+  });
+
+  it('handles empty choices array without crashing', () => {
+    const input = JSON.stringify({
+      id: 'chatcmpl-123',
+      object: 'chat.completion.chunk',
+      created: 1700000000,
+      model: 'accounts/fireworks/models/llama-v3p1-405b-instruct',
+      choices: [],
+      usage: {
+        prompt_tokens: 10,
+        completion_tokens: 5,
+        total_tokens: 15,
+      },
+    });
+
+    const result = FireworksAIChatCompleteStreamChunkTransform(
+      `data: ${input}`
+    );
+    const parsed = JSON.parse(result.replace('data: ', '').trim());
+
+    expect(parsed.id).toBe('chatcmpl-123');
+    expect(parsed.provider).toBe('fireworks-ai');
+    expect(parsed.choices).toEqual([]);
+    expect(parsed.usage).toEqual({
+      prompt_tokens: 10,
+      completion_tokens: 5,
+      total_tokens: 15,
+    });
+  });
+
+  it('handles [DONE] chunk', () => {
+    const result = FireworksAIChatCompleteStreamChunkTransform('data: [DONE]');
+    expect(result).toBe('data: [DONE]\n\n');
+  });
+
+  it('includes usage when present in chunk with choices', () => {
+    const input = JSON.stringify({
+      id: 'chatcmpl-456',
+      object: 'chat.completion.chunk',
+      created: 1700000000,
+      model: 'accounts/fireworks/models/llama-v3p1-405b-instruct',
+      choices: [
+        {
+          index: 0,
+          delta: {},
+          finish_reason: 'stop',
+          logprobs: null,
+        },
+      ],
+      usage: {
+        prompt_tokens: 20,
+        completion_tokens: 10,
+        total_tokens: 30,
+      },
+    });
+
+    const result = FireworksAIChatCompleteStreamChunkTransform(
+      `data: ${input}`
+    );
+    const parsed = JSON.parse(result.replace('data: ', '').trim());
+
+    expect(parsed.usage).toEqual({
+      prompt_tokens: 20,
+      completion_tokens: 10,
+      total_tokens: 30,
+    });
+    expect(parsed.choices[0].finish_reason).toBe('stop');
+  });
+
+  it('omits usage when null', () => {
+    const input = JSON.stringify({
+      id: 'chatcmpl-789',
+      object: 'chat.completion.chunk',
+      created: 1700000000,
+      model: 'accounts/fireworks/models/llama-v3p1-405b-instruct',
+      choices: [
+        {
+          index: 0,
+          delta: { content: 'Hi' },
+          finish_reason: null,
+          logprobs: null,
+        },
+      ],
+      usage: null,
+    });
+
+    const result = FireworksAIChatCompleteStreamChunkTransform(
+      `data: ${input}`
+    );
+    const parsed = JSON.parse(result.replace('data: ', '').trim());
+
+    expect(parsed.usage).toBeUndefined();
+  });
+});

src/providers/fireworks-ai/chatComplete.ts

@@ -222,21 +222,24 @@ export const FireworksAIChatCompleteStreamChunkTransform: (
     return `data: ${chunk}\n\n`;
   }
   const parsedChunk: FireworksAIStreamChunk = JSON.parse(chunk);
+  const choice = parsedChunk.choices?.[0];
   return (
     `data: ${JSON.stringify({
       id: parsedChunk.id,
       object: parsedChunk.object,
       created: parsedChunk.created,
       model: parsedChunk.model,
       provider: FIREWORKS_AI,
-      choices: [
-        {
-          index: parsedChunk.choices[0].index,
-          delta: parsedChunk.choices[0].delta,
-          finish_reason: parsedChunk.choices[0].finish_reason,
-          logprobs: parsedChunk.choices[0].logprobs,
-        },
-      ],
+      choices: choice
+        ? [
+            {
+              index: choice.index,
+              delta: choice.delta,
+              finish_reason: choice.finish_reason,
+              logprobs: choice.logprobs,
+            },
+          ]
+        : [],
       ...(parsedChunk.usage ? { usage: parsedChunk.usage } : {}),
     })}` + '\n\n'
   );