feat: add DeepSeek Chat API streaming wrapper

api/llm/deepseek.js

@@ -0,0 +1,87 @@
+// api/llm/deepseek.js
+const https = require('https');
+const http = require('http');
+
+function createStream(messages, options = {}) {
+  const apiKey = process.env.DEEPSEEK_API_KEY;
+  const baseUrl = process.env.DEEPSEEK_BASE_URL || 'https://api.deepseek.com';
+  const model = process.env.DEEPSEEK_CHAT_MODEL || 'deepseek-chat';
+
+  if (!apiKey) {
+    throw new Error('DEEPSEEK_API_KEY environment variable is required');
+  }
+
+  const body = JSON.stringify({
+    model,
+    messages,
+    stream: true,
+    temperature: options.temperature || 0.7,
+    max_tokens: options.maxTokens || 2048,
+  });
+
+  const url = new URL('/chat/completions', baseUrl);
+  const transport = url.protocol === 'https:' ? https : http;
+
+  const reqOptions = {
+    hostname: url.hostname,
+    port: url.port || (url.protocol === 'https:' ? 443 : 80),
+    path: url.pathname,
+    method: 'POST',
+    headers: {
+      'Content-Type': 'application/json',
+      'Authorization': `Bearer ${apiKey}`,
+      'Content-Length': Buffer.byteLength(body),
+    },
+  };
+
+  return { reqOptions, transport, body };
+}
+
+/**
+ * Stream DeepSeek chat completions as an async iterator of content strings.
+ * @param {Array<{role: string, content: string}>} messages
+ * @param {object} options
+ * @yields {string} content delta
+ */
+async function* streamChat(messages, options = {}) {
+  const { reqOptions, transport, body } = createStream(messages, options);
+
+  const res = await new Promise((resolve, reject) => {
+    const req = transport.request(reqOptions, resolve);
+    req.on('error', reject);
+    req.write(body);
+    req.end();
+  });
+
+  if (res.statusCode !== 200) {
+    const errBody = await new Promise(r => {
+      let data = '';
+      res.on('data', c => data += c);
+      res.on('end', () => r(data));
+    });
+    throw new Error(`DeepSeek API error ${res.statusCode}: ${errBody}`);
+  }
+
+  let buffer = '';
+  for await (const chunk of res) {
+    buffer += chunk.toString();
+    const lines = buffer.split('\n');
+    buffer = lines.pop();
+
+    for (const line of lines) {
+      const trimmed = line.trim();
+      if (!trimmed || !trimmed.startsWith('data: ')) continue;
+      const data = trimmed.slice(6);
+      if (data === '[DONE]') return;
+      try {
+        const parsed = JSON.parse(data);
+        const content = parsed.choices?.[0]?.delta?.content;
+        if (content) yield content;
+      } catch {
+        // skip malformed lines
+      }
+    }
+  }
+}
+
+module.exports = { streamChat };