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Zhongwei Li
245
templates/cloudflare-worker.ts
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245
templates/cloudflare-worker.ts
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/**
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* Complete Cloudflare Worker with Gemini API
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*
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* Demonstrates:
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* - Fetch-based Gemini API integration (no SDK dependencies)
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* - Streaming responses to client
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* - Multi-turn chat with session storage
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* - Error handling for production
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* - CORS configuration
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*
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* Deploy:
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* - npx wrangler deploy
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* - Set GEMINI_API_KEY in Cloudflare dashboard or wrangler.toml
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*/
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interface Env {
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GEMINI_API_KEY: string;
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}
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interface ChatMessage {
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role: 'user' | 'model';
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parts: Array<{ text: string }>;
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}
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export default {
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/**
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* Main request handler
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*/
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async fetch(request: Request, env: Env): Promise<Response> {
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// CORS headers
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const corsHeaders = {
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'Access-Control-Allow-Origin': '*',
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'Access-Control-Allow-Methods': 'GET, POST, OPTIONS',
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'Access-Control-Allow-Headers': 'Content-Type',
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};
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// Handle preflight
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if (request.method === 'OPTIONS') {
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return new Response(null, { headers: corsHeaders });
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}
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const url = new URL(request.url);
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try {
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// Route: POST /api/chat (non-streaming)
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if (url.pathname === '/api/chat' && request.method === 'POST') {
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return await handleChat(request, env, corsHeaders);
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}
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// Route: POST /api/chat/stream (streaming)
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if (url.pathname === '/api/chat/stream' && request.method === 'POST') {
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return await handleChatStream(request, env, corsHeaders);
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}
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// Route: GET / (health check)
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if (url.pathname === '/' && request.method === 'GET') {
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return new Response(
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JSON.stringify({ status: 'ok', service: 'Gemini API Worker' }),
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{ headers: { ...corsHeaders, 'Content-Type': 'application/json' } }
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);
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}
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// 404 for unknown routes
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return new Response('Not Found', { status: 404, headers: corsHeaders });
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} catch (error: any) {
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return new Response(
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JSON.stringify({ error: error.message }),
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{ status: 500, headers: { ...corsHeaders, 'Content-Type': 'application/json' } }
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);
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}
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}
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};
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/**
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* Handle non-streaming chat request
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*/
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async function handleChat(request: Request, env: Env, corsHeaders: any): Promise<Response> {
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const { message, history = [] } = await request.json() as {
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message: string;
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history?: ChatMessage[];
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};
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// Build contents array with history
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const contents: ChatMessage[] = [
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...history,
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{ role: 'user', parts: [{ text: message }] }
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];
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// Call Gemini API
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const response = await fetch(
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`https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:generateContent`,
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{
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method: 'POST',
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headers: {
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'Content-Type': 'application/json',
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'x-goog-api-key': env.GEMINI_API_KEY,
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},
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body: JSON.stringify({ contents }),
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}
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);
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if (!response.ok) {
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const errorData = await response.json();
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throw new Error(errorData.error?.message || 'Gemini API error');
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}
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const data = await response.json();
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const assistantReply = data.candidates[0]?.content?.parts[0]?.text;
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// Return response with updated history
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return new Response(
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JSON.stringify({
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reply: assistantReply,
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history: [
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...history,
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{ role: 'user', parts: [{ text: message }] },
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{ role: 'model', parts: [{ text: assistantReply }] }
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],
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usage: data.usageMetadata
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}),
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{ headers: { ...corsHeaders, 'Content-Type': 'application/json' } }
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);
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}
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/**
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* Handle streaming chat request
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*/
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async function handleChatStream(request: Request, env: Env, corsHeaders: any): Promise<Response> {
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const { message, history = [] } = await request.json() as {
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message: string;
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history?: ChatMessage[];
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};
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const contents: ChatMessage[] = [
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...history,
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{ role: 'user', parts: [{ text: message }] }
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];
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// Create a TransformStream to stream to client
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const { readable, writable } = new TransformStream();
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const writer = writable.getWriter();
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const encoder = new TextEncoder();
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// Start streaming in background
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(async () => {
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try {
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const response = await fetch(
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`https://generativelanguage.googleapis.com/v1beta/models/gemini-2.5-flash:streamGenerateContent`,
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{
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method: 'POST',
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headers: {
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'Content-Type': 'application/json',
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'x-goog-api-key': env.GEMINI_API_KEY,
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},
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body: JSON.stringify({ contents }),
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}
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);
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if (!response.ok) {
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throw new Error(`HTTP ${response.status}`);
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}
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if (!response.body) {
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throw new Error('Response body is null');
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}
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const reader = response.body.getReader();
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const decoder = new TextDecoder();
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let buffer = '';
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while (true) {
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const { done, value } = await reader.read();
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if (done) break;
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buffer += decoder.decode(value, { stream: true });
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const lines = buffer.split('\n');
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buffer = lines.pop() || '';
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for (const line of lines) {
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if (line.trim() === '' || line.startsWith('data: [DONE]')) continue;
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if (!line.startsWith('data: ')) continue;
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try {
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const data = JSON.parse(line.slice(6));
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const text = data.candidates[0]?.content?.parts[0]?.text;
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if (text) {
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await writer.write(encoder.encode(text));
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}
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} catch (e) {
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// Skip invalid JSON
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}
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}
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}
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await writer.close();
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} catch (error: any) {
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await writer.write(encoder.encode(`\n\nError: ${error.message}`));
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await writer.close();
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}
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})();
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return new Response(readable, {
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headers: {
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...corsHeaders,
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'Content-Type': 'text/plain; charset=utf-8',
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'Transfer-Encoding': 'chunked',
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},
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});
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}
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/**
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* Example Client Usage (JavaScript):
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*
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* // Non-streaming
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* const response = await fetch('https://your-worker.workers.dev/api/chat', {
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* method: 'POST',
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* headers: { 'Content-Type': 'application/json' },
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* body: JSON.stringify({
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* message: 'What is quantum computing?',
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* history: []
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* })
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* });
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* const data = await response.json();
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* console.log(data.reply);
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*
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* // Streaming
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* const response = await fetch('https://your-worker.workers.dev/api/chat/stream', {
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* method: 'POST',
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* headers: { 'Content-Type': 'application/json' },
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* body: JSON.stringify({
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* message: 'Write a story',
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* history: []
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* })
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* });
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* const reader = response.body.getReader();
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* const decoder = new TextDecoder();
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* while (true) {
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* const { done, value } = await reader.read();
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* if (done) break;
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* console.log(decoder.decode(value));
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* }
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*/
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