Express API Server

This example demonstrates how to build a complete REST API server using Express and the Decart SDK. It includes endpoints for both synchronous image generation and asynchronous video generation.

What You’ll Build

An Express server with:

Text-to-image generation (synchronous)
Image-to-image transformation (synchronous)
Video generation with job management (asynchronous)
Status checking and result retrieval
Automatic polling endpoints

Prerequisites

Node.js 18 or higher
A Decart API key

Setup

Clone and navigate to the example

git clone https://github.com/decartai/sdk
cd sdk/examples/express-api

Configure your API key

Create a .env file:

DECART_API_KEY=your-api-key-here
PORT=3000

Install dependencies

From the repository root:

cd ../..
pnpm install
pnpm build

Start the server

cd examples/express-api
pnpm dev

Server runs at http://localhost:3000

Complete Server Code

import "dotenv/config";
import express from "express";
import { createDecartClient, models } from "@decartai/sdk";

const app = express();
app.use(express.json());

const client = createDecartClient({
  apiKey: process.env.DECART_API_KEY!,
});

// Generate image from text (sync - returns immediately)
app.post("/api/image/generate", async (req, res) => {
  try {
    const { prompt } = req.body;

    const blob = await client.process({
      model: models.image("lucy-pro-t2i"),
      prompt,
    });

    const buffer = Buffer.from(await blob.arrayBuffer());
    res.setHeader("Content-Type", "image/png");
    res.send(buffer);
  } catch (error) {
    res.status(500).json({ error: String(error) });
  }
});

// Transform image (sync - returns immediately)
app.post("/api/image/transform", async (req, res) => {
  try {
    const { prompt, imageUrl } = req.body;

    const blob = await client.process({
      model: models.image("lucy-pro-i2i"),
      prompt,
      data: imageUrl,
    });

    const buffer = Buffer.from(await blob.arrayBuffer());
    res.setHeader("Content-Type", "image/png");
    res.send(buffer);
  } catch (error) {
    res.status(500).json({ error: String(error) });
  }
});

// Submit video generation job (async - returns job ID)
app.post("/api/video/generate", async (req, res) => {
  try {
    const { prompt } = req.body;

    const job = await client.queue.submit({
      model: models.video("lucy-pro-t2v"),
      prompt,
    });

    res.json({ jobId: job.job_id, status: job.status });
  } catch (error) {
    res.status(500).json({ error: String(error) });
  }
});

// Check video job status
app.get("/api/video/status/:jobId", async (req, res) => {
  try {
    const status = await client.queue.status(req.params.jobId);
    res.json(status);
  } catch (error) {
    res.status(500).json({ error: String(error) });
  }
});

// Get video result (when completed)
app.get("/api/video/result/:jobId", async (req, res) => {
  try {
    const blob = await client.queue.result(req.params.jobId);
    const buffer = Buffer.from(await blob.arrayBuffer());
    res.setHeader("Content-Type", "video/mp4");
    res.send(buffer);
  } catch (error) {
    res.status(500).json({ error: String(error) });
  }
});

// Generate video with automatic polling (convenience endpoint)
app.post("/api/video/generate-sync", async (req, res) => {
  try {
    const { prompt, videoUrl } = req.body;

    const result = await client.queue.submitAndPoll({
      model: videoUrl ? models.video("lucy-pro-v2v") : models.video("lucy-pro-t2v"),
      prompt,
      ...(videoUrl && { data: videoUrl }),
    });

    if (result.status === "completed") {
      const buffer = Buffer.from(await result.data.arrayBuffer());
      res.setHeader("Content-Type", "video/mp4");
      res.send(buffer);
    } else {
      res.status(500).json({ error: result.error });
    }
  } catch (error) {
    res.status(500).json({ error: String(error) });
  }
});

const port = process.env.PORT || 3000;
app.listen(port, () => {
  console.log(`Server running at http://localhost:${port}`);
  console.log("");
  console.log("Available endpoints:");
  console.log("  POST /api/image/generate      - Generate image from text");
  console.log("  POST /api/image/transform     - Transform image");
  console.log("  POST /api/video/generate      - Submit video job");
  console.log("  GET  /api/video/status/:id    - Check job status");
  console.log("  GET  /api/video/result/:id    - Get video result");
  console.log("  POST /api/video/generate-sync - Generate video (wait for result)");
});

API Endpoints

Text-to-Image Generation

Generate an image from a text prompt (synchronous):

curl -X POST http://localhost:3000/api/image/generate \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A beautiful sunset over mountains"}' \
  --output image.png

Image-to-Image Transformation

Transform an existing image with a prompt:

curl -X POST http://localhost:3000/api/image/transform \
  -H "Content-Type: application/json" \
  -d '{
    "prompt": "Oil painting style",
    "imageUrl": "https://example.com/image.jpg"
  }' \
  --output transformed.png

Video Generation (Async)

Submit a video generation job:

curl -X POST http://localhost:3000/api/video/generate \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A cat playing piano"}'

Response:

{
  "jobId": "abc123",
  "status": "pending"
}

Check job status:

curl http://localhost:3000/api/video/status/abc123

Response:

{
  "job_id": "abc123",
  "status": "processing"
}

Get completed video:

curl http://localhost:3000/api/video/result/abc123 --output video.mp4

Video Generation (Sync)

Generate video and wait for completion:

curl -X POST http://localhost:3000/api/video/generate-sync \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A timelapse of clouds moving"}' \
  --output video.mp4

Key Concepts

Process API (Synchronous)

The Process API returns results immediately:

const blob = await client.process({
  model: models.image("lucy-pro-t2i"),
  prompt: "A serene landscape",
});

// Convert to buffer and send
const buffer = Buffer.from(await blob.arrayBuffer());
res.setHeader("Content-Type", "image/png");
res.send(buffer);

Queue API (Asynchronous)

The Queue API uses job IDs for long-running tasks:

// Submit job
const job = await client.queue.submit({
  model: models.video("lucy-pro-t2v"),
  prompt: "A video prompt",
});

// Check status
const status = await client.queue.status(job.job_id);

// Get result when completed
if (status.status === "completed") {
  const blob = await client.queue.result(job.job_id);
}

Content Type Headers

Set appropriate content types:

// For images
res.setHeader("Content-Type", "image/png");

// For videos
res.setHeader("Content-Type", "video/mp4");

Error Handling

Handle errors gracefully:

try {
  const blob = await client.process({ /* ... */ });
  // Success
} catch (error) {
  res.status(500).json({ error: String(error) });
}

Testing with cURL

Here are complete test commands:

# Test text-to-image
curl -X POST http://localhost:3000/api/image/generate \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A sunset over mountains"}' \
  --output test-image.png

# Test video generation (async)
curl -X POST http://localhost:3000/api/video/generate \
  -H "Content-Type: application/json" \
  -d '{"prompt": "A cat playing piano"}'

# Test video generation (sync - may take a while)
curl -X POST http://localhost:3000/api/video/generate-sync \
  -H "Content-Type: application/json" \
  -d '{"prompt": "Waves crashing on a beach"}' \
  --output test-video.mp4

Frontend Integration

Example React component using the API:

import { useState } from "react";

export function ImageGenerator() {
  const [prompt, setPrompt] = useState("");
  const [imageUrl, setImageUrl] = useState<string | null>(null);
  const [loading, setLoading] = useState(false);

  const handleGenerate = async () => {
    setLoading(true);
    try {
      const response = await fetch("http://localhost:3000/api/image/generate", {
        method: "POST",
        headers: { "Content-Type": "application/json" },
        body: JSON.stringify({ prompt }),
      });

      const blob = await response.blob();
      const url = URL.createObjectURL(blob);
      setImageUrl(url);
    } catch (error) {
      console.error("Failed to generate image:", error);
    } finally {
      setLoading(false);
    }
  };

  return (
    <div>
      <input
        value={prompt}
        onChange={(e) => setPrompt(e.target.value)}
        placeholder="Enter a prompt"
      />
      <button onClick={handleGenerate} disabled={loading}>
        {loading ? "Generating..." : "Generate"}
      </button>
      {imageUrl && <img src={imageUrl} alt="Generated" />}
    </div>
  );
}

Production Considerations

Add CORS - Configure CORS for frontend access
Rate Limiting - Implement rate limiting to prevent abuse
Authentication - Add API key or JWT authentication
Job Storage - Store job IDs in a database for persistence
Webhooks - Notify clients when jobs complete
Caching - Cache results for common prompts
Monitoring - Log requests and errors

Real-time Examples

Queue Examples

Server Examples

Proxy Examples

What You’ll Build

Prerequisites

Setup

Complete Server Code

API Endpoints

Text-to-Image Generation

Image-to-Image Transformation

Video Generation (Async)

Video Generation (Sync)

Key Concepts

Process API (Synchronous)

Queue API (Asynchronous)

Content Type Headers

Error Handling

Testing with cURL

Frontend Integration

Production Considerations

Build docs developers (and LLMs) love

Real-time Examples

Queue Examples

Server Examples

Proxy Examples

Documentation Index

​What You’ll Build

​Prerequisites

​Setup

​Complete Server Code

​API Endpoints

​Text-to-Image Generation

​Image-to-Image Transformation

​Video Generation (Async)

​Video Generation (Sync)

​Key Concepts

​Process API (Synchronous)

​Queue API (Asynchronous)

​Content Type Headers

​Error Handling

​Testing with cURL

​Frontend Integration

​Production Considerations

​Related Documentation

Build docs developers (and LLMs) love

What You’ll Build

Prerequisites

Setup

Complete Server Code

API Endpoints

Text-to-Image Generation

Image-to-Image Transformation

Video Generation (Async)

Video Generation (Sync)

Key Concepts

Process API (Synchronous)

Queue API (Asynchronous)

Content Type Headers

Error Handling

Testing with cURL

Frontend Integration

Production Considerations

Related Documentation