Create README.md

README.md

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+# PostConvert – Robust Image & PDF → JPEG Conversion Service
+
+PostConvert is a small, production-oriented HTTP service for converting **images and PDFs into JPEGs**, with strong emphasis on **robustness, predictable resource usage, and operational safety**.
+
+It supports:
+- JPEG → JPEG (resize + recompress)
+- PNG / WebP / TIFF → JPEG
+- HEIC / HEIF → JPEG (via WASM fallback)
+- PDF → JPEG (first page or all pages as a ZIP)
+
+The service is designed to run well in **containers, serverless-ish environments, and small VMs** where disk, memory, and runaway workloads matter.
+
+---
+
+## Primary Use Cases
+
+- Normalize user uploads (receipts, photos, scans) into JPEG
+- Resize and recompress images server-side for storage or ML pipelines
+- Convert PDFs (receipts, invoices, statements) into images
+- Handle HEIC uploads from iOS devices without native libheif dependencies
+- Safely process untrusted user uploads with bounded resource usage
+
+---
+
+## Key Design Goals
+
+- **Always JPEG out**
+- **Bounded `/tmp` usage** (PDFs rendered page-by-page)
+- **No stack traces leaked to clients**
+- **Fast path for common formats**
+- **Graceful abort on client disconnect**
+- **Predictable limits** (size, pages, DPI, timeouts)
+
+---
+
+## Endpoints
+
+### `POST /convert`
+
+Converts a single image **or the first page of a PDF** to a JPEG.
+
+#### Supported inputs
+- JPEG, PNG, WebP, TIFF, etc. (anything Sharp can decode)
+- HEIC / HEIF
+- PDF (first page only)
+
+#### Response
+- `200 image/jpeg` on success
+- JSON error on failure
+
+---
+
+### `POST /convert/pdf`
+
+Converts **all pages of a PDF** into JPEGs and returns a ZIP archive.
+
+Pages are rendered **one at a time** to keep disk usage bounded.
+
+---
+
+## Authentication
+
+All endpoints require a bearer token.
+
+```
+Authorization: Bearer <CONVERTER_TOKEN>
+```
+
+---
+
+## Image Resize & JPEG Options (Headers)
+
+| Header | Type | Default | Description |
+|------|-----|--------|-------------|
+| `x-jpeg-quality` | `0–100` | `100` | JPEG compression quality |
+| `x-max-dimension` | px | none | Max width/height, aspect preserved |
+| `x-width` | px | none | Explicit output width |
+| `x-height` | px | none | Explicit output height |
+| `x-fit` | enum | `inside` | `inside`, `cover`, `contain`, `fill`, `outside` |
+| `x-without-enlargement` | bool | `true` | Prevent upscaling smaller images |
+
+---
+
+## Environment Variables
+
+| Variable | Default | Description |
+|-------|--------|------------|
+| `PORT` | `8080` | Server port |
+| `CONVERTER_TOKEN` | (required) | Bearer auth token |
+
+---
+
+## Runtime Dependencies
+
+- Node.js 18+
+- `pdftoppm` (Poppler utils) **required for PDFs**
+- Sharp native dependencies (per Sharp docs)