Add demo server for http upload feature

upload-server/.gitignore

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+uploads
+node_modules
+yarn*
+.gitfoo

upload-server/README.md

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+# deltachat-upload-server
+
+Demo server for the HTTP file upload feature.
+
+### Usage
+
+```
+npm install
+node server.js
+```
+
+Configure with environment variables:
+* `UPLOAD_PATH`: Path to upload files to (default: `./uploads`)
+* `PORT`: Port to listen on (default: `8080`)
+* `HOSTNAME`: Hostname to listen on (default: `0.0.0.0`)
+* `BASEURL`: Base URL for generated links (default: `http://[hostname]:[port]/`)
+

upload-server/package.json

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+{
+  "name": "deltachat-upload-server",
+  "version": "1.0.0",
+  "main": "server.js",
+  "license": "MIT",
+  "scripts": {
+    "start": "node server.js"
+  },
+  "dependencies": {
+    "express": "^4.17.1"
+  }
+}

upload-server/server.js

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+const p = require('path')
+const crypto = require('crypto')
+const express = require('express')
+const fs = require('fs')
+const { pipeline } = require('stream')
+
+const app = express()
+
+const config = {
+  path: process.env.UPLOAD_PATH || p.resolve('./uploads'),
+  port: process.env.PORT || 8080,
+  hostname: process.env.HOSTNAME || '0.0.0.0',
+  baseurl: process.env.BASE_URL || null
+}
+
+if (!config.baseurl.endsWith('/')) config.baseurl = config.baseurl + '/'
+
+if (!fs.existsSync(config.path)) {
+  fs.mkdirSync(config.path, { recursive: true })
+}
+
+const baseUrl = config.baseurl || `http://${config.hostname}:${config.port}/`
+
+app.post('*', (req, res) => {
+  const filename = crypto.randomBytes(12).toString('hex')
+  const ws = fs.createWriteStream(p.join(config.path, filename))
+  pipeline(req, ws, err => {
+    if (err) console.error(err)
+    if (err) res.status(500).send(err.message)
+    const url = baseUrl + filename
+    console.log('file uploaded: ' + filename)
+    res.send(url)
+  })
+})
+
+app.get('/:filename', (req, res) => {
+  const filepath = p.normalize(p.join(config.path, req.params.filename))
+  if (!filepath.startsWith(config.path)) {
+    return res.code(500).send('bad request')
+  }
+  const rs = fs.createReadStream(filepath)
+  res.setHeader('content-type', 'application/octet-stream')
+  pipeline(rs, res, err => {
+    if (err) console.error(err)
+    if (err) res.status(500).send(err.message)
+    res.end()
+  })
+})
+
+app.listen(config.port, err => {
+  if (err) console.error(err)
+  else console.log('Listening on ' + baseUrl)
+})