（营销）图片上传

通过本接口上传图片后可获得图片url地址。图片url可在微信支付营销相关的API使用，包括商家券、代金券、支付有礼等。 官方文档

const { Multipart } = require('wechatpay-axios-plugin')
const { createReadStream } = require('fs')
const { basename } = require('path')

const localFilePath = '/path/to/merchant-image-file.jpg'
const stream = createReadStream(localFilePath)
const media = new Multipart()
  .append('meta', JSON.stringify({
    filename: basename(localFilePath),
    sha256: 'from upstream or local calculated',
  }))
  .append('file', stream, basename(localFilePath))

wxpay.v3.marketing.favor.media.imageUpload.post(media)
.then(
  ({ 
    data: {
      media_url,
    },
  }) => ({
    media_url,
  })
)