Workaround for uploading files from `assets-library` path on iOS with expo

.js

// img
// {
//   uri: '"assets-library://asset/asset.JPG?id=SOME_ID&ext=JPG"',
//   md5: "some md5"
// }

// copy into cache dir first
const path = FileSystem.cacheDirectory + img.md5
await FileSystem.copyAsync({
  from: img.uri,
  to: path
})

// read that and do upload
const file = await FileSystem.readAsStringAsync(path, {
  encoding: FileSystem.EncodingTypes.Base64
})

const payload = {
  title: 'some awesome photo',
  image: file
}

fetch('somewhere', {
  method: 'POST',
  body: JSON.stringify(payload)
})

Keep in mind that this gist is from 2019.
It might no work or there maybe better way to handle with the latest version of expo.

Alright. I'll bear that in mind. I need this for multiple image selection and upload which expo does not provide

You can get the local file system with the method:

const info = await MediaLibrary.getAssetInfoAsync(img)

this returns:

{
  "creationTime": 1617141592000,
  "duration": 0,
  "exif": Object {
    "ColorModel": "RGB",
    "Depth": 8,
    "PixelHeight": 1536,
    "PixelWidth": 2048,
    "{JFIF}": Object {
      "DensityUnit": 0,
      "IsProgressive": true,
      "JFIFVersion": Array [
        1,
        0,
        1,
      ],
      "XDensity": 1,
      "YDensity": 1,
    },
  },
  "filename": "IMG_0070.JPG",
  "height": 1536,
  "id": "146AE19A-6D7B-4274-BCD3-CAA96DA2373D/L0/001",
  "isFavorite": false,
  "isHidden": false,
  "localUri": "file:///var/mobile/Media/DCIM/100APPLE/IMG_0070.JPG",
  "location": null,
  "mediaSubtypes": Array [],
  "mediaType": "photo",
  "modificationTime": 1617152030064,
  "orientation": 1,
  "uri": "assets-library://asset/asset.JPG?id=146AE19A-6D7B-4274-BCD3-CAA96DA2373D&ext=JPG",
  "width": 2048,
}

So the complete example is:

const info = await MediaLibrary.getAssetInfoAsync(img)
	
const fileBase64 = await FileSystem.readAsStringAsync(info.localUri, {
	 encoding: FileSystem.EncodingType.Base64,
})

Hope its help!