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)
})

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!