Why does writing a string to a file and then reading the same file as a string result in different strings?

Please provide the following:

  1. SDK Version: 43.0.0
  2. Platforms(Android/iOS/web/all): iOS
  3. Add the appropriate “Tag” based on what Expo library you have a question on.

I’m trying to write some code to save photo data to a file.

I read in the photo data, which comes in as base64 string from react native (Expo), and then I decode it. I immediately write that decoded string to a file.

When I read that file that should contain all of the photo data, all I’m getting back are 4 characters when I expect many megabytes-worth of characters.

Does anybody know how to write this decoded base64 string to a file using Expo? Below is my code …

  const fileUri = `${directoryPath}/${today.getTime()}/${fileName}`;

  // this reads us the base64 encoded image data
  const imageString = await FileSystem.readAsStringAsync(
    { encoding: FileSystem.EncodingType.Base64 }

  const fooString = Base64.decode(imageString);

  // write the decoded photo data to a file
  await FileSystem.writeAsStringAsync(fileUri, fooString);

  // read back the file so we can make sure all the data was written
  const blah = await FileSystem.readAsStringAsync(fileUri);

  const photoInfo = await FileSystem.getInfoAsync(fileUri);

    fooStringLength: fooString.length,
    blahLength: blah.length,
    equals: blah === fooString,

You can see it’s pretty straightforward, so I must be missing something? Below is the output of that console.log

Object {
  "blahLength": 4,
  "equals": false,
  "fileUri": "file:///var/mobile/Containers/Data/Application/33EB7A6F-AA1A-42BF-B252-9A5088A906C6/Documents/ExponentExperienceData/%2540anonymous%252FWIB-mobile-12902e68-9c57-4230-a3df-aaa355c3edf1/20220328184945/1648511392902/Right.jpg.enc",
  "fooStringLength": 2953317,
  "photoInfo": Object {
    "exists": true,
    "isDirectory": false,
    "modificationTime": 1648511394.334474,
    "size": 4415423,
    "uri": "file:///var/mobile/Containers/Data/Application/33EB7A6F-AA1A-42BF-B252-9A5088A906C6/Documents/ExponentExperienceData/%2540anonymous%252FWIB-mobile-12902e68-9c57-4230-a3df-aaa355c3edf1/20220328184945/1648511392902/Right.jpg.enc",

You can see the lengths don’t match. Also, if I print out both fooString and blah, which are the before and after strings for comparison, the fooString looks correct to me and how I expect it to look but the blah is only like 4 characters worth of data. Below is the incorrect content of blah string and the file …

enter image description here

I modified an existing snack to show my situation. This snack gives the option to take a photo or select an existing photo. I put my code in the select an existing photo from the photo library handler. This snack shows that when I write my data to a file and then read it back the data does not match. Any ideas why?

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