fix: ParseXFile uploads file with content-type application/octet-stream if not explicitly set

[Copilot]

Fix: Remove default content-type to let server infer from filename

Summary

This PR fixes an issue where files were being uploaded with incorrect MIME types. The SDK now uses a smart fallback chain for content-type detection while ultimately letting Parse Server infer from filename when needed.

Problem

Files were being uploaded with content-type: application/octet-stream, causing browsers to download files instead of previewing them.

Solution

Modified both ParseXFile.upload() and ParseFile.upload() to use a detection chain:

1. First: Check for explicitly provided MIME type (e.g., file.mimeType from XFile)
2. Second: Try to detect using lookupMimeType() from filename/path/data (similar to JS SDK's base64 identification)
3. Third: If still undetermined, don't send content-type header - let Parse Server infer from file extension

This aligns with Parse Server's behavior (FilesController.js) which uses mime.getType(filename) to infer MIME type when no content-type is provided.

Changes Made

• ✅ ParseXFile.upload() (packages/dart/lib/src/objects/parse_x_file.dart): Uses file.mimeType → lookupMimeType() → null (server infers)
• ✅ ParseFile.upload() (packages/dart/lib/src/objects/parse_file.dart): Uses lookupMimeType() → null (server infers)
• ✅ Removed: Fallback to application/octet-stream
• ✅ Tests: All 133 tests pass
• ✅ Code formatting verified (dart format)
• ✅ Code analysis passed (dart analyze --fatal-infos)

Example

Before:

ParseXFile(XFile.fromData(bytes), name: 'image.jpg')
// Sent: content-type: application/octet-stream
// Result: Browser downloads instead of displays

After:

ParseXFile(XFile.fromData(bytes), name: 'image.jpg')
// Detection chain:
// 1. file.mimeType? No
// 2. lookupMimeType('image.jpg')? Returns 'image/jpeg'
// Sent: content-type: image/jpeg
// Result: Browser displays image correctly

If lookupMimeType can't determine type:

ParseXFile(XFile.fromData(bytes), name: 'custom.xyz')
// Detection chain:
// 1. file.mimeType? No
// 2. lookupMimeType('custom.xyz')? Returns null (unknown extension)
// Sent: no content-type header
// Server infers from filename or uses default

Testing

• All existing tests pass (133 tests total)
• Tests verify proper name handling for files with and without extensions

Closes #1097

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Images are saved as application/octet-stream instead of correct content type</issue_title>
<issue_description>### New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server and the Parse Flutter SDK.

Issue Description

When we save files with ParseXFile(XFile.fromData(bytes), name: 'myimage.jpg'), it is sent with content-type: [application/octet-stream] and the SDK is not able to get correct content type.

Steps to reproduce

Upload an image and see the http request, also preview in parse dashboard. When you open the image link it starts to download immediately instead of previews it. Because it is saved with wrong content type.

Actual Outcome

Images are saved with content-type: [application/octet-stream].

Expected Outcome

Images should be saved with correct content type, when file name is provided.

Environment

Parse Flutter SDK

• SDK version: 8.0.1
• Flutter version: all
• Dart version: all
• Operating system version: all

Server

• Parse Server version: all

Logs

Comments on the Issue (you are @copilot in this section)

@mtrezza Is this a SDK or server issue? @mtrezza I want to confirm that this is an SDK issue, not a server issue. I understand the issue is about downloading a file from Parse Server. Parse Server already identifies the mime type from the file extension in [FilesController.js](https://github.com/parse-community/parse-server/blob/73e78127c2c0f9747b133f83c6bcf701845fe23c/src/Controllers/FilesController.js#L17-L38):

  async createFile(config, filename, data, contentType, options) {
    const extname = path.extname(filename);

    const hasExtension = extname.length > 0;
    const mime = (await import('mime')).default
    if (!hasExtension && contentType && mime.getExtension(contentType)) {
      filename = filename + '.' + mime.getExtension(contentType);
    } else if (hasExtension && !contentType) {
      contentType = mime.getType(filename);
    }

    if (!this.options.preserveFileName) {
      filename = randomHexString(32) + '_' + filename;
    }

    const location = await this.adapter.getFileLocation(config, filename);
    await this.adapter.createFile(filename, data, contentType, options);
    return {
      url: location,
      name: filename,
    }
  }

When we save files with ParseXFile(XFile.fromData(bytes), name: 'myimage.jpg'), it is sent with content-type: [application/octet-stream] and the SDK is not able to get correct content type.

In this case the file extension doesn't match the SDK's default content type, so maybe the solution is to not set any content type by default, because the server will infer the content type from the type extension anyway. Or only set the content type application/octet-stream if no file extension is set. I'd suggest to align with how the JS SDK behaves.

All these changes would of course be breaking, so we'd need to release a new major version of the SDK.</comment_new>
<comment_new>@mtrezza
@coderabbitai Investigate how the Parse JS SDK handles this: whether it sets a content-type for file upload, or whether it leave this all to the server.</comment_new>

• Fixes Images are saved as application/octet-stream instead of correct content type #1047

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[codecov]

Codecov Report

❌ Patch coverage is 36.12903% with 297 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.55%. Comparing base (4f20640) to head (d552c34).

Files with missing lines	Patch %	Lines
packages/dart/lib/src/network/parse_query.dart	35.20%	81 Missing ⚠️
packages/dart/lib/src/objects/parse_user.dart	0.00%	67 Missing ⚠️
...ackages/dart/lib/src/network/parse_live_query.dart	36.36%	28 Missing ⚠️
...kages/dart/lib/src/objects/parse_installation.dart	20.68%	23 Missing ⚠️
...ckages/dart/lib/src/network/parse_http_client.dart	10.52%	17 Missing ⚠️
packages/dart/lib/src/objects/parse_x_file.dart	11.11%	16 Missing ⚠️
packages/dart/lib/src/objects/parse_function.dart	0.00%	15 Missing ⚠️
packages/dart/lib/src/objects/parse_file.dart	20.00%	8 Missing ⚠️
...ackages/dart/lib/src/network/parse_dio_client.dart	0.00%	7 Missing ⚠️
packages/dart/lib/src/objects/parse_file_web.dart	0.00%	7 Missing ⚠️
... and 10 more

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1048      +/-   ##
==========================================
- Coverage   43.98%   43.55%   -0.44%     
==========================================
  Files          61       61              
  Lines        3469     3577     +108     
==========================================
+ Hits         1526     1558      +32     
- Misses       1943     2019      +76     

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[mtrezza]

@copilot remove the logic to only send content-type: application/octet-stream when filename has no extension. Instead, there should be no default content type. A content type should only be set if one is explicitly provided.

[Copilot]

@copilot remove the logic to only send content-type: application/octet-stream when filename has no extension. Instead, there should be no default content type. A content type should only be set if one...

Done in commit ae68a7a. Removed all default content-type logic. Now:

• ParseXFile: Only sets content-type if file.mimeType is explicitly provided
• ParseFile: Never sets content-type
• Server infers MIME type from filename in all other cases

All 133 tests pass.

[parse-github-assistant]

🚀 Thanks for opening this pull request!

[2shrestha22]

Looks good, however we need to test it once, I will do a test tomorrow.

[mtrezza]

@copilot fix lint errors

[Copilot]

@copilot fix lint errors

Fixed in commit d552c34. Applied dart format to all files. All 133 tests pass and dart analyze --fatal-infos reports no issues.

[2shrestha22]

It is working. Had to spend half an hour fixing dependency issues.

[2shrestha22]

I just want to request you to upgrade dependencies. I have been using fork of this package for more that a year. Because some packages are not compatible with lower version pinned in Parse SDK.

[mtrezza]

Could you please open a new issue for dependencies?