[CODE-1052] Invalid string length while appending coverage files for upload

[drazisil-codecov]

Describe the bug
On Linux: ['error'] There was an error running the uploader: Invalid string length
On MacOS: : Error: Cannot create a string longer than 0x1fffffe8 characters

This occurs when appending large XML coverage reports during the Processing <filename> step.

To Reproduce
Steps to reproduce the behavior:

1. Download the binary uploader
2. Visit http://mattmahoney.net/dc/textdata.html
3. Download http://mattmahoney.net/dc/enwik9.zip from that page (or here)
4. unzip file
5. attempt to upload it ./codecov -f ~/Downloads/enwik9
6. See error

Expected behavior

The uploader is unable to handle large files concatenated together. This appears to be a V8 limit, see GitHub issue in the additional context section.

Additional context
nodejs/node#35973 (comment)

[hackerrdave]

Think we'll need to refactor away from using readFile and towards using stream via createReadStream

[drazisil-codecov]

Think we'll need to refactor away from using readFile and towards using stream via createReadStream

Will that fix this? The issue, as I understand it, is here

uploader/src/index.ts

Line 214 in 8f317a4

.concat(fileContents)

[hackerrdave]

Yea - on occasion there must be files large enough that we hit the max allowed in node.js process since we read the whole file into memory via readFile() - using the createReadStream approach can stream file contents to upload destination

[drazisil-codecov]

Closed by #746