`headers: true` option doesn't work anymore in version 3.*

[ribanez7]

Steps to reproduce it

csv = ["header_one,header_two", "row_one,row_two"]

CSV.decode!(csv, headers: true) |> Enum.to_list()

The previous example results on empty list in the 3.* versions.
In previous versions it results in:

[%{"header_one" => "row_one", "header_two" => "row_two"}]

[beatrichartz]

Interesting, thanks for sharing! When adding newlines, this should still work:

csv = ["header_one,header_two\n", "row_one,row_two\n"]

CSV.decode!(csv, headers: true) |> Enum.to_list()

This is indeed changed behaviour since 2.x would allow to specify a line by line feed without newlines. When reading from files, we usually get the newlines / delimiters at the end of the line in the stream, and they are part of CSV grammar.

Is this a use case you are encountering? If yes, what’s the source of the CSV? This will help me document the change.

[beatrichartz]

If you get a stream of lines missing delimiters from a source you don’t control, you can map the stream to add newlines before passing it to CSV:

source |>
  Stream.map(fn s -> s <> "\n" end) |> 
  CSV.decode!(headers: true)

This carries a small performance penalty. You probably only want to apply it if for some reason adding newlines at the source is not an option.

[beatrichartz]

Just to add to the thought above, if you have a string with csv data, you would have had to do this in 2.x:

"string,of,csv,data\nsome,data,with,headers" |> String.split("\n") |> CSV.decode(headers: true)

whereas in 3.x you can simply do:

["string,of,csv,data\nsome,data,with,headers"] |> CSV.decode(headers: true)

Not sure if that applies to your case.

[ribanez7]

Hello @beatrichartz , thanks for your answer, the cases I faced were in tests, but I still haven't tried with real CSVs, since in the test I was faking the stream, and that's why I don't have the newline character. Let me try with real files and I will let you know. If I see no problem, then I will simply add this newline into my fake data for the tests. 👍🏼

[ribanez7]

All looks good! thanks for adding this into the migration notes.