Issue #15210 has been reported by foonlyboy (Eike Dierks).

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Bug #15210: UTF-8 BOM should be removed from String in internal representation
https://bugs.ruby-lang.org/issues/15210

* Author: foonlyboy (Eike Dierks)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
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 Hi everyone working on the ruby trunk,

I encountered a problem with a BOM (Byte Order Mark) at the front of UTF-8 string data.

We import some CSV from paypal.
They now include a BOM in front of their UTF-8 encoded CSV data.
This BOM is making some troubles.

I believe this to be a bug in how byte data is converted to the ruby internal String representation.

There is a workaround, but this needs to be documented:
    `IO.read(mode:'r:BOM|UTF-8')`


---

But I'm asking for to improve the UTF-BOM handling:
- The BOM is only used for transfer encoding at the byte stream level.
- The BOM MUST NOT be part of the String in internal representation.


---

BTW: stdlib::CSV chokes on the BOM

I'd like to add some code for a workaround:


`class String

    # delete UTF Byte Order Mark from string
    # returns self (even if no bom was found, contrary to delete_prefix!)
    # NOTE: use with care: better remove the bom when reading the file
    def delete_bom!
        raise 'encoding is not UTF-8' unless self.encoding == Encoding::UTF_8
        delete_prefix!("\xEF\xBB\xBF")
        return self
    end


    # returns a copy of string with UTF Byte Order Mark deleted from string
    def delete_bom
        dup.delete_bom!
    end

end

`

---
~eike







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