A BOM is an acronym for byte-order mark and is essentially used to tell the type of encoding of a data stream or file without having to explicitly specify it (for instance, through the content-type header in HTTP response).

I’d been having a particular issue with an API I built for a web application I’m managing and I just couldn’t figure out what was wrong until I got to using the API in an application that had HEX output.

So I put the application in debug mode and watched the communication stream. The API was supposed to return an integer value but instead, I noticed a EF BB BF hex sequence being prepended in the output. All attempts to remove this were futile.

Since I used the Symfony framework for the application, I suspected that it might be a bug and googled for a solution. The best answer I could get was to upgrade the framework, which I did but the problem persisted.

My big break came when I attempted to make another API call to a separate method that resulted in the correct output. While tracing the source of the problem, I traced it back to a php file that was incorrectly saved in the UTF-8 character encoding format; which was included when making the buggy API call. Opening and saving this file in ANSI format solved the problem.

So next time you run into a problem like this, make sure to check the encoding of your source files. Better still, you can use a tool like iconv to convert your files to the appropriate character encoding format.