Loading pgfkeys key values from an external file?

Question

I've set up some pgfkeys keys and I'm trying to load the settings from an external file. The only way I know in LaTeX to load files is \input, but it seems to not be the right choice.

\begin{filecontents}{keys.def}
  key = Hellò
\end{filecontents}

\documentclass{article}
\usepackage[utf8]{inputenc}

\usepackage{pgfkeys}

\pgfkeys{
  /mykeys/key/.initial = {}
}

\pgfqkeys{/mykeys}{
  \input{keys.def}
}

\begin{document}
  Values: \pgfkeysvalueof{/mykeys/key}
\end{document}

This code fails to compile with awful messages about undefined control sequences.

What's the right way to give the contents of a file to \pgfkeys?

Note: I've included inputenc and an accented letter in the MWE because in the real use case, the keys will be localized strings and I need to be sure there are no encoding issues.

Answer 1

Proof of concept using expl3. This reads the input file one bit at a time and feeds the bit the the key-setting function. Presumably, something similar is possible without expl3, but this method is straightforward.

\begin{filecontents}{keys.def}
  key = Hellò
\end{filecontents}

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{expl3}

\begin{document}
\ExplSyntaxOn
\ior_new:N \l_gigabytes_stream
\ior_open:Nn \l_gigabytes_stream { keys.def }
\ior_get:NN \l_gigabytes_stream \l_tmpa_tl
\keys_define:nn { gigabytes / mykeys }
{
  key .tl_set:N = \l_gigabytes_mykeys_key_tl,
  key .initial:n = ,
}
\ior_map_inline:Nn \l_gigabytes_stream 
{
  \keys_set:nn { gigabytes / mykeys } { #1 }
}
\ior_close:N \l_gigabytes_stream
\l_gigabytes_mykeys_key_tl
\ExplSyntaxOff
\end{document}

The result is unexciting but correct:

EDIT

Note that although it is clearly a bit mad, it is possible to use this to set PGF keys, should you so desire. For example, the following produces the same output as the code above.

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{expl3,pgfkeys}

\begin{document}
\pgfkeys{
  gigabytes pgf/mykeys/.cd,
  key/.initial={},
}
\ExplSyntaxOn
\ior_new:N \l_gigabytes_stream
\ior_open:Nn \l_gigabytes_stream { keys.def }
\ior_map_inline:Nn \l_gigabytes_stream 
{
  \pgfkeys { gigabytes~pgf / mykeys/.cd, #1}
}
\ior_close:N \l_gigabytes_stream
\pgfkeysvalueof{gigabytes~pgf /mykeys / key}
\ExplSyntaxOff
\end{document}