How to deal with % sign in url when using hyperref and bibentry

Question

In few of my citations I have a % sign in the url, which gives a problem when I use the bibentry environment (Paragraph ended before \BR@c@bibitem was complete). How can I deal with the % sign? Without the reference containing the % in the url everything works fine. Also without using the bibentry the % gives no problem. the % sign gives also no problem using a different bibliography stile as unsrt, which is not using the url information (which I don't want to do). (The bibliography style statto can be found here, same problem occurs using plainnat). Not using \begin{NoHyper}\bibentry{goossens93}\end{NoHyper} would be preferred to hyperlink the reference to the website, but I don't know if this would be possible at all.

    \begin{filecontents}{mytestbib.bib}
@book{goossens93,
    author = "Frank Mittelbach and Michel Goossens  and Johannes Braams and David Carlisle  and Chris Rowley",
    title = "The {LaTeX} Companion",
    year = "1993",
    publisher = "Addison-Wesley",
    address = "Reading, Massachusetts"
}

@BOOK{Kymissis__2009,
  title = {Organic Field Effect Transistors - Theory, Fabrication and Characterization},
  publisher = {Springer},
  year = {2009},
  author = {Kymissis, Ioannis},
  abstract = {Organic Field Effect Transistors discusses the fundamental mechanisms
    that apply to {OFETs} fabrication, operation, and characterization.
    This unique book presents the state-of-the-art in organic field effect
    transistors ({OFETs)} with ...},
  isbn = {9780387921341},
  keywords = {Circuits and Systems, Fabrication and Characterization, Organic Chemistry,
    Organic Field Effect Transistors - Theory, Technology \& Engineering
    / Engineering (General)},
  language = {English},
  shorttitle = {Organic Field Effect Transistors},
  timestamp = {2013.10.07},
  url = {http://www.springer.com/engineering/circuits+%26+systems/book/978-0-387-92133-4}
}

\end{filecontents}
\documentclass{article}
\usepackage[pdftex]{hyperref}
\usepackage{filecontents}
\usepackage{natbib}
\usepackage{bibentry}
\nobibliography*


\begin{document}

A full in-text cite of
\begin{NoHyper}\bibentry{goossens93}\end{NoHyper}.

A regular citation of \cite{goossens93}.

Problematic cite \cite{Kymissis__2009}


\bibliographystyle{statto}
\bibliography{mytestbib}

\end{document}

Answer 1

This seems to work: the \BR@c@bibitem macro is patched to change the category code of % before grabbing its argument.

\begin{filecontents}{mytestbib.bib}

@book{goossens93,
  author = {Frank Mittelbach and Michel Goossens and Johannes Braams
            and David Carlisle and Chris Rowley},
  title = {The {LaTeX} Companion},
  year = {1993},
  publisher = {Addison-Wesley},
  address = {Reading, Massachusetts},
}

@BOOK{Kymissis__2009,
  title = {Organic Field Effect Transistors - Theory, Fabrication and Characterization},
  publisher = {Springer},
  year = {2009},
  author = {Kymissis, Ioannis},
  abstract = {Organic Field Effect Transistors discusses the fundamental mechanisms
    that apply to {OFETs} fabrication, operation, and characterization.
    This unique book presents the state-of-the-art in organic field effect
    transistors ({OFETs)} with ...},
  file = {Snapshot:C:\Documents and Settings\haehlen_t\My Documents\Papers\Zotero\storage\KV3VMKEJ\978-0-387-92133-4.html:text/html},
  isbn = {9780387921341},
  keywords = {Circuits and Systems, Fabrication and Characterization, Organic Chemistry,
    Organic Field Effect Transistors - Theory, Technology \& Engineering
    / Engineering (General)},
  language = {English},
  owner = {haehlen_t},
  shorttitle = {Organic Field Effect Transistors},
  timestamp = {2013.10.07},
  url = {http://www.springer.com/engineering/circuits+%26+systems/book/978-0-387-92133-4}
}

\end{filecontents}
\documentclass{article}
\usepackage{hyperref}
\usepackage{natbib}
\usepackage{bibentry}
\usepackage{etoolbox}
\makeatletter
\let\ORIG@BR@c@bibitem\BR@c@bibitem
\apptocmd\ORIG@BR@c@bibitem{\endgroup}{}{}
\def\BR@c@bibitem{\begingroup\catcode`\%=12 \ORIG@BR@c@bibitem}
\makeatother
\nobibliography*


\begin{document}

A full in-text cite of
\begin{NoHyper}\bibentry{goossens93}\end{NoHyper}.

A regular citation of \cite{goossens93}.

Problematic cite \cite{Kymissis__2009}

\begin{NoHyper}\bibentry{Kymissis__2009}\end{NoHyper}

\bibliographystyle{plainnat}
\bibliography{mytestbib}

\end{document}

Some words about the trick.

The bibentry package redefines \bibitem to use the internal macro \BR@c@bibitem which basically grabs the argument of \bibitem and then all that comes up to the first blank line as its second argument. The presence of % in the argument of \url confuses the parser which is unable to see the closing brace, which is behind the %.

Thus we redefine the macro to do the work in two stages:

1. it opens a group;

2. inside this group it sets the category code of % to 12, making it a printable character;

3. calls \ORIG@BR@c@bibitem

The final macro is basically a copy of the original \BR@c@bibitem, with the only change that at the end of its work it issues the \endgroup that balances the \begingroup issued by (the new) \BR@c@bibitem.