Encapsulate libmagic support in a class

This makes the code much easier to read and, additionally, allows to
parse the magic file with magic_load() only once per session.

As a result, getFormatFromFile is slightly faster.

src/Format.cpp

@@ -19,11 +19,12 @@
 #include "frontends/alert.h" //to be removed?
 
 #include "support/debug.h"
+#include "support/docstream.h"
 #include "support/filetools.h"
 #include "support/gettext.h"
 #include "support/lstrings.h"
+#include "support/Magic.h"
 #include "support/mutex.h"
-#include "support/docstream.h"
 #include "support/os.h"
 #include "support/PathChanger.h"
 #include "support/Systemcall.h"
@@ -39,10 +40,6 @@
 #include "support/linkback/LinkBackProxy.h"
 #endif
 
-#ifdef HAVE_MAGIC_H
-#include <magic.h>
-#endif
-
 using namespace std;
 using namespace lyx::support;
 
@@ -407,52 +404,37 @@ string Formats::getFormatFromFile(FileName const & filename) const
 
 	string psformat;
 	string format;
-#ifdef HAVE_MAGIC_H
 	if (filename.exists()) {
-		magic_t magic_cookie = magic_open(MAGIC_MIME);
-		if (magic_cookie) {
-			if (magic_load(magic_cookie, NULL) != 0) {
-				LYXERR(Debug::GRAPHICS, "Formats::getFormatFromFile\n"
-					<< "\tCouldn't load magic database - "
-					<< magic_error(magic_cookie));
-			} else {
-				char const * result = magic_file(magic_cookie,
-					filename.toFilesystemEncoding().c_str());
-				string mime;
-				if (result)
-					mime = token(result, ';', 0);
-				else {
-					LYXERR(Debug::GRAPHICS, "Formats::getFormatFromFile\n"
-						<< "\tCouldn't query magic database - "
-						<< magic_error(magic_cookie));
-				}
-				// our own detection is better for binary files (can be anything)
-				// and different plain text formats
-				if (!mime.empty() && mime != "application/octet-stream" &&
-				    mime != "text/plain") {
-					Formats::const_iterator cit =
-						find_if(formatlist_.begin(), formatlist_.end(),
-							FormatMimeEqual(mime));
-					if (cit != formatlist_.end()) {
-						LYXERR(Debug::GRAPHICS, "\tgot format from MIME type: "
-							<< mime << " -> " << cit->name());
-						// See special eps/ps handling below
-						if (mime == "application/postscript")
-							psformat = cit->name();
-						else
-							format = cit->name();
-					}
-				}
+		// one instance of Magic that will be reused for next calls
+		// This avoids to read the magic file everytime
+		// If libmagic is not available, Magic::file returns an empty string.
+		static Magic magic;
+		string const result = magic.file(filename.toFilesystemEncoding());
+		string const mime = token(result, ';', 0);
+		// our own detection is better for binary files (can be anything)
+		// and different plain text formats
+		if (!mime.empty() && mime != "application/octet-stream" &&
+			mime != "text/plain") {
+			Formats::const_iterator cit =
+				find_if(formatlist_.begin(), formatlist_.end(),
+						FormatMimeEqual(mime));
+			if (cit != formatlist_.end()) {
+				LYXERR(Debug::GRAPHICS, "\tgot format from MIME type: "
+					   << mime << " -> " << cit->name());
+				// See special eps/ps handling below
+				if (mime == "application/postscript")
+					psformat = cit->name();
+				else
+					format = cit->name();
 			}
-			magic_close(magic_cookie);
-			// libmagic recognizes as latex also some formats of ours
-			// such as pstex and pdftex. Therefore we have to perform
-			// additional checks in this case (bug 9244).
-			if (!format.empty() && format != "latex")
-				return format;
 		}
+
+		// libmagic recognizes as latex also some formats of ours
+		// such as pstex and pdftex. Therefore we have to perform
+		// additional checks in this case (bug 9244).
+		if (!format.empty() && format != "latex")
+			return format;
 	}
-#endif
 
 	string const ext = getExtension(filename.absFileName());
 	if (format.empty()) {

src/support/Magic.h

@@ -0,0 +1,77 @@
+// -*- C++ -*-
+/**
+ * \file Magic.h
+ * This file is part of LyX, the document processor.
+ * Licence details can be found in the file COPYING.
+ *
+ * \author Jean-Marc Lasgouttes
+ *
+ * Full author contact details are available in file CREDITS.
+ */
+
+#ifndef LYX_MAGIC_H
+#define LYX_MAGIC_H
+
+namespace lyx {
+
+#ifdef HAVE_MAGIC_H
+
+#include "support/debug.h"
+
+#include <magic.h>
+
+class Magic {
+public:
+	Magic() : ok_(false) {
+		cookie_ = magic_open(MAGIC_MIME);
+		if (cookie_) {
+			if (magic_load(cookie_, NULL) != 0)
+				LYXERR(Debug::GRAPHICS, "Magic: couldn't load magic database - "
+					<< magic_error(cookie_));
+			else
+				ok_ = true;
+		}
+	}
+
+	~Magic() {
+		if(cookie_)
+			magic_close(cookie_);
+	}
+
+	// returns a string of the form "mime-type;encoding", or an empty string on error.
+	std::string file(std::string const & name) const {
+		if (!ok_)
+			return std::string();
+
+		char const * result = magic_file(cookie_, name.c_str());
+		if (result)
+			return result;
+		else
+			LYXERR(Debug::GRAPHICS, "Magic: couldn't query magic database - "
+				   << magic_error(cookie_));
+
+		return std::string();
+	}
+
+private:
+	magic_t cookie_;
+	bool ok_;
+};
+
+#else // !HAVE_MAGIC_T
+
+// A dummy Magic class that always returns an empty result
+class Magic {
+public:
+	Magic() {
+		LYXERR(Debug::GRAPHICS, "Magic: libmagic support not configured");
+	}
+
+	std::string file(std::string const & name) const { return empty_string; }
+};
+
+#endif // HAVE_MAGIC_T
+
+}
+
+#endif // LYX_MAGIC_H

src/support/Makefile.am

@@ -76,6 +76,7 @@ liblyxsupport_a_SOURCES = \
 	lyxlib.h \
 	lyxtime.cpp \
 	lyxtime.h \
+	Magic.h \
 	mutex.h \
 	mutex.cpp \
 	Messages.cpp \