[LyX/master] Refactor computing hashes.

[Thibaut Cuvelier]

commit 789a537182b2d06c97cf6215cdcd09d1e4eb324d
Author: Thibaut Cuvelier <tcuvelier at lyx.org>
Date:   Tue Oct 19 02:24:22 2021 +0200

    Refactor computing hashes.
    
    For now, this is only used in FileName, because it does not change the semantics of DocFileName::mangledFileName.
---
 src/support/FileName.cpp  |   14 ++------------
 src/support/filetools.cpp |   18 +++++++++++++++++-
 src/support/filetools.h   |   10 ++++++++++
 3 files changed, 29 insertions(+), 13 deletions(-)

diff --git a/src/support/FileName.cpp b/src/support/FileName.cpp
index 729e3d0..5d70dd2 100644
--- a/src/support/FileName.cpp
+++ b/src/support/FileName.cpp
@@ -22,7 +22,6 @@
 #include "support/Package.h"
 #include "support/qstring_helpers.h"
 
-#include <QCryptographicHash>
 #include <QDateTime>
 #include <QDir>
 #include <QFile>
@@ -974,17 +973,8 @@ string DocFileName::mangledFileName(string const & dir, bool use_counter, bool e
 	// Now the real work. Remove the extension.
 	string mname = support::changeExtension(name, string());
 
-	if (encrypt_path) {
-		QString qname = toqstr(mname);
-#if QT_VERSION >= 0x050000
-		QByteArray hash  = QCryptographicHash::hash(qname.toLocal8Bit(),QCryptographicHash::Sha256);
-#else
-		QByteArray hash  = QCryptographicHash::hash(qname.toLocal8Bit(),QCryptographicHash::Sha1);
-#endif
-		hash = hash.toHex();
-		mname = fromqstr(QString(hash));
-		mname = "export_" + onlyFileName() + "_" + mname;
-		}
+	if (encrypt_path)
+		mname = "export_" + onlyFileName() + "_" + toHexHash(mname);
 
 	// The mangled name must be a valid LaTeX name.
 	// The list of characters to keep is probably over-restrictive,
diff --git a/src/support/filetools.cpp b/src/support/filetools.cpp
index 41e508b..d022115 100644
--- a/src/support/filetools.cpp
+++ b/src/support/filetools.cpp
@@ -62,6 +62,8 @@
 #include <sstream>
 #include <vector>
 
+#include <QCryptographicHash>
+
 #if defined (_WIN32)
 #include <io.h>
 #include <windows.h>
@@ -1309,5 +1311,19 @@ void fileUnlock(int fd, const char * /* lock_file*/)
 #endif
 }
 
-} //namespace support
+
+std::string toHexHash(const std::string & str)
+{
+	// Use the best available hashing algorithm. Qt 5 proposes SHA-2, but Qt 4 is limited to SHA-1.
+#if QT_VERSION >= 0x050000
+	auto hashAlgo = QCryptographicHash::Sha256;
+#else
+	auto hashAlgo = QCryptographicHash::Sha1;
+#endif
+
+	QByteArray hash = QCryptographicHash::hash(toqstr(str).toLocal8Bit(), hashAlgo);
+	return fromqstr(QString(hash.toHex()));
+}
+
+} // namespace support
 } // namespace lyx
diff --git a/src/support/filetools.h b/src/support/filetools.h
index dd47ba1..84b2378 100644
--- a/src/support/filetools.h
+++ b/src/support/filetools.h
@@ -344,6 +344,16 @@ cmd_ret const runCommand(std::string const & cmd);
 int fileLock(const char * lock_file);
 void fileUnlock(int fd, const char * lock_file);
 
+/** Return the hex-encoded cryptographic hash of a string.
+ * The hash algorithm is not fixed, but it is determined at compile time.
+ * This function is typically used to create relatively stable file names,
+ * because cryptographic hash functions ensure that very small changes in the
+ * input result in large changes in the output.
+ * There is no limit in the length of the input string: it can be a file name
+ * or the contents of a file, for instance.
+ */
+std::string toHexHash(const std::string & str);
+
 } // namespace support
 } // namespace lyx