[preservefiles] Add permissions-parsing code from Scott Harvey

CHANGES

@@ -10,6 +10,7 @@ This release contains contributions from (alphabetically by first name):
  - Caio Carvalho
  - Kevin Kofler
  - Philip Mueller
+ - Scott Harvey
 
 ## Core ##
 
@@ -25,6 +26,8 @@ There are no core changes in this version.
    size is close to the required installation size).
  * The *keyboard* module now handles the (bogus) Austrian keymap for
    the system console properly.
+ * The *preservefiles* module now has a mechanism for setting the permissions
+   (and ownership) of preserved files.
  * New module *fsresizer* can be used to resize filesystems. It is intended
    for use in OEM installs where an image of fixed size is created,
    and then sized to the actual SD card the user has used.

src/modules/preservefiles/permissions.cpp

@@ -0,0 +1,70 @@
+/*
+ *  Copyright (C) 2018 Scott Harvey <scott@spharvey.me>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <QString>
+#include <QStringList>
+#include "permissions.h"
+
+Permissions::Permissions(QString p) :
+    m_username(),
+    m_group(),
+    m_valid(true),
+    m_value(0)
+
+{
+    parsePermissions(p);
+}
+
+const void Permissions::parsePermissions(const QString& p) {
+
+    QStringList segments = p.split(":");
+
+    if (segments.length() != 3) {
+        m_valid = false;
+        return;
+    }
+
+    if (segments[0].isEmpty() || segments[1].isEmpty()) {
+        m_valid = false;
+        return;
+    }
+
+    bool ok;
+    int octal = segments[2].toInt(&ok, 8);
+    if (!ok || octal == 0) {
+        m_valid = false;
+        return;
+    } else {
+        m_value = octal;
+    }
+
+    // We have exactly three segments and the third is valid octal,
+    // so we can declare the string valid and set the user and group names
+    m_valid = true;
+    m_username = segments[0];
+    m_group = segments[1];
+
+    return;
+
+}
+
+
+
+
+
+

src/modules/preservefiles/permissions.h

@@ -0,0 +1,58 @@
+/*
+ *  Copyright (C) 2018 Scott Harvey <scott@spharvey.me>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef PERMISSIONS_H
+#define PERMISSIONS_H
+
+#include <QString>
+
+/**
+ * @brief The Permissions class takes a QString @p in the form of 
+ * <user>:<group>:<permissions>, checks it for validity, and makes the three
+ * components available indivdually.
+ */
+class Permissions
+{
+
+public:
+
+/** Constructor
+ * Splits the string @p at the colon (":") into separate elements for 
+ * <user>, <group>, and <value> (permissions), where <value> is returned as
+ * an **octal** integer.
+ */
+    Permissions(QString p);
+
+    bool isValid() const { return m_valid; }
+    QString username() const { return m_username; }
+    QString group() const { return m_group; }
+    int value() const { return m_value; }
+
+
+private:
+
+    const void parsePermissions(QString const &p);
+
+    QString m_username;
+    QString m_group;
+    bool m_valid;
+    int m_value;
+
+};
+
+#endif // PERMISSIONS_H