install: check file/directory permissions for Shaarli resources

Relates to #40
Relates to #372

Additions:
 - FileUtils: IOException
 - ApplicationUtils:
   - check if Shaarli resources are accessible with sufficient permissions
   - basic test coverage
 - index.php:
   - check access permissions and redirect to an error page if needed:
     - before running the first installation

Modifications:
 - LinkDB:
   - factorize datastore write code
   - check if the datastore
     (exists AND is writeable) OR (doesn't exist AND its parent dir is writable)
   - raise an IOException if needed

Signed-off-by: VirtualTam <virtualtam@flibidi.net>

3 files changed, 114 insertions, 9 deletions

diff --git a/application/ApplicationUtils.php b/application/ApplicationUtils.php
new file mode 100644
index 00000000..6fb07f36
--- /dev/null
+++ b/application/ApplicationUtils.php
@@ -0,0 +1,69 @@
+<?php
+/**
+ * Shaarli (application) utilities
+ */
+class ApplicationUtils
+{
+
+    /**
+     * Checks Shaarli has the proper access permissions to its resources
+     *
+     * @param array $globalConfig The $GLOBALS['config'] array
+     *
+     * @return array A list of the detected configuration issues
+     */
+    public static function checkResourcePermissions($globalConfig)
+    {
+        $errors = array();
+
+        // Check script and template directories are readable
+        foreach (array(
+            'application',
+            'inc',
+            'plugins',
+            $globalConfig['RAINTPL_TPL']
+        ) as $path) {
+            if (! is_readable(realpath($path))) {
+                $errors[] = '"'.$path.'" directory is not readable';
+            }
+        }
+
+        // Check cache and data directories are readable and writeable
+        foreach (array(
+            $globalConfig['CACHEDIR'],
+            $globalConfig['DATADIR'],
+            $globalConfig['PAGECACHE'],
+            $globalConfig['RAINTPL_TMP']
+        ) as $path) {
+            if (! is_readable(realpath($path))) {
+                $errors[] = '"'.$path.'" directory is not readable';
+            }
+            if (! is_writable(realpath($path))) {
+                $errors[] = '"'.$path.'" directory is not writable';
+            }
+        }
+
+        // Check configuration files are readable and writeable
+        foreach (array(
+            $globalConfig['CONFIG_FILE'],
+            $globalConfig['DATASTORE'],
+            $globalConfig['IPBANS_FILENAME'],
+            $globalConfig['LOG_FILE'],
+            $globalConfig['UPDATECHECK_FILENAME']
+        ) as $path) {
+            if (! is_file(realpath($path))) {
+                # the file may not exist yet
+                continue;
+            }
+
+            if (! is_readable(realpath($path))) {
+                $errors[] = '"'.$path.'" file is not readable';
+            }
+            if (! is_writable(realpath($path))) {
+                $errors[] = '"'.$path.'" file is not writable';
+            }
+        }
+
+        return $errors;
+    }
+}
diff --git a/application/FileUtils.php b/application/FileUtils.php
new file mode 100644
index 00000000..6a12ef0e
--- /dev/null
+++ b/application/FileUtils.php
@@ -0,0 +1,19 @@
+<?php
+/**
+ * Exception class thrown when a filesystem access failure happens
+ */
+class IOException extends Exception
+{
+    private $path;
+
+    /**
+     * Construct a new IOException
+     *
+     * @param string $path path to the ressource that cannot be accessed
+     */
+    public function __construct($path)
+    {
+        $this->path = $path;
+        $this->message = 'Error accessing '.$this->path;
+    }
+}
diff --git a/application/LinkDB.php b/application/LinkDB.php
index 84733505..15fadbc3 100644
--- a/application/LinkDB.php
+++ b/application/LinkDB.php
@@ -212,11 +212,7 @@ You use the community supported version of the original Shaarli project, by Seba
         $this->_links[$link['linkdate']] = $link;
 
         // Write database to disk
-        // TODO: raise an exception if the file is not write-able
-        file_put_contents(
-            $this->_datastore,
-            self::$phpPrefix.base64_encode(gzdeflate(serialize($this->_links))).self::$phpSuffix
-        );
+        $this->writeDB();
     }
 
     /**
@@ -270,6 +266,28 @@ You use the community supported version of the original Shaarli project, by Seba
     /**
      * Saves the database from memory to disk
      *
+     * @throws IOException the datastore is not writable
+     */
+    private function writeDB()
+    {
+        if (is_file($this->_datastore) && !is_writeable($this->_datastore)) {
+            // The datastore exists but is not writeable
+            throw new IOException($this->_datastore);
+        } else if (!is_file($this->_datastore) && !is_writeable(dirname($this->_datastore))) {
+            // The datastore does not exist and its parent directory is not writeable
+            throw new IOException(dirname($this->_datastore));
+        }
+
+        file_put_contents(
+            $this->_datastore,
+            self::$phpPrefix.base64_encode(gzdeflate(serialize($this->_links))).self::$phpSuffix
+        );
+
+    }
+
+    /**
+     * Saves the database from memory to disk
+     *
      * @param string $pageCacheDir page cache directory
      */
     public function savedb($pageCacheDir)
@@ -278,10 +296,9 @@ You use the community supported version of the original Shaarli project, by Seba
             // TODO: raise an Exception instead
             die('You are not authorized to change the database.');
         }
-        file_put_contents(
-            $this->_datastore,
-            self::$phpPrefix.base64_encode(gzdeflate(serialize($this->_links))).self::$phpSuffix
-        );
+
+        $this->writeDB();
+
         invalidateCaches($pageCacheDir);
     }