[gparted] Refactor UDF label manipulation code (#784533)

[Mike Fleetwood <mfleetwo src gnome org>]

commit a0c44d766d44afbde6b0c729125223c06b944278
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Thu Jul 27 16:23:11 2017 +0100

    Refactor UDF label manipulation code (#784533)
    
    Make especially the Volume Identifier length limit code simpler to
    understand and therefore easier to maintain.
    
    Bug 784533 - Add support for UDF file system

 include/udf.h |    6 +++
 src/udf.cc    |   98 +++++++++++++++++++++++++++++++-------------------------
 2 files changed, 60 insertions(+), 44 deletions(-)
---
diff --git a/include/udf.h b/include/udf.h
index 929984f..65d1226 100644
--- a/include/udf.h
+++ b/include/udf.h
@@ -21,6 +21,9 @@
 #include "FileSystem.h"
 #include "Partition.h"
 
+#include <stddef.h>
+#include <glibmm/ustring.h>
+
 namespace GParted
 {
 
@@ -33,6 +36,9 @@ public:
        bool create( const Partition & new_partition, OperationDetail & operationdetail );
 
 private:
+       static bool contains_only_ascii( const Glib::ustring & str );
+       static size_t find_first_non_latin1( const Glib::ustring & str );
+
        bool old_mkudffs;  // Pre 1.1 version of mkudffs
 };
 
diff --git a/src/udf.cc b/src/udf.cc
index 184ed81..c0ee8db 100644
--- a/src/udf.cc
+++ b/src/udf.cc
@@ -18,6 +18,9 @@
 #include "Partition.h"
 #include "Utils.h"
 
+#include <stddef.h>
+#include <glibmm/ustring.h>
+
 namespace GParted
 {
 
@@ -74,46 +77,22 @@ bool udf::create( const Partition & new_partition, OperationDetail & operationde
                return false;
        }
 
-       // NOTE: UDF Logical Volume Identifier (--lvid) represents the label but blkid
-       // (from util-linux) prior to version v2.26 used the Volume Identifier (--vid).
-       // Therefore for compatibility reasons store label in both locations.
-
        Glib::ustring label_args;
        if ( ! new_partition.get_filesystem_label().empty() )
        {
                const Glib::ustring label = new_partition.get_filesystem_label();
-               int non_ascii_pos_label = -1;
-               int non_latin1_pos_label = -1;
-               int pos = 0;
-
-               for ( Glib::ustring::const_iterator it = label.begin(); it != label.end(); ++it )
-               {
-                       if ( *it > 0x7F && non_ascii_pos_label == -1 )
-                               non_ascii_pos_label = pos;
-                       if ( *it > 0xFF && non_latin1_pos_label == -1 )
-                               non_latin1_pos_label = pos;
-                       if ( non_ascii_pos_label != -1 && non_latin1_pos_label != -1 )
-                               break;
-                       ++pos;
-               }
 
-               // NOTE: mkudffs from udftools prior to version 1.1 damage label if contains
-               // non-ASCII characters. So do not allow non-ASCII characters in old mkudffs.
-               if ( old_mkudffs && non_ascii_pos_label != -1 )
+               // Mkudffs from udftools prior to version 1.1 damages the label if it
+               // contains non-ASCII characters.  Therefore do not allow a label with
+               // such characters with old versions of mkudffs.
+               if ( old_mkudffs && ! contains_only_ascii( label ) )
                {
                        operationdetail.add_child( OperationDetail(
-                                                  _("mkudffs prior to version 1.1 does not support non-ASCII 
characters in the label."),
-                                                  STATUS_ERROR ) );
+                               _("mkudffs prior to version 1.1 does not support non-ASCII characters in the 
label."),
+                               STATUS_ERROR ) );
                        return false;
                }
 
-               // NOTE: UDF Volume Identifier (--vid) can contain maximally 30 Unicode code
-               // points. And if one is above U+FF then only 15. UDF Logical Volume Identifier
-               // (--lvid) can contain maximally 126 resp. 63 Unicode code points. To allow
-               // long 126 characters in label, UDF Volume Identifier would be truncated.
-               // When UDF Volume Identifier or UDF Logical Volume Identifier is too long
-               // mkuddfs fail with error.
-
                // NOTE: According to the OSTA specification, UDF supports only strings
                // encoded in 8-bit or 16-bit OSTA Compressed Unicode format.  They are
                // equivalent to ISO-8859-1 (Latin 1) and UCS-2BE respectively.
@@ -122,20 +101,25 @@ bool udf::create( const Partition & new_partition, OperationDetail & operationde
                // specification was created before the introduction of UTF-16, but lots
                // of UDF tools are able to decode UTF-16 including UTF-16 Surrogate pairs
                // outside the BMP (Basic Multilingual Plane).
-
-               Glib::ustring vid_arg;
-               if ( non_latin1_pos_label > 30 )
-                       vid_arg = new_partition.get_filesystem_label().substr(0, 30);
-               else if ( non_latin1_pos_label > 15 )
-                       vid_arg = new_partition.get_filesystem_label().substr(0, non_latin1_pos_label-1);
-               else if ( non_latin1_pos_label == -1 && label.length() > 30 )
-                       vid_arg = new_partition.get_filesystem_label().substr(0, 30);
-               else if ( label.length() > 15 )
-                       vid_arg = new_partition.get_filesystem_label().substr(0, 15);
-               else
-                       vid_arg = new_partition.get_filesystem_label();
-
-               label_args = "--lvid=\"" + label + "\" " + "--vid=\"" + vid_arg + "\" ";
+               //
+               // The Volume Identifier (--vid) can only contain 30 bytes, either 30
+               // ISO-8859-1 (Latin 1) characters or 15 UCS-2BE characters.  Store the
+               // most characters possible in the Volume Identifier.  Either up to 15
+               // UCS-2BE characters when a character needing 16-bit encoding is found in
+               // the first 15 characters, or up to 30 characters when a character
+               // needing 16-bit encoding is found in the second 15 characters.
+               Glib::ustring vid = label.substr( 0, 30 );
+               size_t first_non_latin1_pos = find_first_non_latin1( label );
+               if ( first_non_latin1_pos < 15 )
+                       vid = label.substr( 0, 15 );
+               else if ( first_non_latin1_pos < 30 )
+                       vid = label.substr( 0, first_non_latin1_pos );
+
+               // UDF Logical Volume Identifier (--lvid) represents the label, but blkid
+               // (from util-linux) prior to version v2.26 reads the Volume Identifier
+               // (--vid).  Therefore for compatibility reasons store the label in both
+               // locations.
+               label_args = "--lvid=\"" + label + "\" " + "--vid=\"" + vid + "\" ";
        }
 
        // NOTE: UDF block size must match logical sector size of underlying media.
@@ -149,4 +133,30 @@ bool udf::create( const Partition & new_partition, OperationDetail & operationde
                                  EXEC_CHECK_STATUS|EXEC_CANCEL_SAFE );
 }
 
+// Private methods
+
+// Return true only if all the characters in the string are ASCII (<= 0x7F), otherwise false.
+bool udf::contains_only_ascii( const Glib::ustring & str )
+{
+       for ( Glib::ustring::const_iterator it = str.begin() ; it != str.end() ; ++it )
+       {
+               if ( *it > 0x7F )
+                       return false;
+       }
+       return true;
+}
+
+// Return the offset of the first non-Latin1 character (> 0xFF), or npos when none found.
+size_t udf::find_first_non_latin1( const Glib::ustring & str )
+{
+       size_t pos = 0;
+       for ( Glib::ustring::const_iterator it = str.begin() ; it != str.end() ; ++it )
+       {
+               if ( *it > 0xFF )
+                       return pos;
+               ++pos;
+       }
+       return Glib::ustring::npos;
+}
+
 } //GParted