[gparted] Refactor ::OnReadable() creating get_utf8_char_validated() (#136)

[Curtis Gedak <gedakc src gnome org>]

commit b1cad17a144498294ea66614bd3f7286469bf717
Author: Mike Fleetwood <mike fleetwood googlemail com>
Date:   Sat Feb 20 23:30:41 2021 +0000

    Refactor ::OnReadable() creating get_utf8_char_validated() (#136)
    
    Extract call to GLib's g_utf8_get_char_validated() and the associated
    workaround to also read NUL characters into a separate function to make
    PipeCapture::OnReadable() a little smaller and simpler, so easier to
    understand.
    
    Add max_len > 0 clause into get_utf8_char_validated() like this:
        if (uc == UTF8_PARTIAL && max_len > 0)
    so that the NUL character reading workaround is only applied when
    max_len specifies the maximum number of bytes to read, rather than
    when -1 specifies reading a NUL termination string.  This makes
    get_utf8_char_validated() a complete wrapper of
    g_utf8_get_char_validated() [1], even though GParted always specifies
    the maximum number of bytes to read.
    
    No longer describe the inability to read NUL characters as a bug [2]
    since the GLib author's said it wasn't [3].
    
    [1] GLib Reference Manual, Unicode Manipulation Functions,
        g_utf8_get_char_validated ()
        https://developer.gnome.org/glib/stable/glib-Unicode-Manipulation.html#g-utf8-get-char-validated
    
    [2] 8dbbb47ce2db0ee733ff909c1ead2f4de9475596
        Workaround g_utf8_get_char_validate() bug with embedded NUL bytes
        (#777973)
    
    [3] Bug 780095 - g_utf8_get_char_validated() stopping at nul byte even
        for length specified buffers
        https://bugzilla.gnome.org/show_bug.cgi?id=780095#18
            "If g_utf8_get_char_validated() encounters a nul byte in the
            middle of a string of given longer length, it returns -2,
            indicating a partial gunichar.  That is not the obvious
            behaviour, but since g_utf8_get_char_validated() has been API
            for a long time, the behaviour cannot be changed.
            "
    
    Closes #136 - 1.2.0: test suite is failing in test_PipeCapture

 include/PipeCapture.h |  1 +
 src/PipeCapture.cc    | 44 +++++++++++++++++++++++++++++---------------
 2 files changed, 30 insertions(+), 15 deletions(-)
---
diff --git a/include/PipeCapture.h b/include/PipeCapture.h
index 95fc763a..1be1c83f 100644
--- a/include/PipeCapture.h
+++ b/include/PipeCapture.h
@@ -45,6 +45,7 @@ private:
                                     gpointer data );
        static void append_unichar_vector_to_utf8( std::string & str,
                                                   const std::vector<gunichar> & ucvec );
+       static gunichar get_utf8_char_validated(const char *p, gssize max_len);
        static int utf8_char_length( unsigned char firstbyte );
 
        Glib::RefPtr<Glib::IOChannel> channel;  // Wrapper around fd
diff --git a/src/PipeCapture.cc b/src/PipeCapture.cc
index 52e45cc1..d5b6f4f2 100644
--- a/src/PipeCapture.cc
+++ b/src/PipeCapture.cc
@@ -30,6 +30,11 @@ namespace GParted {
 
 const size_t READBUF_SIZE = 64*KIBIBYTE;
 
+
+const gunichar UTF8_PARTIAL = (gunichar)-2;
+const gunichar UTF8_INVALID = (gunichar)-1;
+
+
 PipeCapture::PipeCapture( int fd, Glib::ustring &buffer ) : fill_offset( 0 ),
                                                             cursor( 0 ),
                                                             line_start( 0 ),
@@ -125,21 +130,7 @@ bool PipeCapture::OnReadable( Glib::IOCondition condition )
                fill_offset = 0;
                while ( read_ptr < end_ptr )
                {
-                       const gunichar UTF8_PARTIAL = (gunichar)-2;
-                       const gunichar UTF8_INVALID = (gunichar)-1;
-                       gunichar uc = g_utf8_get_char_validated( read_ptr, end_ptr - read_ptr );
-                       if ( uc == UTF8_PARTIAL )
-                       {
-                               // Workaround bug in g_utf8_get_char_validated() in which
-                               // it reports an partial UTF-8 char when a NUL byte is
-                               // encountered in the middle of a multi-byte character,
-                               // yet there are more bytes available in the length
-                               // specified buffer.  Report as invalid character instead.
-                               int len = utf8_char_length( *read_ptr );
-                               if ( len == -1 || read_ptr + len <= end_ptr )
-                                       uc = UTF8_INVALID;
-                       }
-
+                       gunichar uc = get_utf8_char_validated(read_ptr, end_ptr - read_ptr);
                        if ( uc == UTF8_PARTIAL )
                        {
                                // Partial UTF-8 character at end of read buffer.  Copy to
@@ -258,6 +249,29 @@ void PipeCapture::append_unichar_vector_to_utf8( std::string & str, const std::v
        }
 }
 
+
+// GLib's g_utf8_get_char_validated() always considers strings as being NUL terminated,
+// even when max_len is specified, hence can't read NUL characters.  This wrapper can read
+// NUL characters when max_len is specified.
+// Reference:
+//     https://developer.gnome.org/glib/stable/glib-Unicode-Manipulation.html#g-utf8-get-char-validated
+gunichar PipeCapture::get_utf8_char_validated(const char *p, gssize max_len)
+{
+       gunichar uc = g_utf8_get_char_validated(p, max_len);
+       if (uc == UTF8_PARTIAL && max_len > 0)
+       {
+               // If g_utf8_get_char_validated() found a NUL byte in the middle of a
+               // multi-byte character, even when there are more bytes available as
+               // specified by max_len, it reports a partial UTF-8 character.  Report
+               // this case as an invalid character instead.
+               int len = utf8_char_length(*p);
+               if (len == -1 || (gssize)len <= max_len)
+                       uc = UTF8_INVALID;
+       }
+       return uc;
+}
+
+
 int PipeCapture::utf8_char_length( unsigned char firstbyte )
 {
        // Recognise the size of FSS-UTF (1992) / UTF-8 (1993) characters given the first