Replace file reading code in wxTextFile with wxFile::ReadAll()

There is nothing special about wxTextFile justifying having code for
dealing with non-seekable files in it, so put this code into wxFile
itself and just call its ReadAll() method from here.

This is a better fix than 41f6f17d01
originally applied (and which is going to be reverted next) as it
doesn't break wxFile::Length() for these files and also avoids
triggering an assert if the file we're trying to read was truncated by
another process in the meanwhile -- which can happen and doesn't
indicate a programming error and so shouldn't result in an assert.

Also add a unit test checking that this really works.

See #3802, #8354, #9965.

src/common/textfile.cpp

@@ -93,122 +93,13 @@ bool wxTextFile::OnRead(const wxMBConv& conv)
     // file should be opened
     wxASSERT_MSG( m_file.IsOpened(), wxT("can't read closed file") );
 
-    // read the entire file in memory: this is not the most efficient thing to
-    // do it but there is no good way to avoid it in Unicode build because if
-    // we read the file block by block we can't convert each block to Unicode
-    // separately (the last multibyte char in the block might be only partially
-    // read and so the conversion would fail) and, as the file contents is kept
-    // in memory by wxTextFile anyhow, it shouldn't be a big problem to read
-    // the file entirely
-    size_t bufSize = 0;
-
-    // number of bytes to (try to) read from disk at once
-    static const size_t BLOCK_SIZE = 4096;
-
-    wxCharBuffer buf;
-
-    // first determine if the file is seekable or not and so whether we can
-    // determine its length in advance
-    wxFileOffset fileLength;
+    wxString str;
+    if ( !m_file.ReadAll(&str, conv) )
     {
-        wxLogNull logNull;
-        fileLength = m_file.Length();
-    }
-
-    // some non-seekable files under /proc under Linux pretend that they're
-    // seekable but always return 0; others do return an error
-    const bool seekable = fileLength != wxInvalidOffset && fileLength != 0;
-    if ( seekable )
-    {
-        // we know the required length, so set the buffer size in advance
-        bufSize = fileLength;
-        if ( !buf.extend(bufSize) )
-            return false;
-
-        // if the file is seekable, also check that we're at its beginning
-        wxASSERT_MSG( m_file.Tell() == 0, wxT("should be at start of file") );
-
-        char *dst = buf.data();
-        for ( size_t nRemaining = bufSize; nRemaining > 0; )
-        {
-            size_t nToRead = BLOCK_SIZE;
-
-            // the file size could have changed, avoid overflowing the buffer
-            // even if it did
-            if ( nToRead > nRemaining )
-                nToRead = nRemaining;
-
-            ssize_t nRead = m_file.Read(dst, nToRead);
-
-            if ( nRead == wxInvalidOffset )
-            {
-                // read error (error message already given in wxFile::Read)
+        wxLogError(_("Failed to read text file \"%s\"."), GetName());
         return false;
     }
 
-            if ( nRead == 0 )
-            {
-                // this file can't be empty because we checked for this above
-                // so this must be the end of file
-                break;
-            }
-
-            dst += nRead;
-            nRemaining -= nRead;
-        }
-
-        wxASSERT_MSG( dst - buf.data() == (wxFileOffset)bufSize,
-                      wxT("logic error") );
-    }
-    else // file is not seekable
-    {
-        char block[BLOCK_SIZE];
-        for ( ;; )
-        {
-            ssize_t nRead = m_file.Read(block, WXSIZEOF(block));
-
-            if ( nRead == wxInvalidOffset )
-            {
-                // read error (error message already given in wxFile::Read)
-                return false;
-            }
-
-            if ( nRead == 0 )
-            {
-                // if no bytes have been read, presumably this is a
-                // valid-but-empty file
-                if ( bufSize == 0 )
-                    return true;
-
-                // otherwise we've finished reading the file
-                break;
-            }
-
-            // extend the buffer for new data
-            if ( !buf.extend(bufSize + nRead) )
-                return false;
-
-            // and append it to the buffer
-            memcpy(buf.data() + bufSize, block, nRead);
-            bufSize += nRead;
-        }
-    }
-
-    const wxString str(buf, conv, bufSize);
-
-    // there's no risk of this happening in ANSI build
-#if wxUSE_UNICODE
-    if ( bufSize > 4 && str.empty() )
-    {
-        wxLogError(_("Failed to convert file \"%s\" to Unicode."), GetName());
-        return false;
-    }
-#endif // wxUSE_UNICODE
-
-    // we don't need this memory any more
-    buf.reset();
-
-
     // now break the buffer in lines
 
     // the beginning of the current line, changes inside the loop

tests/textfile/textfiletest.cpp

@@ -338,5 +338,29 @@ void TextFileTestCase::ReadBig()
                           f[NUM_LINES - 1] );
 }
 
-#endif // wxUSE_TEXTFILE
+#ifdef __LINUX__
 
+// Check if using wxTextFile with special files, whose reported size doesn't
+// correspond to the real amount of data in them, works.
+TEST_CASE("wxTextFile::Special", "[textfile][linux][special-file]")
+{
+    SECTION("/proc")
+    {
+        wxTextFile f;
+        CHECK( f.Open("/proc/diskstats") );
+        CHECK( f.GetLineCount() > 1 );
+    }
+
+    SECTION("/sys")
+    {
+        wxTextFile f;
+        CHECK( f.Open("/sys/power/state") );
+        REQUIRE( f.GetLineCount() == 1 );
+        INFO( "/sys/power/state contains \"" << f[0] << "\"" );
+        CHECK( f[0].find("mem") != wxString::npos );
+    }
+}
+
+#endif // __LINUX__
+
+#endif // wxUSE_TEXTFILE