Possible degradation in 0.8.43 when reading PRC files

[pike2000]

After I upgraded Calibre from 0.8.41 to 0.8.43 I see an error while trying to view or convert old PRC files

error: unpack_from requires a buffer of at least 4 bytes

I downloaded these PRC files from WebScriptions (www.baenebooks.com) long time ago. The e-books were either purchased, or taken from Baen's free library.

Note that now it is not possible to download these books as *.prc files, only *.mobi files are available. I have downloaded few of my e-books as *.mobi files and they are viewed/converted fine.

Here is E-book Viewer traceback

calibre, version 0.8.43
ERROR: Could not open ebook: unpack_from requires a buffer of at least 4 bytes

Traceback (most recent call last):
File "site-packages\calibre\gui2\viewer\main.py", line 64, in run
File "threading.py", line 483, in run
File "site-packages\calibre\ebooks\oeb\iterator.py", line 205, in __enter__
File "site-packages\calibre\customize\conversion.py", line 208, in __call__
File "site-packages\calibre\ebooks\conversion\plugins\mobi_in put.py", line 55, in convert
File "site-packages\calibre\ebooks\mobi\reader\mobi6.py", line 105, in __init__
File "site-packages\calibre\ebooks\mobi\reader\headers.py", line 190, in __init__
error: unpack_from requires a buffer of at least 4 bytes

Here is convertor traceback

calibre, version 0.8.43
ERROR: Conversion Error: <b>Failed</b>: Convert book 1 of 1 (Star Flight)

Convert book 1 of 1 (Star Flight)
Resolved conversion options
calibre version: 0.8.43
{'asciiize': False,
'author_sort': None,
'authors': None,
'base_font_size': 16.0,
'book_producer': None,
'change_justification': u'original',
'chapter': u"//*[((name()='h1' or name()='h2') and re:test(., 'chapter|book|section|part|prologue|epilogue\\s+', 'i')) or @class = 'chapter']",
'chapter_mark': u'pagebreak',
'comments': None,
'cover': u'C:\\Users\\xyz\\AppData\\Local\\Temp\\calibre_0. 8.43_tmp_mvf0x1\\gpynra.jpeg',
'debug_pipeline': None,
'dehyphenate': True,
'delete_blank_paragraphs': True,
'disable_font_rescaling': False,
'duplicate_links_in_toc': False,
'enable_heuristics': False,
'extra_css': None,
'fb2_genre': u'antique',
'filter_css': u'',
'fix_indents': True,
'font_size_mapping': u'12.0, 14.0, 16.0, 18.0, 20.0, 22.0, 24.0',
'format_scene_breaks': True,
'html_unwrap_factor': 0.4,
'input_encoding': None,
'input_profile': <calibre.customize.profiles.InputProfile object at 0x04A64590>,
'insert_blank_line': False,
'insert_blank_line_size': 0.5,
'insert_metadata': True,
'isbn': None,
'italicize_common_cases': True,
'keep_ligatures': False,
'language': None,
'level1_toc': None,
'level2_toc': None,
'level3_toc': None,
'line_height': 0.0,
'linearize_tables': False,
'margin_bottom': 5.0,
'margin_left': 5.0,
'margin_right': 5.0,
'margin_top': 5.0,
'markup_chapter_headings': True,
'max_toc_links': 50,
'minimum_line_height': 120.0,
'no_chapters_in_toc': False,
'no_inline_navbars': False,
'output_profile': <calibre.customize.profiles.IRexDR800Output object at 0x04A64890>,
'page_breaks_before': u"//*[name()='h1' or name()='h2']",
'prefer_metadata_cover': False,
'pretty_print': False,
'pubdate': None,
'publisher': None,
'rating': None,
'read_metadata_from_opf': u'C:\\Users\\xyz\\AppData\\Local\\Temp\\calibre_0. 8.43_tmp_mvf0x1\\s4lqqf.opf',
'remove_fake_margins': True,
'remove_first_image': True,
'remove_paragraph_spacing': False,
'remove_paragraph_spacing_indent_size': 1.5,
'renumber_headings': True,
'replace_scene_breaks': u'',
'sectionize': u'files',
'series': None,
'series_index': None,
'smarten_punctuation': False,
'sr1_replace': None,
'sr1_search': None,
'sr2_replace': None,
'sr2_search': None,
'sr3_replace': None,
'sr3_search': None,
'tags': None,
'timestamp': None,
'title': None,
'title_sort': None,
'toc_filter': None,
'toc_threshold': 6,
'unsmarten_punctuation': False,
'unwrap_lines': True,
'use_auto_toc': False,
'verbose': 2}
InputFormatPlugin: MOBI Input running
on C:\Users\xyz\AppData\Local\Temp\calibre_0.8.43_tmp _mvf0x1\lljxt0.prc
Unknown codepage 235802126. Assuming cp1252
Unknown codepage 235802126. Assuming cp1252
Python function terminated unexpectedly
unpack_from requires a buffer of at least 4 bytes (Error Code: 1)
Traceback (most recent call last):
File "site.py", line 132, in main
File "site.py", line 109, in run_entry_point
File "site-packages\calibre\utils\ipc\worker.py", line 191, in main
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 31, in gui_convert_override
File "site-packages\calibre\gui2\convert\gui_conversion.py", line 25, in gui_convert
File "site-packages\calibre\ebooks\conversion\plumber.py", line 963, in run
File "site-packages\calibre\customize\conversion.py", line 208, in __call__
File "site-packages\calibre\ebooks\conversion\plugins\mobi_in put.py", line 55, in convert
File "site-packages\calibre\ebooks\mobi\reader\mobi6.py", line 105, in __init__
File "site-packages\calibre\ebooks\mobi\reader\headers.py", line 190, in __init__
struct.error: unpack_from requires a buffer of at least 4 bytes

[kovidgoyal]

Fixed in next release.

[theducks]

@pike2000

Webscriptions (now Baen ebooks) keeps track of your purchases and ALLOWS you to go back and grab a different format at any time.

NB there are a (very) few titles, where the author has pulled rights
There are also quite a few Previously PAID titles that are now in the free Library

[koland]

I'm seeing same error (x.42), not from Baen books, enough of them it would be a royal pain to have to track them down again.

I'll try to keep an eye out for .44, as I am working on cleaning up my files and fixing the metadata, then ran into a few hundred books that can't be opened (I'm seeing the error in trying to read the books, not just convert - hopefully your fix got both).


calibre, version 0.8.42
ERROR: Could not open ebook: unpack_from requires a buffer of at least 4 bytes

Traceback (most recent call last):
File "site-packages\calibre\gui2\viewer\main.py", line 64, in run
File "threading.py", line 483, in run
File "site-packages\calibre\ebooks\oeb\iterator.py", line 205, in __enter__
File "site-packages\calibre\customize\conversion.py", line 208, in __call__
File "site-packages\calibre\ebooks\conversion\plugins\mobi_in put.py", line 50, in convert
File "site-packages\calibre\ebooks\mobi\reader\mobi6.py", line 105, in __init__
File "site-packages\calibre\ebooks\mobi\reader\headers.py", line 187, in __init__
error: unpack_from requires a buffer of at least 4 bytes