About
-----

The eReader format has evolved and changed over time. Subsequently, there are
multiple versions of the eReader format. There are also two different tools
that can create eReader files. The official tools are Makebook and Dropbook.
Dropbook is the newer official tool that has replaced Makebook. However,
Makebook is still in wide use because it supports a wider range of platforms
than Dropbook. Dropbook is a GUI application that only runs on Windows and
Apple’s OS X.


PDB Identiy
-------

PNRdPPrs


202 and 132 headers
-----------------------------------------

Older files have a record 0 size of 202 and occasionally 116. Newer files have
a record 0 size of 132. As of this writing the 202 files only support text and
images. The image format in the 202 files is the same as the 132 files. The 132
files support a number of additional features.


Record 0, eReader header (202)
------------------

Note all values are in 2 byte increments. Like values are condensed into a
range. The range can be borken into 2 byte sections which represent the actual
stored values.

bytes       content             comments

0-2         Version             Non-DRM books 2 and 4.
2-8         Garbage
8-10        Non-Text Offset     Start of Non text area (images) will run to the
                                end of the section list.
10-14       Unknown
14-24       Garbage
24-28       Unknown
28-98       Garbage
98-100      Unknown
100-110     Garbage
110-114     Unknown
114-116     Garbage
116-202     Unknown

* Garbage: Intentially random values.


Text Records (202)
------------------

Text starts with section 1 and continues until the section indicated by the
Non-Text Offset. All text records are PalmDoc compressed.

Each character in the compressed data is xored with 0xA5.

A decompression example in sudo Python:

for num in range(1, Non-Text Offset):
    text += decompress_pamldoc(''.join([chr(ord(x) ^ 0xA5) for x in section_data(num)])).decode('cp1252', 'replace')


Dropbook 132 files
------------------

The following sections apply to the newer Dropbook created files.


Record 0, eReader header (132)
----------------------------

This is only for 132 byte header files created by Dropbook.

bytes   content                     comments

0-2     compression                 Specifies compression and drm. 2 = palmdoc,
                                    10 = zlib. 260 and 272 = DRM
2-6     unknown                     Value of 0 is used
6-8     encoding                    Always 25152 (0x6240). All text must be
                                    encoded as Latin-1 cp1252
8-10    Number of small pages       The number of small font pages. If page
                                    index is not build in then 0.
10-12   Number of large pages       The number of large font pages. If page
                                    index is not build in then 0.
12-14   Non-Text record start       The location of the first non text records.
                                    record 1 to this value minus 1 are all text
                                    records
14-16   Number of chapters          The number of chapter index records
                                    contained in the file
16-18   Number of small index       The number of small font page index records
                                    contained in the file
18-20   Number of large index       The number of large font page index records
                                    contained in the file
20-22   Number of images            The number of images contained in the file
22-24   Number of links             The number of links contained in the file
24-26   Metadata avaliable          Is there a metadata record in the file?
                                    0 = None, 1 = There is a metadata record
26-28   Unknown                     Value of 0 is used
28-30   Number of Footnotes         The number of footnote records in the file
30-32   Number of Sidebars          The number of sidebar records in the file
32-34   Chapter index record start  The location of chapter index records. If
                                    there are no chapters use the value for the
                                    Last data record.
34-36   2560                        Magic value that must be set to 2560
36-38   Small page index start      The location of small font page index
                                    records. If page table is not built in use
                                    the value for the Last data record.
38-40   Large page index start      The location of large font page index
                                    records. If page table is not built in use
                                    the value for the Last data record.
40-42   Image data record start     The location of the first image record. If
                                    there are no images use the value for the
                                    Last data record.
42-44   Links record start          The location of the first link index
                                    record. If there are no links use the value
                                    for the Last data record.
44-46   Metadata record start       The location of the metadata record. If
                                    there is no metadata use the value for the
                                    Last data record.
46-48   Unknown                     Value of 0 is used
48-50   Footnote record start       The location of the first footnote record.
                                    If there are no footnotes use the value for
                                    the Last data record.
50-52   Sidebar record start        The location of the first sidebar record.
                                    If there are no sidebars use the value for
                                    the Last data record.
52-54   Last data record            The location of the last data record
54-132  Unknown                     Value of 0 is used

Note: All values are in 2 byte increments. All bytes in the table that have a
range larger than 2 can be broken into 2 byte segments and have different
values set for each grouping.


Records Order
-------------

Though the order of this sections is described in eReader header,
DropBook makes the following order:

   1. eReader Header
   2. Compressed text
   3. Small font page index
   4. Large font page index
   5. Chapter index
   6. Links index
   7. Images
   8. (Extrapolation: there should be one more record type here though it has
       not yet been uncovered what it might be).
   9. Metadata
  10. Sidebar records
  11. Footnote records
  12. Text block size record
  13. "MeTaInFo\x00" word record 


Text Records
------------

All text records use cp1252  encoding (although eReader documents talk about
UTF-8 as well). Their total compressed size is unknown however, anything below
3560 Bytes is known to work. The text will be either zlib or palmdoc
compressed. Use the compression value from the eReader header to determine
which. All text utalizes the Palm Markup Language (PML) for formatting.

Starting with DropBook 1.6.0 text is divided into 8KB (8192 bytes) blocks
trimming the end to the closest space character and then being compressed.
Earlier version of DropBook 1.5.2 tries to behave the same way, though
sometimes it trims the block in unexpected place.


Chapter Index Records
---------------------

Each chapter record corresponds to 1 chapter and points at the place in the
book. Chapter record takes a form of 'offset name\x00' First 4 bytes are offset
of the original pml file where the chapter index points to (offset of
the \x|\X?|\C? tags). Then without a space goes a name of a chapter in chapter
index. It should contain only text, all formatting tags should be removed.
\U and \a tags are not permitted in chapter name. To maintain sub-chapters
4*n spaces (\x20) are added to the beginning of the name, where "n" is level of
chapter: 0 for \x tag and N for \CN="" and \XN tags. And then an ending
\x00 symbol.


Image Records
-------------

Image records must be smaller than 65505 Bytes. They must also be 8bit PNG
images.

An image record takes the form 'PNG name\x00... image_data'

bytes   content         comments

0-4     PNG             There must be a space after PNG.
4-36    image name.     The image name must be 32 exactly 32 Bytes long. Pad
                        the right side of the name with \x00 characters for
                        names shorter than 32 characters.
36-58   Unknown	
58-60   width           Width of an image
60-62   height          Height of an image
62-?    The image data  raw image data in 8 bit PNG format

Note: DropBooks seems to change something in png raw data. Like reencoding or
something, but plain insertion of png image there still works. 


Links Records
-------------

Links records are constructed the same way as chapter ones. Each link anchor
record corresponds to 1 link anchor and points at the place in the book. Link
record takes a form of 'offset name\x00' First 4 bytes are offset of the
original pml file where the link anchor points to (offset of the \Q tag). Then
without a space goes a name of a link anchor. It should contain only text, all
formatting tags should be removed. \U and \a tags are not permitted in link
anchor name. And then an ending \x00 symbol.


Footnote Records
----------------

The first footnote record is a \x00 separated list of footnote ids. All
subsequent footnote records are the footnote text corresponding to the id's
position in the list. Footnote text is compressed in the same manner as normal
text records

E.G.

footnote section 1 = 'notice1\x00notice2\x00notice3\x00'
footnote section 2 = 'Text for notice 1'
footnote section 3 = 'Text for notice 2'
footnote section 4 = 'Text for notice 3'

Starting with Dropbook 1.5.2 first record looks a bit different. It is sequence
of \x00\x01 then 1 byte of footnote id length, then footnote id then \x00.

E.G.

footnote section 1 = '\x00\x01\x07notice1\x00\x00\x01\x0Afootnote10\x00'


Sidebar Records
---------------

The first sidebar record is a \x00 separated list of sidebar ids. All
subsequent sidebar records are the sidebar text corresponding to the id's
position in the list. Sidebar text is compressed in the same manner as normal
text records

E.G.

sidebar section 1 = 'notice1\x00notice2\x00notice3\x00'
sidebar section 2 = 'Text for notice 1'
sidebar section 3 = 'Text for notice 2'
sidebar section 4 = 'Text for notice 3'

Starting with Dropbook 1.5.2 first record looks a bit different. It is sequence
of \x00\x01 then 1 byte of sidebar's id length, then sidebar's id then \x00.

E.G.

sidebar section 1 = '\x00\x01\x07notice1\x00\x00\x01\x09sidebar10\x00'


Metadata Record
---------------

\x00 separated list of string.

Metadata takes the form:

  title\x00
  author\x00
  copyright\x00
  publisher\x00
  isbn\x00

E.G.

Gibraltar Earth\x00Michael McCollum\x001999\x00Sci Fi Arizona\x001929381255\x00

The metdata record is always followed by a record which contains 'MeTaInFo\x00'

Note: Starting with DropBook 1.5.2 'MeTaInFo\x00' is not following Metadata
Record. It is a separate record that ends the file and there are some more
records between Metadata record and 'MeTaInFo\x00' record.


Text Sizes Record
-----------------

There is a special record that contains the initial size of all text blocks
before compression. It is just a sequence of 2-byte blocks which are containing
the sizes.

E.G.

\x1F\xFB\x20\x00\x20\x00\x1F\xFE\x1F\xFD\x09\x46

Note: By this we can judge that theoretical maximum of initial block size is
65535 bytes. 

