3 @brief Eet Data Handling Library Public API Calls
5 These routines are used for Eet Library interaction
10 @mainpage Eet Library Documentation
14 @version @PACKAGE_VERSION@
15 @author Carsten Haitzler <raster@@rasterman.com>
16 @author David Goodlad <dgoodlad@@gmail.com>
17 @author Cedric Bail <cedric.bail@@free.fr>
18 @author Arnaud de Turckheim <quarium@@gmail.com>
19 @author Luis Felipe Strano Moraes <lfelipe@@profusion.mobi>
20 @author Chidambar Zinnoury <illogict@@online.fr>
21 @author Vincent Torri <vtorri@@univ-evry.fr>
22 @author Gustavo Sverzut Barbieri <barbieri@@profusion.mobi>
23 @author Raphael Kubo da Costa <kubo@@profusion.mobi>
24 @author Mathieu Taillefumier <mathieu.taillefumier@@free.fr>
25 @author Albin "Lutin" Tonnerre <albin.tonnerre@@gmail.com>
26 @author Adam Simpkins <adam@@adamsimpkins.net>
30 @section toc Table of Contents
38 @li @ref intro_example
40 @section intro What is Eet?
42 It is a tiny library designed to write an arbitary set of chunks of data
43 to a file and optionally compress each chunk (very much like a zip file)
44 and allow fast random-access reading of the file later on. It does not
45 do zip as a zip itself has more complexity than is needed, and it was much
46 simpler to impliment this once here.
48 Eet is extremely fast, small and simple. Eet files can be very small and
49 highly compressed, making them very optimal for just sending across the
50 internet without having to archive, compress or decompress and install them.
51 They allow for lightning-fast random-acess reads once created, making them
52 perfect for storing data that is written once (or rarely) and read many
53 times, but the program does not want to have to read it all in at once.
55 It also can encode and decode data structures in memory, as well as image
56 data for saving to Eet files or sending across the network to other
57 machines, or just writing to arbitary files on the system. All data is
58 encoded in a platform independant way and can be written and read by any
61 @section example A simple example on using Eet
63 Here is a simple example on how to use Eet to save a series of strings to a
64 file and load them again. The advantage of using Eet over just fprintf() and
65 fscanf() is that not only can these entries be strings, they need no special
66 parsing to handle delimiter characters or escaping, they can be binary data,
67 image data, data structures containing integers, strings, other data
68 structures, linked lists and much more, without the programmer having to
69 worry about parsing, and best of all, Eet is very fast.
75 main(int argc, char **argv)
85 "Big text string here compared to others",
91 // blindly open an file for output and write strings with their NUL char
92 ef = eet_open("test.eet", EET_FILE_MODE_WRITE);
93 eet_write(ef, "Entry 1", entries[0], strlen(entries[0]) + 1, 0);
94 eet_write(ef, "Entry 2", entries[1], strlen(entries[1]) + 1, 1);
95 eet_write(ef, "Entry 3", entries[2], strlen(entries[2]) + 1, 0);
98 // open the file again and blindly get the entries we wrote
99 ef = eet_open("test.eet", EET_FILE_MODE_READ);
100 ret = eet_read(ef, "Entry 1", &size);
102 ret = eet_read(ef, "Entry 2", &size);
104 ret = eet_read(ef, "Entry 3", &size);
112 @section format What does an Eet file look like?
114 The file format is very simple. There is a directory block at the start of
115 the file listing entries and offsets into the file where they are stored,
116 their sizes, compression flags etc. followed by all the entry data strung one
117 element after the other.
119 All Eet files start with t a 4 byte magic number. It is written using network
120 byte-order (big endian, or from most significant byte first to least
121 significant byte last) and is 0x1ee7ff00 (or byte by byte 0:1e 1:e7 2:ff
122 3:00). The next 4 bytes are an integer (in big endian notation) indicating
123 how many entries are stored in the Eet file. 0 indicates it is empty. This is
124 a signed integer and thus values less than 0 are invalid, limiting the number
125 of entries in an Eet file to 0x7fffffff entries at most. The next 4 bytes is
126 the size of the directory table, in bytes, encoded in big-endian format. This
127 is a signed integer and cannot be less than 0.
129 The directory table for the file follows immediately, with a continuous list
130 of all entries in the Eet file, their offset in the file etc. The order of
131 these entries is not important, but convention would have them be from first
132 to last entry in the file. Each directory entry consiste of 5 integers, one
133 after the other, each stored as a signed, big endian integer. The first is
134 the offset in the file that the data for this entry is stored at (based from
135 the very start of the file, not relative to the end of the directory block).
136 The second integer holds flags for the entry. currently only the least
137 significant bit (bit 0) holds any useful information, and it is set to 1 if
138 the entry is compressed using zlib compression calls, or 0 if it is not
139 compressed. The next integer is the size of the entry in bytes stored in the
140 file. The next integer is the size of the data when decompressed (if it was
141 compressed) in bytes. This may be the same as the previous integer if the
142 entry was not compressed. The final integer is the number of bytes used by
143 the string identifier for the entry, without the NUL byte terminator, which
144 is not stored. The next series of bytes is the string name of the entry, with
145 the number of bytes being the same as specified in the last integer above.
146 This list of entries continues until there are no more entries left to list.
147 To read an entry from an Eet file, simply find the appropriate entry in the
148 directory table, find it's offset and size, and read it into memory. If it is
149 compressed, decompress it using zlib and then use that data.
151 Here is a data map of an Eet file. All integers are encoded using big-endian
152 notation (most significant byte first) and are signed. There is no alignment
153 of data, so all data types follow immediately on, one after the other. All
154 compressed data is compressed using the zlib compress2() function, and
155 decompressed using the zlib uncompress() function. Please see zlib
156 documentation for more information as to the encoding of compressed data.
160 [INT] Magic number (0x1ee7ff00)
161 [INT] Number of entries in the directory table
162 [INT] The size of the directory table, in bytes
164 DIRECTORY TABLE ENTRIES (as many as specified in the header):
165 [INT] Offest from file start at which entry is stored (in bytes)
166 [INT] Entry flags (1 = compressed, 0 = not compressed)
167 [INT] Size of data chunk in file (in bytes)
168 [INT] Size of the data chunk once decompressed (or the same as above, if not)
169 [INT] The length of the string itendifier, in bytes, without NUL terminator
170 [STR] Series of bytes for the string identifier, no NUL terminator
171 ... more directory entries
173 DATA STORED, ONE AFTER ANOTHER:
174 [DAT] DATA ENTRY 1...
175 [DAT] DATA ENTRY 2...
176 [DAT] DATA ENTRY 3...
180 The contents of each entry in an Eet file has no defined format as such. It
181 is an opaque chunk of data, that is up to the application to deocde, unless
182 it is an image, ecoded by Eet, or a data structure encoded by Eet. The data
183 itself for these entries can be encoded and decoded by Eet with extra helper
184 functions in Eet. eet_data_image_read() and eet_data_image_write() are used
185 to handle reading and writing image data from a known Eet file entry name.
186 eet_data_read() and eet_data_write() are used to decode and encode program
187 data structures from an Eet file, making the loading and saving of program
188 information stored in data structures a simple 1 function call process.
190 Please see src/lib/eet_data.c for information on the format of these
191 specially encoded data entries in an Eet file (for now).
194 @section compiling How to compile using Eet ?
196 Eet is a library your application links to. The procedure for this is very
197 simple. You simply have to compile your application with the appropriate
198 compiler flags that the @p pkg-config script outputs. For example:
200 Compiling C or C++ files into object files:
203 gcc -c -o main.o main.c `pkg-config --cflags eet`
206 Linking object files into a binary executable:
209 gcc -o my_application main.o `pkg-config --libs eet`
212 You simply have to make sure that pkg-config is in your shell's PATH (see
213 the manual page for your appropriate shell) and eet.pc in /usr/lib/pkgconfig
214 or its path is in the PKG_CONFIG_PATH environment variable. It's that simple
215 to link and use Eet once you have written your code to use it.
217 Since the program is linked to Eet, it is now able to use any advertised
218 API calls to serialize your data.
220 You should make sure you add any extra compile and link flags to your
221 compile commands that your application may need as well. The above example
222 is only guaranteed to make Eet add it's own requirements.
225 @section install How is it installed?
237 @section next_steps Next Steps
239 After you understood what Eet is and installed it in your system you
240 should proceed understanding the programming interface. We'd recommend
241 you to take a while to learn Eina
242 (http://docs.enlightenment.org/auto/eina/) as it is very convenient
243 and optimized, and Eet provides integration with it.
247 @li @ref Eet_File_Group to know the basics to open and save files.
248 @li @ref Eet_Data_Group to know the convenient way to serialize and
249 parse your data structures automatically. Just create your
250 descriptors and let Eet do the work for you.
252 @section intro_example Introductory Examples
256 @todo Document data format for images and data structures.