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>
29 @section toc Table of Contents
37 @li @ref intro_example
39 @section intro What is Eet?
41 It is a tiny library designed to write an arbitrary set of chunks of data
42 to a file and optionally compress each chunk (very much like a zip file)
43 and allow fast random-access reading of the file later on. It does not
44 do zip as a zip itself has more complexity than is needed, and it was much
45 simpler to implement this once here.
47 Eet is extremely fast, small and simple. Eet files can be very small and
48 highly compressed, making them very optimal for just sending across the
49 internet without having to archive, compress or decompress and install them.
50 They allow for lightning-fast random-acess reads once created, making them
51 perfect for storing data that is written once (or rarely) and read many
52 times, but the program does not want to have to read it all in at once.
54 It also can encode and decode data structures in memory, as well as image
55 data for saving to Eet files or sending across the network to other
56 machines, or just writing to arbitrary files on the system. All data is
57 encoded in a platform independent way and can be written and read by any
60 @section example A simple example on using Eet
62 Here is a simple example on how to use Eet to save a series of strings to a
63 file and load them again. The advantage of using Eet over just fprintf() and
64 fscanf() is that not only can these entries be strings, they need no special
65 parsing to handle delimiter characters or escaping, they can be binary data,
66 image data, data structures containing integers, strings, other data
67 structures, linked lists and much more, without the programmer having to
68 worry about parsing, and best of all, Eet is very fast.
74 main(int argc, char **argv)
84 "Big text string here compared to others",
90 // blindly open an file for output and write strings with their NUL char
91 ef = eet_open("test.eet", EET_FILE_MODE_WRITE);
92 eet_write(ef, "Entry 1", entries[0], strlen(entries[0]) + 1, 0);
93 eet_write(ef, "Entry 2", entries[1], strlen(entries[1]) + 1, 1);
94 eet_write(ef, "Entry 3", entries[2], strlen(entries[2]) + 1, 0);
97 // open the file again and blindly get the entries we wrote
98 ef = eet_open("test.eet", EET_FILE_MODE_READ);
99 ret = eet_read(ef, "Entry 1", &size);
101 ret = eet_read(ef, "Entry 2", &size);
103 ret = eet_read(ef, "Entry 3", &size);
111 @section format What does an Eet file look like?
113 The file format is very simple. There is a directory block at the start of
114 the file listing entries and offsets into the file where they are stored,
115 their sizes, compression flags etc. followed by all the entry data strung one
116 element after the other.
118 All Eet files start with t a 4 byte magic number. It is written using network
119 byte-order (big endian, or from most significant byte first to least
120 significant byte last) and is 0x1ee7ff00 (or byte by byte 0:1e 1:e7 2:ff
121 3:00). The next 4 bytes are an integer (in big endian notation) indicating
122 how many entries are stored in the Eet file. 0 indicates it is empty. This is
123 a signed integer and thus values less than 0 are invalid, limiting the number
124 of entries in an Eet file to 0x7fffffff entries at most. The next 4 bytes is
125 the size of the directory table, in bytes, encoded in big-endian format. This
126 is a signed integer and cannot be less than 0.
128 The directory table for the file follows immediately, with a continuous list
129 of all entries in the Eet file, their offset in the file etc. The order of
130 these entries is not important, but convention would have them be from first
131 to last entry in the file. Each directory entry consiste of 5 integers, one
132 after the other, each stored as a signed, big endian integer. The first is
133 the offset in the file that the data for this entry is stored at (based from
134 the very start of the file, not relative to the end of the directory block).
135 The second integer holds flags for the entry. currently only the least
136 significant bit (bit 0) holds any useful information, and it is set to 1 if
137 the entry is compressed using zlib compression calls, or 0 if it is not
138 compressed. The next integer is the size of the entry in bytes stored in the
139 file. The next integer is the size of the data when decompressed (if it was
140 compressed) in bytes. This may be the same as the previous integer if the
141 entry was not compressed. The final integer is the number of bytes used by
142 the string identifier for the entry, without the NUL byte terminator, which
143 is not stored. The next series of bytes is the string name of the entry, with
144 the number of bytes being the same as specified in the last integer above.
145 This list of entries continues until there are no more entries left to list.
146 To read an entry from an Eet file, simply find the appropriate entry in the
147 directory table, find it's offset and size, and read it into memory. If it is
148 compressed, decompress it using zlib and then use that data.
150 Here is a data map of an Eet file. All integers are encoded using big-endian
151 notation (most significant byte first) and are signed. There is no alignment
152 of data, so all data types follow immediately on, one after the other. All
153 compressed data is compressed using the zlib compress2() function, and
154 decompressed using the zlib uncompress() function. Please see zlib
155 documentation for more information as to the encoding of compressed data.
159 [INT] Magic number (0x1ee7ff00)
160 [INT] Number of entries in the directory table
161 [INT] The size of the directory table, in bytes
163 DIRECTORY TABLE ENTRIES (as many as specified in the header):
164 [INT] Offest from file start at which entry is stored (in bytes)
165 [INT] Entry flags (1 = compressed, 0 = not compressed)
166 [INT] Size of data chunk in file (in bytes)
167 [INT] Size of the data chunk once decompressed (or the same as above, if not)
168 [INT] The length of the string itendifier, in bytes, without NUL terminator
169 [STR] Series of bytes for the string identifier, no NUL terminator
170 ... more directory entries
172 DATA STORED, ONE AFTER ANOTHER:
173 [DAT] DATA ENTRY 1...
174 [DAT] DATA ENTRY 2...
175 [DAT] DATA ENTRY 3...
179 The contents of each entry in an Eet file has no defined format as such. It
180 is an opaque chunk of data, that is up to the application to deocde, unless
181 it is an image, ecoded by Eet, or a data structure encoded by Eet. The data
182 itself for these entries can be encoded and decoded by Eet with extra helper
183 functions in Eet. eet_data_image_read() and eet_data_image_write() are used
184 to handle reading and writing image data from a known Eet file entry name.
185 eet_data_read() and eet_data_write() are used to decode and encode program
186 data structures from an Eet file, making the loading and saving of program
187 information stored in data structures a simple 1 function call process.
189 Please see src/lib/eet_data.c for information on the format of these
190 specially encoded data entries in an Eet file (for now).
193 @section compiling How to compile using Eet ?
195 Eet is a library your application links to. The procedure for this is very
196 simple. You simply have to compile your application with the appropriate
197 compiler flags that the @p pkg-config script outputs. For example:
199 Compiling C or C++ files into object files:
202 gcc -c -o main.o main.c `pkg-config --cflags eet`
205 Linking object files into a binary executable:
208 gcc -o my_application main.o `pkg-config --libs eet`
211 You simply have to make sure that pkg-config is in your shell's PATH (see
212 the manual page for your appropriate shell) and eet.pc in /usr/lib/pkgconfig
213 or its path is in the PKG_CONFIG_PATH environment variable. It's that simple
214 to link and use Eet once you have written your code to use it.
216 Since the program is linked to Eet, it is now able to use any advertised
217 API calls to serialize your data.
219 You should make sure you add any extra compile and link flags to your
220 compile commands that your application may need as well. The above example
221 is only guaranteed to make Eet add it's own requirements.
224 @section install How is it installed?
236 @section next_steps Next Steps
238 After you understood what Eet is and installed it in your system you
239 should proceed understanding the programming interface. We'd recommend
240 you to take a while to learn Eina
241 (http://docs.enlightenment.org/auto/eina/) as it is very convenient
242 and optimized, and Eet provides integration with it.
246 @li @ref Eet_File_Group to know the basics to open and save files.
247 @li @ref Eet_Data_Group to know the convenient way to serialize and
248 parse your data structures automatically. Just create your
249 descriptors and let Eet do the work for you.
251 @section intro_example Introductory Examples
255 @todo Document data format for images and data structures.