<s>
Bencode	B-Protocol
(	O
pronounced	O
like	O
Bee-encode	O
)	O
is	O
the	O
encoding	B-General_Concept
used	O
by	O
the	O
peer-to-peer	O
file	O
sharing	O
system	O
BitTorrent	B-Protocol
for	O
storing	O
and	O
transmitting	O
loosely	O
structured	O
data	O
.	O
</s>
<s>
byte	B-Application
strings	O
,	O
</s>
<s>
dictionaries	B-Application
(	O
associative	B-Application
arrays	I-Application
)	O
.	O
</s>
<s>
Bencoding	B-Protocol
is	O
most	O
commonly	O
used	O
in	O
torrent	B-Protocol
files	O
,	O
and	O
as	O
such	O
is	O
part	O
of	O
the	O
BitTorrent	B-Protocol
specification	O
.	O
</s>
<s>
These	O
metadata	O
files	O
are	O
simply	O
bencoded	B-Protocol
dictionaries	B-Application
.	O
</s>
<s>
Bencoding	B-Protocol
is	O
simple	O
and	O
(	O
because	O
numbers	O
are	O
encoded	O
as	O
text	O
in	O
decimal	O
notation	O
)	O
is	O
unaffected	O
by	O
endianness	O
,	O
which	O
is	O
important	O
for	O
a	O
cross-platform	B-Operating_System
application	O
like	O
BitTorrent	B-Protocol
.	O
</s>
<s>
It	O
is	O
also	O
fairly	O
flexible	O
,	O
as	O
long	O
as	O
applications	O
ignore	O
unexpected	O
dictionary	B-Application
keys	O
,	O
so	O
that	O
new	O
ones	O
can	O
be	O
added	O
without	O
creating	O
incompatibilities	O
.	O
</s>
<s>
Bencode	B-Protocol
uses	O
ASCII	B-Protocol
characters	I-Protocol
as	O
delimiters	O
and	O
digits	O
.	O
</s>
<s>
An	O
integer	O
is	O
encoded	O
as	O
i	O
<	O
integer	O
encoded	O
in	O
base	O
ten	O
ASCII>e	O
.	O
</s>
<s>
A	O
byte	B-Application
string	O
(	O
a	O
sequence	O
of	O
bytes	B-Application
,	O
not	O
necessarily	O
characters	O
)	O
is	O
encoded	O
as	O
<length>:<contents>	O
.	O
</s>
<s>
The	O
length	O
is	O
encoded	O
in	O
base	O
10	O
,	O
like	O
integers	O
,	O
but	O
must	O
be	O
non-negative	O
(	O
zero	O
is	O
allowed	O
)	O
;	O
the	O
contents	O
are	O
just	O
the	O
bytes	B-Application
that	O
make	O
up	O
the	O
string	O
.	O
</s>
<s>
The	O
specification	O
does	O
not	O
deal	O
with	O
encoding	B-General_Concept
of	O
characters	O
outside	O
the	O
ASCII	B-Protocol
set	O
;	O
to	O
mitigate	O
this	O
,	O
some	O
BitTorrent	B-Protocol
applications	O
explicitly	O
communicate	O
the	O
encoding	B-General_Concept
(	O
most	O
commonly	O
UTF-8	O
)	O
in	O
various	O
non-standard	O
ways	O
.	O
</s>
<s>
This	O
is	O
identical	O
to	O
how	O
netstrings	B-Protocol
work	O
,	O
except	O
that	O
netstrings	B-Protocol
additionally	O
append	O
a	O
comma	O
suffix	O
after	O
the	O
byte	B-Application
sequence	O
.	O
</s>
<s>
The	O
contents	O
consist	O
of	O
the	O
bencoded	B-Protocol
elements	O
of	O
the	O
list	O
,	O
in	O
order	O
,	O
concatenated	O
.	O
</s>
<s>
A	O
dictionary	B-Application
is	O
encoded	O
as	O
d	O
<	O
contents>e	O
.	O
</s>
<s>
The	O
elements	O
of	O
the	O
dictionary	B-Application
are	O
encoded	O
with	O
each	O
key	O
immediately	O
followed	O
by	O
its	O
value	O
.	O
</s>
<s>
All	O
keys	O
must	O
be	O
byte	B-Application
strings	O
and	O
must	O
appear	O
in	O
lexicographical	O
order	O
.	O
</s>
<s>
A	O
dictionary	B-Application
that	O
associates	O
the	O
values	O
42	O
and	O
"	O
spam	O
"	O
with	O
the	O
keys	O
"	O
foo	O
"	O
and	O
"	O
bar	O
"	O
,	O
respectively	O
(	O
in	O
other	O
words	O
,	O
}	O
)	O
,	O
would	O
be	O
encoded	O
as	O
follows	O
:	O
.	O
</s>
<s>
There	O
are	O
no	O
restrictions	O
on	O
what	O
kind	O
of	O
values	O
may	O
be	O
stored	O
in	O
lists	O
and	O
dictionaries	B-Application
;	O
they	O
may	O
(	O
and	O
usually	O
do	O
)	O
contain	O
other	O
lists	O
and	O
dictionaries	B-Application
.	O
</s>
<s>
Bencode	B-Protocol
is	O
a	O
very	O
specialized	O
kind	O
of	O
binary	O
coding	O
with	O
some	O
unique	O
properties	O
:	O
</s>
<s>
For	O
each	O
possible	O
(	O
complex	O
)	O
value	O
,	O
there	O
is	O
only	O
a	O
single	O
valid	O
bencoding	B-Protocol
;	O
i.e.	O
</s>
<s>
there	O
is	O
a	O
bijection	B-Algorithm
between	O
values	O
and	O
their	O
encodings	O
.	O
</s>
<s>
This	O
has	O
the	O
advantage	O
that	O
applications	O
may	O
compare	O
bencoded	B-Protocol
values	O
by	O
comparing	O
their	O
encoded	O
forms	O
,	O
eliminating	O
the	O
need	O
to	O
decode	O
the	O
values	O
.	O
</s>
<s>
Since	O
the	O
bencoded	B-Protocol
values	O
often	O
contain	O
binary	O
data	O
,	O
decoding	O
may	O
become	O
quite	O
complex	O
.	O
</s>
<s>
Bencode	B-Protocol
is	O
not	O
considered	O
a	O
human-readable	B-General_Concept
encoding	B-General_Concept
format	O
.	O
</s>
<s>
Bencoding	B-Protocol
serves	O
similar	O
purposes	O
as	O
data	O
languages	O
like	O
JSON	B-General_Concept
and	O
YAML	B-Protocol
,	O
allowing	O
complex	O
yet	O
loosely	O
structured	O
data	O
to	O
be	O
stored	O
in	O
a	O
platform	B-Operating_System
independent	I-Operating_System
way	O
.	O
</s>
<s>
Because	O
bencoded	B-Protocol
files	O
contain	O
binary	O
data	O
,	O
and	O
because	O
of	O
some	O
of	O
the	O
intricacies	O
involved	O
in	O
the	O
way	O
binary	O
strings	O
are	O
typically	O
stored	O
,	O
it	O
is	O
often	O
not	O
safe	O
to	O
edit	O
bencode	B-Protocol
files	O
in	O
text	O
editors	O
.	O
</s>
