Cap'n Proto - Revision history

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2019-05-29T06:26:04Z

"either" -> "easier"

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2019-05-20T02:27:57Z

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Effect2: Created page with "{{FormatInfo |formattype=electronic |subcat=Serialization |extensions={{ext|capnp}} |released=2013https://capnproto.org/news/2013-04-01-announcing-capn-proto.html }..."

2019-05-20T01:25:30Z

Created page with "{{FormatInfo |formattype=electronic |subcat=Serialization |extensions={{ext|capnp}} |released=2013<ref>https://capnproto.org/news/2013-04-01-announcing-capn-proto.html</ref> }..."

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{{FormatInfo
|formattype=electronic
|subcat=Serialization
|extensions={{ext|capnp}}
|released=2013<ref>https://capnproto.org/news/2013-04-01-announcing-capn-proto.html</ref>
}}
'''Cap'n Proto''' is a [[serialization]] format and RPC system meant to be an improved version of [[Protobuf|Protocol Buffers]], written by the same author<ref>https://capnproto.org/index.html, section "Why do you pick on Protocol Buffers so much?"</ref>. Its major claimed advantage over Protocol Buffers is fast serialization and very fast deserialization; parsing is done lazily and much more simply than in Protocol Buffers, mostly amounting to a small amount of bounds-checking. Compare [[Simple Binary Encoding]] and [[FlatBuffers]] in this regard.

== Extensions ==
Cap'n Proto schema files have the extension ".capnp"<ref>https://capnproto.org/language.html</ref>. It is not clear what, if any, extensions may be in use for the serialized format.

== Segments ==
Cap'n Proto messages are generally divided into several units called "segments" in order to make construction of the message either.<ref>https://capnproto.org/encoding.html#messages</ref> Messages using segments begin with a "segment table"<ref>https://capnproto.org/encoding.html#serialization-over-a-stream; name is from https://capnproto.org/encoding.html#canonicalization</ref> and then the content of those segments. It is possible to write a "flat" message that takes up a single segment, however, the help text of the CLI calls this "rare".

== Packing ==
Cap'n Proto defines a very simple compression format called the "packing" format, which is essentially a variant of [[run-length encoding]] that only encode runs of bytes with value 0x00. This is especially useful because Cap'n Proto does not leave out zero-valued fields<ref>https://capnproto.org/encoding.html#structs, and the fact that fast pointer access requires this to be true</ref><ref>https://capnproto.org/news/2014-06-17-capnproto-flatbuffers-sbe.html</ref>, and so without packing messages may consist of long runs of zero bytes for the values of uninitialized fields. Packing can in many cases significantly reduce file size. See [https://capnproto.org/encoding.html#packing] for details on the format.

== Canonical Form ==
"Canonicalized" messages are those belonging to a well-defined subset of the regular message format. Where packing is used on canonicalized messages, it is taken as a container rather than as part of the format (unlike for non-canonicalized messages). See [https://capnproto.org/encoding.html#canonicalization] for a specification.

== Software ==
* [https://github.com/capnproto/capnproto Official library]
** Includes a CLI capable of dumping, converting, etc. messages
** Debian packages capnproto, libcapnp-*
* List at [https://capnproto.org/otherlang.html]

== Links ==
* [https://capnproto.org/ Official website]
* [https://news.ycombinator.com/item?id=5482081 Show HN: Cap'n Proto, by the ex-maintainer of Protocol Buffers]
* [https://news.ycombinator.com/item?id=12471266 Hacker news: Cap’n Proto]
* [https://stackoverflow.com/questions/25356551/whats-the-difference-between-the-protocol-buffers-and-the-flatbuffers What's the difference between the Protocol Buffers and the Flatbuffers?]

== References ==
<references />

@@ Line 11: / Line 11: @@
 == Segments ==
-Cap'n Proto messages are generally divided into several units called "segments" in order to make construction of the message either.<ref>https://capnproto.org/encoding.html#messages</ref> Messages using segments begin with a "segment table"<ref>https://capnproto.org/encoding.html#serialization-over-a-stream; name is from https://capnproto.org/encoding.html#canonicalization</ref> and then the content of those segments. It is possible to write a "flat" message that takes up a single segment, however, the help text of the CLI calls this "rare".
+Cap'n Proto messages are generally divided into several units called "segments" in order to make construction of the message easier.<ref>https://capnproto.org/encoding.html#messages</ref> Messages using segments begin with a "segment table"<ref>https://capnproto.org/encoding.html#serialization-over-a-stream; name is from https://capnproto.org/encoding.html#canonicalization</ref> and then the content of those segments. It is possible to write a "flat" message that takes up a single segment, however, the help text of the CLI calls this "rare".
 == Packing ==

@@ Line 14: / Line 14: @@
 == Packing ==
-Cap'n Proto defines a very simple compression format called the "packing" format, which is essentially a variant of [[run-length encoding]] that only encode runs of bytes with value 0x00. This is especially useful because Cap'n Proto does not leave out zero-valued fields<ref>https://capnproto.org/encoding.html#structs, and the fact that fast pointer access requires this to be true</ref><ref>https://capnproto.org/news/2014-06-17-capnproto-flatbuffers-sbe.html</ref>, and so without packing messages may consist of long runs of zero bytes for the values of uninitialized fields. Packing can in many cases significantly reduce file size. See [https://capnproto.org/encoding.html#packing] for details on the format.
+Cap'n Proto defines a very simple compression format called the "packing" format, which is essentially a variant of [[run-length encoding]] that only encode runs of bytes with value 0x00. This is especially useful because Cap'n Proto does not leave out zero-valued fields<ref>https://capnproto.org/encoding.html#structs, and the fact that fast pointer access requires this to be true</ref><ref>https://capnproto.org/news/2014-06-17-capnproto-flatbuffers-sbe.html</ref>, and so without packing, messages may consist of long runs of zero bytes for the values of uninitialized fields. Packing can in many cases significantly reduce file size. See [https://capnproto.org/encoding.html#packing] for details on the format.
 == Canonical Form ==