A small library for encoding and parsing CBOR objects. It follows the CBOR specification defined in the RFC 7049. This library is specially useful to encode/decode data in the context of a network protocol. You can use this library in your project with gradle using jitpack:
repositories {
maven { url 'https://jitpack.io' }
}dependencies {
implementation 'com.github.RightMesh:libcbor:v1.0'
}- Encodes and decodes all examples described in RFC 7049
- Supports 64-bit integer values
- Reusable Encoder
- Reactive parsing (callback method for every decoded items)
- Advanced parser builder
- Conditional parsing
- Runtime parser manipulation
The following is a simple encoding of a CBOR packet header that contains only 3 fields:
Header header = Header.create();
CborEncoder enc = CBOR.encoder()
.cbor_start_array(3)
.cbor_encode_int(header.version)
.cbor_encode_int(header.flag)
.cbor_encode_int(header.sequence);The following is an encoding of a similar CBOR packet header but with two additional items:
Header header = Header.create();
CborEncoder enc = CBOR.encoder()
.cbor_start_array(3)
.cbor_encode_int(header.version)
.cbor_encode_int(header.flag)
.cbor_encode_int(header.sequence);
.merge(encodePeer(header.destination))
.merge(encodePeer(header.source));
public CborEncoder encodePeer(Peer peer) {
return CBOR.encoder()
.cbor_start_array(2)
.cbor_encode_text_string(peer.id)
.cbor_encode_int(peer.port);
}In this example, encodePeer returns a CborEncoder that can be merged into our first builder with the keyword merge.
We use the method observe() on the CborEncoder to generate a Flowable of ByteBuffer like so:
Flowable<ByteBuffer> encoded = enc.observe();By default, each ByteBuffer will be of different size, possibly zero and may not be optimised to be sent over the network. Alternatively, you can add a buffer size argument like so:
Flowable<ByteBuffer> encoded = enc.observe(2048);In this case, each ByteBuffer will be of size 2048, the same ByteBuffer will be reused for every call.
The following shows an example of a simple parser to later decode the first header encoded above:
Header header = new Header();
CborParser parser = CBOR.parser()
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_int((__, ___, s) -> header.seq = s);For every parsed item, a callback method is called. Though the callback has a different signature according to what item is parsed, most callback usually have at least three parameters:
- A ParserInCallback pointer which can be used to modify the parser on runtime as during decoding
- A list of CBOR tags that were preceding the parsed item
- the parsed item (it can be a long, float, array, map, or a custom item)
Check the source to see a list of all the method to parse primitive items.
A CborParser can consumes buffer by calling read like so:
public void onRecvBuffer(ByteBuffer buffer) {
while(buffer.hasRemaining()) {
if(parser.read(buffer)) {
parser.reset();
}
}
}read() takes a ByteBuffer as a parameter and will try to parse the buffer as dictated by the CborParser and will advance the ByteBuffer position accordingly. It returns false if more buffer is required and true if the entire parsing sequence has been finished. It will not advance the bytebuffer position more than what it actually decoded, it is thus possible that the CborParser returns true but more data are still available in the bytebuffer. If the buffer stream is a series of similar CBOR pattern, the CborParser can simply be reset and be reused like in the example above.
It is possible to parse a CustomItem by Implementing CborParser.ParseableItem. Such class must implement the getItemparser() that returns a CborParser object used to decode the custom item:
class PeerItem implements CborParser.ParseableItem {
Peer peer;
@Override
public CborParser getItemParser() {
return CBOR.parser()
.cbor_open_array((__, ___, i) -> {
if (i != 2) {
throw new RxParserException("wrong number of element in primary block");
} else {
this.peer = new Peer();
}
})
.cbor_parse_text_string_full((__, id) -> peer.id = id)
.cbor_parse_int((__, ___, i) -> peer.port = i);
}
}We can use PeerItem like so:
Header header = new Header();
CborParser parser = CBOR.parser()
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_int((__, ___, s) -> header.seq = s)
.cbor_parse_custom_item(PeerItem::new, (__, ___, item) -> header.destination = item.peer)
.cbor_parse_custom_item(PeerItem::new, (__, ___, item) -> header.destination = item.peer);cbor_parse_custom_item requires two parameters:
- a Factory to the parseable item
- a callback
On runtime, when the parser state machine advance to the custom item call, it instantiate a new PeerItem using the factory and invoke getItemParser() and uses this parser to parse the data. When the data is parsed, the callback is called at which point we can retrieve the parsed Peer.
Additionally with libcbor, it is possible to do conditional parsing. For instance in the example above, the flag may give an hint wether or not we must parsed the two peer item (source and destination). We can perform conditional parsing like so:
Header header = new Header();
CborParser parser = CBOR.parser()
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_int((__, ___, s) -> header.seq = s)
.do_insert_if(
(__) -> (header.flag == FLAG_HEADER_CONTAINS_DESTINATION),
CBOR.parser().cbor_parse_custom_item(PeerItem::new, (__, ___, item) -> header.destination = item.peer))
.do_insert_if(
(__) -> (header.flag == FLAG_HEADER_CONTAINS_SOURCE),
CBOR.parser().cbor_parse_custom_item(PeerItem::new, (__, ___, item) -> header.destination = item.peer))the do_insert_if call requires two parameters:
- a CallbackCondition that is called on runtime and should return a boolean
- A CborParser that will be inserted if the CallbackCondition returns true
You can also insert a parser next within a callback using do_insert_now:
Header header = new Header();
CborParser parser = CBOR.parser()
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_int((p, ___, s) -> {
header.seq = s
if (header.flag == FLAG_HEADER_CONTAINS_DESTINATION) {
p.insert_now(
CBOR.parser().cbor_parse_custom_item(PeerItem::new, (__, ___, item) -> header.destination = item.peer)
);
}
});Anywhere in the parsing sequence, you can use do_here to perform a certain task, you may for instance print info whenever the parsing start and when it is finish:
Header header = new Header();
CborParser parser = CBOR.parser()
.do_here((__) -> System.out.println("parsing started");
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_int((__, ___, s) -> header.seq = s)
.do_here((__) -> System.out.println("parsing finish");You can use do_for_each to run a certain task for every buffer that was successfully parsed and undo_for_each to stop. For instance, say you are parsing a packet header but you also need to perform a CRC for every buffer that belongs to this header and compare it to the CRC that is right after the header:
HeaderWithCRC header = new HeaderWithCRC();
CborParser parser = CBOR.parser()
.do_here((__) -> crc.init());
.do_for_each("crc-16", (__, buffer) -> crc.read(buffer));
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_int((__, ___, s) -> header.seq = s)
.undo_for_each("crc-16");
.cbor_parse_byte_string(
(parser, tags, size) -> {},
(parser, tags, buffer) -> crc.check(buffer)); do_for_each takes two argument:
- A String that is uses as a key to identify this specific task, it is used to disable it with undo_for_each
- A Callback that takes a ParserInCallback and a buffer as a parameter
Alternatively, you can also trigger do_for_each next within a callback to react to a value that was just parsed. For instance a boolean that indicate weter it is CRC16 or CRC32, in that case we would start consumming both CRC but will disable one of them as soon as we know which one we need:
HeaderWithCRC header = new HeaderWithCRC();
CRC16 crc16 = new CRC16();
CRC32 crc32 = new CRC32();
CborParser parser = CBOR.parser()
.do_here((__) -> {
crc16.init());
crc32.init());
})
.do_for_each("crc-16", (__, buffer) -> crc16.read(buffer));
.do_for_each("crc-32", (__, buffer) -> crc32.read(buffer));
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_boolean((p, b) ->
if(b) {
p.undo_for_each_now("crc-16");
} else {
p.undo_for_each_now("crc-32");
}
.cbor_parse_int((__, ___, s) -> header.seq = s)If a parsed value is needed later in the parsing sequence, you can either save it in a variable outside of the parsing sequence, or use parserInCallback.save() and retrieve it later with get(). For instance in the previous example, we need to check the value of the flag to decide which crc to check:
HeaderWithCRC header = new HeaderWithCRC();
CRC16 crc16 = new CRC16();
CRC32 crc32 = new CRC32();
CborParser parser = CBOR.parser()
.do_here((__) -> {
crc16.init());
crc32.init());
})
.do_for_each("crc-16", (__, buffer) -> crc16.read(buffer));
.do_for_each("crc-32", (__, buffer) -> crc32.read(buffer));
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_boolean((p, b) ->
if(b) {
p.undo_for_each_now("crc-16");
} else {
p.undo_for_each_now("crc-32");
}
.cbor_parse_int((__, ___, s) -> header.seq = s)
.cbor_parse_byte_string(
(p, tags, size) -> {},
(p, tags, buffer) -> {
if(p.<Boolean>get(b)) {
crc32.check(buffer);
} else {
crc16.check(buffer);
}
});save takes two parameters:
- The key to identify the Object to be saved
- the object itself
get takes only one parameter that is the key used to save the object. By default it returns an Object but you can use the template to force cast the object and avoid a manual casting. No check is done to ensure that the object saved is of the same type.
Knowing that, every variable could be processed in-parser and would not require any variable outside, the final example would be a complete self-contained parser:
CBOR.parser()
.do_here((p) -> {
p.save("header", new HeaderWithCRC());
p.save("crc16", CRC16.create());
p.save("crc32", CRC32.create());
})
.do_for_each("crc16consumer", (p, buffer) -> p.<CRC16>get("crc16").read(buffer))
.do_for_each("crc32consumer", (p, buffer) -> p.<CRC16>get("crc32").read(buffer));
.cbor_parse_int((__, ___, v) -> header.version = v)
.cbor_parse_int((__, ___, f) -> header.flag = f)
.cbor_parse_boolean((p, b) ->
if(b) {
p.undo_for_each_now("crc16consumer");
} else {
p.undo_for_each_now("crc32consumer");
})
.cbor_parse_int((__, ___, s) -> header.seq = s)
.undo_for_each("crc16consumer") // one of them was already disabled but it doesn't matter
.undo_for_each("crc32consumer")
.cbor_parse_byte_string(
(parser, tags, size) -> {},
(parser, tags, buffer) -> {
if(parser.<Boolean>get(b)) {
p.<CRC16>get("crc32").check(buffer);
} else {
p.<CRC16>get("crc32").check(buffer);
}
});Copyright 2018 Lucien Loiseau
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.