dag-cbrrr

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A reasonably fast DAG-CBOR parser for Python

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# dag-cbrrr
Convert between DAG-CBOR and Python objects at hundreds of megabytes per second. Take a look at the [benchmarks](https://github.com/DavidBuchanan314/dag-cbor-benchmark)

Other than speed, a distinguishing feature is that it operates *non-recursively*. This means you can decode or encode arbitrarily deeply nested objects without running out of call stack (although of course you might still run out of heap).

Finally, cbrrr aims to be maximally strict regarding DAG-CBOR canonicalization rules. See [below](#strictness) for further details.

## Installation

From pypi:
```
python3 -m pip install cbrrr
```

From git:
```
git clone https://github.com/DavidBuchanan314/dag-cbrrr
cd dag-cbrrr
python3 -m pip install -v .
```

## Quickstart

Here's the basics:
```py
import cbrrr

encoded = cbrrr.encode_dag_cbor({"hello": [b"world", 1, 2, 3]})
print(encoded)  # b'\xa1ehello\x84Eworld\x01\x02\x03'
decoded = cbrrr.decode_dag_cbor(encoded)
print(decoded)  # {'hello': [b'world', 1, 2, 3]}
```

For more detailed API information, take a look at the commented [python source](src/cbrrr/__init__.py), which provides an ergonomic wrapper for the native module (more docs coming soon™)

TL;DR:

```py
class CID:
	def __init__(self, cid_bytes: bytes) -> None:
		...
	def decode(cls, data: Union[bytes, str]) -> "CID":
		...
	def encode(self, base="base32") -> str:
		...
	...

DagCborTypes = Union[str, bytes, int, bool, float, CID, list, dict, None]

def decode_dag_cbor(
	data: bytes,
	atjson_mode: bool=False,
	cid_ctor: Callable[[bytes], Any]=CID
) -> DagCborTypes:
	...

def decode_multi_dag_cbor_in_violation_of_the_spec(
	data: bytes,
	atjson_mode: bool=False,
	cid_ctor: Callable[[bytes], Any]=CID
) -> Iterator[DagCborTypes]:
	...

def encode_dag_cbor(
	obj: DagCborTypes,
	atjson_mode: bool=False,
	cid_type: Type=CID
) -> bytes:
	...
```

"atjson_mode" refers to the representation used in atproto HTTP APIs, documented here [here](https://atproto.com/specs/data-model#json-representation). It is *not* a round-trip-safe representation.

## Strictness

cbrrr aims to conform to all the [strictness rules](https://ipld.io/specs/codecs/dag-cbor/spec/#strictness) set out in the DAG-CBOR specification.

It decodes strictly, and there is no non-strict mode available. This means, among other things:

- Maps must not have duplicate keys
- Map keys must be strings
- Map keys must be canonically sorted
- Only 64-bit floats are allowed
- All integers/lengths must be minimally encoded
- Only tag type 42 is allowed (NOTE: For now, CID values themselves are not validated)

In its default configuration, valid DAG-CBOR should round-trip perfectly, i.e. `encode_dag_cbor(decode_dag_cbor(data)) == data`. (This is not necessarily true if you specify `atjson_mode=True`, or pass a custom CID type (see below) that misbehaves in some way).

## Using `multiformats.CID`

cbrrr brings its own performance-oriented CID class, but it's relatively bare-bones (supporting only base32, for now). If you want more features and broader compatibility, you can use the CID class from [hashberg-io/multiformats](https://github.com/hashberg-io/multiformats) like so:

```py
import cbrrr
import multiformats

encoded = cbrrr.encode_dag_cbor(
	multiformats.CID.decode("bafkreibm6jg3ux5qumhcn2b3flc3tyu6dmlb4xa7u5bf44yegnrjhc4yeq"),
	cid_type=multiformats.CID
)

decoded = cbrrr.decode_dag_cbor(encoded, cid_ctor=multiformats.CID.decode)
print(decoded)  # zb2rhZfjRh2FHHB2RkHVEvL2vJnCTcu7kwRqgVsf9gpkLgteo
```

## Running Tests

```sh
# clone the repo
python3 -m pip install -ve .
python3 -m unittest -v
```

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