Crate cbor_data

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Expand description

A library for using CBOR as in-memory representation for working with dynamically shaped data.

For the details on the data format see RFC 8949. It is normally meant to be used as a data interchange format that models a superset of the JSON features while employing a more compact binary representation. As such, the data representation is biased towards smaller in-memory size and not towards fastest data access speed.

This library presents a range of tradeoffs when using this data format. You can just use the bits you get from the wire or from a file, without paying initial overhead beyond scanning the bytes once for valid encoding, but then possible causing allocations when working with the data. Or you can canonicalise the bits before using them, guaranteeing that indexing into the data will never allocate.

Regarding performance you should keep in mind that arrays and dictionaries are encoded as flat juxtaposition of its elements, meaning that indexing will have to decode items as it skips over them.

Regarding the interpretation of parsed data you have the option of inspecting the particular encoding (by pattern matching on ItemKind) or inspecting the higher-level CborValue. In the latter case, many binary representations may yield the same value, e.g. when asking for an integer the result may stem from a non-optimal encoding (like writing 57 as 64-bit value) or from a BigDecimal with mantissa 570 and exponent -1.

§Example

use cbor_data::{CborBuilder, Encoder, Writer, constants::*};

// create some nonsense CBOR item
let cbor = CborBuilder::new().encode_dict(|builder| {
    builder.with_key("name", |builder| builder.encode_str("Actyx"));
    builder.with_key("founded", |b| b.write_str("2016-02-11T13:00:00+01:00", [TAG_ISO8601]));
    builder.with_key("founders", |builder| builder.encode_array(|builder| {
        builder
            .encode_str("Oliver Stollmann")
            .encode_str("Maximilian Fischer")
            .encode_str("Roland Kuhn");
    }));
});

// access properties
use cbor_data::{PathElement, index_str, CborValue, value::Timestamp};
use std::borrow::Cow::{self, Borrowed};

let item = cbor.index(index_str("name")).unwrap();
assert_eq!(item.decode(), CborValue::Str(Borrowed("Actyx")));

// decoding references source bytes where possible, use make_static() to break ties
let decoded =
    cbor.index([PathElement::String(Borrowed("founded"))]).unwrap().decode().make_static();

// if you know what you’re looking for, you can use the as_* or to_* methods:
let ts = decoded.as_timestamp().unwrap();
assert_eq!(ts.unix_epoch(), 1_455_192_000);
assert_eq!(ts.nanos(), 0);
assert_eq!(ts.tz_sec_east(), 3600);

let item = cbor.index(index_str("founders[1]")).unwrap();
let name = item.decode().to_str();
// to_str() returns an Option<Cow<str>> to allow you to avoid allocations
// (i.e. this still takes the string’s bytes from `&cbor` in this case)
assert_eq!(name.as_ref().map(Cow::as_ref), Some("Maximilian Fischer"));

// access low-level encoding
use cbor_data::ItemKind;

let item = cbor.index(index_str("founded")).unwrap();
assert_eq!(item.tags().collect::<Vec<_>>(), [TAG_ISO8601]);
assert!(matches!(item.kind(), ItemKind::Str(s) if s == "2016-02-11T13:00:00+01:00"));

Re-exports§

Modules§

Macros§

Structs§

  • ArrayIter
    Iterator over the CBOR items within an array
  • ArrayWriter
    Builder for an array value, used by write_array_ret().
  • BytesIter
    Iterator yielding the fragments of a byte string item
  • Cbor
    Wrapper around a byte slice that encodes a valid CBOR item.
  • CborBuilder
    Builder for a single CBOR value.
  • CborOwned
    Wrapper around a vector of bytes, for parsing as CBOR.
  • DictIter
    Iterator over the key–value mappings within a dictionary
  • DictWriter
    Builder for a dict value, used by write_dict_rec().
  • IndexStr
    Iterator returned by index_str
  • KeyBuilder
    Builder for the first step of try_write_pair
  • NoOutput
    Marker type for builders that only append to a provided vector
  • ParseError
    Error container for parsing problems
  • SingleBuilder
    Builder for the single value of a dict key.
  • SingleResult
    Result value of using a SingleBuilder proving that it has been used.
  • StringIter
    Iterator yielding the fragments of a text string item
  • TaggedItem
    Representation of a possibly tagged CBOR data item
  • Tags
    Iterable view onto the CBOR tags applied to an item.
  • TypeError
  • WithOutput
    Marker type for builders that emit an owned value

Enums§

Traits§

  • CborOutput
    Marker trait to distinguish a builder that emits an owned value from one that appends to a vector
  • Encoder
    High-level encoding functions to write values in their canonical format.
  • Visitor
    Visitor for the structure of a CBOR item.
  • Writer
    Low-level primitives for emitting CBOR items.

Functions§