cddl-rs

A Rust implementation of the Concise data definition language (CDDL). CDDL is an IETF standard that "proposes a notational convention to express CBOR and JSON data structures." As of 2019-06-12, it is published as RFC 8610 (Proposed Standard) at https://tools.ietf.org/html/rfc8610.

This crate supports the following CDDL-related RFCs:

RFC	Title	Status
RFC 8610	Concise Data Definition Language (CDDL)	✔️ Full parsing and validation
RFC 9165	Additional Control Operators for CDDL	✔️ `.cat` , `.det` , `.plus` , `.abnf` , `.abnfb` , `.feature`
RFC 9682	Updates to CDDL (Empty Data Models, `\u{hex}` Escapes, Non-Literal Tag Numbers)	✔️ Full grammar and parser support
RFC 9741	Additional Control Operators for Text in CDDL	✔️ `.b64u` , `.b64c` , `.hex` , `.hexlc` , `.hexuc` , `.b32` , `.h32` , `.b45` , `.base10` , `.printf` , `.json` , `.join` and sloppy variants
draft-bormann-cbor-cddl-csv-08	Using CDDL for CSV	✔️ CSV validation via generic data model mapping

This crate uses Pest (a PEG parser generator for Rust) to parse CDDL. The grammar is defined in cddl.pest and closely follows the ABNF grammar in Appendix B. of the spec. All CDDL must use UTF-8 for its encoding per the spec.

This crate supports validation of CBOR, JSON, and CSV data structures. The minimum supported Rust version (MSRV) is 1.88.0.

Also bundled into this repository is a basic language server implementation and extension for Visual Studio Code for editing CDDL. The implementation is backed by the compiled WebAssembly target included in this crate.

Goals

Parse CDDL documents into an AST
Verify conformance of CDDL documents against RFC 8610
Validate CBOR data structures
Validate JSON documents
Validate CSV data
Generate Rust types from CDDL
Generate dummy JSON from conformant CDDL
As close to zero-copy as possible
Compile WebAssembly target for browser and Node.js
no_std support (lexing and parsing only)
Language server implementation and Visual Studio Code Extension

Non-goals

Support CBOR diagnostic notation
I-JSON compatibility

Used in

This crate is used in several notable projects:

Project	Description
google/cddlconv	A command-line utility for converting CDDL to TypeScript and Zod schemas
input-output-hk/catalyst-core	Core Catalyst governance engine for Cardano, uses this crate for CBOR validation of CIP-36 voter registration data

Why Rust?

Rust is a systems programming language designed around safety and is ideally-suited for resource-constrained systems. CDDL and CBOR are designed around small code and message sizes and constrained nodes, scenarios for which Rust has also been designed.

CLI

A CLI is available for various platforms. The tool supports parsing of CDDL files for verifying conformance against RFC 8610. It can also be used to validate JSON documents, CBOR binary files, and CSV files against CDDL documents. Detailed information about the JSON, CBOR, and CSV validation implementation can be found in the sections below.

Installation

GitHub Releases

Binaries for Linux, macOS and Windows can be downloaded from GitHub Releases.

Cargo

cargo install cddl

Docker

docker pull ghcr.io/anweiss/cddl-cli:latest

CLI usage

Instructions for using the tool can be viewed by executing the help subcommand:

cddl help

If using Docker:

Replace <version> with an appropriate release tag. Requires use of the --volume argument for mounting CDDL documents into the container when executing the command. JSON or CBOR files can either be included in the volume mount or passed into the command via STDIN.

docker run -it --rm -v $PWD:/cddl -w /cddl ghcr.io/anweiss/cddl-cli:<version> help

You can validate JSON documents, CBOR binary files, and/or CSV files:

cddl validate [OPTIONS] --cddl <CDDL> <--stdin|--json <JSON>...|--cbor <CBOR>...|--csv <CSV>...>

For CSV files, use the --csv-header flag if the first row is a header:

cddl validate --cddl schema.cddl --csv data.csv --csv-header

It also supports validating files from STDIN (if it detects the input as valid UTF-8, it will attempt to validate the input as JSON, otherwise it will treat it as CBOR):

cat reputon.json | cddl validate --cddl reputon.cddl --stdin
cat reputon.cbor | cddl validate --cddl reputon.cddl --stdin

or using Docker:

docker run -i --rm -v $PWD:/data -w /data ghcr.io/anweiss/cddl-cli:0.10.4 validate --cddl reputon.cddl --stdin < reputon.json

Website

You can also find a simple RFC 8610 conformance tool at https://cddl.anweiss.tech. This same codebase has been compiled for use in the browser via WebAssembly.

Visual Studio Code extension

An extension for editing CDDL documents with Visual Studio Code has been published to the Marketplace here. You can find more information in the README.

Supported features

maps
- structs
- tables
- cuts
groups
arrays
values
choices
ranges
enumeration (building a choice from a group)
root type
occurrence
predefined types
tags
unwrapping
controls
socket/plug
generics
operator precedence
comments
numerical int/uint values
numerical hexfloat values
numerical values with exponents
unprefixed byte strings
prefixed byte strings

Usage

Simply add the dependency to Cargo.toml :

[dependencies]
cddl = "0.10.4"

JSON, CBOR, and CSV validation all require std .

Feature flags

A few convenience features have been included to make the AST more concise and for enabling additional functionality. You can build with default-features = false for a no_std build and selectively enable any of the features below.

--feature ast-span

Add the Span type to the AST for keeping track of the position of the lexer and parser. Enabled by default.

--feature ast-comments

Include comment strings in the AST. Enabled by default.

--feature ast-parent

Add the ParentVisitor implementation so that the AST can be traversed using parent pointers. Enabled by default.

--feature json

Enable JSON validation. Enabled by default.

--feature cbor

Enable CBOR validation. Enabled by default.

--feature csv-validate

Enable CSV validation per draft-bormann-cbor-cddl-csv-08. Enabled by default.

--feature additional-controls

Enable validation support for the additional control operators defined in RFC 9165 and RFC 9741. Enabled by default.

Parsing CDDL

use cddl::parser::cddl_from_str;

let input = r#"myrule = int"#;
assert!(cddl_from_str(input, true).is_ok())

Generating Rust types from CDDL

The companion crate cddl-derive provides proc macros for generating Rust types from CDDL definitions at compile time.

[dependencies]
cddl-derive = "0.1"
serde = { version = "1", features = ["derive"] }

Attribute macro — single struct

Apply #[cddl(path = "...")] to a stub struct. The macro reads the CDDL file, finds the matching rule (by converting the struct name from PascalCase to kebab-case), and replaces the struct with fully populated fields:

use cddl_derive::cddl;

// schema.cddl contains: person = { name: tstr, age: uint, ? email: tstr }
#[cddl(path = "schema.cddl")]
struct Person;

This expands at compile time to:

use serde::{Deserialize, Serialize};

#[derive(Clone, Debug, Deserialize, Serialize)]
pub struct Person {
    pub name: String,
    pub age: u64,
    #[serde(skip_serializing_if = "Option::is_none")]
    pub email: Option<String>,
}

Use the rule attribute to target a specific CDDL rule name when the struct name does not match:

#[cddl(path = "schema.cddl", rule = "person-record")]
struct MyPerson;

Function-like macro — all types

cddl_typegen! generates Rust types for every rule in a CDDL file:

use cddl_derive::cddl_typegen;

cddl_typegen!("schema.cddl");
// Generates: struct Person { ... }, struct Address { ... }, etc.

Supported CDDL-to-Rust mappings

CDDL construct	Rust output
Map types `{ key: type, ... }`	`struct` with named fields
Type choices `a / b / c`	`enum` with variants
Simple type references `foo = tstr`	`type` alias
Array types `[* T]`	`Vec<T>`
Table types `{ * tstr => T }`	`HashMap<String, T>`
Optional fields `? key: type`	`Option<T>` with `skip_serializing_if`
Nullable types `T / null`	`Option<T>`
Hyphenated names `my-field`	snake_case field + `#[serde(rename = "my-field")]`
Rust keywords `type`, `match`	Escaped with trailing `_` + serde rename

All standard prelude types (tstr, uint, int, float, bstr, bool, null, any, etc.) are mapped to their idiomatic Rust equivalents. All generated types include Serialize and Deserialize derives for use with Serde.

Validating JSON

use cddl::validate_json_from_str;

let cddl = r#"person = {
  name: tstr,
  age: uint,
  address: tstr,
}"#;

let json = r#"{
  "name": "John",
  "age": 50,
  "address": "1234 Lakeshore Dr"
}"#;

assert!(validate_json_from_str(cddl, json).is_ok())

This crate uses the Serde framework, and more specifically, the serde_json crate, for parsing and validating JSON. Serde was chosen due to its maturity in the ecosystem and its support for serializing and deserializing CBOR via the ciborium crate.

As outlined in Appendix E. of the standard, only the JSON data model subset of CBOR can be used for validation. The limited prelude from the spec has been included below for brevity:

any = #

uint = #0
nint = #1
int = uint / nint

tstr = #3
text = tstr

number = int / float

float16 = #7.25
float32 = #7.26
float64 = #7.27
float16-32 = float16 / float32
float32-64 = float32 / float64
float = float16-32 / float64

false = #7.20
true = #7.21
bool = false / true
nil = #7.22
null = nil

Furthermore, the following data types from the standard prelude can be used for validating JSON strings and numbers:

tdate = #6.0(tstr)
uri = #6.32(tstr)
b64url = #6.33(tstr)
time = #6.1(number)

The first non-group rule defined by a CDDL data structure definition determines the root type, which is subsequently used for validating the top-level JSON data type.

Supported JSON validation features

The following types and features of CDDL are supported by this crate for validating JSON:

CDDL	JSON
structs	objects
arrays	arrays1
`text / tstr`	string
`uri`	string (valid RFC3986 URI)
`tdate`	string (valid RFC3339 date/time)
`b64url`	string (base64url-encoded)
`time`	number (valid UNIX timestamp integer in seconds)
`number / int / float`	number2
`bool / true / false`	boolean
`null / nil`	null
`any`	any valid JSON
byte strings	not yet implemented
unwrap ( `~` )	any JSON that matches unwrapped type from map, array or tag

CDDL groups, generics, sockets/plugs and group-to-choice enumerations can all be used when validating JSON.

Since JSON objects only support keys whose types are JSON strings, when validating JSON, member keys defined in CDDL structs must use either the colon syntax ( mykey: tstr or "mykey": tstr ) or the double arrow syntax provided that the member key is either a text string value ( "mykey" => tstr ) or a bareword that resolves to either a string data type ( text or tstr ) or another text string value ( * tstr => any ).

Occurrence indicators can be used to validate key/value pairs in a JSON object and the number of elements in a JSON array; depending on how the indicators are defined in a CDDL data definition.

Below is the table of supported control operators:

Control operator	Supported
`.pcre`	✔️3
`.regex`	✔️3 (alias for `.pcre` )
`.size`	✔️
`.bits`	Ignored when validating JSON
`.cbor`	Ignored when validating JSON
`.cborseq`	Ignored when validating JSON
`.within`	✔️
`.and`	✔️
`.lt`	✔️
`.le`	✔️
`.gt`	✔️
`.ge`	✔️
`.eq`	✔️
`.ne`	✔️
`.default`	✔️

1: When groups with multiple group entries are used to validate arrays, occurrence indicators are "greedy" in that only the first occurrence indicator that is come across is used in the validation. Subsequent entries with occurrence indicators are ignored due to complexities involved with processing these ambiguities. For proper JSON validation, avoid writing CDDL that looks like the following: [ * a: int, b: tstr, ? c: int ] .

2: While JSON itself does not distinguish between integers and floating-point numbers, this crate does provide the ability to validate numbers against a more specific numerical CBOR type, provided that its equivalent representation is allowed by JSON. Refer to Appendix E. of the standard for more details on the implications of using CDDL with JSON numbers.

3: Due to Perl-Compatible Regular Expressions (PCREs) being more widely used than XSD regular expressions, this crate also provides support for the proposed .pcre control extension in place of the .regexp operator (see Discussion and CDDL-Freezer proposal). Ensure that your regex string is properly JSON escaped when using this control.

If you've enabled the additional-controls feature, the control operators from RFC 9165 below are also available for use:

Control operator	Supported
`.plus`	✔️
`.cat`	✔️
`.det`	✔️
`.abnf`	✔️
`.abnfb`	Ignored when validating JSON
`.feature`	✔️

The text content control operators from RFC 9741 are also available:

Control operator	Supported
`.b64u`	✔️ Validates base64url-encoded text against byte string controller
`.b64u-sloppy`	✔️ Lenient base64url decoding (tolerates non-zero trailing bits and padding)
`.b64c`	✔️ Validates base64 classic-encoded text against byte string controller
`.b64c-sloppy`	✔️ Lenient base64 classic decoding
`.hex`	✔️ Validates hex-encoded text (case-insensitive)
`.hexlc`	✔️ Validates lowercase hex-encoded text
`.hexuc`	✔️ Validates uppercase hex-encoded text
`.b32`	✔️ Validates base32-encoded text
`.h32`	✔️ Validates base32hex-encoded text
`.b45`	✔️ Validates base45-encoded text
`.base10`	✔️ Validates decimal integer text representation
`.printf`	✔️ Validates text against printf-style format string with arguments
`.json`	✔️ Validates text as JSON matching a CDDL type
`.join`	✔️ Validates text as concatenation of array element values

You can activate features during validation as follows:

use cddl::validate_json_from_str;

let cddl = r#"
  v = JC<"v", 2>
  JC<J, C> =  C .feature "cbor" / J .feature "json"
"#;

let json = r#""v""#;

assert!(validate_json_from_str(cddl, json, Some(&["json"])).is_ok())

Validating CSV

use cddl::validate_csv_from_str;

let cddl = r#"person-file = [*person-record]
person-record = [name: text, age: uint]"#;

let csv = "Alice,30\nBob,25\n";

assert!(validate_csv_from_str(cddl, csv, None, None).is_ok())

This crate implements CSV validation as described in draft-bormann-cbor-cddl-csv-08. CSV data is parsed according to RFC 4180 and mapped to the CDDL generic data model:

csv = [?header, *record]
header = [+header-field]
record = [+field]
header-field = text
field = text

Each row becomes an array of fields, and the entire CSV becomes an array of rows. Fields are text strings by default, but the validator coerces them to their JSON representation when the CDDL schema specifies application-level types such as uint , int , or float .

The has_header parameter controls whether the first row is treated as a header row (kept as text strings without numeric coercion). When using the CLI, pass --csv-header to enable this.

The first non-group rule in the CDDL definition determines the root type for validation, which should describe the entire CSV as an array of records.

Comparing with JSON schema and JSON schema language

CDDL, JSON schema and JSON schema language can all be used to define JSON data structures. However, the approaches taken to develop each of these are vastly different. A good place to find past discussions on the differences between these formats is the IETF mail archive, specifically in the JSON and CBOR lists. The purpose of this crate is not to argue for the use of CDDL over any one of these formats, but simply to provide an example implementation in Rust.

Validating CBOR

use cddl::validate_cbor_from_slice;

let cddl = r#"rule = false"#;

let cbor = b"\xF4";

assert!(validate_cbor_from_slice(cddl, cbor).is_ok())

This crate also uses Serde and ciborium for validating CBOR data structures. CBOR validation is done via the loosely typed ciborium::value::Value enum. In addition to all of the same features implemented by the JSON validator, this crate also supports validating CBOR tags (e.g. #6.32(tstr) ), CBOR major types (e.g. #1.2 ), table types (e.g. { [ + tstr ] => int } ) and byte strings. The .bits , .cbor and .cborseq control operators are all supported as well.

The following tags are supported when validating CBOR:

Tag	Supported
`tdate = #6.0(tstr)`	✔️
`time = #6.1(number)`	✔️
`biguint = #6.2(bstr)`	✔️
`bignint = #6.3(bstr)`	✔️
`decfrac = #6.4([e10: int, m: integer])`	not yet implemented
`bigfloat = #6.5([e2: int, m: integer])`	not yet implemented
`eb64url = #6.21(any)`	✔️
`eb64legacy = #6.22(any)`	✔️
`eb16 = #6.23(any)`	✔️
`encoded-cbor = #6.24(bstr)`	✔️
`uri = #6.32(tstr)`	✔️
`b64url = #6.33(tstr)`	✔️
`b64legacy = #6.34(tstr)`	✔️
`regexp = #6.35(tstr)`	✔️
`mime-message = #6.36(tstr)`	✔️
`cbor-any = #6.55799(any)`	✔️

If you've enabled the additional-controls feature, the control operators from RFC 9165 below are also available for use:

Control operator	Supported
`.plus`	✔️
`.cat`	✔️
`.det`	✔️
`.abnf`	✔️
`.abnfb`	✔️
`.feature`	✔️

The text content control operators from RFC 9741 are also available for CBOR validation:

Control operator	Supported
`.b64u` / `.b64u-sloppy`	✔️
`.b64c` / `.b64c-sloppy`	✔️
`.hex` / `.hexlc` / `.hexuc`	✔️
`.b32` / `.h32`	✔️
`.b45`	✔️
`.base10`	✔️
`.printf`	✔️
`.json`	✔️
`.join`	✔️

You can activate features during validation by passing a slice of feature strings as follows:

use cddl::validate_cbor_from_slice;

let cddl = r#"
  v = JC<"v", 2>
  JC<J, C> =  C .feature "cbor" / J .feature "json"
"#;

let cbor = b"\x02";

assert!(validate_cbor_from_slice(cddl, cbor, Some(&["cbor"])).is_ok())

`no_std` support

Only the lexer and parser can be used in a no_std context provided that a heap allocator is available. This can be enabled by opting out of the default features in your Cargo.toml file as follows:

[dependencies]
cddl = { version = "0.10.4", default-features = false }

Zero-copy parsing is implemented to the extent that is possible. Allocation is required for error handling and diagnostics.

JSON, CBOR, and CSV validation are dependent on their respective heap allocated Value types, but since these types aren't supported in a no_std context, they subsequently aren't supported by this crate in no_std .

cddl 0.10.4

cddl-rs

Goals

Non-goals

Used in

Why Rust?

CLI

Installation

GitHub Releases

Cargo

Docker

CLI usage

Website

Visual Studio Code extension

Supported features

Usage

Feature flags

Parsing CDDL

Generating Rust types from CDDL

Attribute macro — single struct

Function-like macro — all types

Supported CDDL-to-Rust mappings

Validating JSON

Supported JSON validation features

Validating CSV

Comparing with JSON schema and JSON schema language

Validating CBOR

no_std support

`no_std` support