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cborpath

CborPath engine written in Rust

by Michaël Catanzariti

10 releases (4 breaking)

0.5.0 Apr 7, 2023
0.4.1 Feb 25, 2023
0.3.1 Feb 20, 2023
0.2.1 Feb 12, 2023
0.1.0 Jan 31, 2023

#1226 in Parser implementations

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cborpath-rs

cborpath is a CBORPath engine written in Rust.

CBORPath

CBORPath is an adaptation of JSONPath to CBOR based on the JSONPath Internet Draft

Syntax summary

Path

A path expression is a CBOR Array which, when applied to a CBOR value, the argument, selects zero or more nodes of the argument and output these nodes as a nodelist.

A path always begins by an identifier

  • a root identifier ($) for absolute paths,
  • a current node identifier (@) for relative paths. relative path are always used in a filter context.

A path is then followed by one or more segments.

Syntax Description
["$", <segments>] an absolute path composed by an array of segments
and which always begins by a root identifier ($)
["@", <segments>] a relative path composed by an array of segments
and which always begins by a current node identifier (@)

Segment

Segments apply one or more selectors to an input value and concatenate the results into a single nodelist.

Syntax Description
[<selectors>] a child segment, composed by one ore more selectors
<selector> shortcut for a child segment, composed by a unique selector
{"..": [<selectors>]} a descendant segment, composed by one ore more selectors
{"..": <selector>} shortcut for a descendant segment, composed by a unique selector

Selector

A selector produces a nodelist consisting of zero or more children of the input value.

Syntax Description
<CBOR Text>
<CBOR Bytes>
<CBOR Integer>
<CBOR Float>
<CBOR Boolean>
<CBOR Null>		 key selector: selects a child of a CBOR Map based on the child key
{"*": 1} wildcard selector: selects all children of a node
{"#": <index> } index selector: selects an indexed child of an array (from 0)
{":": [<start>, <end>, <step>]} array slice selector: selects a subset of the elements of an array
(between start and end with a step)
{"?": <boolean-expr>} filter selector: selects particular children using a boolean expression

Boolean expression

A boolean expression returns true or false and is used by a filter selector to filter array elements or map items.

Syntax Description
{"&&": [<boolean-expr>, <boolean-expr>]} logical AND
{"||": [<boolean-expr>, <boolean-expr>]} logical OR
{"!": <boolean-expr>} logical NOT
{"<=": [<comparable>, <comparable>]} comparison `lesser than or equal
{"<": [<comparable>, <comparable>]} comparison lesser than
{"==": [<comparable>, <comparable>]} comparison equal
{"!=": [<comparable>, <comparable>]} comparison not equal
{">": [<comparable>, <comparable>]} comparison greater than
{">=": [<comparable>, <comparable>]} comparison greater than or equal
{"match": [<comparable>, <regex>]} match function to compute a regular expression full match.
returns a boolean
{"search": [<comparable>, <regex>]} length function to compute a regular expression substring match.
returns a boolean

Comparable

A comparable is an operand of a filter comparison or an argument of a function.

Syntax Description
<CBOR Text>
<CBOR Bytes>
<CBOR Integer>
<CBOR Float>
<CBOR Boolean>
<CBOR Null>		 a CBOR value
["$", <singular-segments>]
["@", <singular-segments>]		 a singular path (path which procudes a nodelist containing at most one node)
{"length": <comparable>} length function to compute the length of a value.
returns an unsigned integer
{"count": <path>} count function to compute the number of nodes in a path.
returns an unsigned integer
{"value": <path>} value function to get the number of a single node path.
returns a CBOR value

Singular Segment

A singular segment produces a nodelist containing at most one node.

Syntax Description
<CBOR Text>
<CBOR Bytes>
<CBOR Integer>
<CBOR Float>
<CBOR Boolean>
<CBOR Null>		 key selector: selects a child of a CBOR Map based on the child key
{"#": <index> } index selector: selects an indexed child of an array (from 0)

Examples

This section is informative. It provides examples of CBORPath expressions.

The examples are based on the simple CBOR value representing a bookstore (that also has a bicycle).

{ "store": {
    "book": [
      { "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      { "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
      },
      { "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      },
      { "category": "fiction",
        "author": "J. R. R. Tolkien",
        "title": "The Lord of the Rings",
        "isbn": "0-395-19395-8",
        "price": 22.99
      }
    ],
    "bicycle": {
      "color": "red",
      "price": 399
    }
  }
}

This table shows some CBORPath queries that might be applied to this example and their intended results.

Syntax Intended result
["$", "store", "book", {"*": 1}, "author"] the authors of all books in the store
["$", {"..": "author"}] all authors
["$", "store", {"*": 1}] all things in store, which are some books
and a red bicycle
["$", "store", {"..": "price"}] the prices of everything in the store
["$", {"..": "book"}, {"#": 2}] the third book
["$", {"..": "book"}, {"#": -1}] the last book in order
["$", {"..": "book"}, [{"#": 0}, {"#": 1}]]
or
["$", {"..": "book"}, {":": [0, 2, 1]}]		 the first two books
["$", {"..": "book"}, {"?": ["@", "isbn"]}] all books with an ISBN number
["$", {"..": "book"}, {"?": {"<": [["@", "price"], 10.0]}}] all books cheaper than 10
["$", {"..": {"*": 1}}] all map item values and array elements
contained in input value

Library Usage

These are a few samples of code based on the examples of the previous section.

use cborpath::{CborPath, builder, Error};
use cbor_diag::parse_diag;

pub fn diag_to_bytes(cbor_diag_str: &str) -> Vec<u8> {
    parse_diag(cbor_diag_str).unwrap().to_bytes()
}

fn main() -> Result<(), Error> {
  let value = diag_to_bytes(
  r#"{ 
    "store": {
      "book": [
        { "category": "reference",
          "author": "Nigel Rees",
          "title": "Sayings of the Century",
          "price": 8.95
        },
        { "category": "fiction",
          "author": "Evelyn Waugh",
          "title": "Sword of Honour",
          "price": 12.99
        },
        { "category": "fiction",
          "author": "Herman Melville",
          "title": "Moby Dick",
          "isbn": "0-553-21311-3",
          "price": 8.99
        },
        { "category": "fiction",
          "author": "J. R. R. Tolkien",
          "title": "The Lord of the Rings",
          "isbn": "0-395-19395-8",
          "price": 22.99
        }
      ],
      "bicycle": {
        "color": "red",
        "price": 399
      }
    }
  }"#,
  );

  // the authors of all books in the store
  // ["$", "store", "book", {"*": 1}, "author"]
  let cbor_path = CborPath::builder()
      .key("store")
      .key("book")
      .wildcard()
      .key("author")
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[
              "Nigel Rees",
              "Evelyn Waugh",
              "Herman Melville",
              "J. R. R. Tolkien"
          ]"#
      ),
      results
  );

  // all authors
  // ["$", {"..": "author"}]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().key("author"))
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[
              "Nigel Rees",
              "Evelyn Waugh",
              "Herman Melville",
              "J. R. R. Tolkien"
          ]"#
      ),
      results
  );

  // all things in store, which are some books and a red bicycle
  // ["$", "store", {"*": 1}]
  let cbor_path = CborPath::builder().key("store").wildcard().build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[[
                  { "category": "reference",
                      "author": "Nigel Rees",
                      "title": "Sayings of the Century",
                      "price": 8.95
                  },
                  { "category": "fiction",
                      "author": "Evelyn Waugh",
                      "title": "Sword of Honour",
                      "price": 12.99
                  },
                  { "category": "fiction",
                      "author": "Herman Melville",
                      "title": "Moby Dick",
                      "isbn": "0-553-21311-3",
                      "price": 8.99
                  },
                  { "category": "fiction",
                      "author": "J. R. R. Tolkien",
                      "title": "The Lord of the Rings",
                      "isbn": "0-395-19395-8",
                      "price": 22.99
                  }
              ],
              {
                  "color": "red",
                  "price": 399
              }]"#
      ),
      results
  );

  // the prices of everything in the store
  // ["$", "store", {"..": "price"}]
  let cbor_path = CborPath::builder()
      .key("store")
      .descendant(builder::segment().key("price"))
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[
              399,
              8.95,
              12.99,
              8.99,
              22.99
          ]"#
      ),
      results
  );

  // the third book
  // ["$", {"..": "book"}, {"#": 2}]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().key("book"))
      .index(2)
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[{
              "category": "fiction",
              "author": "Herman Melville",
              "title": "Moby Dick",
              "isbn": "0-553-21311-3",
              "price": 8.99
          }]"#
      ),
      results
  );

  // the last book in order
  // ["$", {"..": "book"}, {"#": -1}]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().key("book"))
      .index(-1)
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[{
              "category": "fiction",
              "author": "J. R. R. Tolkien",
              "title": "The Lord of the Rings",
              "isbn": "0-395-19395-8",
              "price": 22.99
          }]"#
      ),
      results
  );

  // the first two books
  // ["$", {"..": "book"}, [{"#": 0}, {"#": 1}]]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().key("book"))
      .child(builder::segment().index(0).index(1))
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[
          {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
          },
          {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
          }]"#
      ),
      results
  );

  // the first two books
  // ["$", {"..": "book"}, {":": [0, 2, 1]}]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().key("book"))
      .slice(0, 2, 1)
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[
          {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
          },
          {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
          }]"#
      ),
      results
  );

  // all books with an ISBN number
  // ["$", {"..": "book"}, {"?": ["@", "isbn"]}]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().key("book"))
      .filter(builder::rel_path().key("isbn"))
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[
          {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
          },
          {
            "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
          }]"#
      ),
      results
  );

  // all books cheaper than 10
  // ["$", {"..": "book"}, {"?": {"<": [["@", "price"], 10.0]}}]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().key("book"))
      .filter(builder::lt(
          builder::sing_rel_path().key("price"),
          builder::val(10.),
      ))
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[
          {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
          },
          {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
          }]"#
      ),
      results
  );

  // all map item values and array elements contained in input value
  // ["$", {"..": {"*": 1}}]
  let cbor_path = CborPath::builder()
      .descendant(builder::segment().wildcard())
      .build();
  let results = cbor_path.read_from_bytes(&value)?;
  assert_eq!(
      diag_to_bytes(
          r#"[{
            "book": [
              {
                "category": "reference",
                "author": "Nigel Rees",
                "title": "Sayings of the Century",
                "price": 8.95
              },
              {
                "category": "fiction",
                "author": "Evelyn Waugh",
                "title": "Sword of Honour",
                "price": 12.99
              },
              {
                "category": "fiction",
                "author": "Herman Melville",
                "title": "Moby Dick",
                "isbn": "0-553-21311-3",
                "price": 8.99
              },
              {
                "category": "fiction",
                "author": "J. R. R. Tolkien",
                "title": "The Lord of the Rings",
                "isbn": "0-395-19395-8",
                "price": 22.99
              }
            ],
            "bicycle": {
              "color": "red",
              "price": 399
            }
          },
          [
            {
              "category": "reference",
              "author": "Nigel Rees",
              "title": "Sayings of the Century",
              "price": 8.95
            },
            {
              "category": "fiction",
              "author": "Evelyn Waugh",
              "title": "Sword of Honour",
              "price": 12.99
            },
            {
              "category": "fiction",
              "author": "Herman Melville",
              "title": "Moby Dick",
              "isbn": "0-553-21311-3",
              "price": 8.99
            },
            {
              "category": "fiction",
              "author": "J. R. R. Tolkien",
              "title": "The Lord of the Rings",
              "isbn": "0-395-19395-8",
              "price": 22.99
            }
          ],
          {
            "color": "red",
            "price": 399
          },
          {
            "category": "reference",
            "author": "Nigel Rees",
            "title": "Sayings of the Century",
            "price": 8.95
          },
          {
            "category": "fiction",
            "author": "Evelyn Waugh",
            "title": "Sword of Honour",
            "price": 12.99
          },
          {
            "category": "fiction",
            "author": "Herman Melville",
            "title": "Moby Dick",
            "isbn": "0-553-21311-3",
            "price": 8.99
          },
          {
            "category": "fiction",
            "author": "J. R. R. Tolkien",
            "title": "The Lord of the Rings",
            "isbn": "0-395-19395-8",
            "price": 22.99
          },
          "red",
          399,
          "reference",
          "Nigel Rees",
          "Sayings of the Century",
          8.95,
          "fiction",
          "Evelyn Waugh",
          "Sword of Honour",
          12.99,
          "fiction",
          "Herman Melville",
          "Moby Dick",
          "0-553-21311-3",
          8.99,
          "fiction",
          "J. R. R. Tolkien",
          "The Lord of the Rings",
          "0-395-19395-8",
          22.99
          ]"#
      ),
      results
  );

  Ok(())
}

Dependencies

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~73K SLoC