bass-clarinet

bass-clarinet

bass-clarinet is a JSON parser.

It was forked from clarinet but the API has been changed significantly. In addition to the port to TypeScript, the following changes have been made:

• The parser was made as robust as possible. It will try to continue parsing after an unexpected event. This is useful for editors as documents will often be in an invalid state during editing.
• onopenobject no longer includes the first key
• JSONTestSuite is added to the test set. All tests pass.
• line and column information is fixed
• the parser accepts multiple subscribers per event type
• trim and normalize options have been dropped. This can be handled by the consumer in the onsimplevalue callback
• there is a stack based wrapper named createStackedDataSubscriber which pairs onopenobject/oncloseobject and onopenarray/onclosearray events in a callback
• the following options have been added (if none are selected, bass-clarinet is a pure JSON-parser):
  • allow:angle_brackets_instead_of_brackets
  • allow:apostrophes_instead_of_quotation_marks
  • allow:comments
  • allow:compact
  • allow:missing_commas
  • allow:parens_instead_of_braces
  • allow:schema
  • allow:trailing_commas
  • allow:tagged_unions
  • require:schema
  • spaces_per_tab
• stream support has been dropped for now. Can be added back upon request
• There is an 'ExpectContext' class that helps processing documents that should conform to an expected structure.

bass-clarinet is a sax-like streaming parser for JSON. works in the browser and node.js. just like you shouldn't use sax when you need dom you shouldn't use bass-clarinet when you need JSON.parse.

Clear reasons to use bass-clarinet over the built-in JSON.parse:

• you want location info
• you want the parser to continue after it encountered an error
• you work with very large files
• you want a syntax that is less strict than JSON. This might be desirable when the file needs to be edited manually. See the options below

design goals

bass-clarinet is very much like yajl but written in TypeScript:

• written in TypeScript
• portable
• no runtime dependency on other modules
• robust (around 400 tests)
• data representation independent
• fast
• generates verbose, useful error messages including context of where the error occurs in the input text.
• simple to use
• tiny

installation

node.js

1. install npm
2. npm install bass-clarinet
3. add this to your .ts file: import * as bc from "bass-clarinet"

usage

high level

//a simple pretty printer
import * as bc from "bass-clarinet"
import * as fs  from "fs"

const [, , path] = process.argv

if (path === undefined) {
    console.error("missing path")
    process.exit(1)
}

const data = fs.readFileSync(path, {encoding: "utf-8"})

export function createValuesPrettyPrinter(indentation: string, writer: (str: string) => void): bc.ValueHandler {
    return {
        array: (_startLocation, openCharacter, _comments) => {
            writer(openCharacter)
            return {
                element: () => createValuesPrettyPrinter(`${indentation}\t`, writer),
                end: ((_endLocation, endCharacter) => {
                    writer(`${indentation}${endCharacter}`)
                }),
            }

        },
        object: (_startlocation, openCharacter, _comments) => {
            writer(openCharacter)
            return {
                property: (key, _keyRange) => {
                    writer(`${indentation}\t"${key}": `)
                    return createValuesPrettyPrinter(`${indentation}\t`, writer)
                },
                end: (_endLocation, endCharacter) => {
                    writer(`${indentation}${endCharacter}`)
                },
            }
        },
        boolean: (isTrue, _range, _comments) => {
            writer(`${isTrue ? "true":"false"}`)
        },
        number: (value, _range, _comments) => {
            writer(`${value.toString(10)}`)//JSON.stringify(value)
        },
        string: (value, _range, _comments) => {
            writer(`${JSON.stringify(value)}`)//JSON.stringify(value)
        },
        null: _comments => {
            writer(`null`)
        },
        taggedUnion: (option, _unionStart, _optionRange, _comments) => {
            writer(`| "${option}" `)
            return createValuesPrettyPrinter(`${indentation}`, writer)
        },
    }
}

export function createPrettyPrinter(indentation: string, writer: (str: string) => void): bc.DataSubscriber {
    return bc.createStackedDataSubscriber(
        createValuesPrettyPrinter(indentation, writer),
        error => {
            console.error("FOUND STACKED DATA ERROR", error.message)
        },
        _comments => {
            //onEnd
        }
    )
}


const parser = new bc.Parser(
    err => { console.error("FOUND PARSER ERROR", err.message) },
    { allow: bc.lax }
)
const tokenizer = new bc.Tokenizer(
    parser,
    err => { console.error("FOUND TOKENIZER ERROR", err.message) }
)
parser.ondata.subscribe(createPrettyPrinter("\r\n", str => process.stdout.write(str)))
tokenizer.write(data)
tokenizer.end()

low level

import * as bc from "bass-clarinet"
import * as fs  from "fs"

const [, , path] = process.argv

if (path === undefined) {
    console.error("missing path")
    process.exit(1)
}

const data = fs.readFileSync(path, {encoding: "utf-8"})


const parser = new bc.Parser(
    err => { console.error("FOUND PARSER ERROR", err.message) },
    { allow: bc.lax }
)
const tokenizer = new bc.Tokenizer(
    parser,
    err => { console.error("FOUND TOKENIZER ERROR", err.message) }
)
parser.ondata.subscribe({
    oncomma: () => {
        //place your code here
    },
    oncolon: () => {
        //place your code here
    },
    onlinecomment: (_comment, _range) => {
        //place your code here
    },
    onblockcomment: (_comment, _range, _indent) => {
        //indent can be used to strip the leading whitespace of all lines of the block comment.
        //indent indicates the indentation string found up to the `/*` characters.
        //this is only provided if the block comment starts on a new line
    },
    onquotedstring: (_value, _quote, _range) => {
        //place your code here
        //in pure JSON, only '"' is valid for _quote
    },
    onunquotedtoken: (_value, _range) => {
        //place your code here
        //in pure JSON, only "null", "true" or "false" are valid for _value
    },
    onopentaggedunion: _range => {
        //place your code here
    },
    onclosetaggedunion: () => {
        //place your code here
    },
    onoption: (_option, _range) => {
        //place your code here
    },
    onopenarray: (_openCharacterRange, _openCharacter) => {
        //place your code here
    },
    onclosearray: (_closeCharacterRange, _closeCharacter) => {
        //place your code here
    },
    onopenobject: (_startRange, _openCharacter) => {
        //place your code here
    },
    oncloseobject: (_endRange, _closeCharacter) => {
        //place your code here
    },
    onkey: (_key, _range) => {
        //place your code here
    },
    onend: () => {
        //place your code here
    },
})
tokenizer.write(data)
tokenizer.end()

if the document needs to conform to an expected structure (or schema)

import * as bc from "bass-clarinet"
import * as fs from "fs"

const [, , path] = process.argv

if (path === undefined) {
    console.error("missing path")
    process.exit(1)
}

const data = fs.readFileSync(path, { encoding: "utf-8" })

const parser = new bc.Parser(
    err => { console.error("FOUND PARSER ERROR", err.message) },
    { allow: bc.lax }
)
const tokenizer = new bc.Tokenizer(
    parser,
    err => { console.error("FOUND TOKENIZER ERROR", err.message) }
)

const ec = new bc.ExpectContext(null, null)

/**
 * expect an object/type with 2 properties, 'prop a' and 'prop b', both numbers
 */
parser.ondata.subscribe(
    bc.createStackedDataSubscriber(
        ec.expectType(
            (_range, _comments) => {
                //prepare code here
            },
            {
                "prop a": (_propRange, _propComments) => ec.expectNumber((_value, _range, _comments) => {
                    //handle 'prop a'
                }),
                "prop b": () => ec.expectNumber(_value => {
                    //handle 'prop b'
                }),
            },
            (_hasErrors, _range, _comments) => {
                //wrap up the object
            }
        ),
        error => {
            if (error.context[0] === "range") {
                throw new bc.RangeError(error.message, error.context[1])
            } else {
                throw new bc.LocationError(error.message, error.context[1])
            }
        },
        _comments => {
            //wrap up the document
        }
    )
)
tokenizer.write(data)
tokenizer.end()

arguments

pass the following arguments to the parser function. all are optional.

opt - object bag of settings.

the supported options are:

• spaces_per_tab - number. needed for proper column info.: Rationale: without knowing how many spaces per tab base-clarinet is not able to determine the colomn of a character. Default is 4 (ofcourse)
• allow:missing_commas - boolean. No comma's are required. Rationale: When manually editing documents, keeping track of the comma's is cumbersome. With this option this is no longer an issue
• allow:trailing_commas - boolean. allows commas before the } or the ]. Rationale: for serializers it is easier to write a comma for every property/element instead of keeping a state that tracks if a property/element is the first one.
• allow:comments - boolean. allows both line comments // and block comments /* */. Rationale: when using JSON-like documents for editing, it is often useful to add comments
• allow:apostrophes_instead_of_quotation_marks - boolean. Allows ' in place of ". Rationale: In an editor this is less intrusive (although only slightly)
• allow:angle_brackets_instead_of_brackets - boolean. Allows < and > in place of [ and ]. Rationale: a semantic distinction can be made between fixed length arrays (ArrayType) and variable length arrays (lists)
• allow:parens_instead_of_braces - boolean. Allows ( and ) in place of { and }. Rationale: a semantic distinction can be made between objctes with known properties (Type) and objects with dynamic keys (dictionary)
• allow:schema - boolean. If enabled, the document may start with a ! followed by a value (object, string etc). This data can be used by a processor for schema validation. For example a string can indicate a URL of the schema.
• require:schema - boolean. see allow:schema. In this case the schema is required. This option overrides the allow option.
• allow:compact - boolean. At the beginning of a document, after the possible schema, a # may be placed. This is an indicator for a processor (code that uses bass-clarinet's API) that the data is compact. base-clarinet only sends the compact flag but does not change any other behaviour. Rationale: If a schema is known, the keys of a Type are known at design time. these types can therefor be converted to ArrayTypes and thus omit the keys without losing information. This trades in readability in favor of size. This option indicates that this happened in this document. The file can only be properly interpreted by a processor in combination with the schema.
• allow:tagged_unions - boolean. This allows an extra value type that is not present in JSON but is very useful. tagged unions are also known as sum types or choices, see taggedunion. The notation is a pipe, followed by a string, followed by any other value. eg: | "the chosen option" { "my data": "foo" }. The same information can ofcourse also be written in pure JSON with an array with 2 elements of which the first element is a string.

(normalize and trim have been dropped as this can equally well be handled in the onsimplevalue handler)

methods

write - write bytes to the parser. you don't have to do this all at once. you can keep writing as much as you want.

end - ends the stream. once ended, no more data may be written, it signals the onend event.

events

onerror - indication that something bad happened. the error will be hanging out on parser.error, and must be deleted before parsing can continue. by listening to this event, you can keep an eye on that kind of stuff. note: this happens much more in strict mode. argument: instance of Error.

onsimplevalue - a simple json value.

onopenobject - object was opened. this is different from clarinet as the first key is not treated separately

onkey - an object key: argument: key, a string with the current key. (Also called for the first key, unlike the behaviour of clarinet)

oncloseobject - indication that an object was closed

onopenarray - indication that an array was opened

onclosearray - indication that an array was closed

onopentaggedunion - indication that a tagged union was opened

onoption - the value of the option (string)

onclosetaggedunion - indication that a tagged union was closed

onend - indication that the closed stream has ended.

roadmap

check issues

contribute

everyone is welcome to contribute. patches, bug-fixes, new features

1. create an issue so the community can comment on your idea
2. fork bass-clarinet
3. create a new branch git checkout -b my_branch
4. create tests for the changes you made
5. make sure you pass both existing and newly inserted tests
6. commit your changes
7. push to your branch git push origin my_branch
8. create an pull request

meta

• code: git clone git://github.com/corno/bass-clarinet.git
• home: http://github.com/corno/bass-clarinet
• bugs: http://github.com/corno/bass-clarinet/issues
• build: