Parse JSON as a stream.

This parser reads the JSON into memory only as it is parsed.
This makes it more complicated than the watt.json.dom parser, but more flexible.

Code Map

//! Parse JSON as a stream.
module watt.json.sax;


//! Type of a JSON value.
enum Type
{
	//! A JSON null value.
	NULL,
	//! A JSON true or false value.
	BOOLEAN,
	//! A JSON number.
	NUMBER,
	//! A JSON string.
	STRING,
	//! A JSON object, everything between {}.
	OBJECT,
	//! A JSON array, everything between [].
	ARRAY,
}

//! Events which will be produced by get.
enum Event
{
	//! The first event, marks the start of the JSON data.
	START,
	//! The last event, marks the end of the JSON data.
	END,
	//! Event which will occour if invalid JSON is encountered.
	ERROR,
	//! A null was encountered.
	NULL,
	//! A boolean was encountered.
	BOOLEAN,
	//! A number was encountered.
	NUMBER,
	//! A string was encountered.
	STRING,
	//! The start of a JSON object was encountered.
	OBJECT_START,
	//! A JSON object key was encountered (this is a string and still needs to
	//! be unescaped).
	OBJECT_KEY,
	//! The end of a JSON object was encountered.
	OBJECT_END,
	//! The start of a JSON array was encountered.
	ARRAY_START,
	//! The end of a JSON array was encountered.
	ARRAY_END,
}

//! Thrown when an error occurs during building.
class BuilderException : util.JSONException
{
public:
	this(msg: string, location: string) { }
}

//! Parses JSON from a given InputStream.
class SAX
{
public:
	//! Ignore garbage/left over data after the root element is parsed.
	ignoreGarbage: bool;


public:
	//! Creates a JSON object from an InputStream.
	this(source: InputStream, bufferSize: size_t, reallocSize: size_t) { }
	//! Creates a JSON object from an array.
	this(data: const(u8)[]) { }
	//! Creates a JSON object from a string.
	this(data: const(char)[]) { }
	//! Continues parsing the input data and calsl the callback with the
	//! appropriate data.
	fn get(callback: scope (void delegate(Event, const(u8)[]))) { }


protected:
	source: InputStream;
	buffer: u8[];
	reallocSize: size_t;
	current: const(u8)[];
	index: size_t;
	savedMark: size_t;
	isMarked: bool;
	state: ParserStack;
	lastError: string;


protected:
	fn error(message: string, file: string, line: const(i32)) { }
	fn eof() bool { }
	fn mark() { }
	fn retrieve() const(u8)[] { }
	fn getImpl(c: char, skip: bool, advance: bool) bool { }
	fn unget() { }
	fn skipWhite() { }
	fn skipDigits() bool { }
	fn expect(c: char, skip: bool) bool { }
	fn getString(array: const(u8)[]) bool { }
	fn getNumber(array: const(u8)[]) bool { }
	fn getBoolean(array: const(u8)[]) bool { }
	fn getNull(array: const(u8)[]) bool { }
}

//! The main class to build/write JSON.
class Builder
{
public:
	//! Creates a new JSONBuilder object.
	this(output: OutputStream, prettyPrint: bool, indent: const(char)[]) { }
	//! Writes a null value.
	fn buildNull() { }
	//! Writes a number.
	fn buildNumber(number: f64) { }
	//! Writes a number.
	fn buildNumber(number: i32) { }
	//! Writes a number.
	fn buildNumber(number: i64) { }
	//! Writes a string.
	fn buildString(str: const(char)[], escape: bool) { }
	//! Writes a boolean.
	fn buildBoolean(b: bool) { }
	//! Writes the start of a JSON object.
	fn buildObjectStart() { }
	//! Writes the end of a JSON object.
	fn buildObjectEnd() { }
	//! Writes the start of a JSON array.
	fn buildArrayStart() { }
	//! Writes the end of a JSON array.
	fn buildArrayEnd() { }
	//! Finalizes the JSON.
	fn finalize() { }


protected:
	output: OutputStream;
	prettyPrint: bool;
	indent: const(char)[];
	indentLevel: size_t;
	buffer: char[];
	state: ParserStack;


protected:
	fn prepareAndCheck(isString: bool) { }
}

//! Turn an Event into a human readable string.
fn eventToString(event: Event) string { }

sax := new Sax(input);  // input is declared in watt.io.std.
loop := true;
fn dgt(event: Event, data: const(u8)[]) {
    loop = event == Event.END || event == Event.ERROR;
}
while (loop) sax.get(dgt);