parser.js

/**
 * @internal
 */
const NULL = 0;
/**
 * @internal
 */
const LF = 10;
/**
 * @internal
 */
const CR = 13;
/**
 * @internal
 */
const COLON = 58;
/**
 * This is an evented, rec descent parser.
 * A stream of Octets can be passed and whenever it recognizes
 * a complete Frame or an incoming ping it will invoke the registered callbacks.
 *
 * All incoming Octets are fed into _onByte function.
 * Depending on current state the _onByte function keeps changing.
 * Depending on the state it keeps accumulating into _token and _results.
 * State is indicated by current value of _onByte, all states are named as _collect.
 *
 * STOMP standards https://stomp.github.io/stomp-specification-1.2.html
 * imply that all lengths are considered in bytes (instead of string lengths).
 * So, before actual parsing, if the incoming data is String it is converted to Octets.
 * This allows faithful implementation of the protocol and allows NULL Octets to be present in the body.
 *
 * There is no peek function on the incoming data.
 * When a state change occurs based on an Octet without consuming the Octet,
 * the Octet, after state change, is fed again (_reinjectByte).
 * This became possible as the state change can be determined by inspecting just one Octet.
 *
 * There are two modes to collect the body, if content-length header is there then it by counting Octets
 * otherwise it is determined by NULL terminator.
 *
 * Following the standards, the command and headers are converted to Strings
 * and the body is returned as Octets.
 * Headers are returned as an array and not as Hash - to allow multiple occurrence of an header.
 *
 * This parser does not use Regular Expressions as that can only operate on Strings.
 *
 * It handles if multiple STOMP frames are given as one chunk, a frame is split into multiple chunks, or
 * any combination there of. The parser remembers its state (any partial frame) and continues when a new chunk
 * is pushed.
 *
 * Typically the higher level function will convert headers to Hash, handle unescaping of header values
 * (which is protocol version specific), and convert body to text.
 *
 * Check the parser.spec.js to understand cases that this parser is supposed to handle.
 *
 * Part of `@stomp/stompjs`.
 *
 * @internal
 */
export class Parser {
    constructor(onFrame, onIncomingPing) {
        this.onFrame = onFrame;
        this.onIncomingPing = onIncomingPing;
        this._encoder = new TextEncoder();
        this._decoder = new TextDecoder();
        this._token = [];
        this._initState();
    }
    parseChunk(segment, appendMissingNULLonIncoming = false) {
        let chunk;
        if (typeof segment === 'string') {
            chunk = this._encoder.encode(segment);
        }
        else {
            chunk = new Uint8Array(segment);
        }
        // See https://github.com/stomp-js/stompjs/issues/89
        // Remove when underlying issue is fixed.
        //
        // Send a NULL byte, if the last byte of a Text frame was not NULL.F
        if (appendMissingNULLonIncoming && chunk[chunk.length - 1] !== 0) {
            const chunkWithNull = new Uint8Array(chunk.length + 1);
            chunkWithNull.set(chunk, 0);
            chunkWithNull[chunk.length] = 0;
            chunk = chunkWithNull;
        }
        // tslint:disable-next-line:prefer-for-of
        for (let i = 0; i < chunk.length; i++) {
            const byte = chunk[i];
            this._onByte(byte);
        }
    }
    // The following implements a simple Rec Descent Parser.
    // The grammar is simple and just one byte tells what should be the next state
    _collectFrame(byte) {
        if (byte === NULL) {
            // Ignore
            return;
        }
        if (byte === CR) {
            // Ignore CR
            return;
        }
        if (byte === LF) {
            // Incoming Ping
            this.onIncomingPing();
            return;
        }
        this._onByte = this._collectCommand;
        this._reinjectByte(byte);
    }
    _collectCommand(byte) {
        if (byte === CR) {
            // Ignore CR
            return;
        }
        if (byte === LF) {
            this._results.command = this._consumeTokenAsUTF8();
            this._onByte = this._collectHeaders;
            return;
        }
        this._consumeByte(byte);
    }
    _collectHeaders(byte) {
        if (byte === CR) {
            // Ignore CR
            return;
        }
        if (byte === LF) {
            this._setupCollectBody();
            return;
        }
        this._onByte = this._collectHeaderKey;
        this._reinjectByte(byte);
    }
    _reinjectByte(byte) {
        this._onByte(byte);
    }
    _collectHeaderKey(byte) {
        if (byte === COLON) {
            this._headerKey = this._consumeTokenAsUTF8();
            this._onByte = this._collectHeaderValue;
            return;
        }
        this._consumeByte(byte);
    }
    _collectHeaderValue(byte) {
        if (byte === CR) {
            // Ignore CR
            return;
        }
        if (byte === LF) {
            this._results.headers.push([
                this._headerKey,
                this._consumeTokenAsUTF8(),
            ]);
            this._headerKey = undefined;
            this._onByte = this._collectHeaders;
            return;
        }
        this._consumeByte(byte);
    }
    _setupCollectBody() {
        const contentLengthHeader = this._results.headers.filter((header) => {
            return header[0] === 'content-length';
        })[0];
        if (contentLengthHeader) {
            this._bodyBytesRemaining = parseInt(contentLengthHeader[1], 10);
            this._onByte = this._collectBodyFixedSize;
        }
        else {
            this._onByte = this._collectBodyNullTerminated;
        }
    }
    _collectBodyNullTerminated(byte) {
        if (byte === NULL) {
            this._retrievedBody();
            return;
        }
        this._consumeByte(byte);
    }
    _collectBodyFixedSize(byte) {
        // It is post decrement, so that we discard the trailing NULL octet
        if (this._bodyBytesRemaining-- === 0) {
            this._retrievedBody();
            return;
        }
        this._consumeByte(byte);
    }
    _retrievedBody() {
        this._results.binaryBody = this._consumeTokenAsRaw();
        try {
            this.onFrame(this._results);
        }
        catch (e) {
            console.log(`Ignoring an exception thrown by a frame handler. Original exception: `, e);
        }
        this._initState();
    }
    // Rec Descent Parser helpers
    _consumeByte(byte) {
        this._token.push(byte);
    }
    _consumeTokenAsUTF8() {
        return this._decoder.decode(this._consumeTokenAsRaw());
    }
    _consumeTokenAsRaw() {
        const rawResult = new Uint8Array(this._token);
        this._token = [];
        return rawResult;
    }
    _initState() {
        this._results = {
            command: undefined,
            headers: [],
            binaryBody: undefined,
        };
        this._token = [];
        this._headerKey = undefined;
        this._onByte = this._collectFrame;
    }
}
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