CompactEncoded.java

/*
 * Copyright © 2025 Indiana University
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 *
 * BSD 3-Clause License
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 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
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 *   list of conditions and the following disclaimer.
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 * - Redistributions in binary form must reproduce the above copyright notice,
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 *   this software without specific prior written permission.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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package iu.crypt;

import java.util.Base64;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Objects;

import edu.iu.IuObject;
import edu.iu.IuText;
import edu.iu.client.IuJson;
import jakarta.json.JsonObject;

/**
 * Encodes {@link byte[]} values for inclusion in JWS and JWE serialized forms
 * as unpadded Base64 URL encoded strings.
 */
public final class CompactEncoded {

	private CompactEncoded() {
	}

	/**
	 * Iterates over segments in a JSON compact serialized structure.
	 * 
	 * @param data compact serialized data
	 * @return {@link Iterator} over data segments
	 */
	public static Iterator<String> compact(final String data) {
		return new Iterator<String>() {
			private int start;
			private int end = -1;

			@Override
			public boolean hasNext() {
				if (end < start) {
					end = data.indexOf('.', start);
					if (end == -1)
						end = data.length();
				}
				return start < data.length();
			}

			@Override
			public String next() {
				if (!hasNext())
					throw new NoSuchElementException();

				final var next = start == end ? null : data.substring(start, end);
				start = end + 1;
				return next;
			}
		};
	}

	/**
	 * Returns the protected header of a compact serialized JWS or JWE.
	 * 
	 * @param compactSerialized compact serialized JWS or JWE
	 * @return protected header
	 */
	public static JsonObject getProtectedHeader(String compactSerialized) {
		final var dot = IuObject.require(//
				Objects.requireNonNull(compactSerialized, "Missing token").indexOf('.'), //
				i -> i != -1, "Invalid compact serialized data");

		final var encodedProtectedHeader = compactSerialized.substring(0, dot);
		return IuJson.parse(IuText.utf8(Base64.getUrlDecoder().decode(encodedProtectedHeader))).asJsonObject();
	}

}