HashCollisionTest Class — netty Architecture

Source Code

codec-http2/src/test/java/io/netty/handler/codec/http2/HashCollisionTest.java lines 40–177

@Disabled
public final class HashCollisionTest {
    private HashCollisionTest() { }

    public static void main(String[] args) throws IllegalAccessException, IOException, URISyntaxException {
        // Big initial size for when all name sources are pulled in.
        List<CharSequence> strings = new ArrayList<CharSequence>(350000);
        addHttpHeaderNames(strings);
        addHttpHeaderValues(strings);
        addHttp2HeaderNames(strings);
        addWordsFromFile(new File("/usr/share/dict/words"), strings);
        // More "english words" can be found here:
        // https://gist.github.com/Scottmitch/de2f03912778016ecee3c140478f07e0#file-englishwords-txt

        Map<Integer, List<CharSequence>> dups = calculateDuplicates(strings, new Function<CharSequence, Integer>() {
            @Override
            public Integer apply(CharSequence string) {
                int h = 0;
                for (int i = 0; i < string.length(); ++i) {
                    // masking with 0x1F reduces the number of overall bits that impact the hash code but makes the hash
                    // code the same regardless of character case (upper case or lower case hash is the same).
                    h = h * 31 + (string.charAt(i) & 0x1F);
                }
                return h;
            }
        });
        PrintStream writer = System.out;
        writer.println("==Old Duplicates==");
        printResults(writer, dups);

        dups = calculateDuplicates(strings, new Function<CharSequence, Integer>() {
            @Override
            public Integer apply(CharSequence string) {
                return PlatformDependent.hashCodeAscii(string);
            }
        });
        writer.println();
        writer.println("==New Duplicates==");
        printResults(writer, dups);
    }

    private static void addHttpHeaderNames(List<CharSequence> values) throws IllegalAccessException {
        for (Field f : HttpHeaderNames.class.getFields()) {
            if (f.getType() == AsciiString.class) {
                values.add((AsciiString) f.get(null));
            }
        }
    }

    private static void addHttpHeaderValues(List<CharSequence> values) throws IllegalAccessException {
        for (Field f : HttpHeaderValues.class.getFields()) {
            if (f.getType() == AsciiString.class) {
                values.add((AsciiString) f.get(null));
            }
        }
    }

    private static void addHttp2HeaderNames(List<CharSequence> values) throws IllegalAccessException {
        for (Http2Headers.PseudoHeaderName name : Http2Headers.PseudoHeaderName.values()) {
            values.add(name.value());
        }
    }

    private static void addWordsFromFile(File file, List<CharSequence> values)
            throws IllegalAccessException, IOException {
        BufferedReader br = new BufferedReader(new FileReader(file));
        try {
            String line;
            while ((line = br.readLine()) != null) {
                // Make a "best effort" to prune input which contains characters that are not valid in HTTP header names
                if (line.indexOf('\'') < 0) {
                    values.add(line);
                }
            }
        } finally {
            br.close();
        }
    }

    private static Map<Integer, List<CharSequence>> calculateDuplicates(List<CharSequence> strings,
                                                                        Function<CharSequence, Integer> hasher) {