버퍼 스트림과 자원 순서

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.EOFException;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.List;

public final class BufferedFrameFileSolution {
    public static void main(String[] args) throws Exception {
        Path file = Files.createTempFile("frames-", ".dat");
        try {
            try (var output = new DataOutputStream(
                    new BufferedOutputStream(Files.newOutputStream(file)))) {
                for (String value : List.of("", "첫째", "second")) {
                    byte[] bytes = value.getBytes(StandardCharsets.UTF_8);
                    output.writeInt(bytes.length);
                    output.write(bytes);
                }
            }
            List<String> restored = new ArrayList<>();
            try (var input = new DataInputStream(
                    new BufferedInputStream(Files.newInputStream(file)))) {
                while (true) {
                    try {
                        int length = input.readInt();
                        if (length < 0 || length > 4096) throw new IllegalStateException("length");
                        restored.add(new String(input.readNBytes(length), StandardCharsets.UTF_8));
                    } catch (EOFException end) {
                        break;
                    }
                }
            }
            System.out.println(restored);
        } finally {
            Files.deleteIfExists(file);
        }
    }
}

import java.io.*;
import java.nio.ByteBuffer;
import java.nio.charset.CodingErrorAction;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import java.util.Optional;

public final class StrictFrameReaderSolution {
    static Optional<String> readOne(InputStream input) throws IOException {
        int first = input.read();
        if (first == -1) return Optional.empty();
        byte[] rest = input.readNBytes(3);
        if (rest.length != 3) throw new EOFException("short int header");
        int length = (first << 24) | ((rest[0] & 0xff) << 16)
                | ((rest[1] & 0xff) << 8) | (rest[2] & 0xff);
        if (length < 0 || length > 4096) throw new IOException("invalid length: " + length);
        byte[] bytes = input.readNBytes(length);
        if (bytes.length != length) throw new EOFException("short frame body");
        String text = StandardCharsets.UTF_8.newDecoder()
                .onMalformedInput(CodingErrorAction.REPORT)
                .onUnmappableCharacter(CodingErrorAction.REPORT)
                .decode(ByteBuffer.wrap(bytes)).toString();
        return Optional.of(text);
    }

    static List<String> readSample(byte[] wire) throws IOException {
        var values = new ArrayList<String>();
        try (var input = new BufferedInputStream(new ByteArrayInputStream(wire))) {
            while (true) {
                var message = readOne(input);
                if (message.isEmpty()) return List.copyOf(values);
                values.add(message.get());
            }
        }
    }

    static void report(byte[] wire) {
        try { System.out.println(readSample(wire)); }
        catch (IOException e) { System.out.println(e.getClass().getSimpleName()); }
    }

    public static void main(String[] args) throws IOException {
        var memory = new ByteArrayOutputStream();
        try (var output = new DataOutputStream(memory)) {
            for (String value : List.of("", "첫째", "second")) {
                byte[] bytes = value.getBytes(StandardCharsets.UTF_8);
                output.writeInt(bytes.length);
                output.write(bytes);
            }
        }
        report(memory.toByteArray());
        report(new byte[] {0, 0}); // 짧은 헤더
        report(new byte[] {0, 0, 0, 3, 9}); // 길이 3인데 본문은 1바이트
        report(new byte[] {0, 0, 0, 2, (byte) 0xC3, 0x28}); // 잘못된 UTF-8
    }
}