Add class for server favicon parsing

minecord-bot/src/main/java/com/tisawesomeness/minecord/mc/Favicon.java

@@ -0,0 +1,125 @@
+package com.tisawesomeness.minecord.mc;
+
+import com.tisawesomeness.minecord.common.util.Either;
+import com.tisawesomeness.minecord.util.type.Dimensions;
+import lombok.*;
+
+import java.io.ByteArrayInputStream;
+import java.io.DataInput;
+import java.io.DataInputStream;
+import java.util.Base64;
+import java.util.Optional;
+import java.util.regex.Pattern;
+
+@RequiredArgsConstructor(access = AccessLevel.PRIVATE)
+public class Favicon {
+
+    /** The expected width and height of a favicon. Older clients may not display favicons with different sizes. */
+    public static final int EXPECTED_SIZE = 64;
+
+    private static final String PREAMBLE = "data:image/png;base64,";
+    private static final Pattern NEWLINES_PATTERN = Pattern.compile("[\r\n]");
+    private static final int MIN_LENGTH = 24;
+    private static final long PNG_SIGNATURE = 0x89_504E47_0D0A_1A_0AL;
+    private static final int IHDR_LENGTH = 13;
+    private static final int IHDR_TYPE = ('I' << 24) + ('H' << 16) + ('D' << 8) + 'R';
+
+    /** The image data for the favicon. */
+    @Getter private final byte[] data;
+    private final boolean usesNewlines;
+
+    /**
+     * Creates a favicon from image bytes.
+     * @param data byte array representing a raw PNG image
+     * @return new favicon
+     */
+    public static Favicon from(byte[] data) {
+        return new Favicon(data, false);
+    }
+
+    /**
+     * Parses a base64-encoded favicon, according to the server ping
+     * <a href="https://wiki.vg/Server_List_Ping#Status_Response">specification</a>. Newlines are accepted and trimmed
+     * before parsing, use {@link #usesNewlines()} to check if newlines were used.
+     * @param str the string to parse
+     * @return the favicon, or empty if the input is malformed
+     */
+    public static Optional<Favicon> parse(@NonNull String str) {
+        if (!str.startsWith(PREAMBLE)) {
+            return Optional.empty();
+        }
+        String imageData = str.substring(PREAMBLE.length());
+        boolean usesNewlines = false;
+        if (imageData.indexOf('\r') == -1 || imageData.indexOf('\n') == -1) {
+            imageData = NEWLINES_PATTERN.matcher(imageData).replaceAll("");
+            usesNewlines = true;
+        }
+        try {
+            byte[] decoded = Base64.getDecoder().decode(imageData);
+            return Optional.of(new Favicon(decoded, usesNewlines));
+        } catch (IllegalArgumentException ignored) {
+            return Optional.empty();
+        }
+    }
+
+    /**
+     * If this favicon was created through {@link #parse(String)}, returns whether newlines were in the original input.
+     * Favicons with newlines no longer work since 1.13.
+     * @return whether newlines were used to create this favicon
+     */
+    public boolean usesNewlines() {
+        return usesNewlines;
+    }
+
+    /**
+     * Checks if the favicon is a valid PNG image. If the PNG can be read, returns the width and height.
+     * This method only checks if a PNG can be <strong>read</strong>, not necessarily displayed.
+     * <br>This method can return any {@link PngError PngError}.
+     * @return the image dimensions if the PNG is valid, or a {@link PngError PngError} otherwise
+     */
+    @SneakyThrows // IOE, not possible with ByteArrayInputStream
+    public Either<PngError, Dimensions> validate() {
+        if (data.length < MIN_LENGTH) {
+            return Either.left(PngError.TOO_SHORT);
+        }
+        DataInput is = new DataInputStream(new ByteArrayInputStream(data));
+        if (is.readLong() != PNG_SIGNATURE) {
+            return Either.left(PngError.BAD_SIGNATURE);
+        }
+        if (is.readInt() != IHDR_LENGTH) {
+            return Either.left(PngError.BAD_IHDR_LENGTH);
+        }
+        if (is.readInt() != IHDR_TYPE) {
+            return Either.left(PngError.BAD_IHDR_TYPE);
+        }
+        int width = is.readInt();
+        if (width < 0) {
+            return Either.left(PngError.NEGATIVE_WIDTH);
+        }
+        int height = is.readInt();
+        if (height < 0) {
+            return Either.left(PngError.NEGATIVE_WIDTH);
+        }
+        return Either.right(new Dimensions(width, height));
+    }
+
+    /**
+     * An error that can occur when validating a PNG image. See the
+     * <a href="https://en.wikipedia.org/wiki/PNG#File_format">Wikipedia page</a> for more details.
+     */
+    public enum PngError {
+        /** Image data is too small to be a valid PNG */
+        TOO_SHORT,
+        /** Does not contain PNG file header */
+        BAD_SIGNATURE,
+        /** IHDR chunk length is invalid */
+        BAD_IHDR_LENGTH,
+        /** First PNG chunk is not IHDR */
+        BAD_IHDR_TYPE,
+        /** Width of PNG is negative (or overflow) */
+        NEGATIVE_WIDTH,
+        /** Height of PNG is negative (or overflow) */
+        NEGATIVE_HEIGHT
+    }
+
+}

minecord-bot/src/main/java/com/tisawesomeness/minecord/util/Strings.java

@@ -59,6 +59,17 @@ private Strings() {}
         return str.substring(Math.max(beginIndex, 0), Math.min(endIndex, str.length()));
     }
 
+    /**
+     * Creates a new string with the character at the given index replaced with the replacement character.
+     * @param str input string
+     * @param idx index of character to replace
+     * @param replacement character to replace with
+     * @return new string
+     */
+    public static String replaceCharAt(String str, int idx, char replacement) {
+        return str.substring(0, idx) + replacement + str.substring(idx + 1);
+    }
+
     /**
      * Joins a list of lines into a series of partitions, ensuring that no line in the returned list
      * has a length over the max length (as long as every input line is no longer than the max length).

minecord-bot/src/main/java/com/tisawesomeness/minecord/util/type/Dimensions.java

@@ -0,0 +1,26 @@
+package com.tisawesomeness.minecord.util.type;
+
+import lombok.Value;
+
+@Value
+public class Dimensions {
+    int width;
+    int height;
+
+    /**
+     * Creates a new Dimensions object
+     * @param width width
+     * @param height height
+     * @throws IllegalArgumentException if width or height are negative
+     */
+    public Dimensions(int width, int height) {
+        if (width < 0) {
+            throw new IllegalArgumentException("width cannot be negative but was " + width);
+        }
+        if (height < 0) {
+            throw new IllegalArgumentException("height cannot be negative but was " + height);
+        }
+        this.width = width;
+        this.height = height;
+    }
+}

minecord-bot/src/test/java/com/tisawesomeness/minecord/mc/FaviconTest.java

@@ -0,0 +1,55 @@
+package com.tisawesomeness.minecord.mc;
+
+import com.tisawesomeness.minecord.common.util.IO;
+import com.tisawesomeness.minecord.util.Strings;
+import com.tisawesomeness.minecord.util.type.Dimensions;
+import org.assertj.core.api.InstanceOfAssertFactories;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+import static com.tisawesomeness.minecord.testutil.assertion.CustomAssertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class FaviconTest {
+
+    private static final String HYPIXEL_FAVICON = IO.loadResource("hypixelFavicon.txt", FaviconTest.class);
+
+    @Test
+    public void testFromEmpty() {
+        Favicon icon = Favicon.from(new byte[0]);
+        assertThat(icon.getData()).isEmpty();
+        assertThat(icon.usesNewlines()).isFalse();
+        assertThat(icon.validate()).asLeft().isEqualTo(Favicon.PngError.TOO_SHORT);
+    }
+
+    @Test
+    public void testParse() {
+        Optional<Favicon> iconOpt = Favicon.parse(HYPIXEL_FAVICON);
+        assertThat(iconOpt).isNotEmpty();
+        Favicon icon = iconOpt.get();
+        assertThat(icon.validate())
+                .asRight(InstanceOfAssertFactories.type(Dimensions.class))
+                .extracting(Dimensions::getWidth, Dimensions::getHeight)
+                .containsExactly(Favicon.EXPECTED_SIZE, Favicon.EXPECTED_SIZE);
+    }
+    @Test
+    public void testParseEmpty() {
+        assertThat(Favicon.parse("")).isEmpty();
+    }
+    @Test
+    public void testParseInvalid() {
+        assertThat(Favicon.parse("data:image/png;base64,!")).isEmpty();
+    }
+    @Test
+    public void testParseBadSignature() {
+        String modified = Strings.replaceCharAt(HYPIXEL_FAVICON, 22, 'j');
+        Optional<Favicon> iconOpt = Favicon.parse(modified);
+        assertThat(iconOpt).isNotEmpty();
+        Favicon icon = iconOpt.get();
+        assertThat(icon.validate())
+                .asLeft()
+                .isEqualTo(Favicon.PngError.BAD_SIGNATURE);
+    }
+
+}

minecord-bot/src/test/java/com/tisawesomeness/minecord/testutil/assertion/EitherAssert.java

@@ -48,7 +48,7 @@ public ObjectAssert<R> asRight() {
         return new ObjectAssert<>(actual.getRight());
     }
     @CheckReturnValue
-    public <ASSERT extends AbstractAssert<ASSERT, L>> ASSERT asRight(InstanceOfAssertFactory<?, ASSERT> assertFactory) {
+    public <ASSERT extends AbstractAssert<ASSERT, R>> ASSERT asRight(InstanceOfAssertFactory<?, ASSERT> assertFactory) {
         return asRight().asInstanceOf(assertFactory);
     }
 

minecord-bot/src/test/java/com/tisawesomeness/minecord/util/StringsTest.java

@@ -2,6 +2,8 @@
 
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 import java.util.ArrayList;
 import java.util.Collections;
@@ -91,6 +93,19 @@ public void testSafeSubstring2to1() {
         assertThat(Strings.safeSubstring("abc", 2, 1)).isEmpty();
     }
 
+    @ParameterizedTest
+    @CsvSource({
+            "abcd, 0, !, !bcd",
+            "abcd, 1, !, a!cd",
+            "abcd, 2, !, ab!d",
+            "abcd, 3, !, abc!",
+            "x, 0, !, !",
+    })
+    public void testReplaceCharAt(String str, int idx, char replacement, String expected) {
+        assertThat(Strings.replaceCharAt(str, idx, replacement))
+                .isEqualTo(expected);
+    }
+
     @Test
     @DisplayName("Splitting a list of empty strings by length returns an empty list")
     public void testSplitEmptyList() {

minecord-bot/src/test/java/com/tisawesomeness/minecord/util/type/DimensionsTest.java

@@ -0,0 +1,33 @@
+package com.tisawesomeness.minecord.util.type;
+
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+public class DimensionsTest {
+
+    @Test
+    public void test() {
+        assertThat(new Dimensions(2, 1))
+                .extracting(Dimensions::getWidth, Dimensions::getHeight)
+                .containsExactly(2, 1);
+    }
+    @Test
+    public void testZero() {
+        assertThat(new Dimensions(0, 0))
+                .extracting(Dimensions::getWidth, Dimensions::getHeight)
+                .containsExactly(0, 0);
+    }
+    @Test
+    public void testNegative() {
+        assertThatThrownBy(() -> new Dimensions(1, -1))
+                .isInstanceOf(IllegalArgumentException.class);
+    }
+    @Test
+    public void testNegative2() {
+        assertThatThrownBy(() -> new Dimensions(-1, 1))
+                .isInstanceOf(IllegalArgumentException.class);
+    }
+
+}