Add Decoder#ofPredicate, Decoder#contramap.
Change-Id: Ifd4e372a6a3c3028d1cd74e6d9a0145c3f571ff5
diff --git a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java
index 33b0480..3beb247 100644
--- a/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java
+++ b/jgvariant-core/src/main/java/eu/mulk/jgvariant/core/Decoder.java
@@ -15,8 +15,11 @@
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
+import java.util.Objects;
import java.util.Optional;
import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.function.UnaryOperator;
import org.apiguardian.api.API;
import org.apiguardian.api.API.Status;
import org.jetbrains.annotations.Nullable;
@@ -101,6 +104,29 @@
}
/**
+ * Creates a new {@link Decoder} from an existing one by applying a function to the input.
+ *
+ * @param function the function to apply.
+ * @return a new, decorated {@link Decoder}.
+ * @see java.util.stream.Stream#map
+ */
+ public final Decoder<T> contramap(UnaryOperator<ByteBuffer> function) {
+ return new ContramappingDecoder(function);
+ }
+
+ /**
+ * Creates a new {@link Decoder} that delegates to one of two other {@link Decoder}s based on a
+ * condition on the input {@link ByteBuffer}.
+ *
+ * @param selector the predicate to use to determine the decoder to use.
+ * @return a new {@link Decoder}.
+ */
+ public static <U> Decoder<U> ofPredicate(
+ Predicate<ByteBuffer> selector, Decoder<U> thenDecoder, Decoder<U> elseDecoder) {
+ return new PredicateDecoder<>(selector, thenDecoder, elseDecoder);
+ }
+
+ /**
* Creates a {@link Decoder} for an {@code Array} type.
*
* @param elementDecoder a {@link Decoder} for the elements of the array.
@@ -773,7 +799,7 @@
private final Function<T, U> function;
- public MappingDecoder(Function<T, U> function) {
+ MappingDecoder(Function<T, U> function) {
this.function = function;
}
@@ -793,11 +819,36 @@
}
}
+ private class ContramappingDecoder extends Decoder<T> {
+
+ private final UnaryOperator<ByteBuffer> function;
+
+ ContramappingDecoder(UnaryOperator<ByteBuffer> function) {
+ this.function = function;
+ }
+
+ @Override
+ public byte alignment() {
+ return Decoder.this.alignment();
+ }
+
+ @Override
+ public @Nullable Integer fixedSize() {
+ return Decoder.this.fixedSize();
+ }
+
+ @Override
+ public T decode(ByteBuffer byteSlice) {
+ var transformedBuffer = function.apply(byteSlice.asReadOnlyBuffer().order(byteSlice.order()));
+ return Decoder.this.decode(transformedBuffer);
+ }
+ }
+
private class ByteOrderFixingDecoder extends Decoder<T> {
private final ByteOrder byteOrder;
- public ByteOrderFixingDecoder(ByteOrder byteOrder) {
+ ByteOrderFixingDecoder(ByteOrder byteOrder) {
this.byteOrder = byteOrder;
}
@@ -822,4 +873,46 @@
private static ByteBuffer slicePreservingOrder(ByteBuffer byteSlice, int index, int length) {
return byteSlice.slice(index, length).order(byteSlice.order());
}
+
+ private static class PredicateDecoder<U> extends Decoder<U> {
+
+ private final Predicate<ByteBuffer> selector;
+ private final Decoder<U> thenDecoder;
+ private final Decoder<U> elseDecoder;
+
+ PredicateDecoder(
+ Predicate<ByteBuffer> selector, Decoder<U> thenDecoder, Decoder<U> elseDecoder) {
+ this.selector = selector;
+ this.thenDecoder = thenDecoder;
+ this.elseDecoder = elseDecoder;
+ if (thenDecoder.alignment() != elseDecoder.alignment()) {
+ throw new IllegalArgumentException(
+ "incompatible alignments in predicate branches: then=%d, else=%d"
+ .formatted(thenDecoder.alignment(), elseDecoder.alignment()));
+ }
+
+ if (!Objects.equals(thenDecoder.fixedSize(), elseDecoder.fixedSize())) {
+ throw new IllegalArgumentException(
+ "incompatible sizes in predicate branches: then=%s, else=%s"
+ .formatted(thenDecoder.fixedSize(), elseDecoder.fixedSize()));
+ }
+ }
+
+ @Override
+ public byte alignment() {
+ return thenDecoder.alignment();
+ }
+
+ @Override
+ public @Nullable Integer fixedSize() {
+ return thenDecoder.fixedSize();
+ }
+
+ @Override
+ public U decode(ByteBuffer byteSlice) {
+ var b = selector.test(byteSlice);
+ byteSlice.rewind();
+ return b ? thenDecoder.decode(byteSlice) : elseDecoder.decode(byteSlice);
+ }
+ }
}
diff --git a/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java b/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
index efbcafa..8c78692 100644
--- a/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
+++ b/jgvariant-core/src/test/java/eu/mulk/jgvariant/core/DecoderTest.java
@@ -507,4 +507,71 @@
var decoder = Decoder.ofByteArray().map(bytes -> bytes.length);
assertEquals(3, decoder.decode(ByteBuffer.wrap(data)));
}
+
+ @Test
+ void testContramap() {
+ var data = new byte[] {0x0A, 0x0B, 0x0C};
+ var decoder = Decoder.ofByteArray().contramap(bytes -> bytes.slice(1, 1));
+ assertArrayEquals(new byte[] {0x0B}, decoder.decode(ByteBuffer.wrap(data)));
+ }
+
+ @Test
+ void testPredicateTrue() {
+ var data = new byte[] {0x00, 0x01, 0x00};
+ var innerDecoder = Decoder.ofShort().contramap(bytes -> bytes.slice(1, 2).order(bytes.order()));
+ var decoder =
+ Decoder.ofPredicate(
+ byteBuffer -> byteBuffer.get(0) == 0,
+ innerDecoder.withByteOrder(LITTLE_ENDIAN),
+ innerDecoder.withByteOrder(BIG_ENDIAN));
+ assertEquals((short) 1, decoder.decode(ByteBuffer.wrap(data)));
+ }
+
+ @Test
+ void testPredicateFalse() {
+ var data = new byte[] {0x01, 0x01, 0x00};
+ var innerDecoder = Decoder.ofShort().contramap(bytes -> bytes.slice(1, 2).order(bytes.order()));
+ var decoder =
+ Decoder.ofPredicate(
+ byteBuffer -> byteBuffer.get(0) == 0,
+ innerDecoder.withByteOrder(LITTLE_ENDIAN),
+ innerDecoder.withByteOrder(BIG_ENDIAN));
+ assertEquals((short) 256, decoder.decode(ByteBuffer.wrap(data)));
+ }
+
+ @Test
+ void testByteOrder() {
+ var data =
+ new byte[] {
+ 0x01, 0x00, 0x02, 0x00, 0x00, 0x03, 0x00, 0x04, 0x05, 0x00, 0x00, 0x06, 0x00, 0x07, 0x08,
+ 0x00
+ };
+
+ record TestChild(short s1, short s2) {}
+ record TestParent(TestChild tc1, TestChild tc2, TestChild tc3, TestChild tc4) {}
+
+ var decoder =
+ Decoder.ofStructure(
+ TestParent.class,
+ Decoder.ofStructure(TestChild.class, Decoder.ofShort(), Decoder.ofShort())
+ .withByteOrder(LITTLE_ENDIAN),
+ Decoder.ofStructure(TestChild.class, Decoder.ofShort(), Decoder.ofShort())
+ .withByteOrder(BIG_ENDIAN),
+ Decoder.ofStructure(
+ TestChild.class,
+ Decoder.ofShort().withByteOrder(LITTLE_ENDIAN),
+ Decoder.ofShort())
+ .withByteOrder(BIG_ENDIAN),
+ Decoder.ofStructure(
+ TestChild.class, Decoder.ofShort().withByteOrder(BIG_ENDIAN), Decoder.ofShort())
+ .withByteOrder(LITTLE_ENDIAN));
+
+ assertEquals(
+ new TestParent(
+ new TestChild((short) 1, (short) 2),
+ new TestChild((short) 3, (short) 4),
+ new TestChild((short) 5, (short) 6),
+ new TestChild((short) 7, (short) 8)),
+ decoder.decode(ByteBuffer.wrap(data)));
+ }
}