Fix Base58 zero buffer bug

Author: garydgregory

src/main/java/org/apache/commons/codec/binary/Base58.java

@@ -184,7 +184,7 @@ private void convertFromBase58(final byte[] base58, final Context context) {
             value = value.add(BigInteger.valueOf(digit).multiply(power));
             power = power.multiply(BASE);
         }
-        byte[] decoded = value.toByteArray();
+        byte[] decoded = value.equals(BigInteger.ZERO) ? EMPTY : value.toByteArray();
         if (decoded.length > 1 && decoded[0] == 0) {
             final byte[] tmp = new byte[decoded.length - 1];
             System.arraycopy(decoded, 1, tmp, 0, tmp.length);

src/test/java/org/apache/commons/codec/binary/Base58OutputStreamTest.java

@@ -23,11 +23,15 @@
 import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.io.ByteArrayOutputStream;
+import java.io.IOException;
 import java.io.OutputStream;
 import java.nio.charset.StandardCharsets;
 import java.util.Arrays;
 
+import org.apache.commons.lang3.ArrayFill;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 /**
  * Tests {@link Base58OutputStream}.
@@ -160,6 +164,39 @@ private void testByteByByte(final byte[] encoded, final byte[] decoded, final in
         assertArrayEquals(decoded, output, "Streaming byte-by-byte Base58 wrap-wrap-wrap!");
     }
 
+    @ParameterizedTest
+    @ValueSource(ints = { 0, 1, 2, 3, 4 })
+    void testDecodeByte49(final int len) throws IOException {
+        // Sanity check, each step from scratch:
+        final byte[] zeros = new byte[len];
+        final byte[] encoded0s = ArrayFill.fill(zeros.clone(), (byte) '1');
+        assertArrayEquals(encoded0s, Base58.builder().get().encode(zeros));
+        final byte[] decoded = Base58.builder().get().decode(encoded0s);
+        assertArrayEquals(zeros, decoded, () -> String.format("zeros=%s, decoded=%s", Arrays.toString(zeros), Arrays.toString(decoded)));
+        // Version 1.21.1:
+        // AssertionFailedError: Streaming byte-by-byte Base58 decode, chunkSize=0, separator=[10], encoded=[49], decoded=[0], output=[0, 0] ==> array lengths
+        // differ, expected: <1> but was: <2>
+        ByteArrayOutputStream byteOut = new ByteArrayOutputStream();
+        final byte[] byteData = new byte[len];
+        try (OutputStream out = Base58OutputStream.builder().setOutputStream(byteOut).setEncode(true).get()) {
+            for (final byte element : byteData) {
+                out.write(element);
+            }
+        }
+        final byte[] output0 = byteOut.toByteArray();
+        assertArrayEquals(encoded0s, output0, () -> String.format("Streaming byte-by-byte Base58 decode, encoded=%s, decoded=%s, output=%s",
+                Arrays.toString(encoded0s), Arrays.toString(byteData), Arrays.toString(output0)));
+        byteOut = new ByteArrayOutputStream();
+        try (OutputStream out = Base58OutputStream.builder().setOutputStream(byteOut).setEncode(false).get()) {
+            for (final byte element : encoded0s) {
+                out.write(element);
+            }
+        }
+        final byte[] output1 = byteOut.toByteArray();
+        assertArrayEquals(byteData, output1, () -> String.format("Streaming byte-by-byte Base58 decode, encoded=%s, decoded=%s, output=%s",
+                Arrays.toString(encoded0s), Arrays.toString(byteData), Arrays.toString(output1)));
+    }
+
     @Test
     void testRfcTestVector1() {
         assertEquals("2NEpo7TZRRrLZSi2U", Base58.builder().get().encodeToString("Hello World!".getBytes(StandardCharsets.US_ASCII)));

src/test/java/org/apache/commons/codec/binary/Base58Test.java

@@ -24,6 +24,7 @@
 import static org.junit.jupiter.api.Assertions.assertThrows;
 import static org.junit.jupiter.api.Assertions.assertTrue;
 
+import java.io.IOException;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 import java.nio.charset.StandardCharsets;
@@ -33,7 +34,10 @@
 
 import org.apache.commons.codec.DecoderException;
 import org.apache.commons.codec.EncoderException;
+import org.apache.commons.lang3.ArrayFill;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.ValueSource;
 
 /**
  * Tests {@link Base58}.
@@ -224,6 +228,17 @@ void testRoundTrip() {
         }
     }
 
+    @ParameterizedTest
+    @ValueSource(ints = { 0, 1, 2, 3, 4 })
+    void testRoundtripByte0(final int len) throws IOException {
+        // Sanity check, each step from scratch:
+        final byte[] zeros = new byte[len];
+        final byte[] encoded0s = ArrayFill.fill(zeros.clone(), (byte) '1');
+        assertArrayEquals(encoded0s, Base58.builder().get().encode(zeros));
+        final byte[] decoded = Base58.builder().get().decode(encoded0s);
+        assertArrayEquals(zeros, decoded, () -> String.format("zeros=%s, decoded=%s", Arrays.toString(zeros), Arrays.toString(decoded)));
+    }
+
     @Test
     void testSingleBytes() {
         // Test encoding of single bytes