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Propagate I/O failures from UnifiedDiffWriter #234

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Merged
wumpz merged 2 commits into from
Oct 9, 2026
+54 −15
Merged

Propagate I/O failures from UnifiedDiffWriter #234

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e3e13e9
Propagate I/O failures from UnifiedDiffWriter
jakezwang Sep 19, 2026
c6905d8
Document no-op methods in failing writer test
jakezwang Sep 19, 2026
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31 changes: 16 additions & 15 deletions java-diff-utils/src/main/java/com/github/difflib/unifieddiff/UnifiedDiffWriter.java
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Original file line number Diff line number Diff line change
Expand Up @@ -17,38 +17,39 @@

import com.github.difflib.patch.AbstractDelta;
import java.io.IOException;
import java.io.UncheckedIOException;
import java.io.Writer;
import java.util.ArrayList;
import java.util.List;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
* @todo use an instance to store contextSize and originalLinesProvider.
* @author Tobias Warneke (t.warneke@gmx.net)
*/
public class UnifiedDiffWriter {

private static final Logger LOG = Logger.getLogger(UnifiedDiffWriter.class.getName());

public static void write(
UnifiedDiff diff, Function<String, List<String>> originalLinesProvider, Writer writer, int contextSize)
throws IOException {
Objects.requireNonNull(originalLinesProvider, "original lines provider needs to be specified");
write(
diff,
originalLinesProvider,
line -> {
try {
writer.append(line).append("\n");
} catch (IOException ex) {
LOG.log(Level.SEVERE, null, ex);
}
},
contextSize);
try {
write(
diff,
originalLinesProvider,
line -> {
try {
writer.append(line).append("\n");
} catch (IOException ex) {
throw new UncheckedIOException(ex);
}
},
contextSize);
} catch (UncheckedIOException ex) {
throw ex.getCause();
}
}

public static void write(
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38 changes: 38 additions & 0 deletions java-diff-utils/src/test/java/com/github/difflib/unifieddiff/UnifiedDiffWriterTest.java
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Original file line number Diff line number Diff line change
Expand Up @@ -16,12 +16,15 @@
package com.github.difflib.unifieddiff;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertSame;
import static org.junit.jupiter.api.Assertions.assertThrows;

import com.github.difflib.DiffUtils;
import com.github.difflib.patch.Patch;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.StringWriter;
import java.io.Writer;
import java.net.URI;
import java.net.URISyntaxException;
import java.nio.charset.Charset;
Expand All @@ -31,6 +34,8 @@
import java.util.Collections;
import java.util.List;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

/**
*
Expand Down Expand Up @@ -81,6 +86,39 @@ public void testWriteWithNewFile() throws URISyntaxException, IOException {
assertEquals("@@ -0,0 +1,2 @@", lines[2]);
}

@ParameterizedTest
@ValueSource(ints = {1, 2, 9, 16})
public void testPropagateWriterFailures(int failOnWrite) {
List<String> original = Collections.singletonList("old");
Patch<String> patch = DiffUtils.diff(original, Collections.singletonList("new"));
UnifiedDiff diff = UnifiedDiff.from("header", "tail", UnifiedDiffFile.from("original", "revised", patch));
IOException failure = new IOException("write failed");
int[] writes = {0};
Writer writer = new Writer() {
@Override
public void write(char[] buffer, int offset, int length) throws IOException {
if (++writes[0] == failOnWrite) {
throw failure;
}
}

@Override
public void flush() {
// No buffered output in this test writer.
}

@Override
public void close() {
// No resources to release.
}
};

assertSame(
failure,
assertThrows(IOException.class, () -> UnifiedDiffWriter.write(diff, name -> original, writer, 0)));
assertEquals(failOnWrite, writes[0]);
}

static String readFile(URI path, Charset encoding) throws IOException {
byte[] encoded = Files.readAllBytes(Paths.get(path));
return new String(encoded, encoding);
Expand Down
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