fix: don't call peek line predicate with empty string if reached EOF

Author: osiegmar

lib/src/intTest/java/blackbox/reader/AbstractSkipLinesTest.java

@@ -8,6 +8,7 @@
 import java.io.UncheckedIOException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.function.Predicate;
 
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.params.ParameterizedTest;
@@ -114,6 +115,16 @@ void skipLinesWithCount(final String input) {
                 .isStartingLineNumber(3).fields().containsExactly("C"));
     }
 
+    @Test
+    void skipUntilLast() {
+        final CsvReader<CsvRecord> csv = crb.ofCsvRecord("A\nB\nC");
+
+        csv.skipLines(3);
+
+        assertThat(csv.stream())
+            .isEmpty();
+    }
+
     @ParameterizedTest
     @ValueSource(strings = {"A\r\nB\r\nC", "A\nB\nC", "A\rB\rC"})
     void tooMany(final String input) {
@@ -182,6 +193,17 @@ void noMatch() {
             .hasMessage("No matching line found. Skipped 2 line(s) before reaching end of data.");
     }
 
+    @Test
+    void lastMatch() {
+        final CsvReader<CsvRecord> csv = crb.ofCsvRecord("A\nB");
+        final int linesSkipped = csv.skipLines("B"::equals, 10);
+        assertThat(linesSkipped).isEqualTo(1);
+        assertThat(csv.stream())
+            .singleElement()
+            .satisfies(rec -> CsvRecordAssert.assertThat(rec)
+                .isStartingLineNumber(2).fields().containsExactly("B"));
+    }
+
     @ValueSource(strings = {
         "some arbitrary text\r\nbefore the actual data\r\n\r\nheader1,header2\r\nvalue1,value2\r\n",
         "some arbitrary text\rbefore the actual data\r\rheader1,header2\rvalue1,value2\r",
@@ -209,4 +231,19 @@ void predicateIoException() {
             .hasMessage("java.io.IOException: Cannot read");
     }
 
+    @Test
+    void predicateNotCalledForEmptyLine() {
+        final Predicate<String> p = line -> {
+            if (!"A".equals(line)) {
+                throw new IllegalArgumentException("Expected line 'A', but got '" + line + "'");
+            }
+            return false;
+        };
+
+        final CsvReader<CsvRecord> csv = crb.ofCsvRecord("A\n");
+        assertThatThrownBy(() -> csv.skipLines(p, 10))
+            .isInstanceOf(CsvParseException.class)
+            .hasMessage("No matching line found. Skipped %d line(s) before reaching end of data.".formatted(1));
+    }
+
 }

lib/src/main/java/de/siegmar/fastcsv/reader/CsvReader.java

@@ -128,17 +128,21 @@ public int skipLines(final Predicate<String> predicate, final int maxLines) {
             return 0;
         }
 
+        int i = 0;
         try {
-            for (int i = 0; i < maxLines; i++) {
+            for (; i < maxLines; i++) {
                 final String line = csvParser.peekLine();
-                if (predicate.test(line)) {
-                    return i;
-                }
 
-                if (!csvParser.skipLine(line.length())) {
+                if (line == null) {
                     throw new CsvParseException(
                         "No matching line found. Skipped %d line(s) before reaching end of data.".formatted(i));
                 }
+
+                if (predicate.test(line)) {
+                    return i;
+                }
+
+                csvParser.skipLine(line.length());
             }
         } catch (final IOException e) {
             throw new UncheckedIOException(e);

lib/src/main/java/de/siegmar/fastcsv/reader/RelaxedCsvParser.java

@@ -282,29 +282,29 @@ public String peekLine() throws IOException {
         return reader.peekLine();
     }
 
-    @SuppressWarnings({
-        "checkstyle:MultipleVariableDeclarations",
-        "PMD.OneDeclarationPerLine",
-        "PMD.AssignmentInOperand"
-    })
+    @SuppressWarnings("checkstyle:MultipleVariableDeclarations")
     @Override
     public boolean skipLine(final int numCharsToSkip) throws IOException {
         reader.skip(numCharsToSkip);
 
-        int i, c;
-        for (i = 0; (c = reader.read()) != EOF; i++) {
+        int c = reader.read();
+        if (c == EOF) {
+            return false;
+        }
+
+        do {
             if (c == CR) {
                 reader.consumeIf(LF);
                 startingLineNumber++;
-                return true;
+                break;
             }
             if (c == LF) {
                 startingLineNumber++;
-                return true;
+                break;
             }
-        }
+        } while ((c = reader.read()) != EOF);
 
-        return numCharsToSkip + i > 0;
+        return true;
     }
 
     @Override
@@ -368,8 +368,7 @@ boolean consumeIf(final char[] chars) throws IOException {
         String peekLine() throws IOException {
             ensureBuffered(buffer.length);
             if (start >= len) {
-                // Keep consistent with StrictCsvParser.peekLine()
-                return "";
+                return null;
             }
             int endIndex = start;
             while (endIndex < len && buffer[endIndex] != CR && buffer[endIndex] != LF) {

lib/src/main/java/de/siegmar/fastcsv/reader/StrictCsvParser.java

@@ -342,6 +342,10 @@ public void close() throws IOException {
 
     @Override
     public String peekLine() throws IOException {
+        if (csvBuffer.pos == csvBuffer.len && !csvBuffer.fetchData()) {
+            return null;
+        }
+
         final int savedPos = csvBuffer.pos;
 
         for (; csvBuffer.pos < csvBuffer.len || csvBuffer.fetchData(); csvBuffer.pos++) {