Fix #45: Add CsvGenerator.Feature.WRITE_LINEFEED_AFTER_LAST_ROW

Author: cowtowncoder

Diff for: csv/src/main/java/com/fasterxml/jackson/dataformat/csv/CsvGenerator.java

@@ -108,7 +108,23 @@ public enum Feature
          *
          * @since 2.9.9
          */
-        ESCAPE_CONTROL_CHARS_WITH_ESCAPE_CHAR(false)
+        ESCAPE_CONTROL_CHARS_WITH_ESCAPE_CHAR(false),
+
+        /**
+         * Feature that determines whether a line-feed will be written at the end of content,
+         * after the last row of output.
+         *<p>
+         * NOTE! When disabling this feature it is important that
+         * {@link #flush()} is NOT called before {@link #close()} is called;
+         * the current implementation relies on ability to essentially remove the
+         * last linefeed that was appended in the output buffer.
+         *<p>
+         * Default value is {@code true} so all rows, including the last, are terminated by
+         * a line feed.
+         *
+         * @since 2.17
+         */
+        WRITE_LINEFEED_AFTER_LAST_ROW(true)
         ;
 
         protected final boolean _defaultState;

Diff for: csv/src/main/java/com/fasterxml/jackson/dataformat/csv/impl/CsvEncoder.java

@@ -162,7 +162,9 @@ public class CsvEncoder
      */
     protected int _lastBuffered = -1;
 
-    /*
+    // @since 2.17 (dataformats-csv#45)
+    protected boolean _trailingLFRemoved = false;
+
     /**********************************************************
     /* Output buffering, low-level
     /**********************************************************
@@ -1097,6 +1099,11 @@ public void flush(boolean flushStream) throws IOException
 
     public void close(boolean autoClose, boolean flushStream) throws IOException
     {
+        // May need to remove the linefeed appended after the last row written
+        // (if not yet done)
+        if (!CsvGenerator.Feature.WRITE_LINEFEED_AFTER_LAST_ROW.enabledIn(_csvFeatures)) {
+            _removeTrailingLF();
+        }
         _flushBuffer();
         if (autoClose) {
             _out.close();
@@ -1108,6 +1115,15 @@ public void close(boolean autoClose, boolean flushStream) throws IOException
         _releaseBuffers();
     }
 
+    private void _removeTrailingLF() throws IOException {
+        if (!_trailingLFRemoved) {
+            _trailingLFRemoved = true;
+            // Remove trailing LF if (but only if) it appears to be in output
+            // buffer (may not be possible if `flush()` has been called)
+            _outputTail = Math.max(0, _outputTail - _cfgLineSeparatorLength);
+        }
+    }
+
     /*
     /**********************************************************
     /* Internal methods

Diff for: csv/src/test/java/com/fasterxml/jackson/dataformat/csv/ser/CSVGeneratorTest.java

@@ -10,7 +10,8 @@
 import com.fasterxml.jackson.core.JsonGenerator;
 
 import com.fasterxml.jackson.core.StreamWriteFeature;
-import com.fasterxml.jackson.databind.JsonMappingException;
+
+import com.fasterxml.jackson.databind.DatabindException;
 import com.fasterxml.jackson.databind.ObjectWriter;
 import com.fasterxml.jackson.databind.node.ObjectNode;
 import com.fasterxml.jackson.dataformat.csv.*;
@@ -88,8 +89,14 @@ public void testSimpleExplicit() throws Exception
 
         FiveMinuteUser user = new FiveMinuteUser("Silu", "Seppala", false, Gender.MALE,
                 new byte[] { 1, 2, 3, 4, 5});
-        String csv = MAPPER.writer(schema).writeValueAsString(user);
-        assertEquals("Silu,Seppala,MALE,AQIDBAU=,false\n", csv);
+        assertEquals("Silu,Seppala,MALE,AQIDBAU=,false\n",
+                MAPPER.writer(schema).writeValueAsString(user));
+
+        // 14-Jan-2024, tatu: [dataformats-text#45] allow suppressing trailing LF:
+        assertEquals("Silu,Seppala,MALE,AQIDBAU=,false",
+                MAPPER.writer(schema)
+                    .without(CsvGenerator.Feature.WRITE_LINEFEED_AFTER_LAST_ROW)
+                    .writeValueAsString(user));
     }
 
     public void testSimpleWithAutoSchema() throws Exception
@@ -102,10 +109,17 @@ public void testWriteHeaders() throws Exception
     {
         CsvSchema schema = MAPPER.schemaFor(FiveMinuteUser.class).withHeader();
         FiveMinuteUser user = new FiveMinuteUser("Barbie", "Benton", false, Gender.FEMALE, null);
-        String result = MAPPER.writer(schema).writeValueAsString(user);
         assertEquals("firstName,lastName,gender,verified,userImage\n"
-                +"Barbie,Benton,FEMALE,false,\n", result);
-    }
+                +"Barbie,Benton,FEMALE,false,\n",
+                MAPPER.writer(schema).writeValueAsString(user));
+
+        // 14-Jan-2024, tatu: [dataformats-text#45] allow suppressing trailing LF:
+        assertEquals("firstName,lastName,gender,verified,userImage\n"
+                +"Barbie,Benton,FEMALE,false,",
+                MAPPER.writer(schema)
+                    .without(CsvGenerator.Feature.WRITE_LINEFEED_AFTER_LAST_ROW)
+                    .writeValueAsString(user));
+}
 
     /**
      * Test that verifies that if a header line is needed, configured schema
@@ -118,7 +132,7 @@ public void testFailedWriteHeaders() throws Exception
         try {
             MAPPER.writer(schema).writeValueAsString(user);
             fail("Should fail without columns");
-        } catch (JsonMappingException e) {
+        } catch (DatabindException e) {
             verifyException(e, "contains no column names");
         }
     }

Diff for: csv/src/test/java/com/fasterxml/jackson/dataformat/csv/ser/MultipleWritesTest.java

@@ -6,6 +6,7 @@
 import com.fasterxml.jackson.annotation.JsonPropertyOrder;
 import com.fasterxml.jackson.core.JsonGenerator;
 import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.dataformat.csv.CsvGenerator;
 import com.fasterxml.jackson.dataformat.csv.CsvMapper;
 import com.fasterxml.jackson.dataformat.csv.CsvSchema;
 import com.fasterxml.jackson.dataformat.csv.ModuleTestBase;
@@ -68,16 +69,30 @@ public void testMultipleListWrites() throws Exception
 
     public void testWriteValuesWithPOJOs() throws Exception
     {
-        CsvSchema schema = MAPPER.schemaFor(Pojo.class).withUseHeader(true);
+        final CsvSchema schema = MAPPER.schemaFor(Pojo.class).withUseHeader(true);
+
         ObjectWriter writer = MAPPER.writer(schema);
         StringWriter sw = new StringWriter();
-        SequenceWriter seqw = writer.writeValues(sw);
-        seqw.write(new Pojo(1, 2, 3));
-        seqw.write(new Pojo(0, 15, 9));
-        seqw.write(new Pojo(7, 8, 9));
-        seqw.flush();
+        try (SequenceWriter seqw = writer.writeValues(sw)) {
+            seqw.write(new Pojo(1, 2, 3));
+            seqw.write(new Pojo(0, 15, 9));
+            seqw.write(new Pojo(7, 8, 9));
+        }
         assertEquals("a,b,c\n1,2,3\n0,15,9\n7,8,9\n",
                 sw.toString());
-        seqw.close();
+
+        // 14-Jan-2024, tatu: [dataformats-text#45] allow suppressing trailing LF.
+        // NOTE! Any form of `flush()` will prevent ability to "remove" trailing LF so...
+        writer = writer
+                .without(SerializationFeature.FLUSH_AFTER_WRITE_VALUE)
+                .without(CsvGenerator.Feature.WRITE_LINEFEED_AFTER_LAST_ROW);
+        sw = new StringWriter();
+        try (SequenceWriter seqw = writer.writeValues(sw)) {
+            seqw.write(new Pojo(1, 2, 3));
+            seqw.write(new Pojo(0, 15, 9));
+            seqw.write(new Pojo(7, 8, 9));
+        }
+        assertEquals("a,b,c\n1,2,3\n0,15,9\n7,8,9",
+                sw.toString());
     }
 }

Diff for: release-notes/CREDITS-2.x

@@ -250,3 +250,9 @@ Arthur Chan (arthurscchan@github)
 * Contributed fix for #445: `YAMLParser` throws unexpected `NullPointerException` in certain
   number parsing cases
  (2.16.1)
+
+Mathieu Lavigne (@mathieu-lavigne)
+
+* Proposed #45 (and suggested implementation): (csv) Allow skipping ending line break
+  (`CsvGenerator.Feature.WRITE_LINEFEED_AFTER_LAST_ROW`)
+ (2.17.0)

Diff for: release-notes/VERSION-2.x

@@ -16,7 +16,9 @@ Active Maintainers:
 
 2.17.0 (not yet released)
 
--
+#45: (csv) Allow skipping ending line break
+  (`CsvGenerator.Feature.WRITE_LINEFEED_AFTER_LAST_ROW`)
+ (proposed by Mathieu L)
 
 2.16.1 (24-Dec-2023)