More efficient filtering of input streams

src/main/java/com/cloudbees/jenkins/support/api/LaunchLogsFileContent.java

@@ -1,16 +1,14 @@
 package com.cloudbees.jenkins.support.api;
 
+import com.cloudbees.jenkins.support.filter.FilteredInputStream;
 import com.cloudbees.jenkins.support.filter.PasswordRedactor;
 import com.cloudbees.jenkins.support.impl.SlaveLaunchLogs;
-import java.io.ByteArrayInputStream;
 import java.io.File;
 import java.io.FileInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.charset.Charset;
-import java.util.List;
-import java.util.stream.Collectors;
-import org.apache.commons.io.IOUtils;
+import java.util.function.Function;
 
 /**
  * @see SlaveLaunchLogs
@@ -23,14 +21,8 @@ public LaunchLogsFileContent(String name, String[] filterableParameters, File fi
 
     @Override
     protected InputStream getInputStream() throws IOException {
-        try (FileInputStream inputStream = new FileInputStream(file)) {
-            List<String> strings = IOUtils.readLines(inputStream, Charset.defaultCharset());
-            byte[] bytes = strings.stream()
-                    .map(line -> PasswordRedactor.get().redact(line))
-                    .collect(Collectors.joining("\n", "", "\n"))
-                    .getBytes(Charset.defaultCharset());
-            return new ByteArrayInputStream(bytes);
-        }
+        Function<String, String> filter = line -> PasswordRedactor.get().redact(line);
+        return new FilteredInputStream(new FileInputStream(file), Charset.defaultCharset(), filter);
     }
 
     @Override

src/main/java/com/cloudbees/jenkins/support/filter/FilteredInputStream.java

@@ -0,0 +1,65 @@
+package com.cloudbees.jenkins.support.filter;
+
+import edu.umd.cs.findbugs.annotations.NonNull;
+import java.io.BufferedReader;
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.nio.charset.Charset;
+import java.util.function.Function;
+
+/**
+ * A custom {@link InputStream} that filters lines of text read from an underlying {@link InputStream} using a provided
+ * mapping function. Each line read from the input stream is processed by the function before being returned, allowing
+ * for modifications such as redaction or transformation of the line content.
+ *
+ * @author Basil Crow
+ */
+public class FilteredInputStream extends InputStream {
+
+    private final Function<String, String> filter;
+    private final Charset encoding;
+    private final BufferedReader reader;
+    private ByteArrayInputStream buffer;
+
+    /**
+     * Constructs a filtered stream using the provided filter and encoding.
+     *
+     * @param is Input stream to read line content from
+     * @param encoding Character set to use for decoding and encoding bytes read from this stream
+     * @param filter Filter to apply to lines read from this stream
+     */
+    public FilteredInputStream(
+            @NonNull InputStream is, @NonNull Charset encoding, @NonNull Function<String, String> filter) {
+        this.encoding = encoding;
+        this.reader = new BufferedReader(new InputStreamReader(is, encoding));
+        this.filter = filter;
+    }
+
+    @Override
+    public int read() throws IOException {
+        if (buffer == null) {
+            String line = reader.readLine();
+            if (line != null) {
+                line = filter.apply(line);
+                line += System.lineSeparator();
+                buffer = new ByteArrayInputStream(line.getBytes(encoding));
+            } else {
+                return -1;
+            }
+        }
+        int ch = buffer.read();
+        if (ch != -1) {
+            return ch;
+        } else {
+            buffer = null;
+            return read();
+        }
+    }
+
+    @Override
+    public void close() throws IOException {
+        reader.close();
+    }
+}

src/test/java/com/cloudbees/jenkins/support/filter/FilteredInputStreamTest.java

@@ -0,0 +1,51 @@
+package com.cloudbees.jenkins.support.filter;
+
+import static org.junit.Assert.assertEquals;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import org.junit.Test;
+
+public class FilteredInputStreamTest {
+
+    @Test
+    public void testReadSingleLine() throws IOException {
+        String input = "foo bar";
+        String output;
+        try (FilteredInputStream fis = new FilteredInputStream(
+                new ByteArrayInputStream(input.getBytes(StandardCharsets.UTF_8)),
+                StandardCharsets.UTF_8,
+                String::toUpperCase)) {
+            output = new String(fis.readAllBytes(), StandardCharsets.UTF_8);
+        }
+        assertEquals("FOO BAR" + System.lineSeparator(), output);
+    }
+
+    @Test
+    public void testReadMultipleLines() throws IOException {
+        String input = "Line 1\nLine 2\nLine 3";
+        String output;
+        try (FilteredInputStream fis = new FilteredInputStream(
+                new ByteArrayInputStream(input.getBytes(StandardCharsets.UTF_8)),
+                StandardCharsets.UTF_8,
+                String::toUpperCase)) {
+            output = new String(fis.readAllBytes(), StandardCharsets.UTF_8);
+        }
+        assertEquals(
+                "LINE 1" + System.lineSeparator() + "LINE 2" + System.lineSeparator() + "LINE 3"
+                        + System.lineSeparator(),
+                output);
+    }
+
+    @Test
+    public void testReadEmptyStream() throws IOException {
+        byte[] input = new byte[0];
+        String output;
+        try (FilteredInputStream fis =
+                new FilteredInputStream(new ByteArrayInputStream(input), StandardCharsets.UTF_8, String::toUpperCase)) {
+            output = new String(fis.readAllBytes(), StandardCharsets.UTF_8);
+        }
+        assertEquals("", output);
+    }
+}