Respect environment variables in jvm.options

tools/jvm-options-parser/src/main/java/org/logstash/launchers/JvmOptionsParser.java

@@ -32,7 +32,6 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
-import java.util.HashSet;
 import java.util.LinkedHashSet;
 import java.util.List;
 import java.util.Locale;
@@ -283,7 +282,7 @@ public List<String> getJvmOptions() {
     }
 
     private static final Pattern OPTION_DEFINITION = Pattern.compile("((?<start>\\d+)(?<range>-)?(?<end>\\d+)?:)?(?<option>-.*)$");
-
+    private static final Pattern ENV_VAR_PATTERN = Pattern.compile("\\$\\{([A-Z_][A-Z0-9_]*)\\}");
     /**
      *
      * If the version syntax specified on a line matches the specified JVM options, the JVM option callback will be invoked with the JVM
@@ -372,13 +371,16 @@ private static Optional<String> jvmOptionFromLine(final int javaMajorVersion, fi
             // Skip comments and blank lines
             return Optional.empty();
         }
-        final Matcher matcher = OPTION_DEFINITION.matcher(line);
+
+        String subbedLine = replaceEnvVariables(line, System.getenv());
+
+        final Matcher matcher = OPTION_DEFINITION.matcher(subbedLine);
         if (matcher.matches()) {
             final String start = matcher.group("start");
             final String end = matcher.group("end");
             if (start == null) {
                 // no range present, unconditionally apply the JVM option
-                return Optional.of(line);
+                return Optional.of(subbedLine);
             } else {
                 final int lower = Integer.parseInt(start);
                 final int upper;
@@ -404,6 +406,20 @@ private static Optional<String> jvmOptionFromLine(final int javaMajorVersion, fi
         return Optional.empty();
     }
 
+    static String replaceEnvVariables(String line, Map<String,String> env) {
+        Matcher matcher = ENV_VAR_PATTERN.matcher(line);
+        StringBuilder sb = new StringBuilder();
+
+        while (matcher.find()) {
+            String varName = matcher.group(1);
+            String replacement = env.getOrDefault(varName, "");
+            matcher.appendReplacement(sb, replacement);
+        }
+        matcher.appendTail(sb);
+
+        return sb.toString();
+    }
+
     private static final Pattern JAVA_VERSION = Pattern.compile("^(?:1\\.)?(?<javaMajorVersion>\\d+)(?:\\.\\d+)?$");
 
     private static int javaMajorVersion() {

tools/jvm-options-parser/src/test/java/org/logstash/launchers/JvmOptionsParserTest.java

@@ -198,4 +198,50 @@ private BufferedReader asReader(String s) {
         return new BufferedReader(new StringReader(s));
     }
 
+
+    @Test
+    public void testSingleEnvSubstitution() throws IOException {
+        String result = JvmOptionsParser.replaceEnvVariables("-XX:HeapDumpPath=${LOGSTASH_HOME}/heapdump.hprof",
+                Map.of("LOGSTASH_HOME", "/path/to/ls_home"));
+        assertEquals("-XX:HeapDumpPath=/path/to/ls_home/heapdump.hprof", result);
+    }
+
+    @Test
+    public void testMultipleEnvSubstitution() throws IOException {
+        String result = JvmOptionsParser.replaceEnvVariables("-XX:HeapDumpPath=${LOGSTASH_HOME}/${ABC}/heapdump.hprof",
+                Map.of("LOGSTASH_HOME", "/path/to/ls_home", "ABC", "abc"));
+        assertEquals("-XX:HeapDumpPath=/path/to/ls_home/abc/heapdump.hprof", result);
+    }
+
+    @Test
+    public void testEmptyEnvSubstitution() throws IOException {
+        String result = JvmOptionsParser.replaceEnvVariables("-XX:HeapDumpPath=${NOT_VALID}/heapdump.hprof", Map.of());
+        assertEquals("-XX:HeapDumpPath=/heapdump.hprof", result);
+    }
+
+    @Test
+    public void testNoSubstitution() throws IOException {
+        String result = JvmOptionsParser.replaceEnvVariables("   ", Map.of());
+        assertEquals("   ", result);
+    }
+
+    @Test
+    public void testEnvSubstitutionInFile() throws IOException {
+        File optionsFile = writeIntoTempOptionsFile(
+                writer -> writer.println("-Xlog:gc*,gc+age=trace,safepoint:file=${UNKNOWN}:"));
+
+        JvmOptionsParser.handleJvmOptions(new String[] {"/path/to/ls_home", optionsFile.toString()}, "-Dcli.opts=something");
+
+        final String output = outputStreamCaptor.toString();
+        assertTrue("env variable should be substituted ", output.contains("-Xlog:gc*,gc+age=trace,safepoint:file=:"));
+    }
+
+    @Test
+    public void testCommentedEnvSubstitution() throws IOException {
+        final BufferedReader options = asReader("# -Xlog:gc*,gc+age=trace,safepoint:file=${UNKNOWN}:");
+        final JvmOptionsParser.ParseResult res = JvmOptionsParser.parse(11, options);
+
+        assertTrue("no invalid lines can be present", res.getInvalidLines().isEmpty());
+        assertFalse(String.join(System.lineSeparator(), res.getJvmOptions()).contains("-Xlog:gc*,gc+age=trace,safepoint"));
+    }
 }