Add flags module

FileFlagSource reads flags from files in /etc/vespa/flags and is a component
that can be injected in host admin, config server, etc. A flag named foo
corresponds to filename foo.

In general a FlagSource manages:
 - Feature flags: A feature is either set (true/enabled) or otherwise false.
   Touching a file foo means the feature flag foo is set (true).
 - Value flags: Either a String or empty if not set. The String corresponds to
   the file content.

The plan is to make the config server another source of flags. A unified
FlagSource can merge the two sources with some priority and used in e.g. parts
of node-admin. In other parts one would only have access to the file source.

Defines various flag facades:
 - FeatureFlag: Used to test whether a feature has been enabled or not.
 - IntFlag
 - JacksonFlag: Deserializes JSON to Jackson class, or return default if unset.
 - LongFlag
 - OptionalJacksonFlag: Deserializes JSON to Jackson class, or empty if unset.
 - OptionalStringFlag
 - StringFlag

This is part of removing some of the last Chef recipes. Some minor tweaks have
been necessary as part of this and are included in this PR (test whether a
systemd service exists, task-friendly file deletion, allow capitalized letters
in YUM package name).

2 files changed, 121 insertions, 0 deletions

diff --git a/flags/src/test/java/com/yahoo/vespa/flags/FileFlagSourceTest.java b/flags/src/test/java/com/yahoo/vespa/flags/FileFlagSourceTest.java
new file mode 100644
index 00000000000..e422057f5fe
--- /dev/null
+++ b/flags/src/test/java/com/yahoo/vespa/flags/FileFlagSourceTest.java
@@ -0,0 +1,49 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import com.yahoo.vespa.test.file.TestFileSystem;
+import org.junit.Test;
+
+import java.io.IOException;
+import java.nio.file.FileSystem;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class FileFlagSourceTest {
+    private final FileSystem fileSystem = TestFileSystem.create();
+    private final FileFlagSource source = new FileFlagSource(fileSystem);
+
+    @Test
+    public void absentThenSet() throws IOException {
+        FlagId id = new FlagId("foo");
+        FeatureFlag featureFlag = new FeatureFlag(id, source);
+        StringFlag stringFlag = new StringFlag(id, "default", source);
+        OptionalStringFlag optionalStringFlag = new OptionalStringFlag(id, source);
+        IntFlag intFlag = new IntFlag(id, -1, source);
+        LongFlag longFlag = new LongFlag(id, -2L, source);
+
+        assertFalse(source.hasFeature(id));
+        assertFalse(source.getString(id).isPresent());
+        assertFalse(featureFlag.isSet());
+        assertEquals("default", stringFlag.value());
+        assertFalse(optionalStringFlag.value().isPresent());
+        assertEquals(-1, intFlag.value());
+        assertEquals(-2L, longFlag.value());
+
+        Path featurePath = fileSystem.getPath(FileFlagSource.FLAGS_DIRECTORY).resolve(id.toString());
+        Files.createDirectories(featurePath.getParent());
+        Files.write(featurePath, "1\n".getBytes());
+
+        assertTrue(source.hasFeature(id));
+        assertTrue(source.getString(id).isPresent());
+        assertTrue(featureFlag.isSet());
+        assertEquals("1\n", stringFlag.value());
+        assertEquals("1\n", optionalStringFlag.value().get());
+        assertEquals(1, intFlag.value());
+        assertEquals(1L, longFlag.value());
+    }
+}
\ No newline at end of file
diff --git a/flags/src/test/java/com/yahoo/vespa/flags/JacksonFlagTest.java b/flags/src/test/java/com/yahoo/vespa/flags/JacksonFlagTest.java
new file mode 100644
index 00000000000..e4424d9886a
--- /dev/null
+++ b/flags/src/test/java/com/yahoo/vespa/flags/JacksonFlagTest.java
@@ -0,0 +1,72 @@
+// Copyright 2018 Yahoo Holdings. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.vespa.flags;
+
+import com.fasterxml.jackson.annotation.JsonIgnoreProperties;
+import com.fasterxml.jackson.annotation.JsonProperty;
+import org.junit.Test;
+
+import java.util.Objects;
+import java.util.Optional;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class JacksonFlagTest {
+    private final FlagId id = new FlagId("id");
+    private final ExampleJacksonClass defaultValue = new ExampleJacksonClass();
+    private final FlagSource source = mock(FlagSource.class);
+    private final JacksonFlag<ExampleJacksonClass> jacksonFlag = new JacksonFlag<>(id.toString(), ExampleJacksonClass.class, defaultValue, source);
+    private final OptionalJacksonFlag<ExampleJacksonClass> optionalJacksonFlag = new OptionalJacksonFlag<>(id, ExampleJacksonClass.class, source);
+
+    @Test
+    public void unsetThenSet() {
+        when(source.getString(id)).thenReturn(Optional.empty());
+        ExampleJacksonClass value = jacksonFlag.value();
+        assertEquals(1, value.integer);
+        assertEquals("2", value.string);
+        assertEquals("3", value.dummy);
+        assertFalse(optionalJacksonFlag.value().isPresent());
+
+        when(source.getString(id)).thenReturn(Optional.of("{\"integer\": 4, \"string\": \"foo\", \"stray\": 6}"));
+        value = jacksonFlag.value();
+        assertEquals(4, value.integer);
+        assertEquals("foo", value.string);
+        assertEquals("3", value.dummy);
+
+        assertTrue(optionalJacksonFlag.value().isPresent());
+        value = optionalJacksonFlag.value().get();
+        assertEquals(4, value.integer);
+        assertEquals("foo", value.string);
+        assertEquals("3", value.dummy);
+    }
+
+    @JsonIgnoreProperties(ignoreUnknown = true)
+    private static class ExampleJacksonClass {
+        @JsonProperty("integer")
+        public int integer = 1;
+
+        @JsonProperty("string")
+        public String string = "2";
+
+        @JsonProperty("dummy")
+        public String dummy = "3";
+
+        @Override
+        public boolean equals(Object o) {
+            if (this == o) return true;
+            if (o == null || getClass() != o.getClass()) return false;
+            ExampleJacksonClass that = (ExampleJacksonClass) o;
+            return integer == that.integer &&
+                    Objects.equals(string, that.string) &&
+                    Objects.equals(dummy, that.dummy);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(integer, string, dummy);
+        }
+    }
+}
\ No newline at end of file