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).

5 files changed, 69 insertions, 11 deletions

diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileDeleter.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileDeleter.java
new file mode 100644
index 00000000000..efb56be56c5
--- /dev/null
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/FileDeleter.java
@@ -0,0 +1,33 @@
+package com.yahoo.vespa.hosted.node.admin.task.util.file;
+
+import com.yahoo.vespa.hosted.node.admin.component.TaskContext;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.logging.Logger;
+
+import static com.yahoo.yolean.Exceptions.uncheck;
+
+/**
+ * Deletes a file or empty directory.
+ *
+ * @author hakonhall
+ */
+public class FileDeleter {
+    private static final Logger logger = Logger.getLogger(FileDeleter.class.getName());
+
+    private final Path path;
+
+    public FileDeleter(Path path) {
+        this.path = path;
+    }
+
+    public boolean converge(TaskContext context) {
+        boolean deleted = uncheck(() -> Files.deleteIfExists(path));
+        if (deleted) {
+            context.recordSystemModification(logger, "Deleted file or directory " + path);
+        }
+
+        return deleted;
+    }
+}
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
index 4bd3aad3f52..1b927cfc682 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/file/UnixPath.java
@@ -49,16 +49,6 @@ public class UnixPath {
         return path;
     }
 
-    public boolean createParents() {
-        Path parent = path.getParent();
-        if (Files.isDirectory(parent)) {
-            return false;
-        }
-
-        uncheck(() -> Files.createDirectories(parent));
-        return true;
-    }
-
     public String readUtf8File() {
         return new String(readBytes(), StandardCharsets.UTF_8);
     }
@@ -141,6 +131,15 @@ public class UnixPath {
         return this;
     }
 
+    public UnixPath createParents() {
+        Path parent = path.getParent();
+        if (!Files.isDirectory(parent)) {
+            uncheck(() -> Files.createDirectories(parent));
+        }
+
+        return this;
+    }
+
     public UnixPath createDirectory(String permissions) {
         Set<PosixFilePermission> set = getPosixFilePermissionsFromString(permissions);
         FileAttribute<Set<PosixFilePermission>> attribute = PosixFilePermissions.asFileAttribute(set);
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/process/CommandLine.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/process/CommandLine.java
index 44b7da9367b..940b3255766 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/process/CommandLine.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/process/CommandLine.java
@@ -180,6 +180,15 @@ public class CommandLine {
     }
 
     /**
+     * By default, a non-zero exit code causes the command execution to fail. This method
+     * will override that predicate.
+     */
+    public CommandLine setSuccessfulExitCodePredicate(Predicate<Integer> successPredicate) {
+        successfulExitCodePredicate = successPredicate;
+        return this;
+    }
+
+    /**
      * By default, the output of the command is parsed as UTF-8. This method will set a
      * different encoding.
      */
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/systemd/SystemCtl.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/systemd/SystemCtl.java
index b61ebb610af..77510f7b6ef 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/systemd/SystemCtl.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/systemd/SystemCtl.java
@@ -20,6 +20,9 @@ public class SystemCtl {
     // Valid systemd property names from looking at a couple of services.
     private static final Pattern PROPERTY_NAME_PATTERN = Pattern.compile("^[a-zA-Z]+$");
 
+    // Last line of `systemctl list-unit-files <unit>` prints '0 unit files listed.'
+    private static final Pattern UNIT_FILES_LISTED_PATTERN = Pattern.compile("([0-9]+) unit files listed\\.");
+
     // Patterns matching properties output by the 'systemctl show' command.
     private static final Pattern UNIT_FILE_STATE_PROPERTY_PATTERN = createPropertyPattern("UnitFileState");
     private static final Pattern ACTIVE_STATE_PROPERTY_PATTERN = createPropertyPattern("ActiveState");
@@ -53,6 +56,20 @@ public class SystemCtl {
     public SystemCtlStop stop(String unit) { return new SystemCtlStop(unit); }
     public SystemCtlRestart restart(String unit) { return new SystemCtlRestart(unit); }
 
+    public boolean serviceExists(TaskContext context, String unit) {
+        return terminal.newCommandLine(context)
+                .add("systemctl").add("list-unit-files").add(unit + ".service").executeSilently()
+                .mapOutput(output -> {
+                    // Last line of the form: "1 unit files listed."
+                    Matcher matcher = UNIT_FILES_LISTED_PATTERN.matcher(output);
+                    if (!matcher.find()) {
+                        throw new IllegalArgumentException();
+                    }
+
+                    return !matcher.group(1).equals("0");
+                });
+    }
+
     public class SystemCtlEnable extends SystemCtlCommand {
         private SystemCtlEnable(String unit) {
             super("enable", unit);
diff --git a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/YumPackageName.java b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/YumPackageName.java
index a3a154e2175..fb85815c70f 100644
--- a/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/YumPackageName.java
+++ b/node-admin/src/main/java/com/yahoo/vespa/hosted/node/admin/task/util/yum/YumPackageName.java
@@ -43,7 +43,7 @@ public class YumPackageName {
     private static final Pattern NAME_VER_REL_PATTERN = Pattern.compile("^((.+)-)?" +
             "([a-z0-9._]*[0-9][a-z0-9._]*)-" + // ver contains at least one digit
             "([a-z0-9._]*[0-9][a-z0-9._]*)$"); // rel contains at least one digit
-    private static final Pattern NAME_PATTERN = Pattern.compile("^[a-z0-9._-]+$");
+    private static final Pattern NAME_PATTERN = Pattern.compile("^[a-zA-Z0-9._-]+$");
 
     private final Optional<String> epoch;
     private final String name;