Create proto file containing server metadata on server startup

This is a combination of all of the other server files (except commandline).
Meant to be used with exec-server to determine when the server is online and
ready. It might also be useful to remove the individual info files
(command_port, request_cookie, response_cookie) in favor of this one.

RELNOTES: None
PiperOrigin-RevId: 264650984

src/main/java/com/google/devtools/build/lib/server/GrpcServerImpl.java

@@ -34,6 +34,7 @@
 import com.google.devtools.build.lib.server.CommandProtos.PingResponse;
 import com.google.devtools.build.lib.server.CommandProtos.RunRequest;
 import com.google.devtools.build.lib.server.CommandProtos.RunResponse;
+import com.google.devtools.build.lib.server.CommandProtos.ServerInfo;
 import com.google.devtools.build.lib.server.CommandProtos.StartupOption;
 import com.google.devtools.build.lib.util.ExitCode;
 import com.google.devtools.build.lib.util.Pair;
@@ -314,6 +315,7 @@ public void run() {
   private static final String PORT_FILE = "command_port";
   private static final String REQUEST_COOKIE_FILE = "request_cookie";
   private static final String RESPONSE_COOKIE_FILE = "response_cookie";
+  private static final String SERVER_INFO_FILE = "server_info.rawproto";
 
   private static final AtomicBoolean runShutdownHooks = new AtomicBoolean(true);
 
@@ -445,10 +447,7 @@ public void serve() throws IOException {
     }
     serving = true;
 
-    writeServerFile(
-        PORT_FILE, InetAddresses.toUriString(address.getAddress()) + ":" + server.getPort());
-    writeServerFile(REQUEST_COOKIE_FILE, requestCookie);
-    writeServerFile(RESPONSE_COOKIE_FILE, responseCookie);
+    writeServerStatusFiles(address);
 
     try {
       server.awaitTermination();
@@ -458,6 +457,30 @@ public void serve() throws IOException {
     }
   }
 
+  private void writeServerStatusFiles(InetSocketAddress address) throws IOException {
+    writeServerFile(
+        PORT_FILE, InetAddresses.toUriString(address.getAddress()) + ":" + server.getPort());
+    writeServerFile(REQUEST_COOKIE_FILE, requestCookie);
+    writeServerFile(RESPONSE_COOKIE_FILE, responseCookie);
+
+    ServerInfo info =
+        ServerInfo.newBuilder()
+            .setPid(Integer.parseInt(pidInFile))
+            .setAddress(address.getAddress() + ":" + server.getPort())
+            .setRequestCookie(requestCookie)
+            .setResponseCookie(responseCookie)
+            .build();
+
+    // Write then mv so the user never sees incomplete contents.
+    Path serverInfoTmpFile = serverDirectory.getChild(SERVER_INFO_FILE + ".tmp");
+    try (OutputStream out = serverInfoTmpFile.getOutputStream()) {
+      info.writeTo(out);
+    }
+    Path serverInfoFile = serverDirectory.getChild(SERVER_INFO_FILE);
+    serverInfoTmpFile.renameTo(serverInfoFile);
+    deleteAtExit(serverInfoFile);
+  }
+
   private void writeServerFile(String name, String contents) throws IOException {
     Path file = serverDirectory.getChild(name);
     FileSystemUtils.writeContentAsLatin1(file, contents);

src/main/protobuf/command_server.proto

@@ -142,6 +142,22 @@ message PingResponse {
   string cookie = 1;
 }
 
+// Describes metadata necessary for connecting to and managing the server.
+message ServerInfo {
+  // The server process's pid.
+  int32 pid = 1;
+
+  // Address the CommandServer is listening on. Can be passed directly to grpc
+  // to create a connection.
+  string address = 2;
+
+  // Client request cookie.
+  string request_cookie = 3;
+
+  // Server response cookie.
+  string response_cookie = 4;
+}
+
 service CommandServer {
   // Run a Bazel command. See documentation of argument/return messages for
   // details.