fix JENKINS-14772

This fix implements an optional retry loop for cli BuildCommand
The retry is not for the actual command, but for reading the log file
(when -v is used) This is so that slow machines, which may create the log
file so slowly that is it not present when reading of it starts,
will optionally  try to start reading it multiple times.

This is implemented via a use of an optional "-r INT" cmd option

core/src/main/java/hudson/cli/BuildCommand.java

@@ -48,6 +48,7 @@ import java.util.HashMap;
 import java.util.List;
 import java.util.ArrayList;
 import java.util.Map.Entry;
+import java.io.FileNotFoundException;
 import java.io.PrintStream;
 
 import jenkins.model.Jenkins;
@@ -82,6 +83,12 @@ public class BuildCommand extends CLICommand {
     @Option(name="-v",usage="Prints out the console output of the build. Use with -s")
     public boolean consoleOutput = false;
 
+    @Option(name="-r", usage="Number of times to retry reading of the output log if it does not exists on first attempt. Defaults to 0. Use with -v.")
+    public String retryCntStr = "0";
+
+    // hold parsed retryCnt;
+    private int retryCnt = 0;
+
     protected int run() throws Exception {
         job.checkPermission(Item.BUILD);
 
@@ -105,6 +112,8 @@ public class BuildCommand extends CLICommand {
             a = new ParametersAction(values);
         }
 
+        retryCnt = Integer.parseInt(retryCntStr);
+
         if (checkSCM) {
             if (job.poll(new StreamTaskListener(stdout, getClientCharset())).change == Change.NONE) {
                 return 0;
@@ -119,7 +128,24 @@ public class BuildCommand extends CLICommand {
 
             if (sync) {
                 if (consoleOutput) {
-                    b.writeWholeLogTo(stdout);
+                    // read output in a retry loop, by default try only once
+                    // writeWholeLogTo may fail with FileNotFound
+                    // exception on a slow/busy machine, if it takes
+                    // longish to create the log file
+                    int retryInterval = 100;
+                    for (int i=0;i<=retryCnt;) {
+                        try {
+                            b.writeWholeLogTo(stdout);
+                            break;
+                        }
+                        catch (FileNotFoundException e) {
+                            if ( i == retryCnt ) {
+                                throw e;
+                            }
+                            i++;
+                            Thread.sleep(retryInterval);
+                        }
+                    }
                 }
                 // TODO: should we abort the build if the CLI is cancelled?
                 f.get();    // wait for the completion