sanitise tags from invalid characters

loggly-client/src/main/java/com/github/tony19/loggly/LogglyClient.java

@@ -80,7 +80,7 @@ public void setTags(String... tags) {
                      if (!first) {
                          builder.append(",");
                      }
-                     builder.append(t);
+                     builder.append(sanitizeTag(t));
                  }
                  first = false;
             }
@@ -212,4 +212,24 @@ private String joinStrings(Collection<String> messages) {
         }
         return b.toString();
     }
+
+    /**
+     * Sanitize the tag based on the restrictions described in
+     * <a href="https://www.loggly.com/docs/tags/">https://www.loggly.com/docs/tags/</a>.
+     * Sanitation works by replacing invalid characters with the _ (underscore) character.
+     *
+     * @param tag tag to be sanitized
+     * @return the tag without invalid characters
+     */
+    private String sanitizeTag(String tag) {
+        // replace invalid characters with _
+        String sanitized = tag.replaceAll("[^A-Za-z0-9_*,.\\-]", "_");
+
+        // don't allow non-alphanumeric values starting the tag
+        if (Character.isLetterOrDigit(tag.charAt(0))) {
+           return sanitized;
+        }
+
+        return sanitized.substring(1);
+    }
 }

loggly-client/src/test/java/com/github/tony19/loggly/LogglyClientTest.java

@@ -15,18 +15,19 @@
  */
 package com.github.tony19.loggly;
 
-import retrofit2.Call;
 import org.junit.Before;
 import org.junit.Rule;
-import org.junit.rules.ExpectedException;
 import org.junit.Test;
+import org.junit.rules.ExpectedException;
 import org.junit.runner.RunWith;
 import org.mockito.Mock;
 import org.mockito.Mockito;
 import org.mockito.runners.MockitoJUnitRunner;
 
-import static org.junit.Assert.assertThat;
+import retrofit2.Call;
+
 import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertThat;
 import static org.mockito.Matchers.anyString;
 import static org.mockito.Matchers.isNull;
 import static org.mockito.Mockito.mock;
@@ -138,4 +139,18 @@ public void emptyTagsResultInNoTags() {
         loggly.logBulk("event");
         Mockito.verify(restApi).logBulk(TOKEN, NO_TAGS, "event\n");
     }
+
+    @Test
+    public void invalidTagsResultInNoTags() {
+        loggly.setTags("", "  ", " ,", ",  ,  ,,  ");
+        loggly.logBulk("event");
+        Mockito.verify(restApi).logBulk(TOKEN, NO_TAGS, "event\n");
+    }
+
+    @Test
+    public void invalidTagsAreSentToLogglySanitized() {
+        loggly.setTags("_startInvalid", "middle@invalid.com", "%how_many$*3");
+        loggly.logBulk("event");
+        Mockito.verify(restApi).logBulk(TOKEN, "startInvalid,middle_invalid.com,how_many_*3", "event\n");
+    }
 }