fix: update HttpRequest#getVersion to use stable logic (#919)

The original implementation of `getVersion` used the implementation
version of the package of the declaring class, however there is
differing behavior between Android and openjdk based jvms.

In order to be consistent across platforms we will now always resolve
the value from the `google-http-client.properties` file that is
generated during the build. This method should be stable as it based
on loading a classpath resource which has cross jvm support.

Fixes #892

google-http-client/src/main/java/com/google/api/client/http/HttpRequest.java

@@ -1224,19 +1224,17 @@ private static void addSpanAttribute(Span span, String key, String value) {
   }
 
   private static String getVersion() {
-    String version = HttpRequest.class.getPackage().getImplementationVersion();
-    // in a non-packaged environment (local), there's no implementation version to read
-    if (version == null) {
-      // fall back to reading from a properties file - note this value is expected to be cached
-      try (InputStream inputStream = HttpRequest.class.getResourceAsStream("/google-http-client.properties")) {
-        if (inputStream != null) {
-          Properties properties = new Properties();
-          properties.load(inputStream);
-          version = properties.getProperty("google-http-client.version");
-        }
-      } catch (IOException e) {
-        // ignore
+    // attempt to read the library's version from a properties file generated during the build
+    // this value should be read and cached for later use
+    String version = "unknown-version";
+    try (InputStream inputStream = HttpRequest.class.getResourceAsStream("/google-http-client.properties")) {
+      if (inputStream != null) {
+        final Properties properties = new Properties();
+        properties.load(inputStream);
+        version = properties.getProperty("google-http-client.version");
       }
+    } catch (IOException e) {
+      // ignore
     }
     return version;
   }

google-http-client/src/test/java/com/google/api/client/http/HttpRequestTest.java

@@ -31,10 +31,6 @@
 import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.Lists;
-
-import java.util.regex.Pattern;
-import junit.framework.TestCase;
-
 import java.io.ByteArrayInputStream;
 import java.io.IOException;
 import java.util.Arrays;
@@ -45,7 +41,8 @@
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.logging.Level;
-
+import java.util.regex.Pattern;
+import junit.framework.TestCase;
 import org.junit.Assert;
 
 /**
@@ -1267,4 +1264,14 @@ public void testExecute_curlLoggerWithContentEncoding() throws Exception {
     }
     assertTrue(found);
   }
+
+  public void testVersion_matchesAcceptablePatterns() throws Exception {
+    String acceptableVersionPattern =
+        "unknown-version|(?:\\d+\\.\\d+\\.\\d+(?:-.*?)?(?:-SNAPSHOT)?)";
+    String version = HttpRequest.VERSION;
+    assertTrue(
+        String.format("the loaded version '%s' did not match the acceptable pattern", version),
+        version.matches(acceptableVersionPattern)
+    );
+  }
 }