Support for build args with space

plugin/src/it/basic-with-build-args/Dockerfile

@@ -2,5 +2,9 @@ FROM hello-world
 MAINTAINER David Flemström <dflemstr@spotify.com>
 
 ARG IMAGE_VERSION
+ARG ARG_WITH_SPACE
+ARG ARG_WITH_PLUS
 
 LABEL version=${IMAGE_VERSION}
+LABEL arg_with_space=${ARG_WITH_SPACE}
+LABEL arg_with_plus=${ARG_WITH_PLUS}

plugin/src/it/basic-with-build-args/pom.xml

@@ -50,6 +50,8 @@
         <configuration>
           <buildArgs>
             <IMAGE_VERSION>0.0.1</IMAGE_VERSION>
+            <ARG_WITH_SPACE>arg with space</ARG_WITH_SPACE>
+            <ARG_WITH_PLUS>arg+with+plus</ARG_WITH_PLUS>
           </buildArgs>
         </configuration>
       </plugin>

plugin/src/it/basic-with-build-args/verify.groovy

@@ -26,3 +26,5 @@ DefaultDockerClient dockerClient = DefaultDockerClient.fromEnv().build()
 imageInfo = dockerClient.inspectImage(imageId)
 
 assert imageInfo.config().labels().get("version") == "0.0.1"
+assert imageInfo.config().labels().get("arg_with_space") == "arg with space"
+assert imageInfo.config().labels().get("arg_with_plus") == "arg+with+plus"

plugin/src/main/java/com/spotify/plugin/dockerfile/BuildMojo.java

@@ -29,6 +29,7 @@
 import java.io.IOException;
 import java.io.UnsupportedEncodingException;
 import java.net.URLEncoder;
+import java.nio.charset.StandardCharsets;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.text.MessageFormat;
@@ -290,7 +291,9 @@ private static void requireValidDockerFilePath(@Nonnull Log log,
 
   private static String encodeBuildParam(Object buildParam) throws MojoExecutionException {
     try {
-      return URLEncoder.encode(new Gson().toJson(buildParam), "utf-8");
+      return URLEncoder.encode(
+               new Gson().toJson(buildParam), StandardCharsets.UTF_8.toString()
+             ).replace('+', ' ');
     } catch (UnsupportedEncodingException e) {
       throw new MojoExecutionException("Could not build image", e);
     }