MultipartContent class uses the same simple string as the default boundary

[fazunenko]

com.google.api.client.http.MultipartContent class by default uses constant '__END_OF_PART__' string as the boundary (part delimiter).
It will cause problem if the data to be transfered includes this string. Such problems could be really hard to investigate.
Example of such problem:
googleapis/google-cloud-java#6386

The class also provides setBoundary(String) method to alter the default boundary, but this method is not accessible from the other project.

[fazunenko]

Suggested fix: use a random UUID string as boundary. It will be next to impossible get bump into such value.

public MultipartContent() {
   super(new HttpMediaType("multipart/related").setParameter("boundary", "__END_OF_PART__"));
}

=>

public MultipartContent() {
    this("____" + java.util.UUID.randomUUID().toString() + "___");
 }
 
public MultipartContent(String boundary) {
    super(new HttpMediaType("multipart/related").setParameter("boundary", boundary));
}

[chanseokoh]

Wouldn't it be more efficient to fix and use a constant (static final String, some random UUID) instead of creating a new UUID everytime the instance is created? (I'm genuinely asking.)

[fazunenko]

I think, generating UUID each time when an instance of MultipartContent is created is a very little overhead.
Having any static string value publicly available will significantly increase the likelihood of being included into someone content. (At least it's possible). With a random value it's very unlikely to repeat that value.