Need descriptor for in memory proto schema

[Vikas Dahiya]

I have an in memory proto schema which I am reading from the schema registry. I am looking for a way or the best way if there are more than one, to get the descriptor for this schema. How can I do that? I am new to protobuf and pardon me if the provided information is not sufficient, but I can provide any required additional details.

Thanks

[Matthew Fowles Kulukundis]

Vikas~

What language are you using (C++, Java, Python, etc)?

Matt

On Fri, Aug 5, 2022 at 5:14 PM Vikas Dahiya <mailto...@gmail.com> wrote:

I have an in memory proto schema which I am reading from the schema registry. I am looking for a way or the best way if there are more than one, to get the descriptor for this schema. How can I do that? I am new to protobuf and pardon me if the provided information is not sufficient, but I can provide any required additional details.

Thanks

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[Vikas Dahiya]

Matt, I am using Java.

Thanks!

Vikas

[Matthew Fowles Kulukundis]

Vikas~

Do you have links to your code or snippets you can share?  Are you using kafka or AWS schema registry or something?

Matt

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[Vikas Dahiya]

Matt, I am using kafka, I don’t have a code snippet as I am just getting the schema from confulant schema registry and need a descriptor to create the object. I can share the schema snippet if that can help.

Vikas

[Matthew Fowles Kulukundis]

Vikas~

I don't really know the Kafka APIs, but it might be better to ask on one of their lists or maybe stack overflow.

Matt

[Vikas Dahiya]

Matt,

Kafka APIs really don't have to do anything here. Think of it as a problem: I got a schema from any random place (in this case it's a schema registry), and now I need to use this schema to create an Object to use in my system. I don't have generated java classes at my disposal. So I am looking to get the descriptor to create an Object out of this schema. Hope that helps to understand the problem. 

Thanks,

Vikas

[Matthew Fowles Kulukundis]

Vikas~

I suspect your best bet is:

```

Schema<?> s = ....

Object o = s.newInstance();

if (o instanceof MessageOrBuilder) {

    return ((MessageOrBuilder)o).getDescriptorForType();
}
return nullptr;

```

If you are using the JavaLite runtime, you may not have descriptor information available, so this can produce nullptr.

Matt

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[Vikas Dahiya]

Thanks, Matt!

The schema I have is in string format. Here is the snippet of the same

syntax = "proto3";
package com.company.qna.enriched;

import "imports/user/token_status.proto";
import "validate/validate.proto";
import "google/protobuf/timestamp.proto";

message QuestionViewEnriched {
  string event_id = 1 [(validate.rules).string.uuid = true];
  string source = 2 [(validate.rules).string.min_len = 3];
  string event_type = 3 [(validate.rules).string.prefix = "com.chegg"];
  .google.protobuf.Timestamp event_time = 4;
  string chegg_user_uuid = 21 [(validate.rules).string.uuid = true];
  string chegg_visitor_id = 22 [(validate.rules).string.uuid = true];
  string chegg_session_id = 23;
  string client_ip_address = 24 [(validate.rules).string.ip = true];
  string user_agent = 25 [(validate.rules).string.well_known_regex = HTTP_HEADER_VALUE];
  string language = 26 [(validate.rules).string.well_known_regex = HTTP_HEADER_VALUE];
  string experiments = 27;
  bool is_internal_user = 28;
  string device_class = 29;
  com.company.user.TokenStatus access_token_status = 30;
  com.company.user.TokenStatus id_token_status = 31;
  string url = 41;
  string referral_url = 42;

[Matthew Fowles Kulukundis]

Vikas~

You are asking how to dynamically compile a .proto message into a descriptor that you can load at runtime.  I don't have a good answer here short of launching `protoc` as a subprocess.

Matt

To view this discussion on the web visit https://groups.google.com/d/msgid/protobuf/43835e46-f786-4756-836a-ece5db30652dn%40googlegroups.com.

[Vikas Dahiya]

Ah, got it, Matt. That's what I was suspecting but wanted to avoid and see if there is any way around it. Thanks for patiently understanding and responding to my queries!

Thanks,

Vikas

[Robert Yokota]

Vikas,

If you are using Confluent Schema Registry, there is a way to do this by using the Confluent libraries, namely `ProtobufSchema.toDescriptor()`.  But it's best that you ask this question in the Confluent Community slack forum or at https://forum.confluent.io/.  

Robert

[Vikas Dahiya]

Thanks, Robert! I'll post it on their forum and see if they suggest something.

Thanks,

Vikas