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Also currently the pubsub emulator doesn't match up with the real API 100% either (e.g. Using gcloud to send topics create request to the emulator fails) which is a more concrete reason to block this.

Thanks for the helpful detail and reasonable explanation for blocking this PUBSUB_EMULATOR_HOST env var feature request—makes sense.

As I mentioned earlier, the pubsub emulator doesn't match up with the actual pubsub service. One thing is that create requests don't work through gcloud when using the emulator. To get around this, either:

1. [...]
2. curl -H "Content-Type: application/json" -X PUT -d '{}' http://localhost:8085/v1/projects/my-project/topics/my-topic

I can't get your curl example working and I have a hunch it's because my message schema is wrong. I tried a couple things:

1. Create message schema based on https://cloud.google.com/pubsub/docs/reference/rest/v1/projects.topics/publish reference—doesn't work.

   % curl --header 'Content-Type: application/json' --request PUT  --data '{"messag
   es":[{"data":"hello world"}]}' http://localhost:8085/v1/projects/myproject/topic
   s/mytopic
   {"error":{"code":400,"message":"Payload isn't valid for request.","status":"INVALID_ARGUMENT"}}
   

2. Another try: Encode data field based on https://cloud.google.com/pubsub/docs/reference/rest/v1/PubsubMessage#:~:text=A%20base64%2Dencoded%20string. example—also doesn't work.

   % echo hello world | base64
   aGVsbG8gd29ybGQK
   
   % curl --header 'Content-Type: application/json' --request PUT  --data '{"messag
   es":[{"data":"aGVsbG8gd29ybGQK"}]}' http://localhost:8085/v1/projects/myproject/
   topics/mytopic
   {"error":{"code":400,"message":"Payload isn't valid for request.","status":"INVALID_ARGUMENT"}}
   

Notice that the payload isn't valid for both requests.

Please expand your curl example to include a sample message, thank you!

Aside: For reference, this is my local Pub/Sub emulator setup:

1. Run Pub/Sub emulator in Docker container.

   docker run --rm --name=pubsub --interactive --tty --publish=8085:8085 us.gcr.io/google.com/cloudsdktool/google-cloud-cli gcloud beta emulators pubsub start --host-port=0.0.0.0:8085 --project=myproject
   

2. Create topic and subscription and wait for messages.

   git clone git@github.com:googleapis/python-pubsub.git
   cd python-pubsub/samples/snippets
   python3 -m venv venv
   source venv/bin/activate
   pip install -r requirements.txt
   PUBSUB_EMULATOR_HOST=localhost:8085 python publisher.py myproject create mytopic
   PUBSUB_EMULATOR_HOST=localhost:8085 python subscriber.py myproject create mytopic mysubscription
   PUBSUB_EMULATOR_HOST=localhost:8085 python publisher.py myproject publish mytopic
   PUBSUB_EMULATOR_HOST=localhost:8085 python subscriber.py myproject receive mysubscription # read earlier messages, then wait for more messages (TODO: Post a message with a curl request)
   

Responding to last commenter about the failure to be able to publish a message using the rest api (curl), after poking around a bit it seems like you two things wrong

1. The URL/path should have ":publish" at the end like this: http://localhost:8085/v1/projects/myproject/topics/mytopic:publish
2. The HTTP method should be POST instead of PUT

curl --header 'Content-Type: application/json' --request POST  --data '{"messages":[{"data":"aGVsbG8gd29ybGQK"}]}' http://localhost:8085/v1/projects/my-project/topics/my-topic:publish
{
  "messageIds": ["6"]
}

The rest api docs are thorough but some things don't seem to be obvious.

Responding to the google employee that suggested using the gcloud config set api_endpoint_overrides/pubsub http://localhost:8085/ command, I'm still not able to get that to work for me in 2025. When I run gcloud pubsub topics list after doing so I get no topics listed, even when I can see there are topics using curl --header 'Content-Type: application/json' --request GET --data '{}' http://localhost:8085/v1/projects/my-project/topics. I also saw some documentation about a CLOUDSDK_API_ENDPOINT_OVERRIDES_PUBSUB env var, which is likely the same functionality, but I also can't get that to work with the emulator. Every time I try to get the list of topics I get nothing.

Bummer because it would be convenient if even some of the gcloud CLI functionality worked with the pubsub emulator since the docs push using the gcloud CLI so hard. I'm very thankful you pointed out the underlying REST api usage in your comment though, so thanks. Double bummer the docs don't even give a whiff of the underlying REST api, not even on the page that documents that emulator.

Last thing, should this ticket be closed?