Snapcraft 7.1.1 gives vague error when it can't process package

[Koen Vervloesem]

Snapcraft 7.1.1 gives me a vague error about "Service unavailable. Please try again later" when uploading a snap package. I first thought the Snapcraft Store was down, as the message suggested it had something to do with the service, but I have been getting this error now for more than three days, and I just tried to upload a previous version of the package and this worked.

Command used:

```
snapcraft upload --release=latest/candidate theengs-gateway_0.4.0_amd64.snap
Issues while processing snap:g
- Service unavailable. Please try again later (d510601fa56b4b2cbc13e60d768e2eca).
Full execution log: '/home/koan/.cache/snapcraft/log/snapcraft-20220808-104616.994183.log'
```

Full execution log:

```
2022-08-08 10:46:16.994 Starting Snapcraft 7.1.1
2022-08-08 10:46:17.078 Retrieving credentials for 'snapcraft' on 'dashboard.snapcraft.io' from keyring 'SecretService Keyring'.
2022-08-08 10:46:17.110 HTTP 'POST' for 'https://dashboard.snapcraft.io/dev/api/snap-push/' with params None and headers {'Accept': 'application/json', 'Authorization': '<macaroon>', 'User-Agent': 'snapcraft/7.1.1 ubuntu/20.04 (x86_64)'}
2022-08-08 10:46:17.350 Uploading... (--->)
2022-08-08 10:46:17.351 Uploading... (<---)
2022-08-08 10:46:17.351 HTTP 'POST' for 'https://storage.snapcraftcontent.com/unscanned-upload/' with params None and headers {'Content-Type': 'multipart/form-data; boundary=61c11bd4790d4d61b455b2dc8e5a28e8', 'Accept': 'application/json', 'User-Agent': 'snapcraft/7.1.1 ubuntu/20.04 (x86_64)'}
2022-08-08 10:46:19.454 Uploading bytes for 'theengs-gateway_0.4.0_amd64.snap' ended, id 'f0e26408-392c-4e4f-830b-d1e24868a2a9'
2022-08-08 10:46:19.454 Retrieving credentials for 'snapcraft' on 'dashboard.snapcraft.io' from keyring 'SecretService Keyring'.
2022-08-08 10:46:19.514 HTTP 'POST' for 'https://dashboard.snapcraft.io/dev/api/snap-push/' with params None and headers {'Accept': 'application/json', 'Authorization': '<macaroon>', 'User-Agent': 'snapcraft/7.1.1 ubuntu/20.04 (x86_64)'}
2022-08-08 10:46:19.662 Retrieving credentials for 'snapcraft' on 'dashboard.snapcraft.io' from keyring 'SecretService Keyring'.
2022-08-08 10:46:19.719 HTTP 'GET' for 'https://dashboard.snapcraft.io/dev/api/snaps/WDvYyYNnf1p9CYuMa9uGYCXB6ZqH1EZp/builds/f0e26408-392c-4e4f-830b-d1e24868a2a9/status' with params None and headers {'Authorization': '<macaroon>', 'User-Agent': 'snapcraft/7.1.1 ubuntu/20.04 (x86_64)'}
2022-08-08 10:46:21.325 Status: processing
2022-08-08 10:46:22.326 Retrieving credentials for 'snapcraft' on 'dashboard.snapcraft.io' from keyring 'SecretService Keyring'.
2022-08-08 10:46:22.367 HTTP 'GET' for 'https://dashboard.snapcraft.io/dev/api/snaps/WDvYyYNnf1p9CYuMa9uGYCXB6ZqH1EZp/builds/f0e26408-392c-4e4f-830b-d1e24868a2a9/status' with params None and headers {'Authorization': '<macaroon>', 'User-Agent': 'snapcraft/7.1.1 ubuntu/20.04 (x86_64)'}
2022-08-08 10:46:23.563 Status: processing
2022-08-08 10:46:24.565 Retrieving credentials for 'snapcraft' on 'dashboard.snapcraft.io' from keyring 'SecretService Keyring'.
2022-08-08 10:46:24.591 HTTP 'GET' for 'https://dashboard.snapcraft.io/dev/api/snaps/WDvYyYNnf1p9CYuMa9uGYCXB6ZqH1EZp/builds/f0e26408-392c-4e4f-830b-d1e24868a2a9/status' with params None and headers {'Authorization': '<macaroon>', 'User-Agent': 'snapcraft/7.1.1 ubuntu/20.04 (x86_64)'}
2022-08-08 10:46:25.669 Status: error while processing
2022-08-08 10:46:25.670 Issues while processing snap:
- Service unavailable. Please try again later (d510601fa56b4b2cbc13e60d768e2eca).
2022-08-08 10:46:25.670 Full execution log: '/home/koan/.cache/snapcraft/log/snapcraft-20220808-104616.994183.log'
```

I see the message that the snap is being uploaded, but then the processing fails.

Snap-review says "pass" for both versions of the snap.

I'd like to know what causes this, so a more concrete error message why this fails would help me.

The snap is created from https://github.com/theengs/gateway-snap with `snapcraft --enable-manifest` (without `--enable-manifest` has the same behavior).

[Koen Vervloesem (koen-vervloesem)]

After a `snapcraft clean`, the build now is processed correctly by `snapcraft upload`. I'm still not sure what was wrong, but a more descriptive error message in this situation could be helpful.