Add SSE events to API v2

[mxsrc]

Detail/list endpoints gain a parameter to toggle streaming. With this set, SSE is used to return the initial representation once and watch the database for future changes. The query parameter watch can be used to indicate this behavior. Watches are centrally managed, with database responses being cached. Upon a change in the database, the modified entity is returned, along with an indication of the event-type (creation, update, deletion).

An example of how this will look in practice:

[simplyblock@simplyblock-webappapi-66877b785-hv499 app]$ curl -sN $TLS -H "$AUTH" https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-pools/649d1860-40ff-47a3-8ed2-593b3f3fa594/volumes/
[{"id":"7d56579b-8cf8-4d47-9dc5-5ba402860a9c","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"3bf373a9-0939-4fe1-94ad-5cb7f6daf422","name":"pvc-f1422b61-0171-4fe9-a650-619c925eebe0","status":"online","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:7d56579b-8cf8-4d47-9dc5-5ba402860a9c","hostname":"vm12_4420","priority_class":0,"namespace":"","fabric":"tcp","nodes":["https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/3bf373a9-0939-4fe1-94ad-5cb7f6daf422/","https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/6968a2a2-d94b-40cb-a51f-139d151354cc/"],"port":4426,"size":10737418240,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"simplyblock/pvc","snapshot_name":"","blobid":4294967297,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":1,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true},{"id":"fe71b591-6aff-45d6-a2fe-10733e48569e","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"3bf373a9-0939-4fe1-94ad-5cb7f6daf422","name":"restored","status":"online","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:fe71b591-6aff-45d6-a2fe-10733e48569e","hostname":"vm12_4420","priority_class":0,"namespace":"","fabric":"tcp","nodes":["https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/3bf373a9-0939-4fe1-94ad-5cb7f6daf422/","https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/6968a2a2-d94b-40cb-a51f-139d151354cc/"],"port":4426,"size":10737418240,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"","snapshot_name":"","blobid":4294967307,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":1,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true}][simplyblock@simplyblock-webappapi-66877b785-hv499 app]$ curl -sN $TLS -H "$AUTH" https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-pools/649d1860-40ff-47a3-8ed2-593b3f3fa594/volumes/?watch=true
event: snapshot
data: [{"id":"7d56579b-8cf8-4d47-9dc5-5ba402860a9c","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"3bf373a9-0939-4fe1-94ad-5cb7f6daf422","name":"pvc-f1422b61-0171-4fe9-a650-619c925eebe0","status":"online","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:7d56579b-8cf8-4d47-9dc5-5ba402860a9c","hostname":"vm12_4420","priority_class":0,"namespace":"","fabric":"tcp","nodes":["https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/3bf373a9-0939-4fe1-94ad-5cb7f6daf422/","https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/6968a2a2-d94b-40cb-a51f-139d151354cc/"],"port":4426,"size":10737418240,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"simplyblock/pvc","snapshot_name":"","blobid":4294967297,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":1,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true},{"id":"fe71b591-6aff-45d6-a2fe-10733e48569e","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"3bf373a9-0939-4fe1-94ad-5cb7f6daf422","name":"restored","status":"online","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:fe71b591-6aff-45d6-a2fe-10733e48569e","hostname":"vm12_4420","priority_class":0,"namespace":"","fabric":"tcp","nodes":["https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/3bf373a9-0939-4fe1-94ad-5cb7f6daf422/","https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/6968a2a2-d94b-40cb-a51f-139d151354cc/"],"port":4426,"size":10737418240,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"","snapshot_name":"","blobid":4294967307,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":1,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true}]
retry: 3000

: ping - 2026-07-02 14:31:30.991114+00:00

: ping - 2026-07-02 14:31:45.994443+00:00

: ping - 2026-07-02 14:32:01.024133+00:00

event: created
data: {"id":"c0976ee5-1d1c-4c1a-8411-df92273d8d11","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"89c7c61a-43cb-41f2-b1a7-d0f816c4c925","name":"testlvol","status":"in_creation","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:c0976ee5-1d1c-4c1a-8411-df92273d8d11","hostname":"vm14_4424","priority_class":0,"namespace":"","fabric":"tcp","nodes":[],"port":4430,"size":1000000000,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"","snapshot_name":"","blobid":0,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":32,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true}

event: updated
data: {"id":"c0976ee5-1d1c-4c1a-8411-df92273d8d11","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"89c7c61a-43cb-41f2-b1a7-d0f816c4c925","name":"testlvol","status":"online","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:c0976ee5-1d1c-4c1a-8411-df92273d8d11","hostname":"vm14_4424","priority_class":0,"namespace":"","fabric":"tcp","nodes":["https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/89c7c61a-43cb-41f2-b1a7-d0f816c4c925/","https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/3bf373a9-0939-4fe1-94ad-5cb7f6daf422/"],"port":4430,"size":1000000000,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"","snapshot_name":"","blobid":4294967297,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":32,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true}

: ping - 2026-07-02 14:32:16.025170+00:00

event: updated
data: {"id":"c0976ee5-1d1c-4c1a-8411-df92273d8d11","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"89c7c61a-43cb-41f2-b1a7-d0f816c4c925","name":"testlvol","status":"in_deletion","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:c0976ee5-1d1c-4c1a-8411-df92273d8d11","hostname":"vm14_4424","priority_class":0,"namespace":"","fabric":"tcp","nodes":["https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/89c7c61a-43cb-41f2-b1a7-d0f816c4c925/","https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/3bf373a9-0939-4fe1-94ad-5cb7f6daf422/"],"port":4430,"size":1000000000,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"","snapshot_name":"","blobid":4294967297,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":32,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true}

: ping - 2026-07-02 14:32:31.028750+00:00

: ping - 2026-07-02 14:32:46.030096+00:00

event: deleted
data: {"id":"c0976ee5-1d1c-4c1a-8411-df92273d8d11","cluster_id":"b18ba793-0fe4-4ae2-8869-190f5be5c11b","storage_node_id":"89c7c61a-43cb-41f2-b1a7-d0f816c4c925","name":"testlvol","status":"in_deletion","health_check":true,"io_error":false,"migrating":false,"nqn":"nqn.2023-02.io.simplyblock:b18ba793-0fe4-4ae2-8869-190f5be5c11b:lvol:c0976ee5-1d1c-4c1a-8411-df92273d8d11","hostname":"vm14_4424","priority_class":0,"namespace":"","fabric":"tcp","nodes":["https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/89c7c61a-43cb-41f2-b1a7-d0f816c4c925/","https://127.0.0.1:5000/api/v2/clusters/b18ba793-0fe4-4ae2-8869-190f5be5c11b/storage-nodes/3bf373a9-0939-4fe1-94ad-5cb7f6daf422/"],"port":4430,"size":1000000000,"ndcs":1,"npcs":1,"pool_uuid":"649d1860-40ff-47a3-8ed2-593b3f3fa594","pool_name":"pool","pvc_name":"","snapshot_name":"","blobid":4294967297,"ns_id":1,"cloned_from":null,"high_availability":true,"do_replicate":false,"max_namespace_per_subsys":32,"max_rw_iops":0,"max_rw_mbytes":0,"max_r_mbytes":0,"max_w_mbytes":0,"allowed_hosts":[],"policy":"","capacity":{"date":0,"size_total":0,"size_prov":0,"size_used":0,"size_free":0,"size_util":0},"rep_info":null,"from_source":true}