add google.api.field_behavior optional/mandatory

[glimchb]

see https://linter.aip.dev/203/optional and https://google.aip.dev/203
example:

diff --git a/storage/v1alpha1/frontend_nvme_pcie.proto b/storage/v1alpha1/frontend_nvme_pcie.proto
index 610239e..303b684 100755
--- a/storage/v1alpha1/frontend_nvme_pcie.proto
+++ b/storage/v1alpha1/frontend_nvme_pcie.proto
@@ -15,8 +15,10 @@ import "object_key.proto";
 import "uuid.proto";
 import "google/protobuf/empty.proto";
 import "google/api/annotations.proto";
+import "google/api/field_behavior.proto";

 // Front End (host-facing) APIs. Mostly used for NVMe/PCIe emulation and host presentation.
+
 service FrontendNvmeService {
     rpc NVMeSubsystemCreate (NVMeSubsystemCreateRequest) returns (NVMeSubsystem) {
         option (google.api.http) = {
@@ -151,7 +153,7 @@ message NVMeController {

     // maximum number of host completion queues allowed.
     // If not set, the xPU will provide a default.
-    int32 max_ncq = 6;
+    int32 max_ncq = 6 [(google.api.field_behavior) = OPTIONAL];

     // maximum number of submission queue entries per submission queue, as a power of 2.
     // default value as per spec is 6
@@ -195,7 +197,7 @@ message NVMeNamespace {

     // 64bit Extended unique identifier for the namespace
     // mandatory if guid is not specified
-    int64 eui64 = 8;
+    int64 eui64 = 8 [(google.api.field_behavior) = OPTIONAL];

     // Globally unique identifier for the namespace
     common.v1.Uuid uuid = 9;
(END)

[jainvipin]

I am curious about the intent of this issue:

• is suggesting that we use google.api.field_behavior to specify optional fields or use protobuf optional parameter, which specifies the protobuf encoding
• Is it suggesting that we we start labeling optional(and therefore mandator to the unlabeled fields) to currently defined APIs?

[glimchb]

Yes, Suggesting that we start labeling optional (and therefore mandatory to the unlabeled fields) to currently defined APIs

[artek-koltun]

REQUIRED annotation is definitely useful. In conjunction with fieldbehavior.ValidateRequiredFields it can be a relative protection against nil pointer dereference in requests.

[glimchb]

frontend added by @artek-koltun #321

[glimchb]

done. all annotations are completed

• feat(storage): set annotations for middleend #344
• feat(storage): set annotations for backend #330
• Set annotations for evpn according to AIP #325
• Set annotations for evpn according to AIP #324
• Set annotations for storage frontend according to AIP #321
• Storage API changes with name and field_behavior #317