Handwritten prototype of presign url client

[skotambkar]

Modifies existing RDS autofill custiomization to show case how we intend to expose pre-sign URL API Clients in the V2 SDK.

Only one operation CopyDBClusterSnapshot was changed (since the change is identical for other operations), we verified that the existing customization's middleware_test for the modified operation works. :)

There are few TODO's listed, that I would be glad to discuss about. Let me know your thoughts.

[jasdel]

Potentially should use a PresignOptions struct to collect options for configuring the presign client. These would include things like the *Client, and the Presigner types as parameters.

type PresignOptions struct {
     Options    func(*Options)
     Presigner HTTPPresigner
}

[jasdel]

For S3 operations that can use the Expires custom header for presign URL expiry, X-Amz-Expires.

presigner.PresignPutObject(ctx, input, func(o *rds.PresignOptions) {
     o.Presigner = v4.NewPresigner()
     o.OptionFns = append(o.OptionFns, func(o*Options){ o.Region = "us-west-2" })

     o.Expires = 20 * time.Minute // Only S3
})

Options for calling presign for an option

PresignPutObject(context.Context, *PutObjectInput, ...func(*PresignOption))

Could have helpers for presign option with expires that uses type alias of the value set to not have a allocation from a function.

func  WithPresignClientClientOptions(optFns ...func(*Options)) func(*PresignOptions) {
     return withPresignClientClientOptions(optFns).options
}
types withPresignClientClientOptions []func(*Options)
func (w withPresignClientClientOptions) option(o *PresignOptions) {
      o.ClientOptions = append(o.ClientOptions, w...)
}


func WithPresignExpires(dur time.Duration) func(*PresignOptions) {
      return withPresignExpires(dur).option
}
types withPresignExpires time.Duration
func (w withPresignExpires) option(o *PresignOptions) {
      o.Expires = time.Duration(w)
}

[jasdel]

If using the PresignOptions type with the constructor this would be adjust to take that value instead of API client's Options.

Taking PresignOption with optional client parameter.

client := rds.New(options)

// e.g. PresignClient creating it own API client with the options provided
presigner := rds.NewPresignClient(options,  func(o *rds.PresignOptions) {
     o.Presigner = v4.NewPresigner(/*signer options*/)
})

// Create presign client from API client with client options for region and presigner options
presigner := rds.NewPresignClientWithClient(client, func(o *rds.PresignOptions) {
     o.Presigner = v4.NewPresigner()
     o.OptionFns = append(o.OptionFns, func(o*Options){ o.Region = "us-west-2" })
})

// To use the presign client from a client with options, need to merge presign options together, before creating 
// copy of the client.
func NewPresignClientWithClient(client *Client, optFns ...func(*PresignOptions)) *PresignClient {
       var presignOptions PresignOptions
       for _, fn := range optFns {
            fn(&presignOptions)
       }

       client = client.copyAPIClient(presignOptions.OptionsFns....)
}

// If user calls NewPresignClientWithClient and provides functional options need to create
// a copy of the API client merging in the new options.
func (c *Client) copyAPIClient(optFns ...func(*Option)) *Client {
      return New(c.getAPIClientOptions(), optFns...)
}

// Create presign client from SDK configuration
presigner := rds.NewPresignClientFromConfig(cfg, func(o *rds.PresignOptions){
     o.Presigner = v4.NewPresigner()
})

// e.g. PresignClient given options, and optional presigner,
presigner := rds.NewPresignClient(options, func(o *rds.PresignOptions){
     o.Presigner = v4.NewPresigner()
})

[skotambkar]

Replaced by #888