You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: api_client.go
    path of file: ./repos/aws-sdk-go-v2/service/transfer
    
    the code of the file until where you have to start completion: // Code generated by smithy-go-codegen DO NOT EDIT.

package transfer

import (
	"context"
	"fmt"
	"github.com/aws/aws-sdk-go-v2/aws"
	"github.com/aws/aws-sdk-go-v2/aws/defaults"
	awsmiddleware "github.com/aws/aws-sdk-go-v2/aws/middleware"
	"github.com/aws/aws-sdk-go-v2/aws/retry"
	"github.com/aws/aws-sdk-go-v2/aws/signer/v4"
	awshttp "github.com/aws/aws-sdk-go-v2/aws/transport/http"
	internalauth "github.com/aws/aws-sdk-go-v2/internal/auth"
	internalauthsmithy "github.com/aws/aws-sdk-go-v2/internal/auth/smithy"
	internalConfig "github.com/aws/aws-sdk-go-v2/internal/configsources"
	smithy "github.com/aws/smithy-go"
	smithydocument "github.com/aws/smithy-go/document"
	"github.com/aws/smithy-go/logging"
	"github.com/aws/smithy-go/middleware"
	smithyhttp "github.com/aws/smithy-go/transport/http"
	"net"
	"net/http"
	"time"
)

const ServiceID = "Transfer"
const ServiceAPIVersion = "2018-11-05"

// Client provides the API client to make operations call for AWS Transfer Family.
type Client struct {
	op
    
func (c *Client) invokeOperation(ctx context.Context, opID string, params interface{}, optFns []func(*Options), stackFns ...func(*middleware.Stack, Options) error) (result interface{}, metadata middleware.Metadata, err error) {
	ctx = middleware.ClearStackValues(ctx)
	stack := middleware.NewStack(opID, smithyhttp.NewStackRequest)
	options := c.options.Copy()

	for _, fn := range optFns {
		fn(&options)
	}

	finalizeOperationRetryMaxAttempts(&options, *c)

	finalizeClientEndpointResolverOptions(&options)

	for _, fn := range stackFns {
		if err := fn(stack, options); err != nil {
			return nil, metadata, err
		}
	}

	for _, fn := range options.APIOptions {
		if err := fn(stack); err != nil {
			return nil, metadata, err
		}
	}

	handler := middleware.DecorateHandler(smithyhttp.NewClientHandler(options.HTTPClient), stack)
	result, metadata, err = handler.Handle(ctx, params)
	if err != nil {
		err = &smithy.OperationError{
			ServiceID:     ServiceID,
			OperationName: opID,
			Err:           err,
		}
	}
	return result, metadata, err
}