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_op_SendMessages.go
    path of file: ./repos/aws-sdk-go-v2/service/pinpoint
    
    the code of the file until where you have to start completion: // Code generated by smithy-go-codegen DO NOT EDIT.

package pinpoint

import (
	"context"
	"fmt"
	awsmiddleware "github.com/aws/aws-sdk-go-v2/aws/middleware"
	"github.com/aws/aws-sdk-go-v2/service/pinpoint/types"
	"github.com/aws/smithy-go/middleware"
	smithyhttp "github.com/aws/smithy-go/transport/http"
)

// Creates and sends a direct message.
func (c *Client) SendMessages(ctx context.Context, params *SendMessagesInput, optFns ...func(*Options)) (*SendMessagesOutput, error) {
	if params == nil {
		params = &SendMessagesInput{}
	}

	result, metadata, err := c.invokeOperation(ctx, "SendMessages", params, optFns, c.addOperationSendMessagesMiddlewares)
	if err != nil {
		return nil, err
	}

	out := result.(*SendMessagesOutput)
	out.ResultMetadata = metadata
	return out, nil
}

type SendMessagesInput struct {

	// The unique identifier for the application. This identifier is displayed as the
	// Project ID on the Amazon Pinpoint console.
	//
	// This member is required.
	ApplicationId *string

	// Specifies the configuration and other settings for a message.
	//
	// This member is required.
	MessageRequest *types.MessageRequest

	noSmithyDocumentSerde
}

type SendMessagesOutput struct {

	// Provides information about the results of a request to send a message to an
	// endpoint address.
	//
	// This member is required.
	MessageResponse *types.MessageResponse

	// Metadata pertaining to the operation's result.
	ResultMetad
    
func (c *Client) addOperationSendMessagesMiddlewares(stack *middleware.Stack, options Options) (err error) {
	if err := stack.Serialize.Add(&setOperationInputMiddleware{}, middleware.After); err != nil {
		return err
	}
	err = stack.Serialize.Add(&awsRestjson1_serializeOpSendMessages{}, middleware.After)
	if err != nil {
		return err
	}
	err = stack.Deserialize.Add(&awsRestjson1_deserializeOpSendMessages{}, middleware.After)
	if err != nil {
		return err
	}
	if err := addProtocolFinalizerMiddlewares(stack, options, "SendMessages"); err != nil {
		return fmt.Errorf("add protocol finalizers: %v", err)
	}

	if err = addlegacyEndpointContextSetter(stack, options); err != nil {
		return err
	}
	if err = addSetLoggerMiddleware(stack, options); err != nil {
		return err
	}
	if err = addClientRequestID(stack); err != nil {
		return err
	}
	if err = addComputeContentLength(stack); err != nil {
		return err
	}
	if err = addResolveEndpointMiddleware(stack, options); err != nil {
		return err
	}
	if err = addComputePayloadSHA256(stack); err != nil {
		return err
	}
	if err = addRetry(stack, options); err != nil {
		return err
	}
	if err = addRawResponseToMetadata(stack); err != nil {
		return err
	}
	if err = addRecordResponseTiming(stack); err != nil {
		return err
	}
	if err = addClientUserAgent(stack, options); err != nil {
		return err
	}
	if err = smithyhttp.AddErrorCloseResponseBodyMiddleware(stack); err != nil {
		return err
	}
	if err = smithyhttp.AddCloseResponseBodyMiddleware(stack); err != nil {
		return err
	}
	if err = addSetLegacyContextSigningOptionsMiddleware(stack); err != nil {
		return err
	}
	if err = addOpSendMessagesValidationMiddleware(stack); err != nil {
		return err
	}
	if err = stack.Initialize.Add(newServiceMetadataMiddleware_opSendMessages(options.Region), middleware.Before); err != nil {
		return err
	}
	if err = addRecursionDetection(stack); err != nil {
		return err
	}
	if err = addRequestIDRetrieverMiddleware(stack); err != nil {
		return err
	}
	if err = addResponseErrorMiddleware(stack); err != nil {
		return err
	}
	if err = addRequestResponseLogging(stack, options); err != nil {
		return err
	}
	if err = addDisableHTTPSMiddleware(stack, options); err != nil {
		return err
	}
	return nil
}