s3dl.go

// Uses the default AWS SDK Credentials;  e.g. via the environment
// AWS_REGION=region AWS_ACCESS_KEY_ID=key AWS_SECRET_ACCESS_KEY=secret
package main

import (
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"time"

	"github.com/aws/aws-sdk-go/aws"
	"github.com/aws/aws-sdk-go/aws/session"
	"github.com/aws/aws-sdk-go/service/s3"
)

func main() {

	var bucket string
	var key string
	var debug bool

	flag.StringVar(&bucket, "bucket", "", "s3 bucket")
	flag.StringVar(&key, "key", "", "s3 key (path)")
	flag.BoolVar(&debug, "debug", false, "show aws sdk debug output")

	flag.Parse()

	if len(bucket) == 0 || len(key) == 0 {
		flag.Usage()
		os.Exit(-1)
	}

	cfg := aws.NewConfig()
	if debug {
		log := log.New(os.Stderr, "", log.LstdFlags)
		cfg = cfg.WithLogger(
			aws.LoggerFunc(func(args ...interface{}) { log.Println(args) }),
		).WithLogLevel(aws.LogDebugWithSigning)
	}

	awsSession := session.New(cfg)

	fmt.Fprintf(os.Stderr, "attempting to download s3://%v/%v\n", bucket, key)

	start := time.Now()

	s3Svc := s3.New(awsSession)
	result, err := s3Svc.GetObject(&s3.GetObjectInput{
		Bucket: aws.String(bucket),
		Key:    aws.String(key),
	})

	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	n, err := io.Copy(os.Stdout, result.Body)
	result.Body.Close()

	if err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(2)
	}

	if n != aws.Int64Value(result.ContentLength) {
		fmt.Fprintf(os.Stderr, "bytes written (%v) != ContentLength (%v)\n", n, aws.Int64Value(result.ContentLength))
		os.Exit(3)
	}

	fmt.Fprintf(os.Stderr, "wrote %v bytes to stdout in %v\n", n, time.Now().Sub(start))

}