feat: optional --range argument for cp to download single part of object

README.md

@@ -80,9 +80,9 @@ You can also install `s5cmd` from [MacPorts](https://ports.macports.org/port/s5c
 > conda config --add channels conda-forge
 > conda config --set channel_priority strict
 > ```
-> 
+>
 > Once the `conda-forge` channel has been enabled, `s5cmd` can be installed with `conda`:
-> 
+>
 > ```
 > conda install s5cmd
 > ```
@@ -319,7 +319,7 @@ folder hierarchy.
 an [open ticket](https://github.com/peak/s5cmd/issues/29) to track the issue.
 
 #### Using Exclude and Include Filters
-`s5cmd` supports the `--exclude` and `--include` flags, which can be used to specify patterns for objects to be excluded or included in commands. 
+`s5cmd` supports the `--exclude` and `--include` flags, which can be used to specify patterns for objects to be excluded or included in commands.
 
 - The `--exclude` flag specifies objects that should be excluded from the operation. Any object that matches the pattern will be skipped.
 - The `--include` flag specifies objects that should be included in the operation. Only objects that match the pattern will be handled.
@@ -540,7 +540,7 @@ The environment variable `SHELL` must be accurate for the autocompletion to func
 The autocompletion is tested with following versions of the shells: \
 ***zsh*** 5.8.1 (x86_64-apple-darwin21.0) \
 GNU ***bash***, version 5.1.16(1)-release (x86_64-apple-darwin21.1.0) \
-***PowerShell*** 7.2.6 
+***PowerShell*** 7.2.6
 
 ### Google Cloud Storage support
 
@@ -687,6 +687,14 @@ s5cmd --numworkers 10 cp --concurrency 10 '/Users/foo/bar/*' s3://mybucket/foo/b
 
 If you have a few, large files to download, setting `--numworkers` to a very high value will not affect download speed. In this scenario setting `--concurrency` to a higher value may have a better impact on the download speed.
 
+### range
+
+`range` is a `cp` command option that targets only a specific byterange in the source object to download. This parameter is used by the AWS Go SDK (setting the [Range header](https://www.rfc-editor.org/rfc/rfc9110.html#name-range) in the GET request). Passing `range` option to `cp` will override any `--concurrency` or `--part_size` arguments (1 thread will be used to download this 1 part specified by the byterange).
+
+```
+s5cmd cp --range bytes=500-999 's3://mybucket/foo/bar/file.txt' partialFile.txt
+```
+
 ## Benchmarks
 Some benchmarks regarding the performance of `s5cmd` are introduced below. For more
 details refer to this [post](https://medium.com/@joshua_robinson/s5cmd-for-high-performance-object-storage-7071352cc09d)

command/cat.go

@@ -150,7 +150,7 @@ func (c Cat) processObjects(ctx context.Context, client *storage.S3, objectChan
 
 func (c Cat) processSingleObject(ctx context.Context, client *storage.S3, url *url.URL) error {
 	buf := orderedwriter.New(os.Stdout)
-	_, err := client.Get(ctx, url, buf, c.concurrency, c.partSize)
+	_, err := client.Get(ctx, url, buf, c.concurrency, c.partSize, nil)
 	return err
 }
 

command/cp.go

@@ -118,6 +118,9 @@ Examples:
 
 	24. Pass arbitrary metadata to the object during upload or copy
 		 > s5cmd {{.HelpName}} --metadata "camera=Nixon D750" --metadata "imageSize=6032x4032" flowers.png s3://bucket/prefix/flowers.png
+
+  25. Copy only a specific byte range out of an S3 object.
+     > s5cmd {{.HelpName}} --range bytes=500-999 s3://bucket/prefix/object .
 `
 
 func NewSharedFlags() []cli.Flag {
@@ -252,6 +255,10 @@ func NewCopyCommandFlags() []cli.Flag {
 			Name:  "version-id",
 			Usage: "use the specified version of an object",
 		},
+		&cli.StringFlag{
+			Name:  "range",
+			Usage: "defines range header for target object, e.g. --range bytes=0-100",
+		},
 		&cli.BoolFlag{
 			Name:    "show-progress",
 			Aliases: []string{"sp"},
@@ -320,6 +327,7 @@ type Copy struct {
 	contentType           string
 	contentEncoding       string
 	contentDisposition    string
+	contentRange          string
 	metadata              map[string]string
 	metadataDirective     string
 	showProgress          bool
@@ -398,6 +406,7 @@ func NewCopy(c *cli.Context, deleteSource bool) (*Copy, error) {
 		contentType:           c.String("content-type"),
 		contentEncoding:       c.String("content-encoding"),
 		contentDisposition:    c.String("content-disposition"),
+		contentRange:          c.String("range"),
 		metadata:              metadata,
 		metadataDirective:     c.String("metadata-directive"),
 		showProgress:          c.Bool("show-progress"),
@@ -665,7 +674,7 @@ func (c Copy) doDownload(ctx context.Context, srcurl *url.URL, dsturl *url.URL)
 	}
 
 	writer := newCountingReaderWriter(file, c.progressbar)
-	size, err := srcClient.Get(ctx, srcurl, writer, c.concurrency, c.partSize)
+	size, err := srcClient.Get(ctx, srcurl, writer, c.concurrency, c.partSize, &c.contentRange)
 	file.Close()
 
 	if err != nil {

storage/s3.go

@@ -600,13 +600,14 @@ func (s *S3) Presign(ctx context.Context, from *url.URL, expire time.Duration) (
 
 // Get is a multipart download operation which downloads S3 objects into any
 // destination that implements io.WriterAt interface.
-// Makes a single 'GetObject' call if 'concurrency' is 1 and ignores 'partSize'.
+// Makes a single 'GetObject' call if 'concurrency' is 1 or contentRange is not nil, ignoring 'partSize'.
 func (s *S3) Get(
 	ctx context.Context,
 	from *url.URL,
 	to io.WriterAt,
 	concurrency int,
 	partSize int64,
+	contentRange *string, // optional
 ) (int64, error) {
 	if s.dryRun {
 		return 0, nil
@@ -620,6 +621,9 @@ func (s *S3) Get(
 	if from.VersionID != "" {
 		input.VersionId = aws.String(from.VersionID)
 	}
+	if contentRange != nil {
+		input.Range = aws.String(*contentRange)
+	}
 
 	return s.downloader.DownloadWithContext(ctx, to, input, func(u *s3manager.Downloader) {
 		u.PartSize = partSize