feat(go): add download file function (#1200)

* add download file function

* add test case

* Update pkg/piperutils/FileUtils.go

* correct test case

* remove FileUtils.Download

* add Downloader

* add Downloader

* fix error

* respect header and cookies

* add test case

* rename files

* correct test case

* remove SendRequest

* correct test case

pkg/http/downloader.go

@@ -0,0 +1,41 @@
+package http
+
+import (
+	"io"
+	"net/http"
+	"os"
+
+	"github.com/pkg/errors"
+)
+
+//Downloader ...
+type Downloader interface {
+	SetOptions(options ClientOptions)
+	DownloadFile(url, filename string, header http.Header, cookies []*http.Cookie) error
+}
+
+// DownloadFile downloads a file's content as GET request from the specified URL to the specified file
+func (c *Client) DownloadFile(url, filename string, header http.Header, cookies []*http.Cookie) error {
+	return c.DownloadRequest(http.MethodPost, url, filename, header, cookies)
+}
+
+// DownloadRequest ...
+func (c *Client) DownloadRequest(method, url, filename string, header http.Header, cookies []*http.Cookie) error {
+	response, err := c.SendRequest(method, url, nil, header, cookies)
+	if err != nil {
+		return errors.Wrapf(err, "HTTP %v request to %v failed with error", method, url)
+	}
+	defer response.Body.Close()
+
+	fileHandler, err := os.Create(filename)
+	if err != nil {
+		return errors.Wrapf(err, "unable to create file %v", filename)
+	}
+	defer fileHandler.Close()
+
+	_, err = io.Copy(fileHandler, response.Body)
+	if err != nil {
+		return errors.Wrapf(err, "unable to copy content from url to file %v", filename)
+	}
+	return err
+}

pkg/http/downloader_test.go

@@ -0,0 +1,43 @@
+package http
+
+import (
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/SAP/jenkins-library/pkg/log"
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDownloadRequest(t *testing.T) {
+	// Start a local HTTP server
+	server := httptest.NewServer(
+		http.HandlerFunc(
+			func(rw http.ResponseWriter, req *http.Request) { rw.Write([]byte("my fancy file content")) }))
+	// Close the server when test finishes
+	defer server.Close()
+
+	client := Client{
+		logger: log.Entry().WithField("package", "SAP/jenkins-library/pkg/http"),
+	}
+
+	workingDir, err := ioutil.TempDir("", "test detailed results")
+	if err != nil {
+		t.Fatal("Failed to create temporary directory")
+	}
+	// clean up tmp dir
+	defer os.RemoveAll(workingDir)
+	targetFile := filepath.Join(workingDir, "abc.xml")
+
+	// function under test
+	err = client.DownloadFile(server.URL, targetFile, nil, nil)
+	// asserts
+	assert.NoError(t, err, "Error occured but none expected")
+	assert.FileExists(t, targetFile, "File not found")
+	bytes, err := ioutil.ReadFile(targetFile)
+	assert.NoError(t, err, "Error occured but none expected")
+	assert.Equal(t, "my fancy file content", string(bytes))
+}

pkg/piperutils/fileUtils_test.go

@@ -11,9 +11,9 @@ import (
 func TestFileExists(t *testing.T) {
 	dir, err := ioutil.TempDir("", "dir")
 	if err != nil {
-		t.Fatal("Failed to create temporary workspace directory")
+		t.Fatal("Failed to create temporary workspace directory")
 	}
-	// clean up tmp dir
+	// clean up tmp dir
 	defer os.RemoveAll(dir)
 
 	result, err := FileExists(dir)
@@ -32,9 +32,9 @@ func TestCopy(t *testing.T) {
 	file := filepath.Join(dir, "testFile")
 	err = ioutil.WriteFile(file, []byte{byte(1), byte(2), byte(3)}, 0700)
 	if err != nil {
-		t.Fatal("Failed to create temporary workspace directory")
+		t.Fatal("Failed to create temporary workspace directory")
 	}
-	// clean up tmp dir
+	// clean up tmp dir
 	defer os.RemoveAll(dir)
 
 	result, err := Copy(file, filepath.Join(dir, "testFile2"))