Fix support for getting single files from GitHub

This currently fails for GitHub (and possibly other Git repositories)
because there is an assumption in the "client.go" file that the "subDir"
segment is always a directory.

However, for this URL:

https://github.com/owner/repo/subdir/file.txt

The "subDir" variable would actually be a file ("subdir/file.txt") and
hence the client should use "copyFile" rather than "copyDir" when
copying the "subDir" to the final destination.

This change fixes that to check whether the "subDir" variable is a file
or a directory, and appropriately uses "copyDir" or "copyFile". It also
returns the single file in the "GetResult" object, if indeed a single
file was requested.

Tests attached.

client.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"io/ioutil"
 	"os"
 	"path/filepath"
@@ -317,11 +318,43 @@ func (c *Client) get(ctx context.Context, req *Request, g Getter) (*GetResult, *
 			return nil, &getError{true, err}
 		}
 
-		err = copyDir(ctx, req.realDst, subDir, false, req.DisableSymlinks, req.umask())
-		if err != nil {
-			return nil, &getError{false, err}
+		if stat, err := os.Stat(subDir); err != nil {
+			return nil, &getError{false, fmt.Errorf("failed to stat '%s': %w", subDir, err)}
+		} else if stat.IsDir() {
+			err = copyDir(ctx, req.realDst, subDir, false, req.DisableSymlinks, req.umask())
+			if err != nil {
+				return nil, &getError{false, err}
+			}
+			return &GetResult{req.realDst}, nil
+		} else {
+			src, err := os.Open(subDir)
+			if err != nil {
+				return nil, &getError{false, fmt.Errorf("failed to open local source file at '%s': %w", subDir, err)}
+			}
+			//goland:noinspection GoUnhandledErrorResult
+			defer src.Close()
+
+			target := filepath.Join(req.realDst, filepath.Base(subDir))
+			dst, err := os.Create(target)
+			if err != nil {
+				return nil, &getError{false, fmt.Errorf("failed to open local target file at '%s': %w", target, err)}
+			}
+			//goland:noinspection GoUnhandledErrorResult
+			defer dst.Close()
+
+			buf := make([]byte, 1024*20) // 20k buffer should usually suffice for 99% of files
+			for {
+				n, err := src.Read(buf)
+				if err != nil && err != io.EOF {
+					return nil, &getError{false, fmt.Errorf("failed to read local source file at '%s': %w", subDir, err)}
+				} else if n == 0 {
+					break
+				} else if _, err := dst.Write(buf[:n]); err != nil {
+					return nil, &getError{false, fmt.Errorf("failed to write to local source file at '%s': %w", target, err)}
+				}
+			}
+			return &GetResult{target}, nil
 		}
-		return &GetResult{req.realDst}, nil
 	}
 
 	return &GetResult{req.Dst}, nil

get_github_test.go

@@ -0,0 +1,76 @@
+package getter
+
+import (
+	"context"
+	testing_helper "github.com/hashicorp/go-getter/v2/helper/testing"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+const basicMainTFExpectedContents = `# Hello
+
+module "foo" {
+    source = "./foo"
+}
+`
+
+func TestGitGetter_githubDirWithModeAny(t *testing.T) {
+	if !testHasGit {
+		t.Skip("git not found, skipping")
+	}
+
+	ctx := context.Background()
+	dst := testing_helper.TempDir(t)
+	defer os.RemoveAll(dst)
+
+	req := &Request{
+		Src:     "git::https://github.com/arikkfir/go-getter.git//testdata/basic?ref=v2",
+		Dst:     dst,
+		GetMode: ModeAny,
+		Copy:    true,
+	}
+	client := Client{}
+	result, err := client.Get(ctx, req)
+	if err != nil {
+		t.Fatalf("Failed fetching GitHub directory: %s", err)
+	} else if stat, err := os.Stat(result.Dst); err != nil {
+		t.Fatalf("Failed stat dst at '%s': %s", result.Dst, err)
+	} else if !stat.IsDir() {
+		t.Fatalf("Expected '%s' to be a directory", result.Dst)
+	} else if entries, err := os.ReadDir(result.Dst); err != nil {
+		t.Fatalf("Failed listing directory '%s': %s", result.Dst, err)
+	} else if len(entries) != 3 {
+		t.Fatalf("Expected dir '%s' to contain 3 items: %s", result.Dst, err)
+	} else {
+		testing_helper.AssertContents(t, filepath.Join(result.Dst, "main.tf"), basicMainTFExpectedContents)
+	}
+}
+
+func TestGitGetter_githubFileWithModeAny(t *testing.T) {
+	if !testHasGit {
+		t.Skip("git not found, skipping")
+	}
+
+	ctx := context.Background()
+	dst := testing_helper.TempDir(t)
+	defer os.RemoveAll(dst)
+
+	req := &Request{
+		Src:     "git::https://github.com/arikkfir/go-getter.git//testdata/basic/main.tf?ref=v2",
+		Dst:     dst,
+		GetMode: ModeAny,
+		Copy:    true,
+	}
+	client := Client{}
+	result, err := client.Get(ctx, req)
+	if err != nil {
+		t.Fatalf("Failed fetching GitHub file: %s", err)
+	} else if stat, err := os.Stat(result.Dst); err != nil {
+		t.Fatalf("Failed stat dst at '%s': %s", result.Dst, err)
+	} else if stat.IsDir() {
+		t.Fatalf("Expected '%s' to be a file", result.Dst)
+	} else {
+		testing_helper.AssertContents(t, result.Dst, basicMainTFExpectedContents)
+	}
+}