embed: Begin refactor to use clearer paths

internal/unpack/file.go

@@ -0,0 +1,76 @@
+package unpack
+
+import (
+	"io"
+	"io/fs"
+	"os"
+
+	"github.com/pkg/errors"
+)
+
+// InstallFile installs the file from src into dst.
+//
+// If the destination path does not exist, it is created.
+func InstallFile(dst string, src fs.File) error {
+	// stat it!
+	srcInfo, err := src.Stat()
+	if err != nil {
+		return err
+	}
+
+	// if this is a directory, something went wrong!
+	if srcInfo.IsDir() {
+		return errExpectedFileButGotDirectory
+	}
+
+	// and store it there!
+	return installFile(dst, srcInfo, src)
+}
+
+func installFile(dst string, srcInfo fs.FileInfo, src fs.File) error {
+	// create the file using the right mode!
+	file, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, srcInfo.Mode())
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	// copy over the content!
+	_, err = io.Copy(file, src)
+	return errors.Wrapf(err, "Error writing to destination %s", dst)
+}
+
+// InstallTemplate unpacks the resource located at src in fsys, then processes it as a template, and eventually writes it to dst.
+// Any existing file is truncated and overwritten.
+//
+// See [WriteTemplate] for possible errors.
+func InstallTemplate(dst string, context map[string]string, src string, fsys fs.FS) error {
+
+	// open the srcFile
+	srcFile, err := fsys.Open(src)
+	if err != nil {
+		return err
+	}
+	defer srcFile.Close()
+
+	// stat it
+	srcInfo, err := srcFile.Stat()
+	if err != nil {
+		return err
+	}
+
+	// check if it is a directory
+	if srcInfo.IsDir() {
+		return errExpectedFileButGotDirectory
+	}
+
+	// open the destination file
+	file, err := os.OpenFile(dst, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, srcInfo.Mode())
+	if err != nil {
+		return err
+	}
+	defer file.Close()
+
+	// write the file!
+	return WriteTemplate(file, context, srcFile)
+}