The release of version 1.16 of the Go
programming language included a standard interface for read-only filesystems,
defined in Go's io/fs standard library package. With this change came some
other standard-library changes, including the fact that archive/zip now
provides a "filesystem" interface for zip files, or the ability of net/http
to serve files from any filesystem providing the io/fs interface. In
conjunction, this means utilities like the HTTP server can now directly serve
content from zip files, without the data needing to be extracted manually.
While that's already pretty cool, wouldn't it be nice if you could, for
example, transparently serve data from multiple zip files as if they were a
single directory? This library provides the means to do so: it implements the
io/fs.FS interface using two underlying filesystems. The underlying
filesystems can even include additional MergedFS instances, enabling
combining an arbitrary number of filesystems into a single io/fs.FS.
This repository provides a roughly similar function to laher/mergefs, but it offers one key distinction: correctly listing contents of merged directories present in both FS's. This adds quite a bit of complexity. However, laher/mergefs will be more performant for filesystems not requiring directory- listing capabilities.
Simply pass two io/fs.FS instances to merged_fs.NewMergedFS(...) to obtain
a new FS serving data from both. See the following example:
import (
"archive/zip"
"github.com/yalue/merged_fs"
"net/http"
)
func main() {
// ...
// Assume that zipFile1 and zipFile2 are two zip files that have been
// opened using os.Open(...).
zipFS1, _ := zip.NewReader(zipFile1, file1Size)
zipFS2, _ := zip.NewReader(zipFile2, file2Size)
// Serve files contained in either zip file.
mergedFS := NewMergedFS(zipFS1, zipFS2)
http.Handle("/", http.FileServer(http.FS(mergedFS)))
// ...
}Additional notes:
-
Both underlying FS's must support the
ReadDirFileinterface when opening directories. Without this, we have no way for determining the contents of merged directories. -
If a file with the same name is present in both
FSs given toNewMergedFS, then the file in the first of the two always overrides the file with the same name in the second FS. -
Following the prior point, if a directory in the second FS has the same name as a regular file in the first, neither the directory in the second FS nor any of its contents will be present in the merged FS (the regular file will take priority). For example, if FS
Acontains a regular file nameda/b, and FSBcontains a regular filecat the patha/b/c(in whicha/bis a directory), thena/b/cwill not be available in the FS returned byNewMergedFS(A, B), because the directorybis overridden by the regular filebin the first FS.
If you want to merge more than two filesystems, you can use the MergeMultiple
function, which takes an arbitrary number of filesystem arguments:
merged := merged_fs.MergeMultiple(fs_1, fs_2, fs_3, fs_4)The earlier arguments to MergeMultiple will have higher priority over the
later filesystems, in the same way that the first argument to NewMergedFS has
priority over the second. For now, the MergeMultiple function just provides
a convenient wrapper for building a tree of MergedFS instances.
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