rename to mergefs

Author: Am Laher

Makefile

@@ -0,0 +1,10 @@
+
+.DEFAULT_GOAL := help
+
+.PHONY: test
+test: ## run tests (using go1.16beta1 for now)
+	go1.16beta1 test -v -race .
+
+.PHONY: help
+help:
+	@grep -E '^[a-zA-Z_-]+:.*?## .*$$' $(MAKEFILE_LIST) | sort | awk 'BEGIN {FS = ":.*?## "}; {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}'

README.md

@@ -1,7 +1,7 @@
-# Chainfs
+# Mergefs
 
-A go package which chains together filesystems so that you can combine fs.FS filesystems.
+A tiny go package which combines together fs.FS filesystems.
 
-`chainfs.FS` keeps looking through a slice of `fs.FS` filesytems in order to find a given file. It returns the first match.
+`mergefs.FS` looks through a slice of `fs.FS` filesytems in order to find a given file. It returns the first match, or `os.ErrNotExist`.
 
 [![Go Reference](https://pkg.go.dev/badge/github.com/laher/chainfs.svg)](https://pkg.go.dev/github.com/laher/chainfs)

chainfs.go

@@ -1,3 +1,3 @@
-module github.com/laher/chainfs
+module github.com/laher/mergefs
 
-go 1.15
+go 1.16

go.mod

@@ -0,0 +1,27 @@
+package mergefs
+
+import (
+	"io/fs"
+	"os"
+)
+
+// Merge filesystems
+func Merge(filesystems ...fs.FS) fs.FS {
+	return MergedFS{filesystems: filesystems}
+}
+
+// MergedFS combines filesystems. Each filesystem can serve different paths. The first FS takes precedence
+type MergedFS struct {
+	filesystems []fs.FS
+}
+
+// Open opens the named file.
+func (mfs MergedFS) Open(name string) (fs.File, error) {
+	for _, fs := range mfs.filesystems {
+		file, err := fs.Open(name)
+		if err == nil { // TODO should we return early when it's not an os.ErrNotExist? Should we offer options to decide this behaviour?
+			return file, nil
+		}
+	}
+	return nil, os.ErrNotExist
+}

mergefs.go

@@ -1,15 +1,16 @@
-package chainfs
+package mergefs_test
 
 import (
-	"io/fs"
 	"testing"
 	"testing/fstest"
+
+	"github.com/laher/mergefs"
 )
 
-func TestChainFS(t *testing.T) {
+func TestMergeFS(t *testing.T) {
 	a := fstest.MapFS{"a": &fstest.MapFile{Data: []byte("text")}}
 	b := fstest.MapFS{"b": &fstest.MapFile{Data: []byte("text")}}
-	fs := FS{Filesystems: []fs.FS{a, b}}
+	fs := mergefs.Merge(a, b)
 
 	if _, err := fs.Open("a"); err != nil {
 		t.Fatalf("file should exist")