From 90ee9f39bc9685969e475b98e23a6d200404d4e8 Mon Sep 17 00:00:00 2001
From: Nigel Sim <nigel.sim@gmail.com>
Date: Tue, 15 Oct 2019 23:02:26 +1000
Subject: [PATCH] feat: recursive fallback resolution

---
 README.md   | 13 +++++++++++--
 fallback.go | 24 ++++++++++++++++++++----
 main.go     |  6 +++---
 3 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/README.md b/README.md
index 1ef8d12..ad9a112 100644
--- a/README.md
+++ b/README.md
@@ -49,7 +49,7 @@ Usage of /goStatic:
   -enable-basic-auth
         Enable basic auth. By default, password are randomly generated. Use --set-basic-auth to set it.
   -fallback string
-    	Default relative to be used when no file requested found. E.g. /index.html
+        Default fallback file. Either absolute for a specific asset (/index.html), or relative to recursively resolve (index.html).
   -password-length int
         Size of the randomized password (default 16)
   -path string
@@ -58,4 +58,13 @@ Usage of /goStatic:
         The listening port (default 8043)
   -set-basic-auth string
         Define the basic auth. Form must be user:password
-```
\ No newline at end of file
+```
+
+#### Fallback
+
+The fallback option is principally useful for single page applications (SPAs) where the browser may request a file, but where part of the path is in fact an internal route in the application, not a file on disk. goStatic supports two possible usages of this option:
+
+1. Using an absolute path so that all not found requests resolve to the same file
+2. Using a relative file, which searches up the tree for the specified file
+
+The second case is useful if you have multiple SPAs within the one filesystem. e.g., */* and */admin*.
diff --git a/fallback.go b/fallback.go
index 20f4159..94ec419 100644
--- a/fallback.go
+++ b/fallback.go
@@ -3,6 +3,7 @@ package main
 import (
 	"net/http"
 	"os"
+	"path"
 )
 
 // fallback opens defaultPath when the underlying fs returns os.ErrNotExist
@@ -11,10 +12,25 @@ type fallback struct {
 	fs          http.FileSystem
 }
 
-func (fb fallback) Open(path string) (http.File, error) {
-	f, err := fb.fs.Open(path)
-	if os.IsNotExist(err) {
-		return fb.fs.Open(fb.defaultPath)
+func OpenDefault(fb fallback, requestPath string) (http.File, error) {
+	requestPath = path.Dir(requestPath)
+	defaultFile := requestPath + "/" + fb.defaultPath;
+	
+	f, err := fb.fs.Open(defaultFile)
+	if os.IsNotExist(err) && requestPath != "" {
+		parentPath, _ := path.Split(requestPath)
+		return OpenDefault(fb, parentPath)
+	}
+	return f, err
+}
+
+func (fb fallback) Open(requestPath string) (http.File, error) {
+	f, err := fb.fs.Open(requestPath)
+	if os.IsNotExist(err) {
+		if len(fb.defaultPath) == 0 || fb.defaultPath[0] == '/' {
+			return fb.fs.Open(fb.defaultPath)
+		}
+		return OpenDefault(fb, requestPath)
 	}
 	return f, err
 }
diff --git a/main.go b/main.go
index f1ae3c2..2c4698c 100644
--- a/main.go
+++ b/main.go
@@ -15,8 +15,8 @@ var (
 	// Def of flags
 	portPtr                  = flag.Int("port", 8043, "The listening port")
 	context                  = flag.String("context", "", "The 'context' path on which files are served, e.g. 'doc' will serve the files at 'http://localhost:<port>/doc/'")
-	path                     = flag.String("path", "/srv/http", "The path for the static files")
-	fallbackPath             = flag.String("fallback", "", "Default relative to be used when no file requested found. E.g. /index.html")
+	basePath                 = flag.String("path", "/srv/http", "The path for the static files")
+	fallbackPath             = flag.String("fallback", "", "Default fallback file. Either absolute for a specific asset (/index.html), or relative to recursively resolve (index.html)")
 	headerFlag               = flag.String("append-header", "", "HTTP response header, specified as `HeaderName:Value` that should be added to all responses.")
 	basicAuth                = flag.Bool("enable-basic-auth", false, "Enable basic auth. By default, password are randomly generated. Use --set-basic-auth to set it.")
 	setBasicAuth             = flag.String("set-basic-auth", "", "Define the basic auth. Form must be user:password")
@@ -49,7 +49,7 @@ func main() {
 
 	port := ":" + strconv.FormatInt(int64(*portPtr), 10)
 
-	var fileSystem http.FileSystem = http.Dir(*path)
+	var fileSystem http.FileSystem = http.Dir(*basePath)
 
 	if *fallbackPath != "" {
 		fileSystem = fallback{