From d5b4fcf0be44db6a8d0b209d53fd80bb2293fee2 Mon Sep 17 00:00:00 2001
From: Laurence Withers <l@lwithers.me.uk>
Date: Sat, 15 Feb 2020 12:26:01 +0000
Subject: [PATCH] Implement library support for Angular-style single page
 applications

---
 README.md  | 32 ++++++++++++++++++++++++++++++++
 handler.go | 30 ++++++++++++++++++++++++++++--
 2 files changed, 60 insertions(+), 2 deletions(-)

diff --git a/README.md b/README.md
index f7f576f..9c38b39 100644
--- a/README.md
+++ b/README.md
@@ -28,3 +28,35 @@ else will be ignored.
 The interaction between range handling and compression also seems a little
 ill-defined; as we have pre-compressed data, however, we can consistently
 serve the exact same byte data for compressed files.
+
+## Angular-style single-page application handling
+
+If you wish to support an angular.js-style single page application, in which
+a Javascript application uses the browser's history API to create a set of
+virtual paths ("routes"), it is necessary to somehow intercept HTTP 404 errors
+being returned from the handler and instead return an HTTP 200 with an HTML
+document.
+
+This can be achieved with a number of methods.
+
+If you have an nginx instance reverse proxying in front of `htpack`, then you
+can use a couple of extra directives, for example:
+
+	# prevent page loaded at "http://server.example/my-application" from
+	# requesting resources at "/*" when it should request them at
+	# "/my-application/*" instead
+	location = /my-application {
+		return 308 /my-application/;
+	}
+
+	location /my-application/ {
+		proxy_to http://htpack-addr:8080/;
+		proxy_intercept_errors on;
+		error_page 404 =200 /my-application/;
+	}
+
+If you are using the handler as a library, then you may call
+`handler.SetNotFound(filename)` to select a resource to return (with HTTP 200)
+if a request is made for a resource that is not found. The filename must match
+a packed resource, so it will be preceded with a `/` (for example it may be
+`"/index.html"`).
diff --git a/handler.go b/handler.go
index a5782a3..92da9d4 100644
--- a/handler.go
+++ b/handler.go
@@ -72,6 +72,7 @@ type Handler struct {
 	dir       map[string]*packed.File
 	headers   map[string]string
 	startTime time.Time
+	notFound  *packed.File
 }
 
 // SetHeader allows a custom header to be set on HTTP responses. These are
@@ -110,6 +111,28 @@ func (h *Handler) SetIndex(filename string) {
 	}
 }
 
+// SetNotFound allows overriding the returned resource when a request is made
+// for a resource that does not exist. The default behaviour would be to return
+// a standard HTTP 404 Not Found response; calling this function with an empty
+// string will restore that behaviour.
+//
+// This function will return an error if the named resource is not present in
+// the packfile.
+func (h *Handler) SetNotFound(notFound string) error {
+	if notFound == "" {
+		h.notFound = nil
+		return nil
+	}
+
+	notFound = path.Clean(notFound)
+	dir := h.dir[path.Clean(notFound)]
+	if dir == nil {
+		return fmt.Errorf("no such resource %q", notFound)
+	}
+	h.notFound = dir
+	return nil
+}
+
 // ServeHTTP handles requests for files. It supports GET and HEAD methods, with
 // anything else returning a 405. Exact path matches are required, else a 404 is
 // returned.
@@ -130,8 +153,11 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 
 	info := h.dir[path.Clean(req.URL.Path)]
 	if info == nil {
-		http.NotFound(w, req)
-		return
+		if h.notFound == nil {
+			http.NotFound(w, req)
+			return
+		}
+		info = h.notFound
 	}
 
 	// set standard headers