fileserver: Add status code override (#4076)

After reading a question about the `handle_response` feature of `reverse_proxy`, I realized that we didn't have a way of serving an arbitrary file with a status code other than 200. This is an issue in situations where you want to serve a custom error page in routes that are not errors, like the aforementioned `handle_response`, where you may want to retain the status code returned by the proxy but write a response with content from a file.

This feature is super simple, basically if a status code is configured (can be a status code number, or a placeholder string) then that status will be written out before serving the file - if we write the status code first, then the stdlib won't write its own (only the first HTTP status header wins).

1 files changed, 112 insertions, 0 deletions

diff --git a/caddytest/integration/caddyfile_adapt/file_server_status.txt b/caddytest/integration/caddyfile_adapt/file_server_status.txt
new file mode 100644
index 0000000..ede1f4a
--- /dev/null
+++ b/caddytest/integration/caddyfile_adapt/file_server_status.txt
@@ -0,0 +1,112 @@
+localhost
+
+root * /srv
+
+handle /nope* {
+	file_server {
+		status 403
+	}
+}
+
+handle /custom-status* {
+	file_server {
+		status {env.CUSTOM_STATUS}
+	}
+}
+----------
+{
+	"apps": {
+		"http": {
+			"servers": {
+				"srv0": {
+					"listen": [
+						":443"
+					],
+					"routes": [
+						{
+							"match": [
+								{
+									"host": [
+										"localhost"
+									]
+								}
+							],
+							"handle": [
+								{
+									"handler": "subroute",
+									"routes": [
+										{
+											"handle": [
+												{
+													"handler": "vars",
+													"root": "/srv"
+												}
+											]
+										},
+										{
+											"group": "group2",
+											"handle": [
+												{
+													"handler": "subroute",
+													"routes": [
+														{
+															"handle": [
+																{
+																	"handler": "file_server",
+																	"hide": [
+																		"./Caddyfile"
+																	],
+																	"status_code": "{env.CUSTOM_STATUS}"
+																}
+															]
+														}
+													]
+												}
+											],
+											"match": [
+												{
+													"path": [
+														"/custom-status*"
+													]
+												}
+											]
+										},
+										{
+											"group": "group2",
+											"handle": [
+												{
+													"handler": "subroute",
+													"routes": [
+														{
+															"handle": [
+																{
+																	"handler": "file_server",
+																	"hide": [
+																		"./Caddyfile"
+																	],
+																	"status_code": 403
+																}
+															]
+														}
+													]
+												}
+											],
+											"match": [
+												{
+													"path": [
+														"/nope*"
+													]
+												}
+											]
+										}
+									]
+								}
+							],
+							"terminal": true
+						}
+					]
+				}
+			}
+		}
+	}
+}
\ No newline at end of file