From 0a37f352a621b41ea7d0c7574255746c0fd0fc46 Mon Sep 17 00:00:00 2001
From: Ludovic Muller <ludovicmuller1@gmail.com>
Date: Tue, 23 Apr 2024 17:48:12 +0200
Subject: [PATCH] feat(purge): purge cache entry using PURGE HTTP method

---
 .changeset/violet-lizards-chew.md |  5 +++++
 config/default.vcl                | 26 ++++++++++++++++----------
 test/docker-compose.yaml          |  2 --
 test/run.sh                       | 20 ++++++++++++++++----
 4 files changed, 37 insertions(+), 16 deletions(-)
 create mode 100644 .changeset/violet-lizards-chew.md

diff --git a/.changeset/violet-lizards-chew.md b/.changeset/violet-lizards-chew.md
new file mode 100644
index 0000000..1afd9fd
--- /dev/null
+++ b/.changeset/violet-lizards-chew.md
@@ -0,0 +1,5 @@
+---
+"varnish-post": minor
+---
+
+Support `PURGE` method to purge the cache
diff --git a/config/default.vcl b/config/default.vcl
index 6e7a799..ccf2613 100644
--- a/config/default.vcl
+++ b/config/default.vcl
@@ -3,14 +3,14 @@ vcl 4.1;
 import std;
 import bodyaccess;
 
-# this is the backend that should be cached
+# Backend server that should be cached
 backend default {
   .host = "$BACKEND_HOST";
   .port = "$BACKEND_PORT";
   .first_byte_timeout = $BACKEND_FIRST_BYTE_TIMEOUT;
 }
 
-# remove cookies from response
+# Remove cookies and other non-cache-friendly headers from the backend response
 sub vcl_backend_response {
   if (beresp.http.Cache-Control) {
     unset beresp.http.Cache-Control;
@@ -22,20 +22,25 @@ sub vcl_backend_response {
 
   set beresp.ttl = $CACHE_TTL;
 
-  # handle errors
+  # Decide not to cache error responses
   if ($DISABLE_ERROR_CACHING && beresp.status >= 400) {
-    # send requests directly to the backend for the next ttl period
     set beresp.ttl = $DISABLE_ERROR_CACHING_TTL;
     set beresp.uncacheable = true;
     return (deliver);
   }
 }
 
-# remove incoming cookies and allow caching POST requests
+# Handles incoming requests and removes incoming cookies
 sub vcl_recv {
   unset req.http.X-Body-Len;
   unset req.http.cookie;
 
+  # Handle PURGE requests
+  if (req.method == "PURGE") {
+    return (purge);
+  }
+
+  # Caching POST requests by caching the request body
   if (req.method == "POST") {
     std.cache_req_body($BODY_SIZE);
     set req.http.X-Body-Len = bodyaccess.len_req_body();
@@ -52,12 +57,12 @@ sub vcl_recv {
   return (hash);
 }
 
-# https://docs.varnish-software.com/tutorials/caching-post-requests/#step-3-change-the-hashing-function
+# Alter the hashing method to include POST bodies
+# See: https://docs.varnish-software.com/tutorials/caching-post-requests/#step-3-change-the-hashing-function
 sub vcl_hash {
   hash_data(req.http.Authorization);
   hash_data(req.url);
 
-  # to cache POST and PUT requests
   if (req.http.X-Body-Len) {
     bodyaccess.hash_req_body();
   } else {
@@ -67,16 +72,17 @@ sub vcl_hash {
   return (lookup);
 }
 
-# https://docs.varnish-software.com/tutorials/caching-post-requests/#step-4-make-sure-the-backend-gets-a-post-request
+# Adjust the request method in the backend fetch phase
+# See: https://docs.varnish-software.com/tutorials/caching-post-requests/#step-4-make-sure-the-backend-gets-a-post-request
 sub vcl_backend_fetch {
   if (bereq.http.X-Body-Len) {
     set bereq.method = "POST";
   }
 }
 
-# add a header to see if it was a cache miss or a cache hit
+# Indicate whether the response was served from cache or not
+# See: https://happyculture.coop/blog/varnish-4-comment-savoir-si-votre-page-vient-du-cache
 sub vcl_deliver {
-  # https://happyculture.coop/blog/varnish-4-comment-savoir-si-votre-page-vient-du-cache
   if (resp.http.X-Varnish ~ "[0-9]+ +[0-9]+") {
     set resp.http.X-Cache = "HIT";
   } else {
diff --git a/test/docker-compose.yaml b/test/docker-compose.yaml
index 6a0dbe5..6c1e60e 100644
--- a/test/docker-compose.yaml
+++ b/test/docker-compose.yaml
@@ -1,5 +1,3 @@
-version: "3"
-
 services:
   backend:
     build: ./app
diff --git a/test/run.sh b/test/run.sh
index f9d69b7..f405d48 100755
--- a/test/run.sh
+++ b/test/run.sh
@@ -4,8 +4,8 @@ BACKEND_ENDPOINT="http://localhost:8080"
 CACHED_ENDPOINT="http://localhost:8081"
 
 # build and start the stack
-docker-compose build
-docker-compose up -d
+docker compose build
+docker compose up -d
 
 # Some useful functions
 
@@ -13,7 +13,7 @@ docker-compose up -d
 ## $1: error message to display
 error () {
   echo "ERROR: $1" >&2
-  docker-compose down
+  docker compose down
   exit 1
 }
 
@@ -220,8 +220,20 @@ if [ "${res1}" -ge "${res2}" ]; then
   error "timestamp is not increasing"
 fi
 
+info "Check if we can purge a cache entry…"
+sleep 3
+# do a request after TTL to invalidate the cache
+res_tmp=$(fetch_time "${CACHED_ENDPOINT}")
+res1=$(fetch_time "${CACHED_ENDPOINT}")
+sleep 1
+curl -sL -X PURGE "${CACHED_ENDPOINT}" >/dev/null
+res2=$(fetch_time "${CACHED_ENDPOINT}")
+if [ "${res1}" -eq "${res2}" ]; then
+  error "cache was not purged"
+fi
+
 
 # If we are at this point, no test failed
 info "All tests passed :)"
-docker-compose down
+docker compose down
 exit 0