test: Etag, X-Ipfs-Path and X-Ipfs-Roots

This documents the current behavior of mentioned headers.

It helped to identify a a bug around index.html responses having etag of
a dir-index-html (to be fixed in a separate change)

core/corehttp/gateway_handler.go

@@ -317,28 +317,12 @@ func (i *gatewayHandler) getOrHeadHandler(w http.ResponseWriter, r *http.Request
 	w.Header().Set("X-IPFS-Path", urlPath)
 	w.Header().Set("Etag", responseEtag)
 
-	// X-Ipfs-Roots array for efficient HTTP cache invalidation
-	//   These are logical roots where each CID represent one path segment
-	//   and resolves to either a directory or the root block of a file
-	var sp strings.Builder
-	var pathRoots []string
-	pathSegments := strings.Split(urlPath[6:], "/")
-	sp.WriteString(urlPath[:5]) // /ipfs or /ipns
-	for _, root := range pathSegments {
-		if root == "" {
-			continue
-		}
-		sp.WriteString("/")
-		sp.WriteString(root)
-		resolvedSubPath, err := i.api.ResolvePath(r.Context(), ipath.New(sp.String()))
-		if err != nil {
-			// this should never happen, as we resolved the full path already
-			webError(w, "error while resolving X-Ipfs-Roots", err, http.StatusInternalServerError)
-			return
-		}
-		pathRoots = append(pathRoots, resolvedSubPath.Cid().String())
+	if rootCids, err := i.buildIpfsRootsHeader(urlPath, r); err == nil {
+		w.Header().Set("X-Ipfs-Roots", rootCids)
+	} else { // this should never happen, as we resolved the urlPath already
+		webError(w, "error while resolving X-Ipfs-Roots", err, http.StatusInternalServerError)
+		return
 	}
-	w.Header().Set("X-Ipfs-Roots", strings.Join(pathRoots, ", "))
 
 	// set these headers _after_ the error, for we may just not have it
 	// and don't want the client to cache a 500 response...
@@ -781,6 +765,50 @@ func (i *gatewayHandler) addUserHeaders(w http.ResponseWriter) {
 	}
 }
 
+// Set X-Ipfs-Roots with logical CID array for efficient HTTP cache invalidation.
+func (i *gatewayHandler) buildIpfsRootsHeader(contentPath string, r *http.Request) (string, error) {
+	/*
+		These are logical roots where each CID represent one path segment
+		and resolves to either a directory or the root block of a file.
+		The main purpose of this header is allow HTTP caches to do smarter decisions
+		around cache invalidation (eg. keep specific subdirectory/file if it did not change)
+
+		A good example is Wikipedia, which is HAMT-sharded, but we only care about
+		logical roots that represent each segment of the human-readable content
+		path:
+
+		Given contentPath = /ipns/en.wikipedia-on-ipfs.org/wiki/Block_of_Wikipedia_in_Turkey
+		rootCidList is a generated by doing `ipfs resolve -r` on each sub path:
+			/ipns/en.wikipedia-on-ipfs.org → bafybeiaysi4s6lnjev27ln5icwm6tueaw2vdykrtjkwiphwekaywqhcjze
+			/ipns/en.wikipedia-on-ipfs.org/wiki/ → bafybeihn2f7lhumh4grizksi2fl233cyszqadkn424ptjajfenykpsaiw4
+			/ipns/en.wikipedia-on-ipfs.org/wiki/Block_of_Wikipedia_in_Turkey → bafkreibn6euazfvoghepcm4efzqx5l3hieof2frhp254hio5y7n3hv5rma
+
+		The result is an ordered array of values:
+			X-Ipfs-Roots: bafybeiaysi4s6lnjev27ln5icwm6tueaw2vdykrtjkwiphwekaywqhcjze,bafybeihn2f7lhumh4grizksi2fl233cyszqadkn424ptjajfenykpsaiw4,bafkreibn6euazfvoghepcm4efzqx5l3hieof2frhp254hio5y7n3hv5rma
+
+		Note that while the top one will change every time any article is changed,
+		the last root (responsible for specific article) may not change at all.
+	*/
+	var sp strings.Builder
+	var pathRoots []string
+	pathSegments := strings.Split(contentPath[6:], "/")
+	sp.WriteString(contentPath[:5]) // /ipfs or /ipns
+	for _, root := range pathSegments {
+		if root == "" {
+			continue
+		}
+		sp.WriteString("/")
+		sp.WriteString(root)
+		resolvedSubPath, err := i.api.ResolvePath(r.Context(), ipath.New(sp.String()))
+		if err != nil {
+			return "", err
+		}
+		pathRoots = append(pathRoots, resolvedSubPath.Cid().String())
+	}
+	rootCidList := strings.Join(pathRoots, ",") // convention from rfc2616#sec4.2
+	return rootCidList, nil
+}
+
 func webError(w http.ResponseWriter, message string, err error, defaultCode int) {
 	if _, ok := err.(resolver.ErrNoLink); ok {
 		webErrorWithCode(w, message, err, http.StatusNotFound)

test/sharness/t0116-gateway-cache.sh

@@ -0,0 +1,88 @@
+#!/usr/bin/env bash
+
+test_description="Test HTTP Gateway Cache Control Support"
+
+. lib/test-lib.sh
+
+test_init_ipfs
+test_launch_ipfs_daemon_without_network
+
+# Cache control support is based on logical roots (each path segment == one logical root).
+# To maximize the test surface, we want to test:
+# - /ipfs/ content path
+# - /ipns/ content path
+# - at least 3 levels
+# - separate tests for a directory listing and a file
+# - have implicit index.html for a good measure
+# /ipns/root1/root2/root3/ (/ipns/root1/root2/root3/index.html)
+
+test_expect_success "Add the test directory" '
+  mkdir -p root2/root3 &&
+  echo "hello" > root2/root3/index.html &&
+  ROOT1_CID=$(ipfs add -Qrw --cid-version 1 root2)
+  ROOT2_CID=$(ipfs resolve -r /ipfs/$ROOT1_CID/root2 | cut -d "/" -f3)
+  ROOT3_CID=$(ipfs resolve -r /ipfs/$ROOT1_CID/root2/root3 | cut -d "/" -f3)
+  FILE_CID=$(ipfs resolve -r /ipfs/$ROOT1_CID/root2/root3/index.html | cut -d "/" -f3)
+'
+
+test_expect_success "Prepare IPNS unixfs content path for testing" '
+  TEST_IPNS_ID=$(ipfs key gen --ipns-base=base36 --type=ed25519 cache_test_key | head -n1 | tr -d "\n")
+  ipfs name publish --key cache_test_key --allow-offline -Q "/ipfs/$ROOT1_CID" > name_publish_out &&
+  test_check_peerid "${TEST_IPNS_ID}" &&
+  ipfs name resolve "${TEST_IPNS_ID}" > output &&
+  printf "/ipfs/%s\n" "$ROOT1_CID" > expected &&
+  test_cmp expected output
+'
+
+test_expect_success "GET for /ipfs/ unixfs dir index succeeds" '
+  curl -svX GET "http://127.0.0.1:$GWAY_PORT/ipfs/$ROOT1_CID/root2/root3/" >/dev/null 2>curl_ipfs_dir_output &&
+  cat curl_ipfs_dir_output
+'
+test_expect_success "GET for /ipfs/ unixfs file succeeds" '
+  curl -svX GET "http://127.0.0.1:$GWAY_PORT/ipfs/$ROOT1_CID/root2/root3/index.html" >/dev/null 2>curl_ipfs_file_output &&
+  cat curl_ipfs_file_output
+'
+test_expect_success "GET for /ipns/ unixfs dir index succeeds" '
+  curl -svX GET "http://127.0.0.1:$GWAY_PORT/ipns/$TEST_IPNS_ID/root2/root3/" >/dev/null 2>curl_ipns_dir_output &&
+  cat curl_ipns_dir_output
+'
+test_expect_success "GET for /ipns/ unixfs file succeeds" '
+  curl -svX GET "http://127.0.0.1:$GWAY_PORT/ipns/$TEST_IPNS_ID/root2/root3/index.html" >/dev/null 2>curl_ipns_file_output &&
+  cat curl_ipns_file_output
+'
+
+# X-Ipfs-Path
+test_expect_success "GET /ipfs/ response has original content path in X-Ipfs-Path" '
+  grep "< X-Ipfs-Path: /ipfs/$ROOT1_CID/root2/root3" curl_ipfs_dir_output
+'
+test_expect_success "GET /ipns/ response has original content path in X-Ipfs-Path" '
+  grep "< X-Ipfs-Path: /ipns/$TEST_IPNS_ID/root2/root3" curl_ipns_dir_output
+'
+
+# X-Ipfs-Roots
+test_expect_success "GET /ipfs/ response has logical CID roots in X-Ipfs-Roots" '
+  grep "< X-Ipfs-Roots: ${ROOT1_CID},${ROOT2_CID},${ROOT3_CID}" curl_ipfs_dir_output
+'
+test_expect_success "GET /ipns/ response has logical CID roots in X-Ipfs-Roots" '
+  grep "< X-Ipfs-Roots: ${ROOT1_CID},${ROOT2_CID},${ROOT3_CID}" curl_ipns_dir_output
+'
+
+# Etag for DirIndex
+test_expect_success "GET /ipfs/ response has special Etag for unixfs dir listing" '
+  grep -E "< Etag: \"DirIndex-.+_CID-${ROOT3_CID}\"" curl_ipfs_dir_output
+'
+test_expect_success "GET /ipns/ response has special Etag for unixfs dir listing" '
+  grep -E "< Etag: \"DirIndex-.+_CID-${ROOT3_CID}\"" curl_ipns_dir_output
+'
+
+# Etag for a file
+test_expect_success "GET /ipfs/ response has CID as Etag for a file" '
+  grep -E "< Etag: \"${FILE_CID}\"" curl_ipfs_file_output
+'
+test_expect_success "GET /ipns/ response has CID as Etag for a file" '
+  grep -E "< Etag: \"${FILE_CID}\"" curl_ipns_file_output
+'
+
+test_kill_ipfs_daemon
+
+test_done