fileserver: Add first_exist_fallback strategy for try_files (#6699)

* feat: add first_exist_or_fallback strategy for try_files

* fix tests

* linter

Author: dunglas

Diff for: caddytest/integration/caddyfile_adapt/php_fastcgi_handle_response.caddyfiletest

@@ -58,6 +58,7 @@
 											"{http.request.uri.path}/index.php",
 											"index.php"
 										],
+										"try_policy": "first_exist_fallback",
 										"split_path": [
 											".php"
 										]

Diff for: caddytest/integration/caddyfile_adapt/php_fastcgi_matcher.caddyfiletest

@@ -73,7 +73,8 @@ php_fastcgi @test localhost:9000
 																			"{http.request.uri.path}",
 																			"{http.request.uri.path}/index.php",
 																			"index.php"
-																		]
+																		],
+																		"try_policy": "first_exist_fallback"
 																	}
 																}
 															]

Diff for: caddytest/integration/caddyfile_adapt/php_fastcgi_subdirectives.caddyfiletest

@@ -59,6 +59,7 @@ php_fastcgi localhost:9000 {
 											"{http.request.uri.path}/index.php5",
 											"index.php5"
 										],
+										"try_policy": "first_exist_fallback",
 										"split_path": [
 											".php",
 											".php5"

Diff for: caddytest/integration/caddyfile_adapt/php_fastcgi_try_files_override_no_dir_index.caddyfiletest

@@ -32,6 +32,7 @@ php_fastcgi localhost:9000 {
 											"{http.request.uri.path}",
 											"index.php"
 										],
+										"try_policy": "first_exist_fallback",
 										"split_path": [
 											".php",
 											".php5"

Diff for: modules/caddyhttp/fileserver/caddyfile.go

@@ -274,7 +274,7 @@ func parseTryFiles(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error)
 			tryPolicy = h.Val()
 
 			switch tryPolicy {
-			case tryPolicyFirstExist, tryPolicyLargestSize, tryPolicySmallestSize, tryPolicyMostRecentlyMod:
+			case tryPolicyFirstExist, tryPolicyFirstExistFallback, tryPolicyLargestSize, tryPolicySmallestSize, tryPolicyMostRecentlyMod:
 			default:
 				return nil, h.Errf("unrecognized try policy: %s", tryPolicy)
 			}

Diff for: modules/caddyhttp/fileserver/matcher.go

@@ -90,6 +90,7 @@ type MatchFile struct {
 	// How to choose a file in TryFiles. Can be:
 	//
 	// - first_exist
+	// - first_exist_fallback
 	// - smallest_size
 	// - largest_size
 	// - most_recently_modified
@@ -415,22 +416,27 @@ func (m MatchFile) selectFile(r *http.Request) (bool, error) {
 	}
 
 	// setPlaceholders creates the placeholders for the matched file
-	setPlaceholders := func(candidate matchCandidate, info fs.FileInfo) {
+	setPlaceholders := func(candidate matchCandidate, isDir bool) {
 		repl.Set("http.matchers.file.relative", filepath.ToSlash(candidate.relative))
 		repl.Set("http.matchers.file.absolute", filepath.ToSlash(candidate.fullpath))
 		repl.Set("http.matchers.file.remainder", filepath.ToSlash(candidate.splitRemainder))
 
 		fileType := "file"
-		if info.IsDir() {
+		if isDir {
 			fileType = "directory"
 		}
 		repl.Set("http.matchers.file.type", fileType)
 	}
 
 	// match file according to the configured policy
 	switch m.TryPolicy {
-	case "", tryPolicyFirstExist:
-		for _, pattern := range m.TryFiles {
+	case "", tryPolicyFirstExist, tryPolicyFirstExistFallback:
+		maxI := -1
+		if m.TryPolicy == tryPolicyFirstExistFallback {
+			maxI = len(m.TryFiles) - 1
+		}
+
+		for i, pattern := range m.TryFiles {
 			// If the pattern is a status code, emit an error,
 			// which short-circuits the middleware pipeline and
 			// writes an HTTP error response.
@@ -440,8 +446,15 @@ func (m MatchFile) selectFile(r *http.Request) (bool, error) {
 
 			candidates := makeCandidates(pattern)
 			for _, c := range candidates {
+				// Skip the IO if using fallback policy and it's the latest item
+				if i == maxI {
+					setPlaceholders(c, false)
+
+					return true, nil
+				}
+
 				if info, exists := m.strictFileExists(fileSystem, c.fullpath); exists {
-					setPlaceholders(c, info)
+					setPlaceholders(c, info.IsDir())
 					return true, nil
 				}
 			}
@@ -465,7 +478,7 @@ func (m MatchFile) selectFile(r *http.Request) (bool, error) {
 		if largestInfo == nil {
 			return false, nil
 		}
-		setPlaceholders(largest, largestInfo)
+		setPlaceholders(largest, largestInfo.IsDir())
 		return true, nil
 
 	case tryPolicySmallestSize:
@@ -486,7 +499,7 @@ func (m MatchFile) selectFile(r *http.Request) (bool, error) {
 		if smallestInfo == nil {
 			return false, nil
 		}
-		setPlaceholders(smallest, smallestInfo)
+		setPlaceholders(smallest, smallestInfo.IsDir())
 		return true, nil
 
 	case tryPolicyMostRecentlyMod:
@@ -506,7 +519,7 @@ func (m MatchFile) selectFile(r *http.Request) (bool, error) {
 		if recentInfo == nil {
 			return false, nil
 		}
-		setPlaceholders(recent, recentInfo)
+		setPlaceholders(recent, recentInfo.IsDir())
 		return true, nil
 	}
 
@@ -708,10 +721,11 @@ var globSafeRepl = strings.NewReplacer(
 )
 
 const (
-	tryPolicyFirstExist      = "first_exist"
-	tryPolicyLargestSize     = "largest_size"
-	tryPolicySmallestSize    = "smallest_size"
-	tryPolicyMostRecentlyMod = "most_recently_modified"
+	tryPolicyFirstExist         = "first_exist"
+	tryPolicyFirstExistFallback = "first_exist_fallback"
+	tryPolicyLargestSize        = "largest_size"
+	tryPolicySmallestSize       = "smallest_size"
+	tryPolicyMostRecentlyMod    = "most_recently_modified"
 )
 
 // Interface guards

Diff for: modules/caddyhttp/reverseproxy/fastcgi/caddyfile.go

@@ -18,6 +18,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"strconv"
+	"strings"
 
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/caddyconfig"
@@ -312,12 +313,18 @@ func parsePHPFastCGI(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error
 	if indexFile != "off" {
 		dirRedir := false
 		dirIndex := "{http.request.uri.path}/" + indexFile
+		tryPolicy := "first_exist_fallback"
 
 		// if tryFiles wasn't overridden, use a reasonable default
 		if len(tryFiles) == 0 {
 			tryFiles = []string{"{http.request.uri.path}", dirIndex, indexFile}
 			dirRedir = true
 		} else {
+			if !strings.HasSuffix(tryFiles[len(tryFiles)-1], ".php") {
+				// use first_exist strategy if the last file is not a PHP file
+				tryPolicy = ""
+			}
+
 			for _, tf := range tryFiles {
 				if tf == dirIndex {
 					dirRedir = true
@@ -357,6 +364,7 @@ func parsePHPFastCGI(h httpcaddyfile.Helper) ([]httpcaddyfile.ConfigValue, error
 		rewriteMatcherSet := caddy.ModuleMap{
 			"file": h.JSON(fileserver.MatchFile{
 				TryFiles:  tryFiles,
+				TryPolicy: tryPolicy,
 				SplitPath: extensions,
 			}),
 		}