fastcgi: Set PATH_INFO to file matcher remainder as fallback (#3739)

* fastcgi: Set PATH_INFO to file matcher remainder as fallback

* fastcgi: Avoid changing scriptName when not necessary

* Stylistic tweaks

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>

3 files changed, 51 insertions, 28 deletions

diff --git a/modules/caddyhttp/fileserver/matcher.go b/modules/caddyhttp/fileserver/matcher.go
index c103b03..44ef9ed 100644
--- a/modules/caddyhttp/fileserver/matcher.go
+++ b/modules/caddyhttp/fileserver/matcher.go
@@ -44,6 +44,8 @@ func init() {
 // of the matched file.
 // - `{http.matchers.file.type}` Set to "directory" if
 // the matched file is a directory, "file" otherwise.
+// - `{http.matchers.file.remainder}` Set to the remainder
+// of the path if the path was split by `split_path`.
 type MatchFile struct {
 	// The root directory, used for creating absolute
 	// file paths, and required when working with
@@ -155,11 +157,12 @@ func (m MatchFile) Validate() error {
 }
 
 // Match returns true if r matches m. Returns true
-// if a file was matched. If so, three placeholders
+// if a file was matched. If so, four placeholders
 // will be available:
 //    - http.matchers.file.relative
 //    - http.matchers.file.absolute
 //    - http.matchers.file.type
+//    - http.matchers.file.remainder
 func (m MatchFile) Match(r *http.Request) bool {
 	return m.selectFile(r)
 }
@@ -179,19 +182,20 @@ func (m MatchFile) selectFile(r *http.Request) (matched bool) {
 	}
 
 	// common preparation of the file into parts
-	prepareFilePath := func(file string) (string, string) {
-		suffix := m.firstSplit(path.Clean(repl.ReplaceAll(file, "")))
+	prepareFilePath := func(file string) (suffix, fullpath, remainder string) {
+		suffix, remainder = m.firstSplit(path.Clean(repl.ReplaceAll(file, "")))
 		if strings.HasSuffix(file, "/") {
 			suffix += "/"
 		}
-		fullpath := sanitizedPathJoin(root, suffix)
-		return suffix, fullpath
+		fullpath = sanitizedPathJoin(root, suffix)
+		return
 	}
 
 	// sets up the placeholders for the matched file
-	setPlaceholders := func(info os.FileInfo, rel string, abs string) {
+	setPlaceholders := func(info os.FileInfo, rel string, abs string, remainder string) {
 		repl.Set("http.matchers.file.relative", rel)
 		repl.Set("http.matchers.file.absolute", abs)
+		repl.Set("http.matchers.file.remainder", remainder)
 
 		fileType := "file"
 		if info.IsDir() {
@@ -203,9 +207,9 @@ func (m MatchFile) selectFile(r *http.Request) (matched bool) {
 	switch m.TryPolicy {
 	case "", tryPolicyFirstExist:
 		for _, f := range m.TryFiles {
-			suffix, fullpath := prepareFilePath(f)
+			suffix, fullpath, remainder := prepareFilePath(f)
 			if info, exists := strictFileExists(fullpath); exists {
-				setPlaceholders(info, suffix, fullpath)
+				setPlaceholders(info, suffix, fullpath, remainder)
 				return true
 			}
 		}
@@ -214,52 +218,58 @@ func (m MatchFile) selectFile(r *http.Request) (matched bool) {
 		var largestSize int64
 		var largestFilename string
 		var largestSuffix string
+		var remainder string
 		var info os.FileInfo
 		for _, f := range m.TryFiles {
-			suffix, fullpath := prepareFilePath(f)
+			suffix, fullpath, splitRemainder := prepareFilePath(f)
 			info, err := os.Stat(fullpath)
 			if err == nil && info.Size() > largestSize {
 				largestSize = info.Size()
 				largestFilename = fullpath
 				largestSuffix = suffix
+				remainder = splitRemainder
 			}
 		}
-		setPlaceholders(info, largestSuffix, largestFilename)
+		setPlaceholders(info, largestSuffix, largestFilename, remainder)
 		return true
 
 	case tryPolicySmallestSize:
 		var smallestSize int64
 		var smallestFilename string
 		var smallestSuffix string
+		var remainder string
 		var info os.FileInfo
 		for _, f := range m.TryFiles {
-			suffix, fullpath := prepareFilePath(f)
+			suffix, fullpath, splitRemainder := prepareFilePath(f)
 			info, err := os.Stat(fullpath)
 			if err == nil && (smallestSize == 0 || info.Size() < smallestSize) {
 				smallestSize = info.Size()
 				smallestFilename = fullpath
 				smallestSuffix = suffix
+				remainder = splitRemainder
 			}
 		}
-		setPlaceholders(info, smallestSuffix, smallestFilename)
+		setPlaceholders(info, smallestSuffix, smallestFilename, remainder)
 		return true
 
 	case tryPolicyMostRecentlyMod:
 		var recentDate time.Time
 		var recentFilename string
 		var recentSuffix string
+		var remainder string
 		var info os.FileInfo
 		for _, f := range m.TryFiles {
-			suffix, fullpath := prepareFilePath(f)
+			suffix, fullpath, splitRemainder := prepareFilePath(f)
 			info, err := os.Stat(fullpath)
 			if err == nil &&
 				(recentDate.IsZero() || info.ModTime().After(recentDate)) {
 				recentDate = info.ModTime()
 				recentFilename = fullpath
 				recentSuffix = suffix
+				remainder = splitRemainder
 			}
 		}
-		setPlaceholders(info, recentSuffix, recentFilename)
+		setPlaceholders(info, recentSuffix, recentFilename, remainder)
 		return true
 	}
 
@@ -297,10 +307,11 @@ func strictFileExists(file string) (os.FileInfo, bool) {
 
 // firstSplit returns the first result where the path
 // can be split in two by a value in m.SplitPath. The
-// result is the first piece of the path that ends with
-// in the split value. Returns the path as-is if the
-// path cannot be split.
-func (m MatchFile) firstSplit(path string) string {
+// return values are the first piece of the path that
+// ends with the split substring and the remainder.
+// If the path cannot be split, the path is returned
+// as-is (with no remainder).
+func (m MatchFile) firstSplit(path string) (splitPart, remainder string) {
 	for _, split := range m.SplitPath {
 		if idx := indexFold(path, split); idx > -1 {
 			pos := idx + len(split)
@@ -308,10 +319,10 @@ func (m MatchFile) firstSplit(path string) string {
 			if pos != len(path) && !strings.HasPrefix(path[pos:], "/") {
 				continue
 			}
-			return path[:pos]
+			return path[:pos], path[pos:]
 		}
 	}
-	return path
+	return path, ""
 }
 
 // There is no strings.IndexFold() function like there is strings.EqualFold(),
diff --git a/modules/caddyhttp/fileserver/matcher_test.go b/modules/caddyhttp/fileserver/matcher_test.go
index ddd4f78..e319907 100644
--- a/modules/caddyhttp/fileserver/matcher_test.go
+++ b/modules/caddyhttp/fileserver/matcher_test.go
@@ -206,9 +206,13 @@ func TestPHPFileMatcher(t *testing.T) {
 
 func TestFirstSplit(t *testing.T) {
 	m := MatchFile{SplitPath: []string{".php"}}
-	actual := m.firstSplit("index.PHP/somewhere")
+	actual, remainder := m.firstSplit("index.PHP/somewhere")
 	expected := "index.PHP"
+	expectedRemainder := "/somewhere"
 	if actual != expected {
-		t.Errorf("Expected %s but got %s", expected, actual)
+		t.Errorf("Expected split %s but got %s", expected, actual)
+	}
+	if remainder != expectedRemainder {
+		t.Errorf("Expected remainder %s but got %s", expectedRemainder, remainder)
 	}
 }
diff --git a/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go b/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go
index de6d0a4..0976437 100644
--- a/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go
+++ b/modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go
@@ -195,19 +195,27 @@ func (t Transport) buildEnv(r *http.Request) (map[string]string, error) {
 	}
 
 	fpath := r.URL.Path
+	scriptName := fpath
 
+	docURI := fpath
 	// split "actual path" from "path info" if configured
-	var docURI, pathInfo string
+	var pathInfo string
 	if splitPos := t.splitPos(fpath); splitPos > -1 {
 		docURI = fpath[:splitPos]
 		pathInfo = fpath[splitPos:]
-	} else {
-		docURI = fpath
+
+		// Strip PATH_INFO from SCRIPT_NAME
+		scriptName = strings.TrimSuffix(scriptName, pathInfo)
 	}
-	scriptName := fpath
 
-	// Strip PATH_INFO from SCRIPT_NAME
-	scriptName = strings.TrimSuffix(scriptName, pathInfo)
+	// Try to grab the path remainder from a file matcher
+	// if we didn't get a split result here.
+	// See https://github.com/caddyserver/caddy/issues/3718
+	if pathInfo == "" {
+		if remainder, ok := repl.GetString("http.matchers.file.remainder"); ok {
+			pathInfo = remainder
+		}
+	}
 
 	// SCRIPT_FILENAME is the absolute path of SCRIPT_NAME
 	scriptFilename := filepath.Join(root, scriptName)