3 files changed, 64 insertions, 2 deletions

diff --git a/contrib/fs/file.go b/contrib/fs/file.go
index 7690a62..9f11f4f 100644
--- a/contrib/fs/file.go
+++ b/contrib/fs/file.go
@@ -2,7 +2,9 @@ package fs
 
 import (
 	"mime"
+	"os"
 	"strings"
+	"unicode/utf8"
 )
 
 func mediaType(filePath string) string {
@@ -21,6 +23,9 @@ func mediaType(filePath string) string {
 
 	mtype := mime.TypeByExtension(ext)
 	if mtype == "" {
+		if contentsAreText(filePath) {
+			return "text/plain"
+		}
 		return "application/octet-stream"
 	}
 	return mtype
@@ -34,3 +39,28 @@ func isPrivate(fullpath string) bool {
 	}
 	return false
 }
+
+func contentsAreText(filepath string) bool {
+	f, err := os.Open(filepath)
+	if err != nil {
+		return false
+	}
+	defer func() { _ = f.Close() }()
+
+	var buf [1024]byte
+	n, err := f.Read(buf[:])
+	if err != nil {
+		return false
+	}
+
+	for i, c := range string(buf[:n]) {
+		if i+utf8.UTFMax > n {
+			// incomplete last char
+			break
+		}
+		if c == 0xFFFD || c < ' ' && c != '\n' && c != '\t' && c != '\f' {
+			return false
+		}
+	}
+	return true
+}
diff --git a/contrib/fs/gopher.go b/contrib/fs/gopher.go
index db21227..0a0b482 100644
--- a/contrib/fs/gopher.go
+++ b/contrib/fs/gopher.go
@@ -185,7 +185,8 @@ func isFile(path string) (bool, error) {
 }
 
 func isMap(path string, settings gophermap.FileSystemSettings) bool {
-	if strings.HasSuffix(path, ".gophermap") {
+	base := filepath.Base(path)
+	if base == "gophermap" || strings.HasSuffix(base, ".gph") || strings.HasSuffix(base, ".gophermap") {
 		return true
 	}
 	return slices.Contains(settings.DirMaps, filepath.Base(path))
diff --git a/gopher/response.go b/gopher/response.go
index c594fa7..269176f 100644
--- a/gopher/response.go
+++ b/gopher/response.go
@@ -5,9 +5,11 @@ import (
 	"fmt"
 	"io"
 	"mime"
+	"os"
 	"path"
 	"strings"
 	"sync"
+	"unicode/utf8"
 
 	"tildegit.org/tjp/sliderule/internal/types"
 )
@@ -173,7 +175,7 @@ func GuessItemType(filepath string) types.Status {
 	case ".txt", ".gmi", ".md":
 		return TextFileType
 	case ".gif":
-		return  GifFileType
+		return GifFileType
 	case ".png":
 		return PngImageFileType
 	case ".jpg", ".jpeg", ".tif", ".tiff":
@@ -205,5 +207,34 @@ func GuessItemType(filepath string) types.Status {
 		return TextFileType
 	}
 
+	if contentsAreText(filepath) {
+		return TextFileType
+	}
+
 	return BinaryFileType
 }
+
+func contentsAreText(filepath string) bool {
+	f, err := os.Open(filepath)
+	if err != nil {
+		return false
+	}
+	defer func() { _ = f.Close() }()
+
+	var buf [1024]byte
+	n, err := f.Read(buf[:])
+	if err != nil {
+		return false
+	}
+
+	for i, c := range string(buf[:n]) {
+		if i+utf8.UTFMax > n {
+			// incomplete last char
+			break
+		}
+		if c == 0xFFFD || c < ' ' && c != '\n' && c != '\t' && c != '\f' {
+			return false
+		}
+	}
+	return true
+}