1 files changed, 57 insertions, 0 deletions
diff --git a/internal/filetypes.go b/internal/filetypes.go
new file mode 100644
index 0000000..6824ffc
--- /dev/null
+++ b/internal/filetypes.go
@@ -0,0 +1,57 @@
+package internal
+
+import (
+	"mime"
+	"os"
+	"strings"
+	"unicode/utf8"
+)
+
+func MediaType(fpath string) string {
+	if strings.HasSuffix(fpath, ".gmi") {
+		// This may not be present in the listings searched by mime.TypeByExtension,
+		// so provide a dedicated fast path for it here.
+		return "text/gemini"
+	}
+
+	slashIdx := strings.LastIndex(fpath, "/")
+	dotIdx := strings.LastIndex(fpath[slashIdx+1:], ".")
+	if dotIdx == -1 {
+		return "application/octet-stream"
+	}
+	ext := fpath[slashIdx+1+dotIdx:]
+
+	mtype := mime.TypeByExtension(ext)
+	if mtype == "" {
+		if ContentsAreText(fpath) {
+			return "text/plain"
+		}
+		return "application/octet-stream"
+	}
+	return mtype
+}
+
+func ContentsAreText(fpath string) bool {
+	f, err := os.Open(fpath)
+	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
+}