add support for stream end

src/main.zig

@@ -149,7 +149,7 @@ const Multipart = struct {
         var reader = self.stream.reader();
         // first self.boundary.len+2 bytes MUST be boundary + \r + \n
         var boundary_buffer: [512]u8 = undefined;
-        const maybe_boundary_raw = (try reader.readUntilDelimiterOrEof(&boundary_buffer, '\n')).?;
+        const maybe_boundary_raw = (try reader.readUntilDelimiterOrEof(&boundary_buffer, '\n')) orelse return null;
 
         const maybe_boundary_strip1 = std.mem.trimRight(u8, maybe_boundary_raw, "\n");
         const maybe_boundary_strip2 = std.mem.trimRight(u8, maybe_boundary_strip1, "\r");
@@ -248,6 +248,9 @@ const Multipart = struct {
         const possible_end = it.next() orelse return error.MissingNextPrefixOrEndSuffix;
 
         if (std.mem.startsWith(u8, possible_end, "--")) {
+            // we just got the ending boundary marker. the reader should be disabled
+            // for future reads.
+            self.stream.pos = self.stream.buffer.len;
             return Part{
                 .allocator = allocator,
                 .disposition = content_disposition.?,
@@ -392,4 +395,10 @@ test "multipart" {
     std.testing.expectEqualSlices(u8, "file2", part2.disposition.name);
     std.testing.expectEqualSlices(u8, "data.json", part2.disposition.filename);
     std.testing.expectEqualSlices(u8, PART2_REAL_BODY, part2.body);
+
+    // stop the loop (if there were any) afterwards
+    std.testing.expectEqual(
+        @as(?Part, null),
+        try multipart.next(&hzzp_buffer, std.testing.allocator),
+    );
 }