1 files changed, 50 insertions, 0 deletions

diff --git a/src/bencode.zig b/src/bencode.zig
index b78ee9f..44dec0d 100644
--- a/src/bencode.zig
+++ b/src/bencode.zig
@@ -2,6 +2,7 @@
 //! See specification here https://wiki.theory.org/BitTorrentSpecification#Bencoding
 
 const std = @import("std");
+const AnyWriter = @import("anywriter.zig");
 
 pub const Error = error.Malformatted || std.io.AnyReader.Error;
 
@@ -12,6 +13,41 @@ pub const BValue = union(enum) {
     list: std.ArrayList(BValue),
     dict: std.StringArrayHashMap(BValue),
 
+    pub fn bencode(self: *const BValue, base_writer: anytype) !void {
+        var wrap = AnyWriter.wrapper(base_writer);
+        var writer = wrap.any();
+        try self.bencodeInner(writer);
+    }
+
+    // Note: uses defined types only to avoid trying to recursively evaulate this function
+    // at compile time, otherwise we run into https://github.com/ziglang/zig/issues/13724
+    fn bencodeInner(self: *const BValue, writer: AnyWriter) !void {
+        switch (self.*) {
+            .string => |s| {
+                try std.fmt.format(writer, "{}:{s}", .{ s.len, s });
+            },
+            .list => |l| {
+                try writer.writeByte('l');
+                for (l.items) |i| {
+                    try i.bencodeInner(writer);
+                }
+                try writer.writeByte('e');
+            },
+            .dict => |d| {
+                try writer.writeByte('d');
+                var it = d.iterator();
+                while (it.next()) |entry| {
+                    try std.fmt.format(writer, "{}:{s}", .{ entry.key_ptr.*.len, entry.key_ptr.* });
+                    try entry.value_ptr.*.bencodeInner(writer);
+                }
+                try writer.writeByte('e');
+            },
+            .int => |i| {
+                try std.fmt.format(writer, "i{}e", .{i});
+            },
+        }
+    }
+
     pub fn deinit(self: *BValue, a: std.mem.Allocator) void {
         switch (self.*) {
             .string => |s| {
@@ -237,3 +273,17 @@ test "nested structure" {
     try std.testing.expectEqualDeep(v2.*.list.items[1], BValue{ .int = 456 });
     try std.testing.expectEqualStrings("nest", v2.*.list.items[2].list.items[0].string);
 }
+
+test "round trip" {
+    var a = std.testing.allocator;
+    const in = "d5:hello5:world2:hili123ei456el4:nesteee";
+    var bval = try bdecodeBuf(a, in);
+    defer bval.deinit(a);
+    var bw = std.ArrayList(u8).init(a);
+    defer bw.deinit();
+    var writer = bw.writer();
+    try bval.bencode(writer);
+    var out = try bw.toOwnedSlice();
+    defer a.free(out);
+    try std.testing.expectEqualStrings(in, out);
+}