1 files changed, 63 insertions, 0 deletions
diff --git a/src/tracker_protocol.zig b/src/tracker_protocol.zig
new file mode 100644
index 0000000..0a6a9c2
--- /dev/null
+++ b/src/tracker_protocol.zig
@@ -0,0 +1,63 @@
+const std = @import("std");
+const bencode = @import("bencode.zig");
+
+// https://wiki.theory.org/BitTorrentSpecification#Tracker_Response
+pub const TrackerResp = struct {
+    // interval: u64,
+    peers: []std.net.Address,
+
+    pub fn parse(a: std.mem.Allocator, b: bencode.BValue) !TrackerResp {
+        var ipl = std.ArrayList(std.net.Address).init(a);
+        defer ipl.deinit();
+        var d = b.asDict() catch return error.Malformatted;
+        var pb = d.get("peers") orelse return error.Malformatted;
+        var ps = pb.asString() catch return error.Malformatted;
+        if ((ps.len % 6) != 0) return error.Malformatted;
+        for (0..ps.len / 6) |ix| {
+            const start = ix * 6;
+            const port = std.mem.readInt(u16, ps[start + 4 .. start + 6][0..2], .big);
+            var ip = [_]u8{0} ** 4;
+            @memcpy(&ip, ps[start .. start + 4]);
+            try ipl.append(std.net.Address.initIp4(ip, port));
+        }
+        return .{
+            .peers = try ipl.toOwnedSlice(),
+        };
+    }
+
+    pub fn deinit(self: *TrackerResp, a: std.mem.Allocator) void {
+        a.free(self.peers);
+    }
+};
+
+pub fn trackerRequestUrl(a: std.mem.Allocator, info_hash: [20]u8, peer_id: [20]u8, left: usize, announce: []const u8) ![]const u8 {
+    var q = std.StringHashMap([]const u8).init(a);
+    defer q.deinit();
+    try q.put("info_hash", &info_hash);
+    try q.put("peer_id", &peer_id);
+    try q.put("port", "6881");
+    try q.put("uploaded", "0");
+    try q.put("downloaded", "0");
+    var buf_left = [_]u8{0} ** 1024;
+    try q.put("left", try std.fmt.bufPrint(&buf_left, "{}", .{left}));
+    try q.put("compact", "1");
+    var qs = try toqs(a, q);
+    defer a.free(qs);
+    return try std.fmt.allocPrint(a, "{s}?{s}", .{ announce, qs });
+}
+
+fn toqs(a: std.mem.Allocator, hm: std.StringHashMap([]const u8)) ![]const u8 {
+    var al = std.ArrayList(u8).init(a);
+    defer al.deinit();
+    var w = al.writer();
+    var it = hm.iterator();
+    var first = true;
+    while (it.next()) |entry| {
+        if (!first) try w.writeByte('&');
+        try std.Uri.writeEscapedQuery(w, entry.key_ptr.*);
+        try w.writeByte('=');
+        try std.Uri.writeEscapedQuery(w, entry.value_ptr.*);
+        first = false;
+    }
+    return try al.toOwnedSlice();
+}