From e3c5be0a33e66b124ff261479cffa9f95ce53dc0 Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Sat, 11 Nov 2023 22:17:31 +0000
Subject: Make request to tracker, get and parse response to find peers list

---
 src/main.zig     | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 src/metainfo.zig | 11 ++++++-
 2 files changed, 104 insertions(+), 4 deletions(-)

(limited to 'src')

diff --git a/src/main.zig b/src/main.zig
index 14ab3c3..9966a55 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,10 +1,101 @@
 const std = @import("std");
+const MetaInfo = @import("metainfo.zig");
+const bencode = @import("bencode.zig");
 
 pub fn main() !void {
-    std.log.info("Hello, World", .{});
+    var gpa = std.heap.GeneralPurposeAllocator(.{}){};
+    defer _ = gpa.deinit();
+    const a = gpa.allocator();
+
+    // open & parse the torrent file
+    const f = try std.fs.cwd().openFile("src/sample.torrent", .{});
+    defer f.close();
+    var fr = f.reader();
+    var mib = try bencode.bdecode(a, fr);
+    defer mib.deinit(a);
+    var mi = try MetaInfo.parse(a, mib);
+    defer mi.deinit(a);
+
+    // call the tracker...
+    var c = std.http.Client{
+        .allocator = a,
+    };
+    defer c.deinit();
+
+    var q = std.StringHashMap([]const u8).init(a);
+    defer q.deinit();
+    var info_hash = try mi.info.hash(a);
+    var buf_left = [_]u8{0} ** 1024;
+    try q.put("info_hash", &info_hash);
+    try q.put("peer_id", "00112233445566778899");
+    try q.put("port", "6881");
+    try q.put("uploaded", "0");
+    try q.put("downloaded", "0");
+    try q.put("left", try std.fmt.bufPrint(&buf_left, "{}", .{mi.info.files[0].length}));
+    try q.put("compact", "1");
+    var qs = try toqs(a, q);
+    defer a.free(qs);
+    var url = try std.fmt.allocPrint(a, "{s}?{s}", .{ mi.announce, qs });
+    defer a.free(url);
+    var res = try c.fetch(a, .{ .location = .{ .url = url } });
+    defer res.deinit();
+    if (res.status == .ok) {
+        var trb = try bencode.bdecodeBuf(a, res.body.?);
+        defer trb.deinit(a);
+        var tr = try TrackerResp.parse(a, trb);
+        defer tr.deinit(a);
+        var w = std.io.getStdOut().writer();
+        for (tr.peers) |peer| {
+            try std.fmt.format(w, "peer: {}\n", .{peer});
+        }
+    }
+}
+
+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();
 }
 
+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);
+    }
+};
+
 test {
-    _ = @import("bencode.zig");
-    _ = @import("metainfo.zig");
+    _ = bencode;
+    _ = MetaInfo;
 }
diff --git a/src/metainfo.zig b/src/metainfo.zig
index 29cc655..cd00438 100644
--- a/src/metainfo.zig
+++ b/src/metainfo.zig
@@ -63,9 +63,13 @@ pub const Info = struct {
             const pri = pr.asInt(u1) catch return error.Malformatted;
             priv = pri == 1;
         }
+        // Validation....
+        const ps = pp.asString() catch return error.Malformatted;
+        if (ps.len % 20 != 0) return error.Malformatted;
+
         return .{
             .piece_length = pl.asInt(u64) catch return error.Malformatted,
-            .pieces = pp.asString() catch return error.Malformatted,
+            .pieces = ps,
             .files = try files.toOwnedSlice(),
             .private = priv,
         };
@@ -112,6 +116,11 @@ pub const Info = struct {
         try b.bencode(w);
         return sha1.finalResult();
     }
+    pub fn pieceHash(self: Info, ix: usize) ?[]const u8 {
+        const start = 20 * ix;
+        if (start >= self.pieces.len) return null;
+        return self.pieces[start .. start + 20];
+    }
 };
 
 info: Info,
-- 
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