From 6c24cd4862cd06f3364810b73e3de1bab411f31a Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Sun, 12 Nov 2023 21:17:01 +0000
Subject: Move tracker protocol into it's own file Change piece_length -> u32,
 protocol constrains that anyway annnnd, successfully download a file (albeit
 from one torrent only with no checking of a ton of stuff)

---
 src/peer_protocol.zig | 130 ++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 130 insertions(+)

(limited to 'src/peer_protocol.zig')

diff --git a/src/peer_protocol.zig b/src/peer_protocol.zig
index cd70ad2..91ea349 100644
--- a/src/peer_protocol.zig
+++ b/src/peer_protocol.zig
@@ -1,5 +1,51 @@
 const std = @import("std");
+const builtin = @import("builtin");
 
+pub fn readMessage(a: std.mem.Allocator, reader: anytype, comptime msgType: type) !msgType {
+    var nka: u32 = 0;
+    while (nka < 1000) {
+        var len = try reader.readInt(u32, .big);
+        // All messages except Keepalive start with a single byte message type.
+        // Skip keepalive messages, we don't care (unless you're spamming them)
+        if (len == 0) {
+            nka += 1; 
+            continue;
+        }
+        var mt = try reader.readByte();
+        if (mt != msgType.Tag) return error.ProtocolError;
+        return try msgType.read(a, len-1, reader);
+    } else {
+        return error.ProtocolError;
+    }
+}
+
+// When you're expecting several possible messages.
+// 'Expected' should be a tagged union of message types you are expecting.
+pub fn readAnyMessage(a: std.mem.Allocator, reader: anytype, comptime Expected: type) !Expected {
+    var nka: u32 = 0;
+    while (nka < 1000) {
+        var len = try reader.readInt(u32, .big);
+        // All messages except Keepalive start with a single byte message type.
+        // Skip keepalive messages, we don't care (unless you're spamming them)
+        if (len == 0) {
+            nka += 1; 
+            continue;
+        }
+        var mt = try reader.readByte();
+        inline for (@typeInfo(Expected).Union.fields) |field| {
+            const msgType = field.type;
+            if (msgType.Tag == mt) {
+                return @unionInit(Expected, field.name, try msgType.read(a, len-1, reader));
+            }
+        } else {
+            return error.ProtocolError;
+        }
+    } else {
+        return error.ProtocolError;
+    }
+}
+
+// Handshake message has a different structure to the rest. And it's only read once per connection.
 pub const Handshake = struct {
     info_hash: [20]u8,
     peer_id: [20]u8,
@@ -24,3 +70,87 @@ pub const Handshake = struct {
         try writer.writeAll(&self.peer_id);
     }
 };
+
+
+pub const Unchoke = struct {
+    pub const Tag: u8 = 1;
+    pub fn read(a: std.mem.Allocator, len: usize, reader: anytype) !Unchoke {
+        _ = a;
+        _ = reader;
+        if (len != 0) return error.ProtocolError;
+        return .{};
+    }
+};
+
+pub const Interested = struct {
+    pub const Tag: u8 = 2;
+    pub fn read(a: std.mem.Allocator, len: usize, reader: anytype) !Interested {
+        _ = a;
+        _ = reader;
+        if (len != 0) return error.ProtocolError;
+        return .{};   
+    }
+    pub fn write(writer: anytype) !void {
+        try writer.writeInt(u32, 1, .big);
+        try writer.writeInt(u8, Tag, .big);
+    }
+};
+
+pub const Bitfield = struct {
+    pub const Tag: u8 = 5;
+    pub fn read(a: std.mem.Allocator, len: usize, reader: anytype) !Bitfield {
+        // TODO actually read this message and do something useful.
+        _ = a;
+        try reader.skipBytes(len, .{}); // 
+        return .{};
+    }
+};
+
+pub const Request = struct {
+    pub const Tag: u8 = 6;
+    index: u32, 
+    begin: u32, 
+    length: u32,
+    pub fn write(self: Request, writer: anytype) !void {
+        try writer.writeInt(u32, 13, .big);
+        try writer.writeInt(u8, Tag, .big);
+        try writer.writeInt(u32,self.index, .big);
+        try writer.writeInt(u32,self.begin, .big);
+        try writer.writeInt(u32,self.length, .big);
+    }
+};
+
+pub const Piece = struct {
+    pub const Tag: u8 = 7;
+    index: u32,
+    begin: u32,
+    block: []const u8,
+    pub fn read(a: std.mem.Allocator, len: usize, reader: anytype) !Piece {
+        if (len <= 8) {
+            std.log.err("Piece#read len {}", .{len});
+            return error.ProtocolError;
+        }
+        var ix = try reader.readInt(u32, .big);
+        var be = try reader.readInt(u32, .big);
+        var bl = try a.alloc(u8, len-8);
+        errdefer a.free(bl);
+        try reader.readNoEof(bl);
+        return .{
+            .index = ix, 
+            .begin = be,
+            .block = bl,
+        };
+    }
+    pub fn deinit(self: *Piece, a: std.mem.Allocator) void {
+        a.free(self.block);
+    }
+};
+
+test "read any" {
+    const a = std.testing.allocator;
+    var fbs = std.io.fixedBufferStream(&[_]u8{0, 0, 0, 1, Unchoke.Tag});
+    var r = fbs.reader();
+    const T = union(enum) {u: Unchoke, i: Interested, b: Bitfield};
+    var msg: T = try readAnyMessage(a, r, T);
+    try std.testing.expect(msg == .u);
+}
\ No newline at end of file
-- 
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