From 7eff166e1f7b440392be1082e3edd0c38b92d77c Mon Sep 17 00:00:00 2001
From: Martin Ashby <martin@ashbysoft.com>
Date: Sat, 11 Nov 2023 11:20:15 +0000
Subject: Add basic meta info file parsing

---
 sample.torrent     |  1 -
 src/bencode.zig    | 23 +++++++++++++++++++++++
 src/main.zig       |  5 ++++-
 src/metainfo.zig   | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 src/sample.torrent |  1 +
 5 files changed, 75 insertions(+), 2 deletions(-)
 delete mode 100644 sample.torrent
 create mode 100644 src/metainfo.zig
 create mode 100644 src/sample.torrent

diff --git a/sample.torrent b/sample.torrent
deleted file mode 100644
index 44d1411..0000000
--- a/sample.torrent
+++ /dev/null
@@ -1 +0,0 @@
-d8:announce55:http://bittorrent-test-tracker.codecrafters.io/announce10:created by13:mktorrent 1.14:infod6:lengthi92063e4:name10:sample.txt12:piece lengthi32768e6:pieces60:�v�z*����kg&���-n"u��vfVsn���R��5�
�z����	r'�����ee
\ No newline at end of file
diff --git a/src/bencode.zig b/src/bencode.zig
index 44dec0d..d09f394 100644
--- a/src/bencode.zig
+++ b/src/bencode.zig
@@ -70,6 +70,29 @@ pub const BValue = union(enum) {
             .int => {},
         }
     }
+
+    pub fn asDict(self: BValue) !std.StringArrayHashMap(BValue) {
+        switch (self) {
+            .dict => |d| return d,
+            else => return error.WrongType,
+        }
+    }
+
+    pub fn asInt(self: BValue, comptime itype: type) !itype {
+        switch (self) {
+            .int => |i| {
+                return std.math.cast(itype, i) orelse error.Overflow;
+            },
+            else => return error.WrongType,
+        }
+    }
+
+    pub fn asString(self: BValue) ![]const u8 {
+        switch (self) {
+            .string => |s| return s,
+            else => return error.WrongType,
+        }
+    }
 };
 
 pub fn bdecodeBuf(a: std.mem.Allocator, buf: []const u8) !BValue {
diff --git a/src/main.zig b/src/main.zig
index fa8a1b6..14ab3c3 100644
--- a/src/main.zig
+++ b/src/main.zig
@@ -1,7 +1,10 @@
 const std = @import("std");
 
-pub fn main() !void {}
+pub fn main() !void {
+    std.log.info("Hello, World", .{});
+}
 
 test {
     _ = @import("bencode.zig");
+    _ = @import("metainfo.zig");
 }
diff --git a/src/metainfo.zig b/src/metainfo.zig
new file mode 100644
index 0000000..9fa4788
--- /dev/null
+++ b/src/metainfo.zig
@@ -0,0 +1,47 @@
+//! https://wiki.theory.org/BitTorrentSpecification#Metainfo_File_Structure
+const std = @import("std");
+const bencode = @import("bencode.zig");
+const MetaInfo = @This();
+
+pub const Info = struct {
+    pub const File = struct {
+        name: []const u8,
+        length: u64,
+        path: []const u8,
+    };
+    piece_length: u64,
+    pieces: []const u8,
+    files: []File,
+    pub fn parse(b: bencode.BValue) !Info {
+        var d = b.asDict() catch return error.Malformatted;
+        const pl = d.get("piece length") orelse return error.Malformatted;
+        const pp = d.get("pieces") orelse return error.Malformatted;
+        return .{
+            .piece_length = pl.asInt(u64) catch return error.Malformatted,
+            .pieces = pp.asString() catch return error.Malformatted,
+            .files = &[_]File{},
+        };
+    }
+};
+
+info: Info,
+announce: []const u8,
+
+pub fn parse(b: bencode.BValue) !MetaInfo {
+    var d = b.asDict() catch return error.Malformatted;
+    const i = d.get("info") orelse return error.Malformatted;
+    const a = d.get("announce") orelse return error.Malformatted;
+    return .{
+        .info = try Info.parse(i),
+        .announce = a.asString() catch return error.Malformatted,
+    };
+}
+
+test "sample" {
+    const a = std.testing.allocator;
+    const sample_str = @embedFile("sample.torrent");
+    var b = try bencode.bdecodeBuf(a, sample_str);
+    defer b.deinit(a);
+    const mi = try MetaInfo.parse(b);
+    try std.testing.expectEqualStrings("http://bittorrent-test-tracker.codecrafters.io/announce", mi.announce);
+}
diff --git a/src/sample.torrent b/src/sample.torrent
new file mode 100644
index 0000000..44d1411
--- /dev/null
+++ b/src/sample.torrent
@@ -0,0 +1 @@
+d8:announce55:http://bittorrent-test-tracker.codecrafters.io/announce10:created by13:mktorrent 1.14:infod6:lengthi92063e4:name10:sample.txt12:piece lengthi32768e6:pieces60:�v�z*����kg&���-n"u��vfVsn���R��5�
�z����	r'�����ee
\ No newline at end of file
-- 
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