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//! Bencoding
//! See specification here https://wiki.theory.org/BitTorrentSpecification#Bencoding
const std = @import("std");
pub const Error = error.Malformatted || std.io.AnyReader.Error;
// All content is owned by the BValue and must be freed with deinit.
pub const BValue = union(enum) {
string: []const u8,
int: i64,
list: std.ArrayList(BValue),
dict: std.StringArrayHashMap(BValue),
pub fn deinit(self: *BValue, a: std.mem.Allocator) void {
switch (self.*) {
.string => |s| {
a.free(s);
},
.list => |*l| {
for (l.items) |*i| {
i.deinit(a);
}
l.deinit();
},
.dict => |*d| {
var it = d.iterator();
while (it.next()) |entry| {
a.free(entry.key_ptr.*);
entry.value_ptr.*.deinit(a);
}
d.deinit();
},
.int => {},
}
}
};
pub fn bdecodeBuf(a: std.mem.Allocator, buf: []const u8) !BValue {
var fbs = std.io.fixedBufferStream(buf);
return try bdecode(a, fbs.reader());
}
pub fn bdecode(a: std.mem.Allocator, base_reader: anytype) anyerror!BValue {
var reader = PeekStream.init(base_reader.any());
return bdecodeInner(a, &reader, 0);
}
const PeekStream = std.io.PeekStream(.{ .Static = 1 }, std.io.AnyReader);
// 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 bdecodeInner(a: std.mem.Allocator, peekStream: *PeekStream, depth: u32) !BValue {
if (depth > 100) {
// TODO diagnostic...
return error.Malformatted;
}
var reader = peekStream.reader();
var byte = try reader.readByte();
if (std.ascii.isDigit(byte)) {
try peekStream.putBackByte(byte);
return .{ .string = try readString(a, peekStream) };
} else {
switch (byte) {
'i' => {
const max_len = comptime std.fmt.comptimePrint("{}", .{std.math.minInt(i64)}).len;
var s = reader.readUntilDelimiterAlloc(a, 'e', max_len) catch return error.Malformatted;
defer a.free(s);
const i = std.fmt.parseInt(i64, s, 10) catch return error.Malformatted;
return .{ .int = i };
},
'l' => {
var list = std.ArrayList(BValue).init(a);
errdefer {
for (list.items) |*i| {
i.deinit(a);
}
list.deinit();
}
while (true) {
const b2 = try reader.readByte();
if (b2 == 'e') break;
try peekStream.putBackByte(b2);
var val = try bdecodeInner(a, peekStream, depth + 1);
errdefer val.deinit(a);
try list.append(val);
}
return .{ .list = list };
},
'd' => {
var dict = std.StringArrayHashMap(BValue).init(a);
errdefer {
var it = dict.iterator();
while (it.next()) |entry| {
a.free(entry.key_ptr.*);
entry.value_ptr.*.deinit(a);
}
dict.deinit();
}
lp: while (true) {
const b2 = try reader.readByte();
if (b2 == 'e') break :lp;
try peekStream.putBackByte(b2);
var key = try readString(a, peekStream);
errdefer a.free(key);
var val = try bdecode(a, reader);
errdefer val.deinit(a);
try dict.put(key, val);
}
return .{ .dict = dict };
},
else => return error.Malformatted, // TODO diagnostics
}
}
}
// Result is owned by the caller and must be freed
fn readString(a: std.mem.Allocator, peekStream: *PeekStream) ![]const u8 {
var reader = peekStream.reader();
const max_len = comptime std.fmt.comptimePrint("{}", .{std.math.maxInt(usize)}).len;
const str_len_s = reader.readUntilDelimiterAlloc(a, ':', max_len) catch {
return error.Malformatted;
};
defer a.free(str_len_s);
var strlen = std.fmt.parseInt(usize, str_len_s, 10) catch return error.Malformatted;
var string = try a.alloc(u8, strlen);
errdefer a.free(string);
reader.readNoEof(string) catch return error.Malformatted;
return string;
}
test "bdecode empty" {
var a = std.testing.allocator;
try std.testing.expectError(error.EndOfStream, bdecodeBuf(a, ""));
}
test "bdecode too short" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "1"));
}
test "bdecode plain number" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "12"));
}
test "bdecode garbage" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "xz1234"));
}
test "bdecode number" {
var a = std.testing.allocator;
var bval = try bdecodeBuf(a, "i123e");
defer bval.deinit(a);
try std.testing.expectEqualDeep(BValue{ .int = 123 }, bval);
}
test "bdecode number negative" {
var a = std.testing.allocator;
var bval = try bdecodeBuf(a, "i-123e");
defer bval.deinit(a);
try std.testing.expectEqualDeep(BValue{ .int = -123 }, bval);
}
test "bdecode number empty" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "ie"));
}
test "bdecode number just sign" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "i-e"));
}
test "bdecode number no end" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "i123123671283"));
}
test "bdecode number out of range" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "i9223372036854775808e"));
}
test "bdecode string" {
var a = std.testing.allocator;
var bval = try bdecodeBuf(a, "5:hello");
defer bval.deinit(a);
try std.testing.expectEqualDeep(BValue{ .string = "hello" }, bval);
}
test "bdecode string too short" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "5:hell"));
}
test "bdecode list" {
var a = std.testing.allocator;
var bval = try bdecodeBuf(a, "l5:hello5:worlde");
defer bval.deinit(a);
try std.testing.expectEqual(@as(usize, 2), bval.list.items.len);
try std.testing.expectEqualStrings("hello", bval.list.items[0].string);
try std.testing.expectEqualStrings("world", bval.list.items[1].string);
}
test "invalid list" {
var a = std.testing.allocator;
try std.testing.expectError(error.EndOfStream, bdecodeBuf(a, "l5:hello5:world")); // missing end
}
test "dict" {
var a = std.testing.allocator;
var bval = try bdecodeBuf(a, "d5:hello5:worlde");
defer bval.deinit(a);
var v = bval.dict.getPtr("hello") orelse return error.TestExpectedNotNull;
try std.testing.expectEqualStrings("world", v.string);
}
test "invalid dict no value" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "d5:hello5:world2:hie"));
}
test "invalid dict wrong key type" {
var a = std.testing.allocator;
try std.testing.expectError(error.Malformatted, bdecodeBuf(a, "di32e5:helloe"));
}
test "nested structure" {
var a = std.testing.allocator;
var bval = try bdecodeBuf(a, "d5:hello5:world2:hili123ei456el4:nesteee");
defer bval.deinit(a);
var v = bval.dict.getPtr("hello") orelse return error.TestExpectedNotNull;
try std.testing.expectEqualStrings("world", v.string);
var v2 = bval.dict.getPtr("hi") orelse return error.TestExpectedNotNull;
try std.testing.expectEqualDeep(v2.*.list.items[0], BValue{ .int = 123 });
try std.testing.expectEqualDeep(v2.*.list.items[1], BValue{ .int = 456 });
try std.testing.expectEqualStrings("nest", v2.*.list.items[2].list.items[0].string);
}
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