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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189const std = @import("std");const assert = std.debug.assert;const io = std.io;
pub const BytePacketBuffer = struct { buf: [512]u8 = undefined, pos: usize = 0,
pub const ReadError = error{ EndOfBuffer, JumpLimitExceeded, };
pub const Reader = io.Reader(*BytePacketBuffer, ReadError, read);
/// Change the buffer position forward a specific number of steps pub fn step(self: *BytePacketBuffer, pos: usize) void { self.pos += pos; }
/// Chanke the buffer position pub fn seek(self: *BytePacketBuffer, pos: usize) void { self.pos = pos; }
pub fn reader(self: *BytePacketBuffer) Reader { return .{ .context = self }; }
/// Read a single byte and move the position one step forward pub fn read(self: *BytePacketBuffer, dest: []u8) ReadError!usize { if (self.pos + dest.len > self.buf.len) return ReadError.EndOfBuffer; const size = dest.len; const end = self.pos + size; @memcpy(dest[0..size], self.buf[self.pos..end]); self.pos = end; return size; }
/// Get a single byte without changing the buffer position pub fn get(self: *const BytePacketBuffer, pos: usize) ReadError!u8 { if (pos >= comptime self.buf.len) return ReadError.EndOfBuffer; return self.buf[pos]; }
/// Get a range of bytes pub fn get_range(self: *const BytePacketBuffer, start: usize, len: usize) ReadError![]const u8 { if (start + len >= comptime self.buf.len) return ReadError.EndOfBuffer; return self.buf[start .. start + len]; }
/// Read a qname /// /// The tricky part: Reading domain names, taking labels into consideration. /// Will take something like [3]www[6]google[3]com and append /// www.google.com to outstr. pub fn read_qname(self: *BytePacketBuffer, outstr: []u8) ReadError!void { // We might encounter jumps, therefore we need to keep thrack of our position locally var pos = self.pos; var out_pos: usize = 0;
// track whether or nor we've jumped var jumped = false; const max_jumps: usize = 5; var jumps_performed: usize = 0;
var delim: ?[]const u8 = null; while (true) { if (jumps_performed > max_jumps) return ReadError.JumpLimitExceeded;
// Each label starts with a length byte const len = try self.get(pos);
// If len has the two most signigicant bit set, it represents a jump to some other // offset in the packet: if ((len & 0xC0) == 0xC0) { // Update the buffer position to a point past the current label if (!jumped) self.seek(2);
// Read another byte, calculate offset and performe the jump by updating our // local position variable const b2 = @as(u16, try self.get(pos + 1)); const offset = ((@as(u16, len) ^ 0xC0) << 8) | b2; pos = @as(usize, offset);
// Indicate that a jump was performed jumped = true; jumps_performed += 1;
continue; } else { // Move a single byte forward to move path the length self.pos += 1; pos += 1;
// Domain names are terminated by an empty label of length 0, so if the length // is zero we're done if (len == 0) break;
if (delim) |del| { @memcpy(outstr[out_pos .. out_pos + del.len], del); out_pos += del.len; }
const read_len = try self.read(outstr[out_pos .. out_pos + len]); assert(read_len == len);
delim = ".";
pos += len; out_pos += len; } }
if (!jumped) self.seek(1); }};
test "BytePacketBuffer.read" { const testing = std.testing; var buf = BytePacketBuffer{}; buf.buf[0] = 0x1; try testing.expectEqual(0x1, try buf.reader().readInt(u8, .big));}
test "BytePacketBuffer.read_u16" { const testing = std.testing; var buf = BytePacketBuffer{}; buf.buf[0] = 0x1; buf.buf[1] = 0x1; try testing.expectEqual(0x101, try buf.reader().readInt(u16, .big));}
test "BytePacketBuffer.read_u32" { const testing = std.testing; var buf = BytePacketBuffer{}; buf.buf[0] = 0x1; buf.buf[1] = 0x1; buf.buf[2] = 0x1; buf.buf[3] = 0x1; try testing.expectEqual(0x1010101, try buf.reader().readInt(u32, .big));}
test "BytePacketBuffer.read last byte" { const testing = std.testing; var buf = BytePacketBuffer{}; buf.buf[buf.buf.len - 1] = 0x1; buf.pos = buf.buf.len - 1; try testing.expectEqual(0x1, try buf.reader().readInt(u8, .big)); try testing.expectError( BytePacketBuffer.ReadError.EndOfBuffer, buf.reader().readInt(u8, .big), );}
test "BytePacketBuffer.read_qname google.com" { const testing = std.testing; const allocator = testing.allocator;
const input = [_]u8{ 0x06, // [6] 0x67, // g 0x6f, // o 0x6f, // o 0x67, // g 0x6c, // l 0x65, // e 0x03, // [3] 0x63, // c 0x6f, // o 0x6d, // m 0x00, // [0] }; const expected = "google.com";
var buf = BytePacketBuffer{}; for (input, 0..) |char, idx| { buf.buf[idx] = char; }
const outstr = try allocator.alloc(u8, expected.len); defer allocator.free(outstr);
try buf.read_qname(outstr);
try testing.expectEqualStrings(expected, outstr);}