altagos.dev
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read qname
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-3
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src/root.zig
+101
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src/root.zig
···
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}
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/// Get a range of bytes
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pub fn get_range(self: *const BytePacketBuffer, start: usize, len: usize) ReadError![]const u8 {
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pub fn getRange(self: *const BytePacketBuffer, start: usize, len: usize) ReadError![]const u8 {
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if (start + len >= comptime self.buf.len) return ReadError.EndOfBuffer;
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return self.buf[start .. start + len];
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}
···
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/// The tricky part: Reading domain names, taking labels into consideration.
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/// Will take something like [3]www[6]google[3]com and append
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/// www.google.com to outstr.
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pub fn read_qname(self: *BytePacketBuffer, outstr: []u8) ReadError!void {
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pub fn readQname(self: *BytePacketBuffer, outstr: []u8) ReadError!void {
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// We might encounter jumps, therefore we need to keep thrack of our position locally
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var pos = self.pos;
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var out_pos: usize = 0;
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if (!jumped) self.seek(1);
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}
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/// Read a qname
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///
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/// The tricky part: Reading domain names, taking labels into consideration.
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/// Will take something like [3]www[6]google[3]com and append
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/// www.google.com to outstr.
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pub fn readQnameAlloc(self: *BytePacketBuffer, alloc: std.mem.Allocator) ![]u8 {
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var buffer: std.ArrayList(u8) = .init(alloc);
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// We might encounter jumps, therefore we need to keep thrack of our position locally
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var pos = self.pos;
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// track whether or nor we've jumped
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var jumped = false;
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const max_jumps: usize = 5;
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var jumps_performed: usize = 0;
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var delim: ?[]const u8 = null;
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while (true) {
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if (jumps_performed > max_jumps) return ReadError.JumpLimitExceeded;
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// Each label starts with a length byte
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const len = try self.get(pos);
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// If len has the two most signigicant bit set, it represents a jump to some other
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// offset in the packet:
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if ((len & 0xC0) == 0xC0) {
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// Update the buffer position to a point past the current label
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if (!jumped) self.seek(2);
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// Read another byte, calculate offset and performe the jump by updating our
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// local position variable
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const b2 = @as(u16, try self.get(pos + 1));
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const offset = ((@as(u16, len) ^ 0xC0) << 8) | b2;
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pos = @as(usize, offset);
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// Indicate that a jump was performed
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jumped = true;
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jumps_performed += 1;
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continue;
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} else {
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// Move a single byte forward to move path the length
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self.pos += 1;
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pos += 1;
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// Domain names are terminated by an empty label of length 0, so if the length
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// is zero we're done
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if (len == 0) break;
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if (delim) |del| {
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try buffer.appendSlice(del);
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}
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try buffer.appendSlice(try self.getRange(pos, len));
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delim = ".";
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pos += len;
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}
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}
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if (!jumped) self.seek(1);
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return buffer.toOwnedSlice();
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}
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};
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test "BytePacketBuffer.read" {
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const outstr = try allocator.alloc(u8, expected.len);
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defer allocator.free(outstr);
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try buf.read_qname(outstr);
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try buf.readQname(outstr);
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try testing.expectEqualStrings(expected, outstr);
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}
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test "BytePacketBuffer.read_qname_alloc google.com" {
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const testing = std.testing;
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const allocator = testing.allocator;
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const input = [_]u8{
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0x06, // [6]
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0x67, // g
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0x6f, // o
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0x6f, // o
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0x67, // g
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0x6c, // l
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0x65, // e
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0x03, // [3]
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0x63, // c
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0x6f, // o
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0x6d, // m
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0x00, // [0]
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};
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const expected = "google.com";
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var buf = BytePacketBuffer{};
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for (input, 0..) |char, idx| {
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buf.buf[idx] = char;
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}
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const outstr = try buf.readQnameAlloc(allocator);
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defer allocator.free(outstr);
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try testing.expectEqualStrings(expected, outstr);
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}
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