1 files changed, 101 insertions, 0 deletions
diff --git a/src/libknot/packet/compr.h b/src/libknot/packet/compr.h
new file mode 100644
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--- /dev/null
+++ b/src/libknot/packet/compr.h
@@ -0,0 +1,101 @@
+/*  Copyright (C) 2018 CZ.NIC, z.s.p.o. <knot-dns@labs.nic.cz>
+
+    This program is free software: you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation, either version 3 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+/*!
+ * \file
+ *
+ * \brief Name compression API.
+ *
+ * \addtogroup pkt
+ * @{
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#include "libknot/packet/wire.h"
+
+/*! \brief Compression hint type. */
+enum knot_compr_hint {
+	KNOT_COMPR_HINT_NONE    = 0, /* No hint. */
+	KNOT_COMPR_HINT_NOCOMP  = 1, /* Don't compress. */
+	KNOT_COMPR_HINT_QNAME   = KNOT_WIRE_HEADER_SIZE /* Name is QNAME. */
+};
+
+/*! \brief Compression hint array offsets. */
+enum knot_compr_offset {
+	KNOT_COMPR_HINT_OWNER = 0,  /* First element in the array is RR owner. */
+	KNOT_COMPR_HINT_RDATA = 1,  /* First name in RDATA is at offset 1. */
+	KNOT_COMPR_HINT_COUNT = 16  /* Maximum number of stored hints per-RR. */
+};
+
+/*
+ * \note A little bit about how compression hints work.
+ *
+ * We're storing a RRSet say 'abcd. CNAME [0]net. [1]com.' (owner=abcd. 2 RRs).
+ * The owner 'abcd.' is same for both RRs, we put it at the offset 0 in rrinfo.compress_ptr
+ * The names 'net.' and 'com.' are in the RDATA, therefore go to offsets 1 and 2.
+ * Now this is useful when solving additionals for example, because we can scan
+ * rrinfo for this RRSet and we know that 'net.' name is at the hint 1 and that leads
+ * to packet position N. With that, we just put the pointer in without any calculation.
+ * This is also useful for positive answers, where we know the RRSet owner is always QNAME.
+ * All in all, we just remember the positions of written domain names.
+ */
+
+/*! \brief Additional information about RRSet position and compression hints. */
+typedef struct {
+	uint16_t pos;   /* RRSet position in the packet. */
+	uint16_t flags; /* RRSet flags. */
+	uint16_t compress_ptr[KNOT_COMPR_HINT_COUNT]; /* Array of compr. ptr hints. */
+} knot_rrinfo_t;
+
+/*!
+ * \brief Name compression context.
+ */
+typedef struct knot_compr {
+	uint8_t *wire;          /* Packet wireformat. */
+	knot_rrinfo_t *rrinfo;  /* Hints for current RRSet. */
+	struct {
+		uint16_t pos;   /* Position of current suffix. */
+		uint8_t labels; /* Label count of the suffix. */
+	} suffix;
+} knot_compr_t;
+
+/*!
+ * \brief Retrieve compression hint from given offset.
+ */
+static inline uint16_t knot_compr_hint(const knot_rrinfo_t *info, uint16_t hint_id)
+{
+	if (hint_id < KNOT_COMPR_HINT_COUNT) {
+		return info->compress_ptr[hint_id];
+	} else {
+		return KNOT_COMPR_HINT_NONE;
+	}
+}
+
+/*!
+ * \brief Store compression hint for given offset.
+ */
+static inline void knot_compr_hint_set(knot_rrinfo_t *info, uint16_t hint_id,
+                                       uint16_t val, uint16_t len)
+{
+	if ((hint_id < KNOT_COMPR_HINT_COUNT) && (val + len < KNOT_WIRE_PTR_MAX)) {
+		info->compress_ptr[hint_id] = val;
+	}
+}
+
+/*! @} */