common: rename decode_short_channel_ids.{c,h} to decode_array.{c.h}

This encoding scheme is no longer just used for short_channel_ids, so make
the names more generic.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

common/decode_array.c

@@ -0,0 +1,105 @@
+#include <ccan/cast/cast.h>
+#include <common/decode_array.h>
+#include <common/utils.h>
+#include <wire/gen_peer_wire.h>
+#include <wire/wire.h>
+#include <zlib.h>
+
+static u8 *unzlib(const tal_t *ctx, const u8 *encoded, size_t len)
+{
+	/* http://www.zlib.net/zlib_tech.html gives 1032:1 as worst-case,
+	 * which is 67632120 bytes for us.  But they're not encoding zeroes,
+	 * and each scid must be unique.  So 1MB is far more reasonable. */
+	unsigned long unclen = 1024*1024;
+	int zerr;
+	u8 *unc = tal_arr(ctx, u8, unclen);
+
+	zerr = uncompress(unc, &unclen, encoded, len);
+	if (zerr != Z_OK)
+		return tal_free(unc);
+
+	/* Truncate and return. */
+	tal_resize(&unc, unclen);
+	return unc;
+}
+
+struct short_channel_id *decode_short_ids(const tal_t *ctx, const u8 *encoded)
+{
+	struct short_channel_id *scids;
+	size_t max = tal_count(encoded);
+	enum arr_encode_types type;
+
+	/* BOLT #7:
+	 *
+	 * The receiver:
+	 *   - if the first byte of `encoded_short_ids` is not a known encoding
+	 *     type:
+	 *     - MAY fail the connection
+	 *   - if `encoded_short_ids` does not decode into a whole number of
+	 *     `short_channel_id`:
+	 *     - MAY fail the connection
+	 */
+	type = fromwire_u8(&encoded, &max);
+	switch (type) {
+	case ARR_ZLIB:
+		encoded = unzlib(tmpctx, encoded, max);
+		if (!encoded)
+			return NULL;
+		max = tal_count(encoded);
+		/* fall thru */
+	case ARR_UNCOMPRESSED:
+		scids = tal_arr(ctx, struct short_channel_id, 0);
+		while (max) {
+			struct short_channel_id scid;
+			fromwire_short_channel_id(&encoded, &max, &scid);
+			tal_arr_expand(&scids, scid);
+		}
+
+		/* encoded is set to NULL if we ran over */
+		if (!encoded)
+			return tal_free(scids);
+		return scids;
+	}
+	return NULL;
+}
+
+bigsize_t *decode_scid_query_flags(const tal_t *ctx,
+				   const struct tlv_query_short_channel_ids_tlvs_query_flags *qf)
+{
+	u8 *encoded = qf->encoded_query_flags;
+	size_t max = tal_count(encoded);
+	bigsize_t *flags;
+
+	/* BOLT #7:
+	 *
+	 * The receiver:
+	 *...
+	 *  - if the incoming message includes `query_short_channel_ids_tlvs`:
+	 *    - if `encoding_type` is not a known encoding type:
+	 *      - MAY fail the connection
+	 *    - if `encoded_query_flags` does not decode to exactly one flag per
+	 *      `short_channel_id`:
+	 *      - MAY fail the connection.
+	 */
+	switch (qf->encoding_type) {
+	case ARR_ZLIB:
+		encoded = unzlib(tmpctx, encoded, max);
+		if (!encoded)
+			return NULL;
+		max = tal_count(encoded);
+		/* fall thru */
+	case ARR_UNCOMPRESSED:
+		flags = tal_arr(ctx, bigsize_t, 0);
+		while (max)
+			tal_arr_expand(&flags,
+				       fromwire_bigsize(cast_const2(const u8 **,
+								    &encoded),
+							&max));
+
+		/* encoded is set to NULL if we ran over */
+		if (!encoded)
+			return tal_free(flags);
+		return flags;
+	}
+	return NULL;
+}