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protocol: no signature in update_commit if receiver has no outputs.

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So if there are no HTLCs, and the receiver can't spend anyway, don't
sign.  This has the added benefit that no two signed commitment
transactions will ever be identical (the revocation preimage changes).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Rusty Russell
2016-08-18 14:25:13 +09:30
parent 5f4b4525b3
commit 8a3c9908ce
8 changed files with 92 additions and 52 deletions
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35
daemon/commit_tx.c
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@@ -111,29 +111,32 @@ u8 *commit_output_to_them(const tal_t *ctx,
}
}
static void add_output(struct bitcoin_tx *tx, u8 *script, u64 amount,
static bool add_output(struct bitcoin_tx *tx, u8 *script, u64 amount,
u64 *total)
{
assert(tx->output_count < tal_count(tx->output));
if (is_dust(amount))
return;
return false;
tx->output[tx->output_count].script = script;
tx->output[tx->output_count].script_length = tal_count(script);
tx->output[tx->output_count].amount = amount;
tx->output_count++;
(*total) += amount;
return true;
}
struct bitcoin_tx *create_commit_tx(const tal_t *ctx,
struct peer *peer,
const struct sha256 *rhash,
const struct channel_state *cstate,
enum htlc_side side)
enum htlc_side side,
bool *otherside_only)
{
struct bitcoin_tx *tx;
uint64_t total = 0;
struct htlc_map_iter it;
struct htlc *h;
bool pays_to[2];
int committed_flag = HTLC_FLAG(side,HTLC_F_COMMITTED);
/* Now create commitment tx: one input, two outputs (plus htlcs) */
@@ -145,21 +148,31 @@ struct bitcoin_tx *create_commit_tx(const tal_t *ctx,
tx->input[0].amount = tal_dup(tx->input, u64, &peer->anchor.satoshis);
tx->output_count = 0;
add_output(tx, commit_output_to_us(tx, peer, rhash, side, NULL),
cstate->side[OURS].pay_msat / 1000, &total);
add_output(tx, commit_output_to_them(tx, peer, rhash, side, NULL),
cstate->side[THEIRS].pay_msat / 1000, &total);
pays_to[LOCAL] = add_output(tx, commit_output_to_us(tx, peer, rhash,
side, NULL),
cstate->side[OURS].pay_msat / 1000,
&total);
pays_to[REMOTE] = add_output(tx, commit_output_to_them(tx, peer, rhash,
side, NULL),
cstate->side[THEIRS].pay_msat / 1000,
&total);
/* If their tx doesn't pay to them, or our tx doesn't pay to us... */
*otherside_only = !pays_to[side];
/* First two outputs done, now for the HTLCs. */
for (h = htlc_map_first(&peer->htlcs, &it);
h;
h = htlc_map_next(&peer->htlcs, &it)) {
const u8 *wscript;
if (!htlc_has(h, committed_flag))
continue;
add_output(tx, scriptpubkey_p2wsh(tx,
wscript_for_htlc(tx, peer, h,
rhash, side)),
h->msatoshis / 1000, &total);
wscript = wscript_for_htlc(tx, peer, h, rhash, side);
/* If we pay any HTLC, it's txout is not just to other side. */
if (add_output(tx, scriptpubkey_p2wsh(tx, wscript),
h->msatoshis / 1000, &total))
*otherside_only = false;
}
assert(total <= peer->anchor.satoshis);