process_estimatefee: fix bad logic.

Refactor the fallback to make it more robust.

Fixes: #28
Reported-by: Jacob <jacobdnd@gmail.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

daemon/bitcoind.c

@@ -176,7 +176,7 @@ start_bitcoin_cli(struct lightningd_state *dstate,
 	next_bcli(dstate);
 }
 
-static void process_estimatefee(struct bitcoin_cli *bcli)
+static void process_estimatefee_6(struct bitcoin_cli *bcli)
 {
 	double fee;
 	char *p, *end;
@@ -189,34 +189,50 @@ static void process_estimatefee(struct bitcoin_cli *bcli)
 		fatal("%s: gave non-numeric fee %s",
 		      bcli_args(bcli), p);
 
-	/* Don't know at 2?  Try 6... */
 	if (fee < 0) {
-		if (streq(bcli->args[3], "2")) {
-			start_bitcoin_cli(bcli->dstate, process_estimatefee,
-					  false, bcli->cb, bcli->cb_arg,
-					  "estimatefee", "6", NULL);
-			return;
-		}
 		log_unusual(bcli->dstate->base_log,
 			    "Unable to estimate fee, using %"PRIu64,
 			    bcli->dstate->config.closing_fee_rate);
 		fee_rate = bcli->dstate->config.closing_fee_rate;
 	} else {
-		/* If we used 6 as an estimate, double it. */
-		if (streq(bcli->args[3], "6"))
-			fee *= 2;
+		/* Since we used 6 as an estimate, double it. */
+		fee *= 2;
 		fee_rate = fee * 100000000;
 	}
 
 	cb(bcli->dstate, fee_rate, bcli->cb_arg);
 }
 
+static void process_estimatefee_2(struct bitcoin_cli *bcli)
+{
+	double fee;
+	char *p, *end;
+	u64 fee_rate;
+	void (*cb)(struct lightningd_state *, u64, void *) = bcli->cb;
+
+	p = tal_strndup(bcli, bcli->output, bcli->output_bytes);
+	fee = strtod(p, &end);
+	if (end == p || *end != '\n')
+		fatal("%s: gave non-numeric fee %s",
+		      bcli_args(bcli), p);
+
+	/* Don't know at 2?  Try 6... */
+	if (fee < 0) {
+		start_bitcoin_cli(bcli->dstate, process_estimatefee_6,
+				  false, bcli->cb, bcli->cb_arg,
+				  "estimatefee", "6", NULL);
+		return;
+	}
+	fee_rate = fee * 100000000;
+	cb(bcli->dstate, fee_rate, bcli->cb_arg);
+}
+
 void bitcoind_estimate_fee_(struct lightningd_state *dstate,
 			    void (*cb)(struct lightningd_state *dstate,
 				       u64, void *),
 			    void *arg)
 {
-	start_bitcoin_cli(dstate, process_estimatefee, false, cb, arg,
+	start_bitcoin_cli(dstate, process_estimatefee_2, false, cb, arg,
 			  "estimatefee", "2", NULL);
 }