[PATCH 5/7] alfred: gpsd: report failures while reading the answer

gpsd_receive_answer_packet() returns NULL for a:

* closed connection
* read error
* malformed packet
* unexpected answer

All of them were indistinguishable from the latter regular end of the
answer. Even on errors alfred-gpsd printed an empty (well formed document).
An error could not directly be detected by the return code.

Report the error state of the packet parsing separately and use it for the
exit code.

Fixes: 2b901d69d8fb ("alfred: Add support for passing location information over alfred.")
Signed-off-by: Sven Eckelmann <[email protected]>
---
 gpsd/alfred-gpsd.c | 40 ++++++++++++++++++++++++++++++----------
 1 file changed, 30 insertions(+), 10 deletions(-)

diff --git a/gpsd/alfred-gpsd.c b/gpsd/alfred-gpsd.c
index 43a3a83..57ac9cf 100644
--- a/gpsd/alfred-gpsd.c
+++ b/gpsd/alfred-gpsd.c
@@ -164,7 +164,7 @@ static ssize_t read_full(int fd, void *buf, size_t count)
 }
 
 static struct gpsd_v1 *gpsd_receive_answer_packet(int sock, uint16_t *len,
-						  uint8_t *source)
+						  uint8_t *source, int *error)
 {
 	struct alfred_push_data_v0 *push;
 	static uint8_t buf[65536];
@@ -173,15 +173,29 @@ static struct gpsd_v1 *gpsd_receive_answer_packet(int sock, uint16_t *len,
 	int ret;
 	int l;
 
+	*error = -1;
+
 	ret = read_full(sock, buf, sizeof(*tlv));
-	if (ret < 0)
+	if (ret < 0) {
+		perror("read from unix socket failed");
 		return NULL;
+	}
+
+	/* end of the answer */
+	if (ret == 0) {
+		*error = 0;
+		return NULL;
+	}
 
 	if (ret < (int)sizeof(*tlv))
 		return NULL;
 
 	tlv = (struct alfred_tlv *)buf;
-	/* TODO: might return an ALFRED_STATUS_ERROR too, handle it */
+	if (tlv->type == ALFRED_STATUS_ERROR) {
+		fprintf(stderr, "Request of gpsd data failed\n");
+		return NULL;
+	}
+
 	if (tlv->type != ALFRED_PUSH_DATA)
 		return NULL;
 
@@ -209,6 +223,8 @@ static struct gpsd_v1 *gpsd_receive_answer_packet(int sock, uint16_t *len,
 	if (data->header.version != GPSD_PACKETVERSION)
 		return NULL;
 
+	*error = 0;
+
 	memcpy(source, data->source, ETH_ALEN);
 	return (struct gpsd_v1 *) data->data;
 }
@@ -219,12 +235,12 @@ static int gpsd_read_answer(struct globals *globals)
 	uint8_t source[ETH_ALEN];
 	bool first_line = true;
 	uint16_t len;
+	int ret = 0;
 
 	printf("[\n");
 
 	while ((gpsd_data = gpsd_receive_answer_packet(globals->unix_sock,
-						       &len,
-						       source)) != NULL) {
+						       &len, source, &ret)) != NULL) {
 		if (len < sizeof(*gpsd_data))
 			break;
 
@@ -246,7 +262,7 @@ static int gpsd_read_answer(struct globals *globals)
 	printf("\n]\n");
 
 
-	return 0;
+	return ret;
 }
 
 /* Standard parsing of a GPS data source spec. Taken from gpsdclient.c
@@ -300,14 +316,16 @@ static void alfred_gpsd_source_spec(const char *arg,
 
 static int gpsd_get_data(struct globals *globals)
 {
+	int ret;
+
 	globals->unix_sock = gpsd_request_data(globals);
 	if (globals->unix_sock < 0)
 		return -1;
 
-	gpsd_read_answer(globals);
+	ret = gpsd_read_answer(globals);
 	close(globals->unix_sock);
 
-	return 0;
+	return ret;
 }
 
 static void gpsd_connect_gpsd(struct globals *globals)
@@ -584,8 +602,10 @@ int main(int argc, char *argv[])
 		return gpsd_server(globals);
 		break;
 	case OPMODE_CLIENT:
-		return gpsd_get_data(globals);
-		break;
+		if (gpsd_get_data(globals) < 0)
+			return EXIT_FAILURE;
+
+		return EXIT_SUCCESS;
 	}
 
 	return EXIT_FAILURE;

-- 
2.47.3