net: mqtt: add mqtt_readall_publish_payload()

This function uses mqtt_read_publish_payload_blocking to perform a
blocking read of the specified number of bytes.

When reading out a payload, the normal use case is to read the
entire payload. This function facilitates that use case.

Signed-off-by: Håkon Øye Amundsen <haakon.amundsen@nordicsemi.no>

include/net/mqtt.h

@@ -715,6 +715,21 @@ int mqtt_read_publish_payload(struct mqtt_client *client, void *buffer,
 int mqtt_read_publish_payload_blocking(struct mqtt_client *client, void *buffer,
 				       size_t length);
 
+/**
+ * @brief Blocking version of @ref mqtt_read_publish_payload function which
+ *        runs until the required number of bytes are read.
+ *
+ * @param[in] client Client instance for which the procedure is requested.
+ *                   Shall not be NULL.
+ * @param[out] buffer Buffer where payload should be stored.
+ * @param[in] length Number of bytes to read.
+ *
+ * @return 0 if success, otherwise a negative error code (errno.h) indicating
+ *         reason of failure.
+ */
+int mqtt_readall_publish_payload(struct mqtt_client *client, u8_t *buffer,
+				 size_t length);
+
 #ifdef __cplusplus
 }
 #endif

subsys/net/lib/mqtt/mqtt.c

@@ -647,3 +647,25 @@ int mqtt_read_publish_payload_blocking(struct mqtt_client *client, void *buffer,
 {
 	return read_publish_payload(client, buffer, length, true);
 }
+
+int mqtt_readall_publish_payload(struct mqtt_client *client, u8_t *buffer,
+				 size_t length)
+{
+	u8_t *end = buffer + length;
+
+	while (buffer < end) {
+		int ret = mqtt_read_publish_payload_blocking(client, buffer,
+							     end - buffer);
+
+		if (ret < 0) {
+			return ret;
+		} else if (ret == 0) {
+			return -EIO;
+		}
+
+		buffer += ret;
+	}
+
+	return 0;
+}
+

tests/net/lib/mqtt_pubsub/src/test_mqtt_pubsub.c

@@ -101,8 +101,7 @@ void publish_handler(struct mqtt_client *const client,
 		    const struct mqtt_evt *evt)
 {
 	int rc;
-	u8_t buf[16];
+	static u8_t buf[sizeof(payload_long)];
-	u32_t offset = 0U;
 
 	if (evt->result != 0) {
 		TC_PRINT("MQTT PUBLISH error: %d\n", evt->result);
@@ -115,26 +114,19 @@ void publish_handler(struct mqtt_client *const client,
 		goto error;
 	}
 
-	while (payload_left > 0) {
+	rc = mqtt_readall_publish_payload(client, buf, payload_left);
-		rc = mqtt_read_publish_payload_blocking(client, buf,
+	if (rc != 0) {
-							sizeof(buf));
+		TC_PRINT("Error while reading publish payload\n");
-		if (rc <= 0) {
+		goto error;
-			TC_PRINT("Failed to receive payload, err: %d\n", -rc);
-			if (rc == -EAGAIN) {
-				continue;
-			}
-			goto error;
-		}
-
-		if (memcmp(payload + offset, buf, rc) != 0) {
-			TC_PRINT("Invalid payload content\n");
-			goto error;
-		}
-
-		payload_left -= rc;
-		offset += rc;
 	}
 
+	if (memcmp(payload, buf, evt->param.publish.message.payload.len != 0)) {
+		TC_PRINT("Invalid payload content\n");
+		goto error;
+	}
+
+	payload_left = 0;
+
 	return;
 
 error: