scpi: Add support for arbitray/definite length block data retrieval

Binary block data is specified in IEEE 488.2. First character is '#',
followed by a single ascii digit denoting the the number of digits needed
for the length specification. Length is given in bytes.

This allows drivers to replace retrieval of comma separated ASCII values
with binary formats. See bug #791.

src/scpi.h

@@ -128,6 +128,10 @@ SR_PRIV int sr_scpi_get_floatv(struct sr_scpi_dev_inst *scpi,
 			const char *command, GArray **scpi_response);
 SR_PRIV int sr_scpi_get_uint8v(struct sr_scpi_dev_inst *scpi,
 			const char *command, GArray **scpi_response);
+SR_PRIV int sr_scpi_get_data(struct sr_scpi_dev_inst *scpi,
+			const char *command, GString **scpi_response);
+SR_PRIV int sr_scpi_get_block(struct sr_scpi_dev_inst *scpi,
+			const char *command, GByteArray **scpi_response);
 SR_PRIV int sr_scpi_get_hw_id(struct sr_scpi_dev_inst *scpi,
 			struct sr_scpi_hw_info **scpi_response);
 SR_PRIV void sr_scpi_hw_info_free(struct sr_scpi_hw_info *hw_info);

src/scpi/scpi.c

@@ -387,41 +387,13 @@ SR_PRIV void sr_scpi_free(struct sr_scpi_dev_inst *scpi)
 SR_PRIV int sr_scpi_get_string(struct sr_scpi_dev_inst *scpi,
 			       const char *command, char **scpi_response)
 {
-	char buf[256];
-	int len;
 	GString *response;
-	gint64 laststart;
-	unsigned int elapsed_ms;
+	response = g_string_sized_new(1024);
 
-	if (command)
-		if (sr_scpi_send(scpi, command) != SR_OK)
-			return SR_ERR;
-
-	if (sr_scpi_read_begin(scpi) != SR_OK)
+	if (sr_scpi_get_data(scpi, command, &response) != SR_OK) {
+		if (response)
+			g_string_free(response, TRUE);
 		return SR_ERR;
-
-	laststart = g_get_monotonic_time();
-
-	response = g_string_new("");
-
-	*scpi_response = NULL;
-
-	while (!sr_scpi_read_complete(scpi)) {
-		len = sr_scpi_read_data(scpi, buf, sizeof(buf));
-		if (len < 0) {
-			sr_err("Incompletely read SCPI response.");
-			g_string_free(response, TRUE);
-			return SR_ERR;
-		} else if (len > 0) {
-		        laststart = g_get_monotonic_time();
-		}
-		g_string_append_len(response, buf, len);
-		elapsed_ms = (g_get_monotonic_time() - laststart) / 1000;
-		if (elapsed_ms >= scpi->read_timeout_ms) {
-			sr_err("Timed out waiting for SCPI response.");
-			g_string_free(response, TRUE);
-			return SR_ERR;
-		}
 	}
 
 	/* Get rid of trailing linefeed if present */
@@ -440,6 +412,54 @@ SR_PRIV int sr_scpi_get_string(struct sr_scpi_dev_inst *scpi,
 	return SR_OK;
 }
 
+SR_PRIV int sr_scpi_get_data(struct sr_scpi_dev_inst *scpi,
+			     const char *command, GString **scpi_response)
+{
+	int len;
+	GString *response;
+	gint64 laststart;
+	unsigned int elapsed_ms;
+	unsigned int offset = 0;
+	int space;
+
+	if (command)
+		if (sr_scpi_send(scpi, command) != SR_OK)
+			return SR_ERR;
+
+	if (sr_scpi_read_begin(scpi) != SR_OK)
+		return SR_ERR;
+
+	laststart = g_get_monotonic_time();
+
+	response = *scpi_response;
+
+	offset = response->len;
+
+	while (!sr_scpi_read_complete(scpi)) {
+		space = response->allocated_len - response->len;
+		if (space < 128) {
+			g_string_set_size(response, response->len + 1024);
+			space = response->allocated_len - response->len;
+		}
+		len = sr_scpi_read_data(scpi, &response->str[offset], space);
+		if (len < 0) {
+			sr_err("Incompletely read SCPI response.");
+			return SR_ERR;
+		} else if (len > 0) {
+		        laststart = g_get_monotonic_time();
+		}
+		offset += len;
+		g_string_set_size(response, offset);
+		elapsed_ms = (g_get_monotonic_time() - laststart) / 1000;
+		if (elapsed_ms >= scpi->read_timeout_ms) {
+			sr_err("Timed out waiting for SCPI response.");
+			return SR_ERR;
+		}
+	}
+
+	return SR_OK;
+}
+
 /**
  * Send a SCPI command, read the reply, parse it as a bool value and store the
  * result in scpi_response.
@@ -703,6 +723,79 @@ SR_PRIV int sr_scpi_get_uint8v(struct sr_scpi_dev_inst *scpi,
 
 	return ret;
 }
+/**
+ * Send a SCPI command, read the reply, parse it as binary data with a
+ * "definite length block" header and store the as an result in scpi_response.
+ *
+ * @param scpi Previously initialised SCPI device structure.
+ * @param command The SCPI command to send to the device (can be NULL).
+ * @param scpi_response Pointer where to store the parsed result.
+ *
+ * @return SR_OK upon successfully parsing all values, SR_ERR* upon a parsing
+ *         error or upon no response. The allocated response must be freed by
+ *         the caller in the case of an SR_OK as well as in the case of
+ *         parsing error.
+ */
+SR_PRIV int sr_scpi_get_block(struct sr_scpi_dev_inst *scpi,
+			       const char *command, GByteArray **scpi_response)
+{
+	int ret;
+	GString* response;
+
+	char buf[10] = { 0 };
+	long llen;
+	long datalen;
+
+	response = g_string_sized_new(1024);
+	*scpi_response = NULL;
+
+	ret = sr_scpi_get_data(scpi, command, &response);
+	if (ret != SR_OK) {
+		g_string_free(response, TRUE);
+		return ret;
+	}
+
+	if (response->str[0] != '#') {
+		g_string_free(response, TRUE);
+		return SR_ERR_DATA;
+	}
+
+	buf[0] = response->str[1];
+	ret = sr_atol(buf, &llen);
+	if ((ret != SR_OK) || (llen == 0)) {
+		g_string_free(response, TRUE);
+		return ret;
+	}
+
+	memcpy(buf, &response->str[2], llen);
+	ret = sr_atol(buf, &datalen);
+	if ((ret != SR_OK) || (datalen == 0)) {
+		g_string_free(response, TRUE);
+		return ret;
+	}
+
+	// strip header
+	g_string_erase(response, 0, 2 + llen);
+
+	if (response->len < (unsigned long)(datalen)) {
+		int oldlen = response->len;
+		g_string_set_size(response, datalen);
+		g_string_set_size(response, oldlen);
+	}
+
+	while (response->len < (unsigned long)(datalen)) {
+		if (sr_scpi_get_data(scpi, NULL, &response) != SR_OK) {
+			g_string_free(response, TRUE);
+			return ret;
+		}
+	}
+
+	*scpi_response = g_byte_array_new_take(
+		(guint8*)g_string_free(response, FALSE), datalen);
+
+	return ret;
+}
+
 
 /**
  * Send the *IDN? SCPI command, receive the reply, parse it and store the