iiod-client: Support new protocol without ZSTD

Support the PRINT command sending an uncompressed XML string, instead of
requiring ZSTD compression.

This makes it easier for embedded tinyiiod applications, which then
don't need to duplicate the XML string (once in plain text to create the
Libiio context using the XML backend, and once ZSTD-compressed for
tinyiiod).

Signed-off-by: Paul Cercueil <[email protected]>

iiod-client.c

@@ -944,13 +944,16 @@ iiod_client_create_context_private_new(struct iiod_client *client,
 	struct iio_context *ctx = NULL;
 	unsigned long long len;
 	char *xml_zstd, *xml;
+	bool is_zstd;
 	int ret;
 
-	xml = malloc(xml_len);
+	xml = malloc(xml_len + uri_len);
 	if (!xml)
 		return iio_ptr(-ENOMEM);
 
-	ret = iiod_client_send_print(client, xml, xml_len);
+	memcpy(xml, "xml:", uri_len);
+
+	ret = iiod_client_send_print(client, &xml[uri_len], xml_len);
 	if (ret < 0) {
 		prm_perror(client->params, -ret,
 			   "Unable to send PRINT command");
@@ -959,37 +962,42 @@ iiod_client_create_context_private_new(struct iiod_client *client,
 
 	xml_len = ret;
 
+	is_zstd = strncmp(xml, "xml:<?xml", sizeof("xml:<?xml") - 1) != 0;
+	if (is_zstd)
+		prm_dbg(client->params, "Received ZSTD-compressed XML string.\n");
+	else
+		prm_dbg(client->params, "Received uncompressed XML string.\n");
 
-	prm_dbg(client->params, "Received ZSTD-compressed XML string.\n");
-
-	len = ZSTD_getFrameContentSize(xml, xml_len);
-	if (len == ZSTD_CONTENTSIZE_UNKNOWN ||
-	    len == ZSTD_CONTENTSIZE_ERROR) {
-		ret = -EIO;
-		goto out_free_xml;
-	}
+	if (is_zstd) {
+		len = ZSTD_getFrameContentSize(&xml[uri_len], xml_len);
+		if (len == ZSTD_CONTENTSIZE_UNKNOWN ||
+		    len == ZSTD_CONTENTSIZE_ERROR) {
+			ret = -EIO;
+			goto out_free_xml;
+		}
 
-	xml_zstd = malloc(uri_len + len + 1);
-	if (!xml_zstd) {
-		ret = -ENOMEM;
-		goto out_free_xml;
-	}
+		xml_zstd = malloc(uri_len + len + 1);
+		if (!xml_zstd) {
+			ret = -ENOMEM;
+			goto out_free_xml;
+		}
 
-	xml_len = ZSTD_decompress(xml_zstd + uri_len, len, xml, xml_len);
-	if (ZSTD_isError(xml_len)) {
-		prm_err(client->params, "Unable to decompress ZSTD data: %s\n",
-			ZSTD_getErrorName(xml_len));
-		ret = -EIO;
-		free(xml_zstd);
-		goto out_free_xml;
-	}
+		xml_len = ZSTD_decompress(&xml_zstd[uri_len], len, &xml[uri_len], xml_len);
+		if (ZSTD_isError(xml_len)) {
+			prm_err(client->params, "Unable to decompress ZSTD data: %s\n",
+				ZSTD_getErrorName(xml_len));
+			ret = -EIO;
+			free(xml_zstd);
+			goto out_free_xml;
+		}
 
-	memcpy(xml_zstd, "xml:", uri_len);
-	xml_zstd[uri_len + xml_len] = '\0';
+		memcpy(xml_zstd, "xml:", uri_len);
+		xml_zstd[uri_len + xml_len] = '\0';
 
-	/* Free compressed data, make "xml" point to uncompressed data */
-	free(xml);
-	xml = xml_zstd;
+		/* Free compressed data, make "xml" point to uncompressed data */
+		free(xml);
+		xml = xml_zstd;
+	}
 
 	prm_dbg(client->params, "Creating context\n");