use const for char buffer in uclient_write

We are not supposed to modify it and ustream accepts const already.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>

uclient-backend.h

@@ -32,7 +32,7 @@ struct uclient_backend {
 	void (*disconnect)(struct uclient *cl);
 
 	int (*read)(struct uclient *cl, char *buf, unsigned int len);
-	int (*write)(struct uclient *cl, char *buf, unsigned int len);
+	int (*write)(struct uclient *cl, const char *buf, unsigned int len);
 };
 
 void uclient_backend_set_error(struct uclient *cl, int code);

uclient-http.c

@@ -931,7 +931,7 @@ uclient_http_set_header(struct uclient *cl, const char *name, const char *value)
 }
 
 static int
-uclient_http_send_data(struct uclient *cl, char *buf, unsigned int len)
+uclient_http_send_data(struct uclient *cl, const char *buf, unsigned int len)
 {
 	struct uclient_http *uh = container_of(cl, struct uclient_http, uc);
 

uclient.c

@@ -221,7 +221,7 @@ void uclient_free(struct uclient *cl)
 	free(url);
 }
 
-int uclient_write(struct uclient *cl, char *buf, int len)
+int uclient_write(struct uclient *cl, const char *buf, int len)
 {
 	if (!cl->backend->write)
 		return -1;

uclient.h

@@ -106,7 +106,7 @@ int uclient_connect(struct uclient *cl);
 void uclient_disconnect(struct uclient *cl);
 
 int uclient_read(struct uclient *cl, char *buf, int len);
-int uclient_write(struct uclient *cl, char *buf, int len);
+int uclient_write(struct uclient *cl, const char *buf, int len);
 int uclient_request(struct uclient *cl);
 
 char *uclient_get_addr(char *dest, int *port, union uclient_addr *a);