diff --git a/CMakeLists.txt b/CMakeLists.txt
index d939bc1..90f1da1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -15,6 +15,7 @@ add_library(mfapi SHARED
 	mfapi/file.c
 	mfapi/folder.c
 	mfapi/patch.c
+	mfapi/apicalls.c
 	mfapi/apicalls/file_get_info.c
 	mfapi/apicalls/user_get_info.c
 	mfapi/apicalls/file_get_links.c
diff --git a/mfapi/apicalls.c b/mfapi/apicalls.c
new file mode 100644
index 0000000..c16232d
--- /dev/null
+++ b/mfapi/apicalls.c
@@ -0,0 +1,104 @@
+/*
+ * Copyright (C) 2014 Johannes Schauer <j.schauer@email.de>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2, as published by
+ * the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 51
+ * Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+ *
+ */
+
+#include <jansson.h>
+#include <string.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#include "../utils/http.h"
+#include "../utils/json.h"
+
+int mfapi_check_response(json_t * response, const char *apicall)
+{
+    json_t         *j_obj;
+    int             error_code;
+
+    j_obj = json_object_get(response, "result");
+    if (j_obj == NULL || strcmp(json_string_value(j_obj), "Success") != 0) {
+        // an error occurred
+        j_obj = json_object_get(response, "message");
+        if (j_obj == NULL) {
+            fprintf(stderr, "no error message\n");
+        } else {
+            fprintf(stderr, "error message: %s\n", json_string_value(j_obj));
+        }
+        j_obj = json_object_get(response, "error");
+        if (j_obj == NULL) {
+            fprintf(stderr, "unknown error code\n");
+            error_code = -1;
+        } else {
+            fprintf(stderr, "error code: %s\n", json_string_value(j_obj));
+            error_code = atol(json_string_value(j_obj));
+            if (error_code == 0)
+                error_code = -1;
+        }
+        return error_code;
+    }
+
+    j_obj = json_object_get(response, "action");
+    if (j_obj == NULL) {
+        fprintf(stderr, "no value for action\n");
+        return -1;
+    }
+
+    if (strcmp(json_string_value(j_obj), apicall) != 0) {
+        fprintf(stderr, "expected action %s but got %s", apicall,
+                json_string_value(j_obj));
+        return -1;
+    }
+
+    return 0;
+}
+
+int mfapi_decode_common(mfhttp * conn, void *user_ptr)
+{
+    json_t         *root;
+    json_t         *node;
+    json_error_t    error;
+    int             retval;
+    char           *apicall;
+
+    if (user_ptr == NULL) {
+        fprintf(stderr, "user_ptr must not be null\n");
+        return -1;
+    }
+
+    apicall = (char *)user_ptr;
+
+    root = http_parse_buf_json(conn, 0, &error);
+
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, apicall);
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
+    json_decref(root);
+
+    return 0;
+}
diff --git a/mfapi/apicalls.h b/mfapi/apicalls.h
index 383c6bd..8aa7bf9 100644
--- a/mfapi/apicalls.h
+++ b/mfapi/apicalls.h
@@ -20,6 +20,7 @@
 #ifndef _MFAPI_APICALLS_H_
 #define _MFAPI_APICALLS_H_
 
+#include <jansson.h>
 #include <stdint.h>
 #include <stdio.h>
 
@@ -27,6 +28,7 @@
 #include "folder.h"
 #include "patch.h"
 #include "mfconn.h"
+#include "../utils/http.h"
 
 #define MFAPI_MAX_LEN_KEY 15
 #define MFAPI_MAX_LEN_NAME 255
@@ -46,6 +48,10 @@ struct mfconn_device_change {
     char            parent[16];
 };
 
+int             mfapi_check_response(json_t * response, const char *apicall);
+
+int             mfapi_decode_common(mfhttp * conn, void *user_ptr);
+
 int             mfconn_api_file_get_info(mfconn * conn, mffile * file,
                                          const char *quickkey);
 
diff --git a/mfapi/apicalls/device_get_changes.c b/mfapi/apicalls/device_get_changes.c
index 45f1e1d..baa2d12 100644
--- a/mfapi/apicalls/device_get_changes.c
+++ b/mfapi/apicalls/device_get_changes.c
@@ -103,6 +103,7 @@ static int _decode_device_get_changes(mfhttp * conn, void *user_ptr)
     json_t         *parent;
     json_t         *revision;
     json_t         *device_revision;
+    int             retval;
 
     int             array_sz;
     int             i = 0;
@@ -116,12 +117,26 @@ static int _decode_device_get_changes(mfhttp * conn, void *user_ptr)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
     node = json_object_by_path(root, "response");
 
+    retval = mfapi_check_response(node, "device/get_changes");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     device_revision = json_object_get(node, "device_revision");
     if (device_revision == NULL) {
         fprintf(stderr,
                 "response/device_revision is not part of the result\n");
+        json_decref(root);
         return -1;
     }
 
@@ -204,8 +219,7 @@ static int _decode_device_get_changes(mfhttp * conn, void *user_ptr)
     (*changes)[len_changes - 1].revision =
         atoll(json_string_value(device_revision));
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/device_get_patch.c b/mfapi/apicalls/device_get_patch.c
index 2c15a19..71c9c6f 100644
--- a/mfapi/apicalls/device_get_patch.c
+++ b/mfapi/apicalls/device_get_patch.c
@@ -21,6 +21,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <inttypes.h>
+#include <stdio.h>
 
 #include "../../utils/http.h"
 #include "../../utils/json.h"
@@ -77,6 +78,7 @@ static int _decode_device_get_patch(mfhttp * conn, void *data)
     mfpatch        *patch;
     json_t         *root;
     json_t         *node;
+    int             retval;
 
     if (data == NULL)
         return -1;
@@ -85,8 +87,21 @@ static int _decode_device_get_patch(mfhttp * conn, void *data)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
     node = json_object_by_path(root, "response");
 
+    retval = mfapi_check_response(node, "device/get_patch");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     obj = json_object_get(node, "patch_hash");
     if (obj != NULL)
         patch_set_hash(patch, json_string_value(obj));
@@ -95,8 +110,7 @@ static int _decode_device_get_patch(mfhttp * conn, void *data)
     if (obj != NULL)
         patch_set_link(patch, json_string_value(obj));
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/device_get_status.c b/mfapi/apicalls/device_get_status.c
index f2d13dd..3c9896c 100644
--- a/mfapi/apicalls/device_get_status.c
+++ b/mfapi/apicalls/device_get_status.c
@@ -61,6 +61,7 @@ static int _decode_device_get_status(mfhttp * conn, void *data)
     json_t         *node;
     json_t         *device_revision;
     uint64_t       *revision;
+    int             retval;
 
     revision = (uint64_t *) data;
     if (data == NULL)
@@ -68,8 +69,21 @@ static int _decode_device_get_status(mfhttp * conn, void *data)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
     node = json_object_by_path(root, "response");
 
+    retval = mfapi_check_response(node, "device/get_status");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     device_revision = json_object_get(node, "device_revision");
     if (device_revision != NULL) {
         fprintf(stderr, "device_revision: %s\n",
@@ -77,8 +91,7 @@ static int _decode_device_get_status(mfhttp * conn, void *data)
         *revision = atoll(json_string_value(device_revision));
     }
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/device_get_updates.c b/mfapi/apicalls/device_get_updates.c
index 90f17a8..548deff 100644
--- a/mfapi/apicalls/device_get_updates.c
+++ b/mfapi/apicalls/device_get_updates.c
@@ -95,6 +95,7 @@ static int _decode_device_get_updates(mfhttp * conn, void *user_ptr)
 
     int             array_sz;
     int             i;
+    int             retval;
 
     mfpatch      ***patches;
     mfpatch        *tmp_patch;
@@ -107,8 +108,21 @@ static int _decode_device_get_updates(mfhttp * conn, void *user_ptr)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
     node = json_object_by_path(root, "response");
 
+    retval = mfapi_check_response(node, "device/get_updates");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     len_patches = 0;
     obj_array = json_object_get(node, "updates");
     if (json_is_array(obj_array)) {
@@ -149,8 +163,7 @@ static int _decode_device_get_updates(mfhttp * conn, void *user_ptr)
     // write an empty last element
     (*patches)[len_patches - 1] = NULL;
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/file_delete.c b/mfapi/apicalls/file_delete.c
index 091b497..dcca305 100644
--- a/mfapi/apicalls/file_delete.c
+++ b/mfapi/apicalls/file_delete.c
@@ -45,7 +45,7 @@ int mfconn_api_file_delete(mfconn * conn, const char *quickkey)
                                         quickkey);
 
     http = http_create();
-    retval = http_get_buf(http, api_call, NULL, NULL);
+    retval = http_get_buf(http, api_call, mfapi_decode_common, "file/delete");
     http_destroy(http);
 
     free((void *)api_call);
diff --git a/mfapi/apicalls/file_get_info.c b/mfapi/apicalls/file_get_info.c
index a48f0aa..742f391 100644
--- a/mfapi/apicalls/file_get_info.c
+++ b/mfapi/apicalls/file_get_info.c
@@ -86,8 +86,21 @@ static int _decode_file_get_info(mfhttp * conn, void *data)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
     node = json_object_by_path(root, "response/file_info");
 
+    retval = mfapi_check_response(node, "file/get_info");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     quickkey = json_object_get(node, "quickkey");
     if (quickkey != NULL)
         file_set_key(file, json_string_value(quickkey));
@@ -133,8 +146,7 @@ static int _decode_file_get_info(mfhttp * conn, void *data)
     if (quickkey == NULL)
         retval = -1;
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return retval;
 }
diff --git a/mfapi/apicalls/file_get_links.c b/mfapi/apicalls/file_get_links.c
index 196e877..3bf8547 100644
--- a/mfapi/apicalls/file_get_links.c
+++ b/mfapi/apicalls/file_get_links.c
@@ -85,8 +85,21 @@ static int _decode_file_get_links(mfhttp * conn, void *data)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
     node = json_object_by_path(root, "response");
 
+    retval = mfapi_check_response(node, "file/get_links");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     links_array = json_object_get(node, "links");
     if (!json_is_array(links_array)) {
         json_decref(root);
@@ -116,8 +129,7 @@ static int _decode_file_get_links(mfhttp * conn, void *data)
     if (share_link == NULL)
         retval = -1;
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return retval;
 }
diff --git a/mfapi/apicalls/folder_create.c b/mfapi/apicalls/folder_create.c
index 7609510..743ca69 100644
--- a/mfapi/apicalls/folder_create.c
+++ b/mfapi/apicalls/folder_create.c
@@ -58,7 +58,8 @@ int mfconn_api_folder_create(mfconn * conn, const char *parent,
     }
 
     http = http_create();
-    retval = http_get_buf(http, api_call, NULL, NULL);
+    retval = http_get_buf(http, api_call, mfapi_decode_common,
+                          "folder/create");
     http_destroy(http);
 
     free((void *)api_call);
diff --git a/mfapi/apicalls/folder_delete.c b/mfapi/apicalls/folder_delete.c
index 4a29eb4..83cddcf 100644
--- a/mfapi/apicalls/folder_delete.c
+++ b/mfapi/apicalls/folder_delete.c
@@ -45,7 +45,8 @@ int mfconn_api_folder_delete(mfconn * conn, const char *folderkey)
                                         folderkey);
 
     http = http_create();
-    retval = http_get_buf(http, api_call, NULL, NULL);
+    retval = http_get_buf(http, api_call, mfapi_decode_common,
+                          "folder/delete");
     http_destroy(http);
 
     free((void *)api_call);
diff --git a/mfapi/apicalls/folder_get_content.c b/mfapi/apicalls/folder_get_content.c
index 8e7d54e..888ff94 100644
--- a/mfapi/apicalls/folder_get_content.c
+++ b/mfapi/apicalls/folder_get_content.c
@@ -109,6 +109,7 @@ static int _decode_folder_get_content_folders(mfhttp * conn, void *user_ptr)
 
     char           *ret;
     struct tm       tm;
+    int             retval;
 
     int             array_sz;
     int             i = 0;
@@ -123,6 +124,21 @@ static int _decode_folder_get_content_folders(mfhttp * conn, void *user_ptr)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, "folder/get_content");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     /*json_t *result = json_object_by_path(root, "response/action");
        fprintf(stderr, "response/action: %s\n", (char*)json_string_value(result)); */
 
@@ -206,6 +222,7 @@ static int _decode_folder_get_content_files(mfhttp * conn, void *user_ptr)
     json_t         *quickkey;
     json_t         *file_name;
     json_t         *j_obj;
+    int             retval;
 
     char           *ret;
     struct tm       tm;
@@ -223,6 +240,21 @@ static int _decode_folder_get_content_files(mfhttp * conn, void *user_ptr)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, "folder/get_content");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     node = json_object_by_path(root, "response/folder_content");
 
     files_array = json_object_get(node, "files");
@@ -290,8 +322,7 @@ static int _decode_folder_get_content_files(mfhttp * conn, void *user_ptr)
     // write an empty last element
     (*mffile_result)[len_mffile_result - 1] = NULL;
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/folder_get_info.c b/mfapi/apicalls/folder_get_info.c
index 73c22ee..453e18f 100644
--- a/mfapi/apicalls/folder_get_info.c
+++ b/mfapi/apicalls/folder_get_info.c
@@ -92,6 +92,21 @@ static int _decode_folder_get_info(mfhttp * conn, void *data)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, "folder/get_info");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     node = json_object_by_path(root, "response/folder_info");
 
     folderkey = json_object_get(node, "folderkey");
@@ -129,8 +144,7 @@ static int _decode_folder_get_info(mfhttp * conn, void *data)
     if (folderkey == NULL)
         retval = -1;
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return retval;
 }
diff --git a/mfapi/apicalls/upload_poll_upload.c b/mfapi/apicalls/upload_poll_upload.c
index c624724..78ac10f 100644
--- a/mfapi/apicalls/upload_poll_upload.c
+++ b/mfapi/apicalls/upload_poll_upload.c
@@ -21,6 +21,7 @@
 #include <stdlib.h>
 #include <string.h>
 #include <stddef.h>
+#include <stdio.h>
 
 #include "../../utils/http.h"
 #include "../../utils/json.h"
@@ -74,6 +75,7 @@ static int _decode_upload_poll_upload(mfhttp * conn, void *user_ptr)
     json_t         *root;
     json_t         *node;
     json_t         *j_obj;
+    int             retval;
 
     struct upload_poll_upload_response *response;
 
@@ -86,6 +88,21 @@ static int _decode_upload_poll_upload(mfhttp * conn, void *user_ptr)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, "upload/poll_upload");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     node = json_object_by_path(root, "response/doupload");
 
     // make sure that the result code is zero (success)
@@ -105,8 +122,7 @@ static int _decode_upload_poll_upload(mfhttp * conn, void *user_ptr)
         response->fileerror = atol(json_string_value(j_obj));
     }
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/upload_simple.c b/mfapi/apicalls/upload_simple.c
index f990aaa..969e66a 100644
--- a/mfapi/apicalls/upload_simple.c
+++ b/mfapi/apicalls/upload_simple.c
@@ -97,6 +97,7 @@ static int _decode_upload_simple(mfhttp * conn, void *user_ptr)
     json_t         *root;
     json_t         *node;
     json_t         *j_obj;
+    int             retval;
 
     char          **upload_key;
 
@@ -106,6 +107,21 @@ static int _decode_upload_simple(mfhttp * conn, void *user_ptr)
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, "upload/simple");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     node = json_object_by_path(root, "response/doupload");
 
     j_obj = json_object_get(node, "key");
@@ -119,8 +135,7 @@ static int _decode_upload_simple(mfhttp * conn, void *user_ptr)
         *upload_key = NULL;
     }
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/user_get_info.c b/mfapi/apicalls/user_get_info.c
index 4925135..5d398f2 100644
--- a/mfapi/apicalls/user_get_info.c
+++ b/mfapi/apicalls/user_get_info.c
@@ -59,12 +59,28 @@ static int _decode_user_get_info(mfhttp * conn, void *data)
     json_t         *email;
     json_t         *first_name;
     json_t         *last_name;
+    int             retval;
 
     if (data != NULL)
         return -1;
 
     root = http_parse_buf_json(conn, 0, &error);
 
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
+        return -1;
+    }
+
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, "user/get_info");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
     node = json_object_by_path(root, "response/user_info");
 
     email = json_object_get(node, "email");
@@ -81,8 +97,7 @@ static int _decode_user_get_info(mfhttp * conn, void *data)
 
     printf("\n\r");
 
-    if (root != NULL)
-        json_decref(root);
+    json_decref(root);
 
     return 0;
 }
diff --git a/mfapi/apicalls/user_session.c b/mfapi/apicalls/user_session.c
index 46a5f7e..fb2a79d 100644
--- a/mfapi/apicalls/user_session.c
+++ b/mfapi/apicalls/user_session.c
@@ -96,11 +96,12 @@ static int _decode_get_session_token(mfhttp * conn, void *user_ptr)
 {
     json_error_t    error;
     json_t         *root = NULL;
-    json_t         *data;
+    json_t         *node;
     json_t         *session_token;
     json_t         *secret_key;
     json_t         *secret_time;
     struct user_get_session_token_response *response;
+    int             retval;
 
     if (user_ptr == NULL)
         return -1;
@@ -109,13 +110,22 @@ static int _decode_get_session_token(mfhttp * conn, void *user_ptr)
 
     root = http_parse_buf_json(conn, 0, &error);
 
-    data = json_object_by_path(root, "response");
-    if (data == NULL) {
-        fprintf(stderr, "json: no /response content\n");
+    if (root == NULL) {
+        fprintf(stderr, "http_parse_buf_json failed at line %d\n", error.line);
+        fprintf(stderr, "error message: %s\n", error.text);
         return -1;
     }
 
-    session_token = json_object_get(data, "session_token");
+    node = json_object_by_path(root, "response");
+
+    retval = mfapi_check_response(node, "user/get_session_token");
+    if (retval != 0) {
+        fprintf(stderr, "invalid response\n");
+        json_decref(root);
+        return retval;
+    }
+
+    session_token = json_object_get(node, "session_token");
     if (session_token == NULL) {
         json_decref(root);
         fprintf(stderr, "json: no /session_token content\n");
@@ -124,7 +134,7 @@ static int _decode_get_session_token(mfhttp * conn, void *user_ptr)
 
     response->session_token = strdup(json_string_value(session_token));
 
-    secret_key = json_object_get(data, "secret_key");
+    secret_key = json_object_get(node, "secret_key");
     if (secret_key != NULL)
         response->secret_key = atoll(json_string_value(secret_key));
 
@@ -132,7 +142,7 @@ static int _decode_get_session_token(mfhttp * conn, void *user_ptr)
        time looks like a float but we must store it as a string to
        remain congruent with the server on decimal place presentation.
      */
-    secret_time = json_object_get(data, "time");
+    secret_time = json_object_get(node, "time");
     if (secret_time != NULL)
         response->secret_time = strdup(json_string_value(secret_time));