Reply from REST can come in pieces

Maximum length on one message is 4096 characters. When the reply is
longer than that it will come in multiple messages. In such case we need to
connect them before trying to parse such message.

This for example happens when there are multiple containers and `Stats` often
are split into multiple messages.

Fixes cockpit-project#1025

src/rest.js

@@ -20,12 +20,23 @@ function connect(address, system) {
 
     connection.monitor = function(options, callback, system, return_raw) {
         return new Promise((resolve, reject) => {
+            let buffer = "";
+
             http.request(options)
                     .stream(data => {
                         if (return_raw)
                             callback(data);
-                        else
-                            callback(JSON.parse(data));
+                        else {
+                            buffer += data;
+
+                            try {
+                                const message = JSON.parse(buffer);
+                                buffer = "";
+                                callback(message);
+                            } catch {
+                                // Ignore, we already stored it is buffer
+                            }
+                        }
                     })
                     .catch((error, content) => {
                         manage_error(reject, error, content);

test/check-application

@@ -2122,6 +2122,15 @@ class TestApplication(testlib.MachineCase):
         self.execute(auth, f"podman inspect --format '{{{{.Id}}}}' {container_name_new}").strip()
         self.waitContainerRow(container_name_new)
 
+    def testMultipleContainers(self):
+        # Create 31 containers
+        for i in range(31):
+            self.execute(True, f"podman run -dt --name container{i} quay.io/libpod/busybox:latest")
+
+        self.login()
+
+        self.waitContainerRow("container30")
+
 
 if __name__ == '__main__':
     testlib.test_main()