fix(storage): add retry mechanism to recover from a full input queue

If the client writes data too quickly, the agent may see its input queue
full. Give ourselves up to 30 seconds to submit the data to be written to
the shared storage before giving up.

Signed-off-by: Cedric Hombourger <cedric.hombourger@siemens.com>

mtda/client.py

@@ -525,18 +525,18 @@ def copy(self):
                 self.progress()
 
                 # Write block to shared storage device
-                bytes_wanted = self._agent.storage_write(data, self._session)
+                bytes_wanted = self._write(data)
 
                 # Check what to do next
                 if bytes_wanted < 0:
-                    raise IOError('write or decompression error from the '
-                                  'shared storage')
+                    exc = 'write or decompression error from shared storage'
+                    raise IOError(exc)
+                elif bytes_wanted == 0:
+                    exc = 'timeout from shared storage'
+                    raise IOError(exc)
                 elif bytes_wanted > 0:
                     # Read next block
                     data = inputstream.read(bytes_wanted)
-                else:
-                    # Agent may continue without further data
-                    data = b''
 
         finally:
             if comp_on_the_fly:
@@ -548,6 +548,16 @@ def size(self):
         st = os.stat(self._path)
         return st.st_size
 
+    def _write(self, data):
+        max_tries = int(CONSTS.STORAGE.TIMEOUT / CONSTS.STORAGE.RETRY_INTERVAL)
+
+        for _ in range(max_tries):
+            result = self._agent.storage_write(data, self._session)
+            if result != 0:
+                return result
+            time.sleep(CONSTS.STORAGE.RETRY_INTERVAL)
+        return 0
+
 
 class ImageS3(ImageFile):
     """ An image to be downloaded from a S3 bucket """

mtda/constants.py

@@ -67,6 +67,8 @@ class STORAGE:
     LOCKED = "LOCKED"
     UNLOCKED = "UNLOCKED"
     UNKNOWN = "???"
+    RETRY_INTERVAL = 0.5
+    TIMEOUT = 30
 
 
 class WRITER: