[BEAM-3887] Python SDK harness retrieves element codes from gRPC read/write nodes

• Type: Sub-task
• Status: Resolved
• Priority: P3
• Resolution: Fixed
• Fix Version/s: Missing
• Component/s: sdk-py-core
• Assignee: Unassigned
• Reporter: Ben Sidhom
• Created: 19/Mar/18 23:28
• Updated: 13/Jan/22 21:52
• Resolved: 29/Sep/21 00:42

Description

The python harness does not correctly get coders from the gRPC read/write transforms but rather from PCollection inputs/outputs. This prevents the harness from correctly receiving/transmitting prefix-encoded elements (seen as prefix-encoded byte arrays by the runner).

It should instead retrieve input and output coders from the gRPC nodes.