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Legacy handler ignores history_length on message/stream #1363
Description
What happens
With the legacy request handler, message/stream with history_length=0 still returns the full history on Task events, and history_length=-1 is not rejected. message/send trims and rejects both correctly.
Why
LegacyRequestHandler.on_message_send calls validate_history_length and apply_history_length (default_request_handler.py), but on_message_send_stream calls neither. The v2 handler already applies it on streams.
Version
main @ d316d0e
Activity
rohityan commentedon Oct 22, 2026
Hi @ConnorMoss02, thanks for reporting this and opening the fix PR #1364. Your approach for the fix looks correct.
In
src/a2a/server/request_handlers/default_request_handler.py,LegacyRequestHandler.on_message_send_streamfails to validatehistory_lengthat request start and never truncatestask.historyon emittedTaskevents viaapply_history_length. As a result, negative values are not rejected, and streamed tasks return their full history regardless of configuration.Assigning this issue to you until the PR is reviewed. Meanwhile, clients can manually slice
task.history[-history_length:] if history_length > 0 else []on receivedTaskobjects and guard outbound requests against negativehistory_lengthvalues.fix(server): apply history_length to legacy streaming sends (a2aproje…