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Python: case-insensitive User-Agent detection prevents duplicate headers - #8521
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Eduard van Valkenburg (eavanvalkenburg) merged 1 commit intoSep 21, 2026
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prepend_agent_framework_to_user_agent looked up the exact key
"User-Agent" when deciding whether an incoming headers dict already
carries a user agent. HTTP header names are case-insensitive, so a caller
passing default_headers={"user-agent": "my-app/1.0"} (for example to
OpenAI clients or the A2A agent) ended up with two User-Agent entries:
their original one plus a new agent-framework one. httpx then sends both
header lines, and which value a server honors is undefined.
Find the existing entry case-insensitively and prepend to it in place, so
exactly one User-Agent header survives.
Manohar Paturi (ManoharPaturi)
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prepend_agent_framework_to_user_agent looked up the exact key
"User-Agent" when deciding whether an incoming headers dict already
carries a user agent. HTTP header names are case-insensitive, so a caller
passing default_headers={"user-agent": "my-app/1.0"} (for example to
OpenAI clients or the A2A agent) ended up with two User-Agent entries:
their original one plus a new agent-framework one. httpx then sends both
header lines, and which value a server honors is undefined.
Find the existing entry case-insensitively and prepend to it in place, so
exactly one User-Agent header survives.
Co-authored-by: Manohar Paturi <186662190+ManoharPaturi@users.noreply.github.com>
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Motivation & Context
Fixes #8520. exact-case "User-Agent" detection let a lowercase user-agent through, producing duplicate UA header lines.
Description & Review Guide
Related Issue
Fixes #8520
Contribution Checklist