transport/http: make inbound header preallocation configurable - #2536
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Summary: Intent: - Preserve the default post-system-header sizing from PR #2521 while giving header-heavy services an escape hatch for requests dominated by unrelated HTTP headers. - Let downstream services choose the CPU and memory tradeoff that matches their inbound header mix. Changes: - Added remaining, scan, and disabled inbound header preallocation strategies through the Go API and HTTP transport configuration. - Made the opt-in scan count unique application, tracing, proxy, and grabbed headers, including collision and minimum-threshold handling. - Precomputed grabbed-header lookup keys per inbound so scanning adds no per-request allocations, with focused tests and benchmarks for each strategy. Jira Issues: T3-RPC-11408 --- <sub>Generated by the 🪄 [pr-create](https://sg.uberinternal.com/code.uber.internal/uber-code/devexp-agent-marketplace/-/blob/claude-code/plugins/dev/uber-dev/skills/pr-create/SKILL.md) skill in devexp-agent-marketplace</sub>
bananacocodrilo
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August 19, 2026 11:20
bananacocodrilo
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Aug 24, 2026
maryis
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Aug 26, 2026
| grabHeaders []headerPreallocationGrabHeader, | ||
| ) int { | ||
| switch strategy { | ||
| case "", HeaderPreallocationUnfiltered: |
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I'm removing it and making it so "no config" gets set to unfiltered to make it more clear
maryis
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Aug 26, 2026
| grabHeaders []headerPreallocationGrabHeader, | ||
| ) int { | ||
| switch strategy { | ||
| case "", HeaderPreallocationUnfiltered: |
| } | ||
| } | ||
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| // Raw and prefixed forms can produce the same canonical transport key. |
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should we move this comment to line 108?
| if len(values) > 0 { | ||
| return values[0] | ||
| } | ||
| return "" |
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Is there possibility that value for canonicalKey is empty, but not for lowerKey? In this case we bypass the lowerKey one
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There was!
| ttl := popHeader(req.Header, TTLMSHeader) | ||
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| transportHeader := transport.NewHeadersWithCapacity(len(req.Header)) | ||
| transportHeader := transport.NewHeadersWithCapacity(inboundHeaderCapacity( |
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inboundHeaderCapacity returns 0 for Disabled option, and we end up having an empty map without item or originalItem keys.
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transport.Headers.With lazily allocates both maps when the first header is added. No headers ends with no allocations.
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maryis
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Description
Intent:
Changes:
unfiltered,scan, anddisabledinbound header preallocation strategies through the Go API and HTTP transport configuration.HeaderPreallocationStrategyenum while preserving omitted-versus-explicit configuration semantics.unfilteredthe default; it uses the unfiltered number of request headers remaining after YARPC system headers are removed.Test Plan
go test ./transport/httpaifx verifygo test ./transport/http -run '^$' -bench '^BenchmarkFromHTTPHeadersCapacity' -benchmem -benchtime=200ms -count=3Revert Plan
Revert this PR to restore PR #2521's unconditional post-system-header request-header-count preallocation.
Issues
T3-RPC-11408
RELEASE NOTES:
Added configurable inbound HTTP header preallocation strategies.