Deduplicate identical key/value pairs in user agent builder#1718
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`useragent.data.With()` appended every key/value pair unconditionally and never deduplicated. When the same user-agent dimension is injected repeatedly onto a reused or long-lived context (a caller that threads one context across many operations), the per-context user-agent data accumulated duplicate entries and `FromContext` produced a User-Agent string that grew without bound. Skip appending a pair when an identical key/value is already present. Distinct values for the same key are still preserved, so existing multi-value behavior (e.g. multiple partners) is unchanged.
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Summary
useragent.data.With()appended every key/value pair unconditionally and never deduplicated. When the same user-agent dimension is injected repeatedly onto a reused or long-livedcontext.Context— for example a caller that threads a single context across many operations — the per-context user-agent data accumulates duplicate entries, soFromContextproduces aUser-Agentstring that grows without bound (e.g.... sdk/x sdk/x resource/y resource/y ...). Sufficiently large headers can be rejected or truncated downstream.Note that
With's doc comment claimed it "always uses the latest value for a given alphanumeric key", but the implementation always appended, and existing tests rely on multiple distinct values per key being preserved (e.g. multiple partners). This change keeps that behavior and only removes exact duplicates.Change
data.With()now skips appending a key/value pair when an identical pair is already present. Distinct values for the same key are still preserved, so no existing behavior or tests change. The doc comment is updated to describe the actual behavior.Testing
go test ./useragent/— all pass, includingTestMultiplePartnersandTestFromContext_Custom.TestInContext_DeduplicatesIdenticalPairs: 100 repeated identical injections collapse to one entry each; distinct values still preserved.go vet ./useragent/andgofmtclean.🤖 Generated with Claude Code.