fix(h1): append duplicate trailer values when encoding (match #4107)#4118
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seanmonstar merged 1 commit intoJun 29, 2026
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The chunked trailer encoder built allowed_trailers with HeaderMap::insert, which overwrites prior values for the same name. When a user sets the same trailer field multiple times, only the last value was written to the wire. This mirrors the decode-side fix (hyperium#4107): use append so duplicate trailer values are preserved on encode, matching how regular headers are emitted.
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#4107 fixed the decode side:
decode_trailersswitched fromHeaderMap::inserttoappend, so repeated trailer values received on the wire are preserved. The encode side is the unfixed sibling:Encoder::encode_trailers(src/proto/h1/encode.rs) buildsallowed_trailerswithinsert, so when a user sets the same trailer field multiple times, only the last value reaches the wire.The one-line fix mirrors #4107 (
insert→append). Verified both ways withcargo test --features full: a regression test fails on the old code (only the second value reaches the wire) and passes after; encode module 10/10, full lib suite 100 passed, 0 regression.