[python] support custom wire names for etags defined with `Azure.Core.eTag` by iscai-msft · Pull Request #10494 · microsoft/typespec

iscai-msft · 2026-04-24T22:22:20Z

Problem

Custom etag-typed headers (e.g. x-ms-if-blob-match, x-ms-if-blob-none-match) were being assigned to the wrong if-match/if-none-match slot during preprocessing. The slot assignment and the per-parameter conversion used different logic to classify headers, and synthetic partners inherited incorrect wire names.

Changes

Added _etag_kind() helper — centralizes etag classification using none-match substring (stricter than the previous none check which could false-positive on unrelated headers)
Fixed slot assignment — uses _etag_kind() to correctly classify custom etag headers before pairing
Fixed synthetic partner creation — strips isEtag from synthetic clones to prevent re-conversion with wrong originalWireName, falls back to standard If-Match/If-None-Match wire names
Unified classification — both slot assignment and per-parameter conversion now use the same _etag_kind() logic

pkg-pr-new · 2026-04-24T22:24:00Z

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npm i https://pkg.pr.new/@typespec/http-client-python@10494

commit: a1fc7a6

github-actions · 2026-04-24T22:25:23Z

All changed packages have been documented.

✅ @typespec/http-client-python

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`@typespec/http-client-python` - fix ✏️

Support custom wire names for etags defined with Azure.Core.eTag (e.g. x-ms-blob-if-match)

azure-sdk · 2026-04-24T22:46:36Z

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Copilot

Pull request overview

This PR fixes how the Python HTTP client generator handles custom ETag-typed header parameters (e.g. x-ms-if-blob-match, x-ms-if-blob-none-match) by centralizing ETag header classification and ensuring serialization uses the real HTTP header name.

Changes:

Add a shared _etag_kind() helper to consistently classify ETag headers as if-match vs if-none-match.
Preserve the actual header name via originalWireName during preprocessing and use it during header serialization.
Emit an isEtag flag from the TypeScript emitter so preprocessing can detect custom ETag-typed headers.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
packages/http-client-python/generator/pygen/preprocess/init.py	Centralizes ETag header classification, fixes slot pairing, and preserves `originalWireName` during header conversion.
packages/http-client-python/generator/pygen/codegen/serializers/parameter_serializer.py	Builds ETag header serialization using `original_wire_name` instead of hard-coded `If-Match`/`If-None-Match`.
packages/http-client-python/generator/pygen/codegen/models/parameter.py	Adds `original_wire_name` field to parameter model for downstream serialization.
packages/http-client-python/emitter/src/http.ts	Emits `isEtag` for header parameters by detecting `Azure.Core.eTag` scalar types.
.chronus/changes/python-etagMatchCondition-2026-04-24-18-22-00.md	Changelog entry documenting the fix.

Copilot · 2026-04-27T03:35:11Z

+                    # For standard headers, use "if-match". For custom etag
+                    # headers, we can't derive the partner's real wire name,
+                    # so fall back to the standard "If-Match" header.
                    property_if_match["wireName"] = "if-match"
+                    property_if_match.pop("isEtag", None)
                if not property_if_none_match and property_if_match:
                    property_if_none_match = property_if_match.copy()
                    property_if_none_match["wireName"] = "if-none-match"


Synthetic partner parameters are created with wireName set to lowercase ("if-match" / "if-none-match"). Since this PR now uses originalWireName to determine the actual HTTP header name during serialization, these synthetic partners will generate lowercase header keys (e.g. "if-match") rather than the canonical "If-Match" / "If-None-Match" (and the nearby comment explicitly says to fall back to the standard header). Consider setting the synthetic partner wireName to the canonical casing (or explicitly setting originalWireName to If-Match / If-None-Match) before conversion so generated code stays consistent/stable.

Suggested change

# For standard headers, use "if-match". For custom etag

# headers, we can't derive the partner's real wire name,

# so fall back to the standard "If-Match" header.

property_if_match["wireName"] = "if-match"

property_if_match.pop("isEtag", None)

if not property_if_none_match and property_if_match:

property_if_none_match = property_if_match.copy()

property_if_none_match["wireName"] = "if-none-match"

# For standard headers, use "If-Match". For custom etag

# headers, we can't derive the partner's real wire name,

# so fall back to the standard "If-Match" header.

property_if_match["wireName"] = "If-Match"

property_if_match["originalWireName"] = "If-Match"

property_if_match.pop("isEtag", None)

if not property_if_none_match and property_if_match:

property_if_none_match = property_if_match.copy()

property_if_none_match["wireName"] = "If-None-Match"

property_if_none_match["originalWireName"] = "If-None-Match"

Copilot · 2026-04-27T03:35:12Z

+        elif (
+            self.version_tolerant
+            and yaml_data["location"] == "header"
+            and yaml_data.get("isEtag")
+            and wire_name_lower not in HEADERS_CONVERT_IN_METHOD
+        ):
+            # Custom etag-typed headers (e.g. x-ms-if-blob-match) get the same
+            # etag/match_condition treatment as standard If-Match/If-None-Match.
+            kind = _etag_kind(yaml_data)
+            if kind == "if-none-match":
+                headers_convert(yaml_data, HEADERS_CONVERT_IN_METHOD["if-none-match"])
+            else:
+                headers_convert(yaml_data, HEADERS_CONVERT_IN_METHOD["if-match"])


The new custom etag header flow (isEtag + _etag_kind + originalWireName-based serialization) doesn’t appear to have coverage in the existing generator/unit tests. It would be good to add a test case that feeds a custom etag-typed header like x-ms-if-blob-none-match through preprocessing and asserts that (1) it’s classified into the correct slot and paired correctly, and (2) the generated serializer emits the custom header name rather than If-None-Match.

Custom headers typed as Azure.Core.eTag (e.g. x-ms-blob-if-match, x-ms-source-if-match) now get the same etag/match_condition treatment as standard If-Match/If-None-Match headers. The original wire name is preserved via originalWireName so the correct HTTP header is sent. - Add isEtag flag in emitter for Azure.Core.eTag-typed headers - Add _is_etag_match/_is_etag_none_match helpers in preprocessor - Preserve originalWireName in headers_convert for custom headers - Use originalWireName in serializer for dynamic header name - Use identity-based removal for etag param reordering Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Move etagRole determination into the emitter's getEtagRole() function. Standard If-Match/If-None-Match headers work with any type. Non-standard headers (e.g. x-ms-blob-if-match) require Azure.Core.eTag type. Simplify preprocess _get_etag_role to just read the etagRole field. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

msyyc

Overall looks good to me. Maybe we could ask TCGC to provide a helper function to help judge etag type in the future.

iscai-msft requested review from ChenxiJiang333, catalinaperalta, lmazuel, mccoyp, msyyc, swathipil, tadelesh and timotheeguerin as code owners April 24, 2026 22:22

microsoft-github-policy-service Bot added the emitter:client:python Issue for the Python client emitter: @typespec/http-client-python label Apr 24, 2026

msyyc requested a review from Copilot April 27, 2026 03:29

Copilot started reviewing on behalf of msyyc April 27, 2026 03:30 View session

Copilot AI reviewed Apr 27, 2026

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iscai-msft force-pushed the python/etagMatchCondition branch from 15ed29c to f9b7c14 Compare April 27, 2026 17:33

iscai-msft and others added 3 commits April 27, 2026 14:10

simplify check

c1fdbb4

don't special case for swagger generations

c23753c

iscai-msft changed the title ~~fix(http-client-python): correct etag slot assignment for custom etag-typed headers~~ [python] support custom wire names for etags defined with Azure.Core.eTag Apr 27, 2026

chore: update changeset description

a1fc7a6

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

msyyc approved these changes Apr 28, 2026

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msyyc self-requested a review April 28, 2026 03:32

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[python] support custom wire names for etags defined with `Azure.Core.eTag`#10494

[python] support custom wire names for etags defined with `Azure.Core.eTag`#10494
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`@typespec/http-client-python` - fix ✏️

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iscai-msft commented Apr 24, 2026

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`@typespec/http-client-python` - fix ✏️

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