Sample

Extract and validate Header, Cookie, and Path parameters with underscore-to-hyphen conversion, multi-value header parsing, catch-all routing, and HTTPBearer authentication

sha256:ccf237ce0f266d463c20e4aecf8533f09462a3412c3a6efd3f6be83e4641bebe

Case

Goal

Extract and validate Header, Cookie, and Path parameters with underscore-to-hyphen conversion, multi-value header parsing, catch-all routing, and HTTPBearer authentication HOW

Packages

fastapi 0.141.1 starlette 1.6.0 pydantic 2.13.4 httpx2 2.10.0

Environment

python

Created

2026-08-17T17:57:04Z

Commonly assumed

Declaring a Header parameter in Python with snake_case matches the exact header name with underscores and splitting comma-separated headers into list types occurs automatically

The sample's author recorded this as what a developer or model would expect here. The contract below is what actually ran.

Contract

• Header parameters defined with underscores automatically translate to hyphenated HTTP header lookups unless convert_underscores is explicitly disabled, and multi-value header lists only capture distinct HTTP headers rather than splitting comma-separated values
• assert Header(convert_underscores=True) maps snake_case python names to hyphenated headers and rejects literal underscores with 422 Unprocessable Entity
• assert Header(convert_underscores=False) matches literal underscore headers and rejects hyphenated headers with 422 Unprocessable Entity
• assert Header(default=[]) receives multiple distinct headers as a list and retains single comma-separated headers as a single un-split string element
• assert Header(alias=...) matches explicitly aliased HTTP header names
• assert Cookie(...) extracts values from request Cookie headers and returns 422 with cookie loc when required cookies are missing
• assert Cookie(default=...) populates fallback values when the cookie is omitted
• assert Path(gt=0, le=1000) rejects non-integer strings with int_parsing and rejects out-of-bounds values with less_than_equal
• assert Path parameter on catch-all {file_path:path} captures arbitrary subpaths including forward slashes
• assert HTTPBearer(auto_error=True) returns 401 Unauthorized with WWW-Authenticate Bearer header on missing or non-bearer credentials
• assert HTTPBearer(auto_error=False) resolves to None without raising 401 when the Authorization header is omitted

Files

• NOTES.md
• csx.json
• requirements.txt
• src/__init__.py
• src/app.py
• test/__init__.py
• test/contract.py

Download the source artifact (tar.gz)

Origin Seeder

csx-seed

Verification receipts

• python 3.12 · linux alpine/x64 · docker · CONTAINER_RUN · compile:SKIPPED · contract:PASS · load:PASS · resolve:PASS · python@1 · 2026-08-17 · ed25519:d91480838ac982c9