Header Parameter Models¶
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If you have a group of related header parameters, you can create a Pydantic model to declare them.
This would allow you to re-use the model in multiple places and also to declare validations and metadata for all the parameters at once. 😎
Note
This is supported since FastAPI version 0.115.0. 🤓
Header Parameters with a Pydantic Model¶
Declare the header parameters that you need in a Pydantic model, and then declare the parameter as Header:
from typing import Annotated
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: str | None = None
traceparent: str | None = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: Annotated[CommonHeaders, Header()]):
return headers
🤓 Other versions and variants
from typing import Annotated, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: Annotated[CommonHeaders, Header()]):
return headers
from typing import List, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
from typing_extensions import Annotated
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: List[str] = []
@app.get("/items/")
async def read_items(headers: Annotated[CommonHeaders, Header()]):
return headers
Tip
Prefer to use the Annotated version if possible.
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: str | None = None
traceparent: str | None = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header()):
return headers
Tip
Prefer to use the Annotated version if possible.
from typing import Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header()):
return headers
Tip
Prefer to use the Annotated version if possible.
from typing import List, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: List[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header()):
return headers
FastAPI will extract the data for each field from the headers in the request and give you the Pydantic model you defined.
Check the Docs¶
You can see the required headers in the docs UI at /docs:
Forbid Extra Headers¶
In some special use cases (probably not very common), you might want to restrict the headers that you want to receive.
You can use Pydantic's model configuration to forbid any extra fields:
from typing import Annotated
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
model_config = {"extra": "forbid"}
host: str
save_data: bool
if_modified_since: str | None = None
traceparent: str | None = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: Annotated[CommonHeaders, Header()]):
return headers
🤓 Other versions and variants
from typing import Annotated, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
model_config = {"extra": "forbid"}
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: Annotated[CommonHeaders, Header()]):
return headers
from typing import List, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
from typing_extensions import Annotated
app = FastAPI()
class CommonHeaders(BaseModel):
model_config = {"extra": "forbid"}
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: List[str] = []
@app.get("/items/")
async def read_items(headers: Annotated[CommonHeaders, Header()]):
return headers
Tip
Prefer to use the Annotated version if possible.
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
model_config = {"extra": "forbid"}
host: str
save_data: bool
if_modified_since: str | None = None
traceparent: str | None = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header()):
return headers
Tip
Prefer to use the Annotated version if possible.
from typing import Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
model_config = {"extra": "forbid"}
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header()):
return headers
Tip
Prefer to use the Annotated version if possible.
from typing import List, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
model_config = {"extra": "forbid"}
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: List[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header()):
return headers
If a client tries to send some extra headers, they will receive an error response.
For example, if the client tries to send a tool header with a value of plumbus, they will receive an error response telling them that the header parameter tool is not allowed:
{
"detail": [
{
"type": "extra_forbidden",
"loc": ["header", "tool"],
"msg": "Extra inputs are not permitted",
"input": "plumbus",
}
]
}
Disable Convert Underscores¶
The same way as with regular header parameters, when you have underscore characters in the parameter names, they are automatically converted to hyphens.
For example, if you have a header parameter save_data in the code, the expected HTTP header will be save-data, and it will show up like that in the docs.
If for some reason you need to disable this automatic conversion, you can do it as well for Pydantic models for header parameters.
from typing import Annotated
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: str | None = None
traceparent: str | None = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(
headers: Annotated[CommonHeaders, Header(convert_underscores=False)],
):
return headers
🤓 Other versions and variants
from typing import Annotated, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(
headers: Annotated[CommonHeaders, Header(convert_underscores=False)],
):
return headers
from typing import List, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
from typing_extensions import Annotated
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: List[str] = []
@app.get("/items/")
async def read_items(
headers: Annotated[CommonHeaders, Header(convert_underscores=False)],
):
return headers
Tip
Prefer to use the Annotated version if possible.
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: str | None = None
traceparent: str | None = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header(convert_underscores=False)):
return headers
Tip
Prefer to use the Annotated version if possible.
from typing import Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: list[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header(convert_underscores=False)):
return headers
Tip
Prefer to use the Annotated version if possible.
from typing import List, Union
from fastapi import FastAPI, Header
from pydantic import BaseModel
app = FastAPI()
class CommonHeaders(BaseModel):
host: str
save_data: bool
if_modified_since: Union[str, None] = None
traceparent: Union[str, None] = None
x_tag: List[str] = []
@app.get("/items/")
async def read_items(headers: CommonHeaders = Header(convert_underscores=False)):
return headers
Warning
Before setting convert_underscores to False, bear in mind that some HTTP proxies and servers disallow the usage of headers with underscores.
Summary¶
You can use Pydantic models to declare headers in FastAPI. 😎