Reputation: 671
I am using FastAPI to upload a file according to the official documentation, as shown below:
@app.post("/create_file")
async def create_file(file: UploadFile = File(...)):
file2store = await file.read()
# some code to store the BytesIO(file2store) to the other database
When I send a request using Python requests
library, as shown below:
f = open(".../file.txt", 'rb')
files = {"file": (f.name, f, "multipart/form-data")}
requests.post(url="SERVER_URL/create_file", files=files)
the file2store
variable is always empty. Sometimes (rarely seen), it can get the file bytes, but almost all the time it is empty, so I can't restore the file to the other database.
I also tried the bytes
rather than UploadFile
, but I get the same results. Is there something wrong with my code, or is the way I use FastAPI to upload a file wrong?
Upvotes: 67
Views: 184095
Reputation: 34600
First, as per FastAPI documentation, you need to install python-multipart
—if you haven't already—as uploaded files are sent as "form data". For instance:
pip install python-multipart
The examples below use the .file
attribute of the UploadFile
object to get the actual Python file (i.e., SpooledTemporaryFile
), which allows you to call the SpooledTemporaryFile
's methods, such as .read()
and .close()
, without having to await
them. It is important, however, to define your endpoint with def
in this case—otherwise, if the endpoint was defined with async def
, such operations would block the server until they are completed. In FastAPI, a normal def
endpoint is run in an external threadpool that is then await
ed, instead of being called directly (as it would block the server). I would highly suggest having a look at this answer, which explains the difference between def
and async def
endpoints, as well as provides a number of solutions when one needs to run blocking operations inside async def
endpoints.
The SpooledTemporaryFile
used by FastAPI/Starlette has the max_size
attribute set to 1 MB, meaning that the data are spooled in memory until the file size exceeds 1 MB, at which point the data are written to a temporary file on disk, under the OS's temp directory. Hence, if you uploaded a file larger than 1 MB, it wouldn't be stored in memory, and calling file.file.read()
would actually read the data from disk into memory. Thus, if the file is too large to fit into your server's RAM, you should rather read the file in chunks and process one chunk at a time, as described in "Read the File in chunks" section below.
As explained above and in this answer as well, FastAPI/Starlette uses AnyIO threads to run blocking functions, such as endpoints defined with normal def
, in an external threadpool and then await
them (so that FastAPI would still work asynchronously), in order to prevent them from blocking the event loop (of the main thread), and hence, the entire server. Therefore, every time an HTTP request arrives at an endpoint defined with normal def
, a new thread will be spawned (or an idle thread will be used, if available), and thus, depending on the requirements of your project, the expected traffic (i.e., number of users simultaneously accessing your API), as well as any other blocking functions in your API that will eventually run in that threadpool (see the linked answers above for more details), you might need to adjust the maximum number of threads in that threadpool (see the linked answer above on how to do that).
However, you should always aim at using asynchronous code (i.e., using async
/await
), wherever is possible, as async
code runs directly in the event loop which runs in a single thread (in this case, the main thread). One option would be to define the endpoint with async def
and use the asynchronous read()
/write()
/close()
/etc. file methods provided by FastAPI, as demonstrated in this answer. You should, however, note that, as explained in this answer, FastAPI, behind the scenes, actually calls the corresponding synchronous Python File methods in a separate thread from the external threadpool described earlier. Thus, it might or might not make a big difference (always perform and compare tests before choosing one approach over the other).
Note that in the bottom part of this answer, as well as in this answer, another approach is explained and demonstrated on how to upload large files in chunks, using Starlette's request.stream()
, which results in considerably minimizing the time required to upload files, as well as avoiding the use of threads from that threadpool. Thus, I would highly recommend taking a look.
app.py
from fastapi import File, UploadFile, HTTPException
@app.post("/upload")
def upload(file: UploadFile = File(...)):
try:
contents = file.file.read()
with open(file.filename, 'wb') as f:
f.write(contents)
except Exception:
raise HTTPException(status_code=500, detail='Something went wrong')
finally:
file.file.close()
return {"message": f"Successfully uploaded {file.filename}"}
As described earlier and in this answer, if the file is too big to fit into memory—for instance, if you have 8GB of RAM, you can't load a 50GB file (not to mention that the available RAM will always be less than the total amount installed on your machine, as other applications will be using some of the RAM)—you should rather load the file into memory in chunks and process the data one chunk at a time. This method, however, may take longer to complete, depending on the chunk size you choose—in the example below, the chunk size is 1024 * 1024
bytes (i.e., 1MB). You can adjust the chunk size as desired.
from fastapi import File, UploadFile, HTTPException
@app.post("/upload")
def upload(file: UploadFile = File(...)):
try:
with open(file.filename, 'wb') as f:
while contents := file.file.read(1024 * 1024):
f.write(contents)
except Exception:
raise HTTPException(status_code=500, detail='Something went wrong')
finally:
file.file.close()
return {"message": f"Successfully uploaded {file.filename}"}
Another option would be to use shutil.copyfileobj()
, which is used to copy the contents of a file-like
object to another file-like
object (have a look at this answer too). By default, the data is read in chunks with the default buffer (chunk) size being 1MB (i.e., 1024 * 1024
bytes) for Windows and 64KB for other platforms, as shown in the source code here. You can specify the buffer size by passing the optional length
parameter. Note: If negative length
value is passed, the entire contents of the file will be read instead—see f.read()
as well, which .copyfileobj()
uses under the hood (as can be seen in the source code here).
from fastapi import File, UploadFile, HTTPException
import shutil
@app.post("/upload")
def upload(file: UploadFile = File(...)):
try:
with open(file.filename, 'wb') as f:
shutil.copyfileobj(file.file, f)
except Exception:
raise HTTPException(status_code=500, detail='Something went wrong')
finally:
file.file.close()
return {"message": f"Successfully uploaded {file.filename}"}
test.py (using requests
)
import requests
url = 'http://127.0.0.1:8000/upload'
file = {'file': open('images/1.png', 'rb')}
resp = requests.post(url=url, files=file)
print(resp.json())
test.py (using httpx
)
import httpx
url = 'http://127.0.0.1:8000/upload'
file = {'file': open('images/1.png', 'rb')}
resp = httpx.post(url=url, files=file)
print(resp.json())
For an HTML <form>
example, see here.
app.py
from fastapi import File, UploadFile, HTTPException
from typing import List
@app.post("/upload")
def upload(files: List[UploadFile] = File(...)):
for file in files:
try:
contents = file.file.read()
with open(file.filename, 'wb') as f:
f.write(contents)
except Exception:
raise HTTPException(status_code=500, detail='Something went wrong')
finally:
file.file.close()
return {"message": f"Successfuly uploaded {[file.filename for file in files]}"}
As described earlier in this answer, if you expect some rather large file(s) and don't have enough RAM to accommodate all the data from the beginning to the end, you should rather load the file into memory in chunks, thus processing the data one chunk at a time (Note: adjust the chunk size as desired, below that is 1024 * 1024
bytes).
from fastapi import File, UploadFile, HTTPException
from typing import List
@app.post("/upload")
def upload(files: List[UploadFile] = File(...)):
for file in files:
try:
with open(file.filename, 'wb') as f:
while contents := file.file.read(1024 * 1024):
f.write(contents)
except Exception:
raise HTTPException(status_code=500, detail='Something went wrong')
finally:
file.file.close()
return {"message": f"Successfuly uploaded {[file.filename for file in files]}"}
or, using shutil.copyfileobj()
:
from fastapi import File, UploadFile, HTTPException
from typing import List
import shutil
@app.post("/upload")
def upload(files: List[UploadFile] = File(...)):
for file in files:
try:
with open(file.filename, 'wb') as f:
shutil.copyfileobj(file.file, f)
except Exception:
raise HTTPException(status_code=500, detail='Something went wrong')
finally:
file.file.close()
return {"message": f"Successfuly uploaded {[file.filename for file in files]}"}
test.py (using requests
)
import requests
url = 'http://127.0.0.1:8000/upload'
files = [('files', open('images/1.png', 'rb')), ('files', open('images/2.png', 'rb'))]
resp = requests.post(url=url, files=files)
print(resp.json())
test.py (using httpx
)
import httpx
url = 'http://127.0.0.1:8000/upload'
files = [('files', open('images/1.png', 'rb')), ('files', open('images/2.png', 'rb'))]
resp = httpx.post(url=url, files=files)
print(resp.json())
For an HTML <form>
example, see here.
Upvotes: 127
Reputation: 93
@app.post("/create_file/")
async def image(image: UploadFile = File(...)):
print(image.file)
# print('../'+os.path.isdir(os.getcwd()+"images"),"*************")
try:
os.mkdir("images")
print(os.getcwd())
except Exception as e:
print(e)
file_name = os.getcwd()+"/images/"+image.filename.replace(" ", "-")
with open(file_name,'wb+') as f:
f.write(image.file.read())
f.close()
file = jsonable_encoder({"imagePath":file_name})
new_image = await add_image(file)
return {"filename": new_image}
Upvotes: 6