Efficient Chunked Uploads of Binary Files Using Python
Written on
Chapter 1: Understanding Chunked Uploads
When it comes to chunked uploads in Python, many resources predominantly showcase methods for handling text files. However, the need often arises to upload other file types, such as videos, which necessitate dealing with binary files. This task introduces unique challenges and potential pitfalls that may not be immediately apparent. In this guide, we’ll explore the common issues you might face when uploading large non-text files in chunks.
Handling Binary Files
The first challenge when working with non-text files is the temptation to treat them as text. If you encounter a tutorial that works for text files, it often can be adapted for binary files with slight modifications to help Python identify the file type. Whenever you're opening or reading a file, remember to specify binary mode by adding 'b'. For example:
file = open(content_path, "rb")
Use "wb" for writing. Keeping this in mind will simplify your work with binary files.
Header Challenges in Chunked Uploads
Understanding headers is essential, as they can be confusing in the context of chunked uploads. Common headers you may encounter include:
- Custom headers
- application/octet-stream
- multipart/form-data
- content-type/whatever
- content-range
Let's break these down briefly.
Custom Headers
Different APIs have unique requirements, so always verify what headers are necessary for your chunked upload. Pay special attention to custom headers, as they often vary by service. Ensure that you format these headers correctly to avoid errors.
Application/Octet-Stream Header
The application/octet-stream header signals that the file is binary. This header ensures that the file is not executed upon arrival, indicating that it should be opened with an appropriate application. For instance, .doc files may be opened with Microsoft Word or Google Docs, while video files might require additional information for correct reassembly and playback.
Multipart/Form-Data Header
The multipart/form-data header can be misleading. It's easy to assume it indicates multiple chunks, but it actually communicates that you're sending a collection of files, possibly along with form data. You can include as many files as the server allows.
Content-Type Header
The significance of the content-type header varies. Check your service's documentation to see if this header is necessary. Sometimes, it’s optional, but an incorrect content-type can lead to errors.
Content-Range Header
The content-range header is crucial for chunked uploads and can lead to perplexing errors if not formatted correctly. It typically appears as follows:
Content-Range: bytes start-end/total
Each content-range header in your series of requests informs the server where the current data chunk fits among the entire file being uploaded. A common mistake is miscalculating byte positions, which can trigger unexpected errors, such as:
UnicodeDecodeError: 'utf-8' codec can't decode byte -somebyte- ...
Before assuming the issue lies with file encoding or corruption, double-check your code related to chunking and ensure the content-range header is accurately set up.
Using a Generator with the Requests Library
Utilizing a generator in conjunction with the requests library can streamline the chunked upload process. However, it's important to understand how generators operate. A generator creates an iterator that yields values instead of returning them, allowing it to maintain state between calls.
Here's an example of a generator function designed for chunk reading:
def read_in_chunks(file_object, chunk_size):
while True:
data = file_object.read(chunk_size)
if not data:
breakyield data
When invoking the generator, it continues from where it left off each time you request a new chunk. In the context of a file upload, the generator facilitates the retrieval and sending of each data chunk seamlessly.
Sample Upload Code
Here's how you might implement this generator in your upload function:
def upload(file, url):
content_name = str(file)
content_path = os.path.abspath(file)
content_size = os.stat(content_path).st_size
print(content_name, content_path, content_size)
file_object = open(content_path, "rb")
index = 0
offset = 0
headers = {}
for chunk in read_in_chunks(file_object, CHUNK_SIZE):
offset = index + len(chunk)
headers['Content-Range'] = f'bytes {index}-{offset - 1}/{content_size}'
headers['Authorization'] = auth_string
index = offset
try:
file = {"file": chunk}
r = requests.post(url, files=file, headers=headers)
print(r.json())
print(f"r: {r}, Content-Range: {headers['Content-Range']}")
except Exception as e:
print(e)
In this function, the generator yields chunks of data which are then sent in a POST request. If executed with the proper headers and content-range information, the entire file will be successfully uploaded and reassembled.
I hope this guide helps you navigate the common challenges associated with chunked uploads of binary files in Python. If you have suggestions for improvement, feel free to share your thoughts in the comments!
A comprehensive guide on working with binary files in Python, focusing on chunked uploads.
Learn the essentials of reading binary files in Python, including practical examples and tips for success.