Add HTTP range support for file downloads

[AndreyVMarkelov]

Summary

Add first-class HTTP Range support for file downloads.

This change adds an optional extra_headers parameter to files_download and files_download_to_file, allowing callers to pass request-specific HTTP headers such as Range.

It also adds a public build_range_headers helper for constructing valid HTTP Range headers.

Example

from dropbox import Dropbox, build_range_headers

dbx = Dropbox(oauth2_access_token=ACCESS_TOKEN)

metadata, response = dbx.files_download(
    "/large-file.bin",
    extra_headers=build_range_headers((0, 1023)),
)

Changes

• add extra_headers to files_download
• add extra_headers to files_download_to_file
• forward request-specific headers through the transport layer
• add format_byte_range and build_range_headers
• export build_range_headers from the top-level dropbox package
• add a Dropbox-specific Python client generator backend
• add unit tests for Range formatting, header forwarding, and SDK-managed header precedence

Backward compatibility

The new arguments are optional and are appended to the existing method signatures.

Existing calls continue to work unchanged:

dbx.files_download("/file.txt")
dbx.files_download("/file.txt", rev="...")
dbx.files_download_to_file("local.txt", "/remote.txt")

SDK-managed headers such as Authorization, Content-Type, and Dropbox-API-Arg continue to take precedence over conflicting values supplied through extra_headers.

Fixes #79.

[codecov]

Codecov Report

❌ Patch coverage is 97.43590% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 65.20%. Comparing base (8d013bd) to head (6f32a0d).

Files with missing lines	Patch %	Lines
dropbox/dropbox_client.py	87.50%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #578      +/-   ##
==========================================
+ Coverage   65.18%   65.20%   +0.01%     
==========================================
  Files          34       35       +1     
  Lines       66330    66363      +33     
  Branches     4716     4729      +13     
==========================================
+ Hits        43239    43271      +32     
  Misses      22930    22930              
- Partials      161      162       +1     

Flag	Coverage Δ
integration	65.02% <28.20%> (-0.03%)	⬇️
unit	64.86% <92.30%> (+0.05%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.