chunk transfer

[geospatial-jeff]

Implements chunk transfer encoding. This was already enabled through the Filesystem.read() method, so this mostly involved improving the efficiency of tag reading. I did have to remove parallel tag reading (#92) since the tags are not aware of each other and would send the same 16kb request multiple times, but overall this makes things faster.

To make things simpler for now, we coerce the chunk size to be at least the minimum size required to accomplish the operation that initiated the request (ex. chunk size is 10k but reading a tag value requires 15k bytes). This also makes it possible to test the differences between chunk sizes, as setting a chunk size of 0 will essentially disable chunking for all header requests. This could be an issue on larger images with really big offset tags, but aiocogeo doesn't support BigTiff yet anyways!

Closes #76

TODOs:

• [x] differentiate between INGESTED_BYTES_AT_OPEN and the chunk size used to request data beyond the initial request. And make them both configurable.

[codecov-io]

Codecov Report

Merging #95 (16a750f) into master (e5b7b48) will increase coverage by 0.01%. The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #95      +/-   ##
==========================================
+ Coverage   93.23%   93.25%   +0.01%     
==========================================
  Files          12       12              
  Lines        1079     1082       +3     
==========================================
+ Hits         1006     1009       +3     
  Misses         73       73              

Impacted Files	Coverage Δ
aiocogeo/cog.py	93.87% <100.00%> (+0.02%)	:arrow_up:
aiocogeo/config.py	100.00% <100.00%> (ø)
aiocogeo/filesystems.py	83.25% <100.00%> (+0.07%)	:arrow_up:
aiocogeo/ifd.py	96.68% <100.00%> (ø)
aiocogeo/tag.py	100.00% <100.00%> (ø)

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