docker cp: report both content size and transferred size

[thaJeztah]

• alternative to, closes docker cp: report both content size and transferred size #6800
• fixes Docker cp success message shows wrong size #5777

When copying files to a container, the docker cp command would print a message reporting the size of files copied. However, this size was based on the size of the TAR stream sent, which includes the size of the TAR headers.

docker container create --name my-container busybox

touch empty-file
docker cp empty-file my-container:/empty-file
Successfully copied 1.54kB to my-container:/empty-file

This patch adds a calcTARContentSize utility, which uses the TAR headers to calculate the size of files included.

With this patch applied, the content size is reported, instead of the size of the TAR stream used for transport;

docker container create --name my-container busybox

touch empty-file
docker cp empty-file my-container:/empty-file
Successfully copied 0B (transferred 1.54kB) to my-container:/empty-file

mkdir empty-dir
docker cp ./empty-dir my-container:/somewhere/
Successfully copied 0B (transferred 1.54kB) to my-container:/somewhere/

docker cp ./cli/command my-container:/files/
Successfully copied 2.01MB (transferred 2.53MB) to my-container:/files/

- What I did

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docker cp: report both content size and transferred size

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 3.03030% with 32 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cli/command/container/cp.go	3.03%	32 Missing ⚠️

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