return errors from cmds.Copy directly

[whyrusleeping]

Fixes the issue seen in ipfs/kubo#4683 But i'm not 100% sure this is the right way.

cc @kevina, you mentioned you could help look into cmds lib issues.

[codecov]

Codecov Report

Merging #64 into master will decrease coverage by 0.04%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
- Coverage      44%   43.95%   -0.05%     
==========================================
  Files          23       23              
  Lines        1925     1927       +2     
==========================================
  Hits          847      847              
- Misses        938      939       +1     
- Partials      140      141       +1

Impacted Files	Coverage Δ
responseemitter.go	54.54% <0%> (-5.46%)	⬇️

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[kevina]

This might be a problem if multiple errors are emitted, but I am not sure yet. Right now I don't think we do it and it could be that emitting multiple errors was part of the original design, but only @keks can know for sure.

[Stebalien]

As far as I can tell, this code is already doing what it's supposed to do. Response.Next() is supposed to determine that the value is actually an error and return it as an error.

[Stebalien]

I believe the correct fix is #66. The other Response implementations already do this.

[kevina]

This changes the output of the repo gc command that does essentially emit two errors. Before t0087-repo-robust-gc.sh 48 - 'ipfs repo gc --stream-errors' should abort and report each error separately the output would be:

Error: could not retrieve links for QmSijovevteoY63Uj1uC5b8pkpDU5Jgyk2dYBqz3sMJUPc: merkledag: not found
Error: could not retrieve links for QmTbPEyrA1JyGUHFvmtx1FNZVzdBreMv8Hc8jV9sBRWhNA: The block referred to by 'QmTbPEyrA1JyGUHFvmtx1FNZVzdBreMv8Hc8jV9sBRWhNA' was not a valid merkledag node
Error: encountered errors during gc run
Error: garbage collection aborted: could not retrieve some links

Now it is just

Error: could not retrieve links for QmTbPEyrA1JyGUHFvmtx1FNZVzdBreMv8Hc8jV9sBRWhNA: The block referred to by 'QmTbPEyrA1JyGUHFvmtx1FNZVzdBreMv8Hc8jV9sBRWhNA' was not a valid merkledag node
Error: encountered errors during gc run

The last error not emitted is the error returned from the GC() function, which is concerning.

This needs to sorted out.