feat(gateway): visualize dag-cbor and dag-json

[hacdias]

Closes #307. Builds on top of #298.

• Adds minimal DAG preview for DAG-CBOR and DAG-JSON
• You can preview how it looks by following gateway/assets/README.md
  • For live version, clone Kubo and this PR and then go mod edit -replace=github.com/ipfs/boxo=path/to/your/local/boxo
• Sharness fails here due to a bug fix: see feat(gateway): human error pages, dag-cbor/dag-json preview kubo#9904.

[codecov]

Codecov Report

Merging #315 (b1349b3) into main (c23df38) will increase coverage by 0.29%.
The diff coverage is 63.38%.

@@            Coverage Diff             @@
##             main     #315      +/-   ##
==========================================
+ Coverage   49.36%   49.66%   +0.29%     
==========================================
  Files         281      282       +1     
  Lines       33708    33878     +170     
==========================================
+ Hits        16640    16824     +184     
+ Misses      15329    15300      -29     
- Partials     1739     1754      +15     

Impacted Files	Coverage Δ
gateway/assets/assets.go	69.62% <ø> (ø)
gateway/assets/node.go	55.95% <55.95%> (ø)
gateway/handler_codec.go	53.99% <61.22%> (+21.41%)	⬆️
gateway/assets/test/main.go	40.40% <63.04%> (+20.03%)	⬆️
gateway/handler.go	69.42% <80.00%> (+1.38%)	⬆️
gateway/assets/templates.go	64.70% <100.00%> (+1.44%)	⬆️
gateway/handler_unixfs_dir.go	62.06% <100.00%> (-2.57%)	⬇️

... and 14 files with indirect coverage changes

[hacdias]

I'm opening this for review to get feedback and for others to take it for a spin. I was quite conservative on how we handle the preview. If some error happens, no preview is shown (this usually means that the DAG isn't valid). If it all works, we show a preview.

[lidel]

Thank you @hacdias I think this is good enough to ship, but needs:

• Kubo PR to be green, fine to reuse one from #298 (review) after that PR lands: ipfs/kubo#9904
• Add a regression test that confirms CBOR bytes that get turned into strings in HTML get sanitized (just to be sure)

[hacdias]

Kubo is green: ipfs/kubo#9904

[lidel]

@hacdias while testing in Kubo, I've found some things we should address before merging:

• subdomain gateways should never return dag.html from a path, only return redirect: http://localhost:8080/ipfs/bafyreihnpl7ami7esahkfdnemm6idx4r2n6u3apmtcrxlqwuapgjsciihy MUST redirect to http://bafyreihnpl7ami7esahkfdnemm6idx4r2n6u3apmtcrxlqwuapgjsciihy.ipfs.localhost:8080
• while at this, for HTML responses, we should also ensure the generated HTML document is returned with a scope limited to the CID, the same way dir listings are. On path gateway http://127.0.0.1:8080/ipfs/bafyreihnpl7ami7esahkfdnemm6idx4r2n6u3apmtcrxlqwuapgjsciihy MUST return HTTP 301 redirect to http://127.0.0.1:8080/ipfs/bafyreihnpl7ami7esahkfdnemm6idx4r2n6u3apmtcrxlqwuapgjsciihy/ (normalize with / at the end, just like unixfs dirs)
  • this is an important precaution in case there is ever a bug in sanitization and/or our service worker protection is ever removed

[hacdias]

@lidel I just pushed a fix for both, including tests. In addition, I have a few notes:

• The codec handler was never redirecting properly. I changed the converted and the raw to wrap the ResponseWriter with statusResponseWriter so we preserve the redirection status. Similar to UnixFS files.
• HTML response now redirects to /. Therefore, some sharness tests in Kubo fail where we used to check if we got HTML back. I fixed them by simply requesting the path with trailing slash. The redirection is tested in the new tests in this PR. feat(gateway): human error pages, dag-cbor/dag-json preview kubo#9904

[hacdias]

@lidel regarding our redirects and body conversations, I did not include it here because we have some tests currently checking for that: #326 - let's keep it separate. However, I do think we should clean it up asap.

[lidel]

Thank you, lgtm, merging. I will bubble up to ipfs/kubo#9904 and review there after CI is green.