fix: witness not provided for fallback on routes with an alias

[sesi200]

Description

The asset canister does not provide all required absence proofs when the file is not found if the folders are nested deep enough with a few present files. This PR adds the last corner case that wasn't covered before and (at least in my eyes) simplifies proof generation.

Also see original bug report below

Fixes SDK-1298

How Has This Been Tested?

Added a file to the existing test case which matches the minimal repro from the bug report. Compared against master and there the test does not pass with the same changes.

Checklist:

• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have updated asset.wasm

Original bug report:

The asset canister is not providing a witness for fallback responses on routes with an alias.

For example:

If the /hello.html path exists in the asset canister, then making a request against /hello/world will return a fallback to /index.html as expected.

However, if the /hello/index.html path exists in the asset canister then making a request against /hello/world will not work.

This is an example tree returned in this scenario:

55799(
	[1, 
		[4, h'ADE6FBA949CFF9CCE12F3BA7C5C43A99D4166A2C44C477DBA04FD9DD19B579C1'], 
		[2, h'687474705F65787072',  // http_expr
			[1, 
				[1, 
					[1, 
						[2, h'', 
							[2, h'3C243E', // <$>
								[4, h'1437EE3D48A40762C8FDF72EE779466EF67F0D8BA1CA1DF40AA467467621A036']
							]
						],
						[1, 
							[2, h'3C2A3E', // <$>
								[1, 
									[2, h'162BD2F8BA53318BDF0289F9B70393E98E51DF0A3EE6DD79F53399DFE7888ED7', 
										[2, h'', 
											[2, h'49E9CF44E617D88CA88D293FC481E27CBD342D84DC41A3BFFC56999A30EA3626', 
												[3, h'']
											]
										]
									],
									[2, h'C504735B4B6812FD0292109ADCF7C5757C3F34BE28A9BB6DF3F9A55BACCE112C',
										[2, h'',
											[2, h'06C44C86B219D1FDDAE568187643D3954AD683AFF6774CC9E9525244325BA757',
												[3, h'']
											]
										]
									]
								]
							], 
							[4, h'B36CBF7EBF56FDA84A6D1C28F77FE0B5DDC04BE75E0E41546F2516FD5B4A51BF']
						]
					],
					[1, 
						[4, h'255C240DFCFA0F9A2FF734ACFE78CA9A4F03A2CBEAFFAF0C489CAB9AE738AAA4'],
						[1, 
							[1, 
								[2, h'68656C6C6F', // hello
									[1, 
										[4, h'DAB792DA7FEF5FEDE38CB0DA667ED0263A2B9E0F8AF18ABD1BA0BCE344452379'], 
										[1, 
											[2, h'3C243E', // <$>
												[4, h'70BD8799C26666D3A3F66BB2EAE6A1966CB71E7C25E324B76244BC6565A67F43']
											],
											[1, 
												[2, h'696E646578', // index
													[4, h'1EA146409F4F856B5554A0240E1C68A303CA9E31D77A7106A7D89D5C54827361']
												],
												[2, h'696E6465782E68746D6C',  // index.html
													[4, h'1EA146409F4F856B5554A0240E1C68A303CA9E31D77A7106A7D89D5C54827361']
												]
											]
										]
									]
								], 
								[4, h'051F604A8D380B764638B19563B715A5FE71570B0EE9E892D229ED5B5C4D4157']
							],
							[4, h'7000A190977ABC4E6F5A5E810B4A1A0F3CAC15B393E6B592DE810B4A4DCE5209']
						]
					]
				], 
				[4, h'47AC2ABC8EE67BE2D6ED51A94D23E99100E18FD2E0005833F319BB93B7270F5E']
			]
		]
	]
)

Response verification is failing on this tree because the lookup operation is returning Unknown. The lookup path that returns Unknown is [687474705F65787072, 68656C6C6F, , 3C2A3E] (this translates to ["http_expr", "hello", ""]).  Following that path in the tree above reaches the Pruned node with DAB792DA7FEF5FEDE38CB0DA667ED0263A2B9E0F8AF18ABD1BA0BCE344452379 as it's label. Since empty string is lower than DAB79... it will return absent.

If the asset canister provides a witness for ["http_expr", "hello", ""] then this should fix the issue.

[ericswanson-dfinity]

This doesn't fail the test if verify_response() returns false.

I applied the change on line 512 to master and the test failed, as expected
I applied this change as well and the test passed, when it should have failed.

[ericswanson-dfinity]

Also I think it would be helpful to display (panic with) the ResponseVerificationError (inside the Err) as well as the response

[sesi200]

Thanks for catching that! New version reports all available information