Return correct download link for requests for non-standard crate names.

[smarnach]

Fixes #1687.

Crates are uploaded to S3 under the name they were first published as, but the download endpoint always uses the name as written in the request. If these names differ in their use of dashes vs. underscores, the download endpoint returns an invalid link.

To avoid adding another database request for every single crate download, this fix changes the database request that updates the download count to also return the original crate name. We will need to confirm that the performance impact of this change is negligible.

[smarnach]

Looks like the query plan remains virtually the same with this change. Old version:

                                                               QUERY PLAN                                                                
-----------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.15..6.69 rows=1 width=4) (actual time=0.087..0.090 rows=1 loops=1)
   ->  Nested Loop  (cost=0.15..13.23 rows=2 width=4) (actual time=0.084..0.084 rows=1 loops=1)
         Join Filter: (versions.crate_id = crates.id)
         ->  Index Scan using index_version_num on versions  (cost=0.15..12.18 rows=2 width=8) (actual time=0.035..0.036 rows=1 loops=1)
               Index Cond: ((num)::text = '0.1.0'::text)
         ->  Materialize  (cost=0.00..1.02 rows=1 width=4) (actual time=0.044..0.044 rows=1 loops=1)
               ->  Seq Scan on crates  (cost=0.00..1.02 rows=1 width=4) (actual time=0.039..0.039 rows=1 loops=1)
                     Filter: (replace(lower((name)::text), '-'::text, '_'::text) = 'crate_with_dashes'::text)
                     Rows Removed by Filter: 1
 Planning Time: 0.802 ms
 Execution Time: 0.151 ms

New version:

                                                               QUERY PLAN                                                                
-----------------------------------------------------------------------------------------------------------------------------------------
 Limit  (cost=0.15..6.69 rows=1 width=36) (actual time=0.091..0.094 rows=1 loops=1)
   ->  Nested Loop  (cost=0.15..13.23 rows=2 width=36) (actual time=0.088..0.089 rows=1 loops=1)
         Join Filter: (versions.crate_id = crates.id)
         ->  Index Scan using index_version_num on versions  (cost=0.15..12.18 rows=2 width=8) (actual time=0.036..0.036 rows=1 loops=1)
               Index Cond: ((num)::text = '0.1.0'::text)
         ->  Materialize  (cost=0.00..1.02 rows=1 width=36) (actual time=0.047..0.048 rows=1 loops=1)
               ->  Seq Scan on crates  (cost=0.00..1.02 rows=1 width=36) (actual time=0.037..0.037 rows=1 loops=1)
                     Filter: (replace(lower((name)::text), '-'::text, '_'::text) = 'crate_with_dashes'::text)
                     Rows Removed by Filter: 1
 Planning Time: 0.645 ms
 Execution Time: 0.173 ms

[sgrif]

@bors: r+

[bors]

📌 Commit 076e7ce has been approved by sgrif

[bors]

⌛ Testing commit 076e7ce with merge 09c3715...

[bors]

☀️ Test successful - checks-travis
Approved by: sgrif
Pushing 09c3715 to master...