Add documentation section with commands to query the cache

web/content/hut/_index.md

@@ -23,7 +23,7 @@ a good candidate for low noise executions.
 We provide a binary cache in `hut`, with the aim of avoiding unnecessary
 recompilation of packages.
 
-The cache should contain common packages from bsckpkgs, but we don't provide
+The cache should contain common packages from bscpkgs, but we don't provide
 any guarantee that of what will be available in the cache, or for how long.
 We recommend following the latest version of the `jungle` flake to avoid cache
 misses.
@@ -38,7 +38,7 @@ enable it for all builds in the system.
 ```nix
 { ... }: {
   nix.settings = {
-    substituters = [ "https://jungle.bsc.es" ];
+    substituters = [ "https://jungle.bsc.es/cache" ];
     trusted-public-keys = [ "jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" ];
   };
 }
@@ -53,13 +53,15 @@ The cache can also be specified in a per-command basis through the flags
 nix build --substituters "https://jungle.bsc.es/cache" --trusted-public-keys "jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" <...>
 ```
 
+Note: you'll have to be a trusted user.
+
 ### Nix configuration file (non-nixos)
 
 If using nix outside of NixOS, you'll have to update `nix.conf`
 
-```bash
+```
-echo "substituters = https://jungle.bsc.es" >> /etc/nix/nix.conf
+# echo "substituters = https://jungle.bsc.es/cache" >> /etc/nix/nix.conf
-echo "trusted-public-keys = jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" >> /etc/nix/nix.conf
+# echo "trusted-public-keys = jungle.bsc.es:pEc7MlAT0HEwLQYPtpkPLwRsGf80ZI26aj29zMw/HH0=" >> /etc/nix/nix.conf
 ```
 
 ### Hint in flakes
@@ -82,3 +84,44 @@ By adding the configuration below to a `flake.nix`, when someone uses the flake,
   };
 }
 ```
+
+### Querying the cache
+
+Check if the cache is available:
+```sh
+$ curl https://jungle.bsc.es/cache/nix-cache-info
+StoreDir: /nix/store
+WantMassQuery: 1
+Priority: 30
+```
+
+Prevent nix from building locally:
+```bash
+nix build --max-jobs 0 <...>
+```
+
+Check if a package is in cache:
+```bash
+# Do a raw eval on the <package>.outPath (this should not build the package)
+$ nix eval --raw jungle#openmp.outPath
+/nix/store/dwnn4dgm1m4184l4xbi0qfrprji9wjmi-openmp-2024.11
+# Take the hash (everything from / to - in the basename) and curl <hash>.narinfo
+# if it exists in the cache, it will return HTTP 200 and some information
+# if not, it will return 404
+$ curl https://jungle.bsc.es/cache/dwnn4dgm1m4184l4xbi0qfrprji9wjmi.narinfo
+StorePath: /nix/store/dwnn4dgm1m4184l4xbi0qfrprji9wjmi-openmp-2024.11
+URL: nar/dwnn4dgm1m4184l4xbi0qfrprji9wjmi-17imkdfqzmnb013d14dx234bx17bnvws8baf3ii1xra5qi2y1wiz.nar
+Compression: none
+NarHash: sha256:17imkdfqzmnb013d14dx234bx17bnvws8baf3ii1xra5qi2y1wiz
+NarSize: 1519328
+References: 4gk773fqcsv4fh2rfkhs9bgfih86fdq8-gcc-13.3.0-lib nqb2ns2d1lahnd5ncwmn6k84qfd7vx2k-glibc-2.40-36
+Deriver: vcn0x8hikc4mvxdkvrdxp61bwa5r7lr6-openmp-2024.11.drv
+Sig: jungle.bsc.es:GDTOUEs1jl91wpLbb+gcKsAZjpKdARO9j5IQqb3micBeqzX2M/NDtKvgCS1YyiudOUdcjwa3j+hyzV2njokcCA==
+# In oneline:
+$ curl "https://jungle.bsc.es/cache/$(nix eval --raw jungle#<package>.outPath | cut -d '/' -f4 | cut -d '-' -f1).narinfo"
+```
+
+#### References
+
+- https://nix.dev/guides/recipes/add-binary-cache.html
+- https://nixos.wiki/wiki/Binary_Cache