substitute-binary: Add a local cache.

* guix/scripts/substitute-binary.scm (%narinfo-cache-directory,
  %narinfo-ttl, %narinfo-negative-ttl): New variables.
  (with-atomic-file-output, object->fields, read-narinfo,
  write-narinfo, narinfo->string, string->narinfo, lookup-narinfo): New
  procedures.
  (fetch-narinfo): Adjust to use `read-narinfo'.
  (guix-substitute-binary): Ensure the existence of
  %NARINFO-CACHE-DIRECTORY.  Use `lookup-narinfo' instead of
  `fetch-narinfo'.

1 files changed, 5 insertions, 1 deletions

diff --git a/test-env.in b/test-env.in
index 9a6257197c7..64440fb86af 100644
--- a/test-env.in
+++ b/test-env.in
@@ -45,9 +45,13 @@ then
     rm -rf "$NIX_STATE_DIR/substituter-data"
     mkdir -p "$NIX_STATE_DIR/substituter-data"
 
+    # Place for the substituter's cache.
+    XDG_CACHE_HOME="$NIX_STATE_DIR/cache-$$"
+
     export NIX_IGNORE_SYMLINK_STORE NIX_STORE_DIR                       \
         NIX_LOCALSTATE_DIR NIX_LOG_DIR NIX_STATE_DIR NIX_DB_DIR         \
-        NIX_ROOT_FINDER NIX_SETUID_HELPER GUIX_BINARY_SUBSTITUTE_URL
+        NIX_ROOT_FINDER NIX_SETUID_HELPER GUIX_BINARY_SUBSTITUTE_URL    \
+        XDG_CACHE_HOME
 
     # Do that because store.scm calls `canonicalize-path' on it.
     mkdir -p "$NIX_STORE_DIR"