daemon: Read substitute nar size as 'unsigned long long'.

Fixes <https://issues.guix.gnu.org/46212>.
Reported by Christopher Baines <mail@cbaines.net>.

Previously, the nar size returned by 'guix substitute' would be read as
an 'int'; thus, values above 2^31 - 1 would be read and then stored as
negative integers in the database.

Regression introduced in 9dfa20a22a.

* nix/libstore/build.cc (SubstitutionGoal::finished): Use templatized
'string2Int' instead of 'std::atoi' to get an 'unsigned long long',
which is the type of 'hash.second'.
* tests/store.scm ("substitute and large size"): New test.

nix/libstore/build.cc

@@ -3102,7 +3102,8 @@ void SubstitutionGoal::finished()
 		throw Error(format("unknown hash algorithm in `%1%'") % hashStr);
 	    case htSHA256:
 		hash.first = parseHash16or32(hashType, string(hashStr, n + 1));
-		hash.second = std::atoi(statusList[2].c_str());
+		if (!string2Int(statusList[2], hash.second))
+		    throw Error(format("invalid nar size for '%1%' substitute") % storePath);
 		break;
 	    default:
 		/* The database only stores SHA256 hashes, so compute it.  */

tests/store.scm

@@ -976,6 +976,50 @@ System: x86_64-linux~%"
          (and (equal? (substitutable-path s) item)
               (substitutable-nar-size s)))))))
 
+(test-equal "substitute and large size"
+  (+ 100 (expt 2 31))                     ;<https://issues.guix.gnu.org/46212>
+  (with-store s
+    (let* ((size (+ 100 (expt 2 31)))            ;does not fit in signed 'int'
+           (item (string-append (%store-prefix)
+                                "/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa-bad-size-"
+                                (random-text)))
+           (nar  (string-append (%substitute-directory) "/nar")))
+      ;; Create a dummy nar to allow for substitution.
+      (call-with-output-file nar
+        (lambda (port)
+          (write-file-tree (store-path-package-name item) port
+                           #:file-type+size (lambda _
+                                              (values 'regular 12))
+                           #:file-port (lambda _
+                                         (open-input-string "Hello world.")))))
+
+      ;; Create fake substituter data, to be read by 'guix substitute'.
+      (call-with-output-file (string-append (%substitute-directory)
+                                            "/" (store-path-hash-part item)
+                                            ".narinfo")
+        (lambda (port)
+          (format port "StorePath: ~a
+URL: file://~a
+Compression: none
+NarSize: ~a
+NarHash: sha256:~a
+References: 
+System: x86_64-linux~%"
+                  item nar size
+                  (bytevector->nix-base32-string (gcrypt:file-sha256 nar)))))
+
+      ;; Remove entry from the local cache.
+      (false-if-exception
+       (delete-file-recursively (string-append (getenv "XDG_CACHE_HOME")
+                                               "/guix/substitute")))
+
+      ;; Make sure 'guix substitute' correctly communicates the above
+      ;; data.
+      (set-build-options s #:use-substitutes? #t
+                         #:substitute-urls (%test-substitute-urls))
+      (ensure-path s item)
+      (path-info-nar-size (query-path-info s item)))))
+
 (test-assert "export/import several paths"
   (let* ((texts (unfold (cut >= <> 10)
                         (lambda _ (random-text))