14/14: substitute: Rework connection error handling.

[guix-commits]

cbaines pushed a commit to branch master
in repository guix.

commit 20c08a8a45d0f137ead7c05e720456b2aea44402
Author: Christopher Baines <mail@cbaines.net>
AuthorDate: Sat Feb 13 11:06:37 2021 +0000

    substitute: Rework connection error handling.
    
    This is part of trying to reduce the interdependency of code within the
    substitute module.
    
    This commit addresses some of the error handling that was performed through
    open-connection-for-uri/maybe. The new approach is to use
    call-with-connection-error-handling, and wrap calls to http-multiple-get and
    http-fetch with that procedure, which takes care of handling connection
    errors.
    
    I think this is even slightly more rigerous than the previous setup, because
    this approach handles connection errors that occur when http-multiple-get
    reconnects to a host.
    
    * guix/scripts/substitute.scm (open-connection-for-uri/maybe): Transform in 
to
    call-with-connection-error-handling.
    (fetch-narinfos): Use call-with-connection-error-handling.
    (process-query): Replace open-connection-for-uri/maybe with
    open-connection-for-uri/cached.
    (open-connection-for-uri/cached): Set a default timeout, matching the
    behaviour in open-connection-for-uri/maybe.
    (process-substitution): Use call-with-connection-error-handling.
---
 guix/scripts/substitute.scm | 47 +++++++++++++++++++++------------------------
 1 file changed, 22 insertions(+), 25 deletions(-)

diff --git a/guix/scripts/substitute.scm b/guix/scripts/substitute.scm
index fea2cec..a3a0349 100755
--- a/guix/scripts/substitute.scm
+++ b/guix/scripts/substitute.scm
@@ -281,22 +281,13 @@ if file doesn't exist, and the narinfo otherwise."
   ;; Set of names of unreachable hosts.
   (make-hash-table))
 
-(define* (open-connection-for-uri/maybe uri
-                                        #:key
-                                        fresh?
-                                        (time %fetch-timeout)
-                                        verify-certificate?)
-  "Open a connection to URI via 'open-connection-for-uri/cached' and return a
-port to it, or, if connection failed, print a warning and return #f.  Pass
-#:fresh? to 'open-connection-for-uri/cached'."
+(define* (call-with-connection-error-handling uri proc)
+  "Call PROC, and catch if a connection fails, print a warning and return #f."
   (define host
     (uri-host uri))
 
   (catch #t
-    (lambda ()
-      (open-connection-for-uri/cached uri #:timeout time
-                                      #:fresh? fresh?
-                                      #:verify-certificate? 
verify-certificate?))
+    proc
     (match-lambda*
       (('getaddrinfo-error error)
        (unless (hash-ref %unreachable-hosts host)
@@ -377,11 +368,14 @@ port to it, or, if connection failed, print a warning and 
return #f.  Pass
        (let* ((requests (map (cut narinfo-request url <>) paths))
               (result   (begin
                           (update-progress!)
-                          (http-multiple-get uri
-                                             handle-narinfo-response '()
-                                             requests
-                                             #:open-connection open-connection
-                                             #:verify-certificate? #f))))
+                          (call-with-connection-error-handling
+                           uri
+                           (lambda ()
+                             (http-multiple-get uri
+                                                handle-narinfo-response '()
+                                                requests
+                                                #:open-connection 
open-connection
+                                                #:verify-certificate? #f))))))
          (newline (current-error-port))
          result))
       ((file #f)
@@ -595,7 +589,7 @@ authorized substitutes."
      ;; Return the subset of PATHS available in CACHE-URLS.
      (let ((substitutable (lookup-narinfos/diverse
                            cache-urls paths valid?
-                           #:open-connection open-connection-for-uri/maybe)))
+                           #:open-connection open-connection-for-uri/cached)))
        (for-each (lambda (narinfo)
                    (format #t "~a~%" (narinfo-path narinfo)))
                  substitutable)
@@ -604,7 +598,7 @@ authorized substitutes."
      ;; Reply info about PATHS if it's in CACHE-URLS.
      (let ((substitutable (lookup-narinfos/diverse
                            cache-urls paths valid?
-                           #:open-connection open-connection-for-uri/maybe)))
+                           #:open-connection open-connection-for-uri/cached)))
        (for-each display-narinfo-data substitutable)
        (newline)))
     (wtf
@@ -617,7 +611,7 @@ authorized substitutes."
 
 (define open-connection-for-uri/cached
   (let ((cache '()))
-    (lambda* (uri #:key fresh? timeout verify-certificate?)
+    (lambda* (uri #:key fresh? (timeout %fetch-timeout) verify-certificate?)
       "Return a connection for URI, possibly reusing a cached connection.
 When FRESH? is true, delete any cached connections for URI and open a new one.
 Return #f if URI's scheme is 'file' or #f.
@@ -704,11 +698,14 @@ the current output port."
              (warning (G_ "while fetching ~a: server is somewhat slow~%")
                       (uri->string uri))
              (warning (G_ "try `--no-substitutes' if the problem persists~%")))
-           (http-fetch uri #:text? #f
-                       #:open-connection open-connection-for-uri/maybe
-                       #:keep-alive? #t
-                       #:buffered? #f
-                       #:verify-certificate? #f))))
+           (call-with-connection-error-handling
+            uri
+            (lambda ()
+              (http-fetch uri #:text? #f
+                          #:open-connection open-connection-for-uri/cached
+                          #:keep-alive? #t
+                          #:buffered? #f
+                          #:verify-certificate? #f))))))
       (else
        (leave (G_ "unsupported substitute URI scheme: ~a~%")
               (uri->string uri)))))