unofficial mirror of bug-guix@gnu.org 
 help / color / mirror / code / Atom feed
blob df7a9bed4a6c9b3ffb1a2e86066aad01e5159c6e 24164 bytes (raw)
name: guix/ssh.scm 	 # note: path name is non-authoritative(*)

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
 
;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
;;;
;;; This file is part of GNU Guix.
;;;
;;; GNU Guix is free software; you can redistribute it and/or modify it
;;; under the terms of the GNU General Public License as published by
;;; the Free Software Foundation; either version 3 of the License, or (at
;;; your option) any later version.
;;;
;;; GNU Guix is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;;; GNU General Public License for more details.
;;;
;;; You should have received a copy of the GNU General Public License
;;; along with GNU Guix.  If not, see <http://www.gnu.org/licenses/>.

(define-module (guix ssh)
  #:use-module (guix store)
  #:use-module (guix inferior)
  #:use-module (guix i18n)
  #:use-module ((guix utils) #:select (&fix-hint))
  #:use-module (gcrypt pk-crypto)
  #:use-module (ssh session)
  #:use-module (ssh auth)
  #:use-module (ssh key)
  #:use-module (ssh channel)
  #:use-module (ssh popen)
  #:use-module (ssh session)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-11)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-35)
  #:use-module (ice-9 match)
  #:use-module (ice-9 format)
  #:use-module (ice-9 binary-ports)
  #:export (open-ssh-session
            authenticate-server*

            remote-inferior
            remote-daemon-channel
            connect-to-remote-daemon
            remote-system
            remote-authorize-signing-key
            send-files
            retrieve-files
            retrieve-files*
            remote-store-host

            report-guile-error
            report-module-error))

;;; Commentary:
;;;
;;; This module provides tools to support communication with remote stores
;;; over SSH, using Guile-SSH.
;;;
;;; Code:

(define %compression
  "zlib@openssh.com,zlib")

(define (host-key->type+key host-key)
  "Destructure HOST-KEY, an OpenSSH host key string, and return two values:
its key type as a symbol, and the actual base64-encoded string."
  (define (type->symbol type)
    (and (string-prefix? "ssh-" type)
         (string->symbol (string-drop type 4))))

  (match (string-tokenize host-key)
    ((type key x)
     (values (type->symbol type) key))
    ((type key)
     (values (type->symbol type) key))))

(define (authenticate-server* session key)
  "Make sure the server for SESSION has the given KEY, where KEY is a string
such as \"ssh-ed25519 AAAAC3Nz… root@example.org\".  Raise an exception if the
actual key does not match."
  (let-values (((server)   (get-server-public-key session))
               ((type key) (host-key->type+key key)))
    (unless (and (or (not (get-key-type server))
                     (eq? (get-key-type server) type))
                 (string=? (public-key->string server) key))
      ;; Key mismatch: something's wrong.  XXX: It could be that the server
      ;; provided its Ed25519 key when we where expecting its RSA key.  XXX:
      ;; Guile-SSH 0.10.1 doesn't know about ed25519 keys and 'get-key-type'
      ;; returns #f in that case.
      (raise (condition
              (&message
               (message (format #f (G_ "server at '~a' returned host key \
'~a' of type '~a' instead of '~a' of type '~a'~%")
                                (session-get session 'host)
                                (public-key->string server)
                                (get-key-type server)
                                key type))))))))

(define* (open-ssh-session host #:key user port identity
                           host-key
                           (compression %compression)
                           (timeout 3600))
  "Open an SSH session for HOST and return it.  IDENTITY specifies the file
name of a private key to use for authenticating with the host.  When USER,
PORT, or IDENTITY are #f, use default values or whatever '~/.ssh/config'
specifies; otherwise use them.

When HOST-KEY is true, it must be a string like \"ssh-ed25519 AAAAC3Nz…
root@example.org\"; the server is authenticated and an error is raised if its
host key is different from HOST-KEY.

Install TIMEOUT as the maximum time in seconds after which a read or write
operation on a channel of the returned session is considered as failing.

Throw an error on failure."
  (let ((session (make-session #:user user
                               #:identity identity
                               #:host host
                               #:port port
                               #:timeout 10       ;seconds
                               ;; #:log-verbosity 'protocol

                               ;; Prevent libssh from reading
                               ;; ~/.ssh/known_hosts when the caller provides
                               ;; a HOST-KEY to match against.
                               #:knownhosts (and host-key "/dev/null")

                               ;; We need lightweight compression when
                               ;; exchanging full archives.
                               #:compression compression
                               #:compression-level 3

                               #:nodelay #t)))

    ;; Honor ~/.ssh/config.
    (session-parse-config! session)

    (match (connect! session)
      ('ok
       (if host-key
           ;; Make sure the server's key is what we expect.
           (authenticate-server* session host-key)

           ;; Authenticate against ~/.ssh/known_hosts.
           (match (authenticate-server session)
             ('ok #f)
             (reason
              (raise (condition
                      (&message
                       (message (format #f (G_ "failed to authenticate \
server at '~a': ~a")
                                        (session-get session 'host)
                                        reason))))))))

       ;; Use public key authentication, via the SSH agent if it's available.
       (match (userauth-public-key/auto! session)
         ('success
          (session-set! session 'timeout timeout)
          session)
         (x
          (match (userauth-gssapi! session)
            ('success
             (session-set! session 'timeout timeout)
             session)
            (x
             (disconnect! session)
             (raise (condition
                     (&message
                      (message (format #f (G_ "SSH authentication failed for '~a': ~a~%")
                                       host (get-error session)))))))))))
      (x
       ;; Connection failed or timeout expired.
       (raise (condition
               (&message
                (message (format #f (G_ "SSH connection to '~a' failed: ~a~%")
                                 host (get-error session))))))))))

(define* (remote-inferior session #:optional become-command)
  "Return a remote inferior for the given SESSION.  If BECOME-COMMAND is
given, use that to invoke the remote Guile REPL."
  (let* ((repl-command (append (or become-command '())
                               '("guix" "repl" "-t" "machine")))
         (pipe (apply open-remote-pipe* session OPEN_BOTH repl-command)))
    (when (eof-object? (peek-char pipe))
      (let ((status (channel-get-exit-status pipe)))
        (close-port pipe)
        (raise (condition
                (&message
                 (message (format #f (G_ "remote command '~{~a~^ ~}' failed \
with status ~a")
                                  repl-command status)))))))
    (port->inferior pipe)))

(define* (inferior-remote-eval exp session #:optional become-command)
  "Evaluate EXP in a new inferior running in SESSION, and close the inferior
right away.  If BECOME-COMMAND is given, use that to invoke the remote Guile
REPL."
  (let ((inferior (remote-inferior session become-command)))
    (dynamic-wind
      (const #t)
      (lambda ()
        (inferior-eval exp inferior))
      (lambda ()
        ;; Close INFERIOR right away to prevent finalization from happening in
        ;; another thread at the wrong time (see
        ;; <https://bugs.gnu.org/26976>.)
        (close-inferior inferior)))))

(define* (remote-daemon-channel session
                                #:optional
                                (socket-name
                                 "/var/guix/daemon-socket/socket"))
  "Return an input/output port (an SSH channel) to the daemon at SESSION."
  (define redirect
    ;; Code run in SESSION to redirect the remote process' stdin/stdout to the
    ;; daemon's socket, à la socat.  The SSH protocol supports forwarding to
    ;; Unix-domain sockets but libssh doesn't have an API for that, hence this
    ;; hack.
    `(begin
       (use-modules (ice-9 match) (rnrs io ports)
                    (rnrs bytevectors))

       (let ((sock    (socket AF_UNIX SOCK_STREAM 0))
             (stdin   (current-input-port))
             (stdout  (current-output-port))
             (select* (lambda (read write except)
                        ;; This is a workaround for
                        ;; <https://bugs.gnu.org/30365> in Guile < 2.2.4:
                        ;; since 'select' sometimes returns non-empty sets for
                        ;; no good reason, call 'select' a second time with a
                        ;; zero timeout to filter out incorrect replies.
                        (match (select read write except)
                          ((read write except)
                           (select read write except 0))))))
         (setvbuf stdout 'none)

         ;; Use buffered ports so that 'get-bytevector-some' returns up to the
         ;; whole buffer like read(2) would--see <https://bugs.gnu.org/30066>.
         (setvbuf stdin 'block 65536)
         (setvbuf sock 'block 65536)

         (connect sock AF_UNIX ,socket-name)

         (let loop ()
           (match (select* (list stdin sock) '() '())
             ((reads () ())
              (when (memq stdin reads)
                (match (get-bytevector-some stdin)
                  ((? eof-object?)
                   (primitive-exit 0))
                  (bv
                   (put-bytevector sock bv)
                   (force-output sock))))
              (when (memq sock reads)
                (match (get-bytevector-some sock)
                  ((? eof-object?)
                   (primitive-exit 0))
                  (bv
                   (put-bytevector stdout bv))))
              (loop))
             (_
              (primitive-exit 1)))))))

  (open-remote-pipe* session OPEN_BOTH
                     ;; Sort-of shell-quote REDIRECT.
                     "guile" "-c"
                     (object->string
                      (object->string redirect))))

(define* (connect-to-remote-daemon session
                                   #:optional
                                   (socket-name
                                    "/var/guix/daemon-socket/socket"))
  "Connect to the remote build daemon listening on SOCKET-NAME over SESSION,
an SSH session.  Return a <store-connection> object."
  (open-connection #:port (remote-daemon-channel session socket-name)))


(define (store-import-channel session)
  "Return an output port to which archives to be exported to SESSION's store
can be written."
  ;; Using the 'import-paths' RPC on a remote store would be slow because it
  ;; makes a round trip every time 32 KiB have been transferred.  This
  ;; procedure instead opens a separate channel to use the remote
  ;; 'import-paths' procedure, which consumes all the data in a single round
  ;; trip.  This optimizes the successful case at the expense of error
  ;; conditions: errors can only be reported once all the input has been
  ;; consumed.
  (define import
    `(begin
       (use-modules (guix) (srfi srfi-34)
                    (rnrs io ports) (rnrs bytevectors))

       (define (consume-input port)
         (let ((bv (make-bytevector 32768)))
           (let loop ()
             (let ((n (get-bytevector-n! port bv 0
                                         (bytevector-length bv))))
               (unless (eof-object? n)
                 (loop))))))

       ;; Upon completion, write an sexp that denotes the status.
       (write
        (catch #t
          (lambda ()
            (guard (c ((nix-protocol-error? c)
                       ;; Consume all the input since the only time we can
                       ;; report the error is after everything has been
                       ;; consumed.
                       (consume-input (current-input-port))
                       (list 'protocol-error (nix-protocol-error-message c))))
              (with-store store
                (setvbuf (current-input-port) 'none)
                (import-paths store (current-input-port))
                '(success))))
          (lambda args
            (cons 'error args))))))

  (open-remote-pipe session
                    (string-join
                     `("guile" "-c"
                       ,(object->string (object->string import))))
                    OPEN_BOTH))

(define* (store-export-channel session files
                               #:key recursive?)
  "Return an input port from which an export of FILES from SESSION's store can
be read.  When RECURSIVE? is true, the closure of FILES is exported."
  ;; Same as above: this is more efficient than calling 'export-paths' on a
  ;; remote store.
  (define export
    `(begin
       (eval-when (load expand eval)
         (unless (resolve-module '(guix) #:ensure #f)
           (write `(module-error))
           (exit 7)))

       (use-modules (guix) (srfi srfi-1)
                    (srfi srfi-26) (srfi srfi-34))

       (guard (c ((nix-connection-error? c)
                  (write `(connection-error ,(nix-connection-error-file c)
                                            ,(nix-connection-error-code c))))
                 ((nix-protocol-error? c)
                  (write `(protocol-error ,(nix-protocol-error-status c)
                                          ,(nix-protocol-error-message c))))
                 (else
                  (write `(exception))))
         (with-store store
           (let* ((files ',files)
                  (invalid (remove (cut valid-path? store <>)
                                   files)))
             (unless (null? invalid)
               (write `(invalid-items ,invalid))
               (exit 1))

             ;; TODO: When RECURSIVE? is true, we could send the list of store
             ;; items in the closure so that the other end can filter out
             ;; those it already has.

             (write '(exporting))                 ;we're ready
             (force-output)

             (setvbuf (current-output-port) 'none)
             (export-paths store files (current-output-port)
                           #:recursive? ,recursive?))))))

  (open-remote-input-pipe session
                          (string-join
                           `("guile" "-c"
                             ,(object->string
                               (object->string export))))))

(define (remote-system session)
  "Return the system type as expected by Nix, usually ARCHITECTURE-KERNEL, of
the machine on the other end of SESSION."
  (inferior-remote-eval '(begin (use-modules (guix utils)) (%current-system))
                        session))

(define* (remote-authorize-signing-key key session #:optional become-command)
  "Send KEY, a canonical sexp containing a public key, over SESSION and add it
to the system ACL file if it has not yet been authorized."
  (inferior-remote-eval
   `(begin
      (use-modules (guix build utils)
                   (guix pki)
                   (guix utils)
                   (gcrypt pk-crypto)
                   (srfi srfi-26))

      (define acl (current-acl))
      (define key (string->canonical-sexp ,(canonical-sexp->string key)))

      (unless (authorized-key? key)
        (let ((acl (public-keys->acl (cons key (acl->public-keys acl)))))
          (mkdir-p (dirname %acl-file))
          (with-atomic-file-output %acl-file
            (cut write-acl acl <>)))))
   session
   become-command))

(define* (send-files local files remote
                     #:key
                     recursive?
                     (log-port (current-error-port)))
  "Send the subset of FILES from LOCAL (a local store) that's missing to
REMOTE, a remote store.  When RECURSIVE? is true, send the closure of FILES.
Return the list of store items actually sent."
  (define (inferior-remote-eval* exp session)
    (guard (c ((inferior-exception? c)
               (match (inferior-exception-arguments c)
                 (('quit 7)
                  (report-module-error (remote-store-host remote)))
                 (_
                  (report-inferior-exception c (remote-store-host remote))))))
      (inferior-remote-eval exp session)))

  ;; Compute the subset of FILES missing on SESSION and send them.
  (let* ((files   (if recursive? (requisites local files) files))
         (session (channel-get-session (store-connection-socket remote)))
         (missing (inferior-remote-eval*
                   `(begin
                      (eval-when (load expand eval)
                        (unless (resolve-module '(guix) #:ensure #f)
                          (exit 7)))

                      (use-modules (guix)
                                   (srfi srfi-1) (srfi srfi-26))

                      (with-store store
                        (remove (cut valid-path? store <>)
                                ',files)))
                   session))
         (count   (length missing))
         (sizes   (map (lambda (item)
                         (path-info-nar-size (query-path-info local item)))
                       missing))
         (port    (store-import-channel session)))
    (format log-port (N_ "sending ~a store item (~h MiB) to '~a'...~%"
                         "sending ~a store items (~h MiB) to '~a'...~%" count)
            count
            (inexact->exact (round (/ (reduce + 0 sizes) (expt 2. 20))))
            (session-get session 'host))

    ;; Send MISSING in topological order.
    (export-paths local missing port)

    ;; Tell the remote process that we're done.  (In theory the end-of-archive
    ;; mark of 'export-paths' would be enough, but in practice it's not.)
    (channel-send-eof port)

    ;; Wait for completion of the remote process and read the status sexp from
    ;; PORT.  Wait for the exit status only when 'read' completed; otherwise,
    ;; we might wait forever if the other end is stuck.
    (let* ((result (false-if-exception (read port)))
           (status (and result
                        (zero? (channel-get-exit-status port)))))
      (close-port port)
      (match result
        (('success . _)
         missing)
        (('protocol-error message)
         (raise (condition
                 (&store-protocol-error (message message) (status 42)))))
        (('error key args ...)
         (raise (condition
                 (&store-protocol-error
                  (message (call-with-output-string
                             (lambda (port)
                               (print-exception port #f key args))))
                  (status 43)))))
        (_
         (raise (condition
                 (&store-protocol-error
                  (message "unknown error while sending files over SSH")
                  (status 44)))))))))

(define (remote-store-session remote)
  "Return the SSH channel beneath REMOTE, a remote store as returned by
'connect-to-remote-daemon', or #f."
  (channel-get-session (store-connection-socket remote)))

(define (remote-store-host remote)
  "Return the name of the host REMOTE is connected to, where REMOTE is a
remote store as returned by 'connect-to-remote-daemon'."
  (match (remote-store-session remote)
    (#f #f)
    ((? session? session)
     (session-get session 'host))))

(define* (file-retrieval-port files remote
                              #:key recursive?)
  "Return an input port from which to retrieve FILES (a list of store items)
from REMOTE, along with the number of items to retrieve (lower than or equal
to the length of FILES.)"
  (values (store-export-channel (remote-store-session remote) files
                                #:recursive? recursive?)
          (length files)))            ;XXX: inaccurate when RECURSIVE? is true

(define-syntax raise-error
  (syntax-rules (=>)
    ((_ fmt args ... (=> hint-fmt hint-args ...))
     (raise (condition
             (&message
              (message (format #f fmt args ...)))
             (&fix-hint
              (hint (format #f hint-fmt hint-args ...))))))
    ((_ fmt args ...)
     (raise (condition
             (&message
              (message (format #f fmt args ...))))))))

(define* (retrieve-files* files remote
                          #:key recursive? (log-port (current-error-port))
                          (import (const #f)))
  "Pass IMPORT an input port from which to read the sequence of FILES coming
from REMOTE.  When RECURSIVE? is true, retrieve the closure of FILES."
  (let-values (((port count)
                (file-retrieval-port files remote
                                     #:recursive? recursive?)))
    (match (read port)                            ;read the initial status
      (('exporting)
       (format #t (N_ "retrieving ~a store item from '~a'...~%"
                      "retrieving ~a store items from '~a'...~%" count)
               count (remote-store-host remote))

       (dynamic-wind
         (const #t)
         (lambda ()
           (import port))
         (lambda ()
           (close-port port))))
      ((? eof-object?)
       (report-guile-error (remote-store-host remote)))
      (('module-error . _)
       (report-module-error (remote-store-host remote)))
      (('connection-error file code . _)
       (raise-error (G_ "failed to connect to '~A' on remote host '~A': ~a")
                    file (remote-store-host remote) (strerror code)))
      (('invalid-items items . _)
       (raise-error (N_ "no such item on remote host '~A':~{ ~a~}"
                        "no such items on remote host '~A':~{ ~a~}"
                        (length items))
                    (remote-store-host remote) items))
      (('protocol-error status message . _)
       (raise-error (G_ "protocol error on remote host '~A': ~a")
                    (remote-store-host remote) message))
      (_
       (raise-error (G_ "failed to retrieve store items from '~a'")
                    (remote-store-host remote))))))

(define* (retrieve-files local files remote
                         #:key recursive? (log-port (current-error-port)))
  "Retrieve FILES from REMOTE and import them using the 'import-paths' RPC on
LOCAL.  When RECURSIVE? is true, retrieve the closure of FILES."
  (retrieve-files* (remove (cut valid-path? local <>) files)
                   remote
                   #:recursive? recursive?
                   #:log-port log-port
                   #:import (lambda (port)
                              (import-paths local port))))

\f
;;;
;;; Error reporting.
;;;

(define (report-guile-error host)
  (raise-error (G_ "failed to start Guile on remote host '~A'") host
               (=> (G_ "Make sure @command{guile} can be found in
@code{$PATH} on the remote host.  Run @command{ssh ~A guile --version} to
check.")
                   host)))

(define (report-module-error host)
  "Report an error about missing Guix modules on HOST."
  ;; TRANSLATORS: Leave "Guile" untranslated.
  (raise-error (G_ "Guile modules not found on remote host '~A'") host
               (=> (G_ "Make sure @code{GUILE_LOAD_PATH} includes Guix'
own module directory.  Run @command{ssh ~A env | grep GUILE_LOAD_PATH} to
check.")
                   host)))

(define (report-inferior-exception exception host)
  "Report EXCEPTION, an &inferior-exception that occurred on HOST."
  (raise-error (G_ "exception occurred on remote host '~A': ~s")
               host (inferior-exception-arguments exception)))

;;; ssh.scm ends here

debug log:

solving df7a9bed4a ...
found df7a9bed4a in https://yhetil.org/guix-bugs/20200702120333.GB4532@zpidnp36/
found 2d7ca7d01d in https://git.savannah.gnu.org/cgit/guix.git
preparing index
index prepared:
100644 2d7ca7d01d62b13f4a95502e2d29f936e01ef694	guix/ssh.scm

applying [1/1] https://yhetil.org/guix-bugs/20200702120333.GB4532@zpidnp36/
diff --git a/guix/ssh.scm b/guix/ssh.scm
index 2d7ca7d01d..df7a9bed4a 100644

Checking patch guix/ssh.scm...
Applied patch guix/ssh.scm cleanly.

index at:
100644 df7a9bed4a6c9b3ffb1a2e86066aad01e5159c6e	guix/ssh.scm

(*) Git path names are given by the tree(s) the blob belongs to.
    Blobs themselves have no identifier aside from the hash of its contents.^

Code repositories for project(s) associated with this public inbox

	https://git.savannah.gnu.org/cgit/guix.git

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).