path: root/guix/scripts/publish.scm

;;; GNU Guix --- Functional package management for GNU
;;; Copyright © 2015 David Thompson <davet@gnu.org>
;;; Copyright © 2020 by Amar M. Singh <nly@disroot.org>
;;; Copyright © 2015, 2016, 2017, 2018, 2019, 2020 Ludovic Courtès <ludo@gnu.org>
;;; Copyright © 2020 Maxim Cournoyer <maxim.cournoyer@gmail.com>
;;; Copyright © 2021 Simon Tournier <zimon.toutoune@gmail.com>
;;;
;;; 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 scripts publish)
  #:use-module ((system repl server) #:prefix repl:)
  #:use-module (ice-9 binary-ports)
  #:use-module (ice-9 format)
  #:use-module (ice-9 match)
  #:use-module (ice-9 regex)
  #:use-module (ice-9 rdelim)
  #:use-module (ice-9 threads)
  #:use-module (rnrs bytevectors)
  #:use-module (srfi srfi-1)
  #:use-module (srfi srfi-2)
  #:use-module (srfi srfi-9)
  #:use-module (srfi srfi-9 gnu)
  #:use-module (srfi srfi-19)
  #:use-module (srfi srfi-26)
  #:use-module (srfi srfi-34)
  #:use-module (srfi srfi-37)
  #:use-module (web http)
  #:use-module (web request)
  #:use-module (web response)
  #:use-module (web server)
  #:use-module (web uri)
  #:autoload   (sxml simple) (sxml->xml)
  #:autoload   (guix avahi) (avahi-publish-service-thread)
  #:use-module (guix base32)
  #:use-module (guix base64)
  #:use-module (guix config)
  #:use-module (guix derivations)
  #:use-module (gcrypt hash)
  #:use-module (guix pki)
  #:use-module (gcrypt pk-crypto)
  #:use-module (guix workers)
  #:use-module (guix store)
  #:use-module ((guix serialization) #:select (write-file))
  #:use-module (zlib)
  #:autoload   (lzlib) (call-with-lzip-output-port
                        make-lzip-output-port)
  #:autoload   (zstd)  (call-with-zstd-output-port
                        make-zstd-output-port)
  #:use-module (guix cache)
  #:use-module (guix ui)
  #:use-module (guix scripts)
  #:use-module ((guix utils)
                #:select (with-atomic-file-output compressed-file?))
  #:use-module ((guix build utils)
                #:select (dump-port mkdir-p find-files))
  #:use-module ((guix build syscalls) #:select (set-thread-name))
  #:export (%default-gzip-compression

            %public-key
            %private-key
            signed-string

            open-server-socket
            publish-service-type
            run-publish-server
            guix-publish))

(define (show-help)
  (format #t (G_ "Usage: guix publish [OPTION]...
Publish ~a over HTTP.\n") %store-directory)
  (display (G_ "
  -p, --port=PORT        listen on PORT"))
  (display (G_ "
      --listen=HOST      listen on the network interface for HOST"))
  (display (G_ "
  -u, --user=USER        change privileges to USER as soon as possible"))
  (display (G_ "
  -a, --advertise        advertise on the local network"))
  (display (G_ "
  -C, --compression[=METHOD:LEVEL]
                         compress archives with METHOD at LEVEL"))
  (display (G_ "
  -c, --cache=DIRECTORY  cache published items to DIRECTORY"))
  (display (G_ "
      --cache-bypass-threshold=SIZE
                         serve store items below SIZE even when not cached"))
  (display (G_ "
      --workers=N        use N workers to bake items"))
  (display (G_ "
      --ttl=TTL          announce narinfos can be cached for TTL seconds"))
  (display (G_ "
      --nar-path=PATH    use PATH as the prefix for nar URLs"))
  (display (G_ "
      --public-key=FILE  use FILE as the public key for signatures"))
  (display (G_ "
      --private-key=FILE use FILE as the private key for signatures"))
  (display (G_ "
  -r, --repl[=PORT]      spawn REPL server on PORT"))
  (newline)
  (display (G_ "
  -h, --help             display this help and exit"))
  (display (G_ "
  -V, --version          display version information and exit"))
  (newline)
  (show-bug-report-information))

(define (getaddrinfo* host)
  "Like 'getaddrinfo', but properly report errors."
  (catch 'getaddrinfo-error
    (lambda ()
      (getaddrinfo host))
    (lambda (key error)
      (leave (G_ "lookup of host '~a' failed: ~a~%")
             host (gai-strerror error)))))

;; Nar compression parameters.
(define-record-type <compression>
  (compression type level)
  compression?
  (type   compression-type)
  (level  compression-level))

(define %no-compression
  (compression 'none 0))

(define %default-gzip-compression
  ;; Since we compress on the fly, default to fast compression.
  (compression 'gzip 3))

(define (default-compression type)
  (compression type 3))

(define (actual-compressions item requested)
  "Return the actual compressions used for ITEM, which may be %NO-COMPRESSION
if ITEM is already compressed."
  (if (compressed-file? item)
      (list %no-compression)
      requested))

(define (low-compression c)
  "Return <compression> of the same type as C, but optimized for low CPU
usage."
  (compression (compression-type c)
               (min (compression-level c) 2)))

(define %options
  (list (option '(#\h "help") #f #f
                (lambda _
                  (show-help)
                  (exit 0)))
        (option '(#\V "version") #f #f
                (lambda _
                  (show-version-and-exit "guix publish")))
        (option '(#\a "advertise") #f #f
                (lambda (opt name arg result)
                  (alist-cons 'advertise? #t result)))
        (option '(#\u "user") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'user arg result)))
        (option '(#\p "port") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'port (string->number* arg) result)))
        (option '("listen") #t #f
                (lambda (opt name arg result)
                  (match (getaddrinfo* arg)
                    ((info _ ...)
                     (alist-cons 'address (addrinfo:addr info)
                                 result))
                    (()
                     (leave (G_ "lookup of host '~a' returned nothing")
                            name)))))
        (option '(#\C "compression") #f #t
                (lambda (opt name arg result)
                  (let* ((colon (string-index arg #\:))
                         (type  (cond
                                 (colon (string-take arg colon))
                                 ((string->number arg) "gzip")
                                 (else arg)))
                         (level (if colon
                                    (string->number*
                                     (string-drop arg (+ 1 colon)))
                                    (or (string->number arg) 3))))
                    (match level
                      (0
                       (alist-cons 'compression %no-compression result))
                      (level
                       (match (string->compression-type type)
                         ((? symbol? type)
                          (alist-cons 'compression
                                      (compression type level)
                                      result))
                         (_
                          (warning (G_ "~a: unsupported compression type~%")
                                   type)
                          result)))))))
        (option '(#\c "cache") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'cache arg result)))
        (option '("cache-bypass-threshold") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'cache-bypass-threshold (size->number arg)
                              result)))
        (option '("workers") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'workers (string->number* arg)
                              result)))
        (option '("ttl") #t #f
                (lambda (opt name arg result)
                  (let ((duration (string->duration arg)))
                    (unless duration
                      (leave (G_ "~a: invalid duration~%") arg))
                    (alist-cons 'narinfo-ttl (time-second duration)
                                result))))
        (option '("nar-path") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'nar-path arg result)))
        (option '("public-key") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'public-key-file arg result)))
        (option '("private-key" "secret-key") #t #f
                (lambda (opt name arg result)
                  (alist-cons 'private-key-file arg result)))
        (option '(#\r "repl") #f #t
                (lambda (opt name arg result)
                  ;; If port unspecified, use default Guile REPL port.
                  (let ((port (and arg (string->number* arg))))
                    (alist-cons 'repl (or port 37146) result))))))

(define %default-options
  `((port . 8080)

    ;; By default, serve nars under "/nar".
    (nar-path . "nar")

    (public-key-file . ,%public-key-file)
    (private-key-file . ,%private-key-file)

    ;; Default number of workers when caching is enabled.
    (workers . ,(current-processor-count))

    (address . ,(make-socket-address AF_INET INADDR_ANY 0))
    (repl . #f)))

;; The key pair used to sign narinfos.
(define %private-key
  (make-parameter #f))
(define %public-key
  (make-parameter #f))

(define %nix-cache-info
  `(("StoreDir" . ,%store-directory)
    ("WantMassQuery" . 0)
    ("Priority" . 100)))

;;; A common buffer size value used for the TCP socket SO_SNDBUF option and
;;; the gzip compressor buffer size.
(define %default-buffer-size
  (* 208 1024))

(define %default-socket-options
  ;; List of options passed to 'setsockopt' when transmitting files.
  (list (list SO_SNDBUF %default-buffer-size)))

(define* (configure-socket socket #:key (level SOL_SOCKET)
                           (options %default-socket-options))
  "Apply multiple option tuples in OPTIONS to SOCKET, using LEVEL."
  (for-each (cut apply setsockopt socket level <>)
            options))

(define (signed-string s)
  "Sign the hash of the string S with the daemon's key.  Return a canonical
sexp for the signature."
  (let* ((public-key (%public-key))
         (hash (bytevector->hash-data (sha256 (string->utf8 s))
                                      #:key-type (key-type public-key))))
    (signature-sexp hash (%private-key) public-key)))

(define base64-encode-string
  (compose base64-encode string->utf8))

(define* (store-item->recutils store-item
                               #:key
                               (nar-path "nar")
                               (compression %no-compression)
                               file-size)
  "Return the 'Compression' and 'URL' fields of the narinfo for STORE-ITEM,
with COMPRESSION, starting at NAR-PATH."
  (let ((url (encode-and-join-uri-path
              `(,@(split-and-decode-uri-path nar-path)
                ,@(match compression
                    (($ <compression> 'none)
                     '())
                    (($ <compression> type)
                     (list (symbol->string type))))
                ,(basename store-item)))))
    (format #f "URL: ~a~%Compression: ~a~%~@[FileSize: ~a~%~]"
            url (compression-type compression) file-size)))

(define* (narinfo-string store store-path key
                         #:key (compressions (list %no-compression))
                         (nar-path "nar") (file-sizes '()))
  "Generate a narinfo key/value string for STORE-PATH; an exception is raised
if STORE-PATH is invalid.  Produce a URL that corresponds to COMPRESSION.  The
narinfo is signed with KEY.  NAR-PATH specifies the prefix for nar URLs.

Optionally, FILE-SIZES is a list of compression/integer pairs, where the
integer is size in bytes of the compressed NAR; it informs the client of how
much needs to be downloaded."
  (let* ((path-info  (query-path-info store store-path))
         (compressions (actual-compressions store-path compressions))
         (hash       (bytevector->nix-base32-string
                      (path-info-hash path-info)))
         (size       (path-info-nar-size path-info))
         (file-sizes `((,%no-compression . ,size) ,@file-sizes))
         (references (string-join
                      (map basename (path-info-references path-info))
                      " "))
         (deriver    (path-info-deriver path-info))
         (base-info  (format #f
                             "\
StorePath: ~a
~{~a~}\
NarHash: sha256:~a
NarSize: ~d
References: ~a~%"
                             store-path
                             (map (lambda (compression)
                                    (let ((size (assoc-ref file-sizes
                                                           compression)))
                                      (store-item->recutils store-path
                                                            #:file-size size
                                                            #:nar-path nar-path
                                                            #:compression
                                                            compression)))
                                  compressions)
                             hash size references))
         ;; Do not render a "Deriver" or "System" line if we are rendering
         ;; info for a derivation.
         (info       (if (not deriver)
                         base-info
                         (catch 'system-error
                           (lambda ()
                             (let ((drv (read-derivation-from-file deriver)))
                               (format #f "~aSystem: ~a~%Deriver: ~a~%"
                                       base-info (derivation-system drv)
                                       (basename deriver))))
                           (lambda args
                             ;; DERIVER might be missing, but that's fine:
                             ;; it's only used for <substitutable> where it's
                             ;; optional.  'System' is currently unused.
                             (if (= ENOENT (system-error-errno args))
                                 base-info
                                 (apply throw args))))))
         (signature  (base64-encode-string
                      (canonical-sexp->string (signed-string info)))))
    (format #f "~aSignature: 1;~a;~a~%" info (gethostname) signature)))

(define* (not-found request
                    #:key (phrase "Resource not found")
                    ttl)
  "Render 404 response for REQUEST."
  (values (build-response #:code 404
                          #:headers (if ttl
                                        `((cache-control (max-age . ,ttl)))
                                        '()))
          (string-append phrase ": "
                         (uri-path (request-uri request)))))

(define (render-nix-cache-info)
  "Render server information."
  (values '((content-type . (text/plain)))
          (lambda (port)
            (for-each (match-lambda
                       ((key . value)
                        (format port "~a: ~a~%" key value)))
                      %nix-cache-info))))

(define* (render-narinfo store request hash
                         #:key ttl (compressions (list %no-compression))
                         (nar-path "nar"))
  "Render metadata for the store path corresponding to HASH.  If TTL is true,
advertise it as the maximum validity period (in seconds) via the
'Cache-Control' header.  This allows 'guix substitute' to cache it for an
appropriate duration.  NAR-PATH specifies the prefix for nar URLs."
  (let ((store-path (hash-part->path store hash)))
    (if (string-null? store-path)
        (not-found request #:phrase "")
        (values `((content-type . (application/x-nix-narinfo))
                  ,@(if ttl
                        `((cache-control (max-age . ,ttl)))
                        '()))
                (cut display
                  (narinfo-string store store-path (%private-key)
                                  #:nar-path nar-path
                                  #:compressions compressions)
                  <>)))))

(define* (nar-cache-file directory item
                             #:key (compression %no-compression))
  (string-append directory "/"
                 (symbol->string (compression-type compression))
                 "/" (basename item) ".nar"))

(define* (narinfo-cache-file directory item
                             #:key (compression %no-compression))
  (string-append directory "/"
                 (symbol->string (compression-type compression))
                 "/" (basename item)
                 ".narinfo"))

(define (hash-part-mapping-cache-file directory hash)
  (string-append directory "/hashes/" hash))

(define run-single-baker
  (let ((baking (make-weak-value-hash-table))
        (mutex  (make-mutex)))
    (lambda (item thunk)
      "Run THUNK, which is supposed to bake ITEM, but make sure only one
thread is baking ITEM at a given time."
      (define selected?
        (with-mutex mutex
          (and (not (hash-ref baking item))
               (begin
                 (hash-set! baking item (current-thread))
                 #t))))

      (when selected?
        (dynamic-wind
          (const #t)
          thunk
          (lambda ()
            (with-mutex mutex
              (hash-remove! baking item))))))))

(define-syntax-rule (single-baker item exp ...)
  "Bake ITEM by evaluating EXP, but make sure there's only one baker for ITEM
at a time."
  (run-single-baker item (lambda () exp ...)))


(define (narinfo-files cache)
  "Return the list of .narinfo files under CACHE."
  (if (file-is-directory? cache)
      (find-files cache
                  (lambda (file stat)
                    (string-suffix? ".narinfo" file)))
      '()))

(define (nar-expiration-time ttl)
  "Return the narinfo expiration time (in seconds since the Epoch).  The
expiration time is +inf.0 when passed an item that is still in the store; in
other cases, it is the last-access time of the item plus TTL.

This policy allows us to keep cached nars that correspond to valid store
items.  Failing that, we could eventually have to recompute them and return
404 in the meantime."
  (let ((expiration-time (file-expiration-time ttl)))
    (lambda (file)
      (let ((item (string-append (%store-prefix) "/"
                                 (basename file ".narinfo"))))
        ;; Note: We don't need to use 'valid-path?' here because FILE would
        ;; not exist if ITEM were not valid in the first place.
        (if (file-exists? item)
            +inf.0
            (expiration-time file))))))

(define (hash-part->path* store hash cache)
  "Like 'hash-part->path' but cache results under CACHE.  This ensures we can
still map HASH to the corresponding store file name, even if said store item
vanished from the store in the meantime."
  (let ((cached (hash-part-mapping-cache-file cache hash)))
    (catch 'system-error
      (lambda ()
        (call-with-input-file cached read-string))
      (lambda args
        (if (= ENOENT (system-error-errno args))
            (match (hash-part->path store hash)
              ("" "")
              (result
               (mkdir-p (dirname cached))
               (call-with-output-file (string-append cached ".tmp")
                 (lambda (port)
                   (display result port)))
               (rename-file (string-append cached ".tmp") cached)
               result))
            (apply throw args))))))

(define cache-bypass-threshold
  ;; Maximum size of a store item that may be served by the '/cached' handlers
  ;; below even when not in cache.
  (make-parameter (* 10 (expt 2 20))))

(define (bypass-cache? store item)
  "Return true if we allow ITEM to be downloaded before it is cached.  ITEM is
interpreted as the basename of a store item."
  (guard (c ((store-error? c) #f))
    (< (path-info-nar-size (query-path-info store item))
       (cache-bypass-threshold))))

(define* (render-narinfo/cached store request hash
                                #:key ttl (compressions (list %no-compression))
                                (nar-path "nar")
                                cache pool)
  "Respond to the narinfo request for REQUEST.  If the narinfo is available in
CACHE, then send it; otherwise, return 404 and \"bake\" that nar and narinfo
requested using POOL."
  (define (delete-entry narinfo)
    ;; Delete NARINFO and the corresponding nar from CACHE.
    (let* ((nar     (string-append (string-drop-right narinfo
                                                      (string-length ".narinfo"))
                                   ".nar"))
           (base    (basename narinfo ".narinfo"))
           (hash    (string-take base (string-index base #\-)))
           (mapping (hash-part-mapping-cache-file cache hash)))
      (delete-file* narinfo)
      (delete-file* nar)
      (delete-file* mapping)))

  (let* ((item         (hash-part->path* store hash cache))
         (compressions (actual-compressions item compressions))
         (cached       (and (not (string-null? item))
                            (narinfo-cache-file cache item
                                                #:compression
                                                (first compressions)))))
    (cond ((string-null? item)
           (not-found request))
          ((file-exists? cached)
           ;; Narinfo is in cache, send it.
           (values `((content-type . (application/x-nix-narinfo))
                     ,@(if ttl
                           `((cache-control (max-age . ,ttl)))
                           '()))
                   (lambda (port)
                     (display (call-with-input-file cached
                                read-string)
                              port))))
          ((and (file-exists? item)        ;cheaper than the 'valid-path?' RPC
                (valid-path? store item))
           ;; Nothing in cache: bake the narinfo and nar in the background and
           ;; return 404.
           (eventually pool
             (single-baker item
               ;; Check whether CACHED has been produced in the meantime.
               (unless (file-exists? cached)
                 ;; (format #t "baking ~s~%" item)
                 (bake-narinfo+nar cache item
                                   #:ttl ttl
                                   #:compressions compressions
                                   #:nar-path nar-path)))

             (when ttl
               (single-baker 'cache-cleanup
                 (maybe-remove-expired-cache-entries cache
                                                     narinfo-files
                                                     #:entry-expiration
                                                     (nar-expiration-time ttl)
                                                     #:delete-entry delete-entry
                                                     #:cleanup-period ttl))))

           ;; If ITEM passes 'bypass-cache?', render a temporary narinfo right
           ;; away, with a short TTL.  The narinfo is temporary because it
           ;; lacks 'FileSize', for instance, which the cached narinfo will
           ;; have.  Chances are that the nar will be baked by the time the
           ;; client asks for it.
           (if (bypass-cache? store item)
               (render-narinfo store request hash
                               #:ttl 300          ;temporary
                               #:nar-path nar-path
                               #:compressions compressions)
               (not-found request
                          #:phrase "We're baking it"
                          #:ttl 300)))          ;should be available within 5m
          (else
           (not-found request #:phrase "")))))

(define (compress-nar cache item compression)
  "Save in directory CACHE the nar for ITEM compressed with COMPRESSION."
  (define nar
    (nar-cache-file cache item #:compression compression))

  (define (write-compressed-file call-with-compressed-output-port)
    ;; Note: the file port gets closed along with the compressed port.
    (call-with-compressed-output-port (open-output-file (string-append nar ".tmp"))
      (lambda (port)
        (write-file item port))
      #:level (compression-level compression))
    (rename-file (string-append nar ".tmp") nar))

  (mkdir-p (dirname nar))
  (match (compression-type compression)
    ('gzip
     (write-compressed-file call-with-gzip-output-port))
    ('lzip
     (write-compressed-file call-with-lzip-output-port))
    ('zstd
     (write-compressed-file call-with-zstd-output-port))
    ('none
     ;; Cache nars even when compression is disabled so that we can
     ;; guarantee the TTL (see <https://bugs.gnu.org/28664>.)
     (with-atomic-file-output nar
       (lambda (port)
         (write-file item port)
         ;; Make the file world-readable, contrary to what
         ;; 'with-atomic-file-output' does.
         (chmod port (logand #o644 (lognot (umask)))))))))

(define* (bake-narinfo+nar cache item
                           #:key ttl (compressions (list %no-compression))
                           (nar-path "/nar"))
  "Write the narinfo and nar for ITEM to CACHE."
  (define (compressed-nar-size compression)
    (let* ((nar  (nar-cache-file cache item #:compression compression))
           (stat (stat nar #f)))
      (and stat
           (cons compression (stat:size stat)))))

  (let ((compression (actual-compressions item compressions)))

    (for-each (cut compress-nar cache item <>) compressions)

    (match compressions
      ((main others ...)
       (let ((narinfo (narinfo-cache-file cache item
                                          #:compression main)))
         (with-atomic-file-output narinfo
           (lambda (port)
             ;; Open a new connection to the store.  We cannot reuse the main
             ;; thread's connection to the store since we would end up sending
             ;; stuff concurrently on the same channel.
             (with-store store
               (let ((sizes (filter-map compressed-nar-size compression)))
                 (display (narinfo-string store item
                                          (%private-key)
                                          #:nar-path nar-path
                                          #:compressions compressions
                                          #:file-sizes sizes)
                          port)))

             ;; Make the cached narinfo world-readable, contrary to what
             ;; 'with-atomic-file-output' does, so that other users can rsync
             ;; the whole cache.
             (chmod port (logand #o644 (lognot (umask))))))

         ;; Make narinfo files for OTHERS hard links to NARINFO such that the
         ;; atime-based cache eviction considers either all the nars or none
         ;; of them as candidates.
         (for-each (lambda (other)
                     (let ((other (narinfo-cache-file cache item
                                                      #:compression other)))
                       (link narinfo other)))
                   others))))))

;; XXX: Declare the 'X-Nar-Compression' HTTP header, which is in fact for
;; internal consumption: it allows us to pass the compression info to
;; 'http-write', as part of the workaround to <http://bugs.gnu.org/21093>.
(declare-header! "X-Nar-Compression"
                 (lambda (str)
                   (match (call-with-input-string str read)
                     (('compression type level)
                      (compression type level))))
                 compression?
                 (lambda (compression port)
                   (match compression
                     (($ <compression> type level)
                      (write `(compression ,type ,level) port)))))

(define* (render-nar store request store-item
                     #:key (compression %no-compression))
  "Render archive of the store path corresponding to STORE-ITEM."
  (let ((store-path (string-append %store-directory "/" store-item)))
    ;; The ISO-8859-1 charset *must* be used otherwise HTTP clients will
    ;; interpret the byte stream as UTF-8 and arbitrarily change invalid byte
    ;; sequences.
    (if (valid-path? store store-path)
        (values `((content-type . (application/x-nix-archive
                                   (charset . "ISO-8859-1")))
                  (x-nar-compression . ,compression))
                ;; XXX: We're not returning the actual contents, deferring
                ;; instead to 'http-write'.  This is a hack to work around
                ;; <http://bugs.gnu.org/21093>.
                store-path)
        (not-found request))))

(define* (render-nar/cached store cache request store-item
                            #:key ttl (compression %no-compression))
  "Respond to REQUEST with a nar for STORE-ITEM.  If the nar is in CACHE,
return it; otherwise, return 404.  When TTL is true, use it as the
'Cache-Control' expiration time."
  (let ((cached (nar-cache-file cache store-item
                                #:compression compression)))
    (cond ((file-exists? cached)
           (values `((content-type . (application/octet-stream
                                      (charset . "ISO-8859-1")))
                     ,@(if ttl
                           `((cache-control (max-age . ,ttl)))
                           '())

                     ;; XXX: We're not returning the actual contents, deferring
                     ;; instead to 'http-write'.  This is a hack to work around
                     ;; <http://bugs.gnu.org/21093>.
                     (x-raw-file . ,cached))
                   #f))
          ((let* ((hash (and=> (string-index store-item #\-)
                               (cut string-take store-item <>)))
                  (item (and hash
                             (guard (c ((store-error? c) #f))
                               (hash-part->path store hash)))))
             (and item (not (string-null? item))
                  (bypass-cache? store item)))
           ;; Render STORE-ITEM live.  We reach this because STORE-ITEM is
           ;; being baked but clients are already asking for it.  Thus, we're
           ;; duplicating work, but doing so allows us to reduce delays.
           (render-nar store request store-item
                       #:compression (low-compression compression)))
          (else
           (not-found request)))))

(define (render-content-addressed-file store request
                                       name algo hash)
  "Return the content of the result of the fixed-output derivation NAME that
has the given HASH of type ALGO."
  ;; TODO: Support other hash algorithms.
  (if (and (eq? algo 'sha256) (= 32 (bytevector-length hash)))
      (let ((item (fixed-output-path name hash
                                     #:hash-algo algo
                                     #:recursive? #f)))
        (if (valid-path? store item)
            (values `((content-type . (application/octet-stream
                                       (charset . "ISO-8859-1")))
                      ;; XXX: We're not returning the actual contents,
                      ;; deferring instead to 'http-write'.  This is a hack to
                      ;; work around <http://bugs.gnu.org/21093>.
                      (x-raw-file . ,item))
                    #f)
            (not-found request)))
      (not-found request)))

(define (render-log-file store request name)
  "Render the log file for NAME, the base name of a store item.  Don't attempt
to compress or decompress the log file; just return it as-is."
  (define (response-headers file)
    ;; XXX: We're not returning the actual contents, deferring instead to
    ;; 'http-write'.  This is a hack to work around
    ;; <http://bugs.gnu.org/21093>.
    (cond ((string-suffix? ".gz" file)
           `((content-type . (text/plain (charset . "UTF-8")))
             (content-encoding . (gzip))
             (x-raw-file . ,file)))
          ((string-suffix? ".bz2" file)
           `((content-type . (application/x-bzip2
                              (charset . "ISO-8859-1")))
             (x-raw-file . ,file)))
          (else                                   ;uncompressed
           `((content-type . (text/plain (charset . "UTF-8")))
             (x-raw-file . ,file)))))

  (let ((log (log-file store
                       (string-append (%store-prefix) "/" name))))
    (if log
        (values (response-headers log) log)
        (not-found request))))

(define (render-signing-key)
  "Render signing key."
  (let ((file %public-key-file))
    (values `((content-type . (text/plain (charset . "UTF-8")))
              (x-raw-file . ,file))
            file)))

(define (render-home-page request)
  "Render the home page."
  (values `((content-type . (text/html (charset . "UTF-8"))))
          (call-with-output-string
            (lambda (port)
              (sxml->xml '(html
                           (head (title "GNU Guix Substitute Server"))
                           (body
                            (h1 "GNU Guix Substitute Server")
                            (p "Hi, "
                               (a (@ (href
                                      "https://guix.gnu.org/manual/en/html_node/Invoking-guix-publish.html"))
                                  (tt "guix publish"))
                               " speaking.  Welcome!")
                            (p "Here is the "
                               (a (@ (href
                                      "signing-key.pub"))
                                  (tt "signing key"))
                               " for this server. Knock yourselves out!")))
                         port)))))

(define (extract-narinfo-hash str)
  "Return the hash within the narinfo resource string STR, or false if STR
is invalid."
  (and (string-suffix? ".narinfo" str)
       (let ((base (string-drop-right str 8)))
         (and (string-every %nix-base32-charset base)
              base))))

(define (get-request? request)
  "Return #t if REQUEST uses the GET method."
  (eq? (request-method request) 'GET))

(define (request-path-components request)
  "Split the URI path of REQUEST into a list of component strings.  For
example: \"/foo/bar\" yields '(\"foo\" \"bar\")."
  (split-and-decode-uri-path (uri-path (request-uri request))))


;;;
;;; Server.
;;;

(define %http-write
  (@@ (web server http) http-write))

(define (strip-headers response)
  "Return RESPONSE's headers minus 'Content-Length' and our internal headers."
  (fold alist-delete
        (response-headers response)
        '(content-length x-raw-file x-nar-compression)))

(define (sans-content-length response)
  "Return RESPONSE without its 'content-length' header."
  (set-field response (response-headers)
             (strip-headers response)))

(define (with-content-length response length)
  "Return RESPONSE with a 'content-length' header set to LENGTH."
  (set-field response (response-headers)
             (alist-cons 'content-length length
                         (strip-headers response))))

(define-syntax-rule (swallow-EPIPE exp ...)
  "Swallow EPIPE errors raised by EXP..."
  (catch 'system-error
    (lambda ()
      exp ...)
    (lambda args
      (if (= EPIPE (system-error-errno args))
          (values)
          (apply throw args)))))

(define-syntax-rule (swallow-zlib-error exp ...)
  "Swallow 'zlib-error' exceptions raised by EXP..."
  (catch 'zlib-error
    (lambda ()
      exp ...)
    (const #f)))

(define (nar-response-port response compression)
  "Return a port on which to write the body of RESPONSE, the response of a
/nar request, according to COMPRESSION."
  (match compression
    (($ <compression> 'gzip level)
     ;; Note: We cannot used chunked encoding here because
     ;; 'make-gzip-output-port' wants a file port.
     (make-gzip-output-port (response-port response)
                            #:level level
                            #:buffer-size %default-buffer-size))
    (($ <compression> 'lzip level)
     (make-lzip-output-port (response-port response)
                            #:level level))
    (($ <compression> 'zstd level)
     (make-zstd-output-port (response-port response)
                            #:level level))
    (($ <compression> 'none)
     (response-port response))
    (#f
     (response-port response))))

(define (http-write server client response body)
  "Write RESPONSE and BODY to CLIENT, possibly in a separate thread to avoid
blocking."
  (match (response-content-type response)
    (('application/x-nix-archive . _)
     ;; Sending the the whole archive can take time so do it in a separate
     ;; thread so that the main thread can keep working in the meantime.
     (call-with-new-thread
      (lambda ()
        (set-thread-name "publish nar")
        (let* ((compression (assoc-ref (response-headers response)
                                       'x-nar-compression))
               (response    (write-response (sans-content-length response)
                                            client))
               (port        (begin
                              (force-output client)
                              (configure-socket client)
                              (nar-response-port response compression))))
          ;; XXX: Given our ugly workaround for <http://bugs.gnu.org/21093> in
          ;; 'render-nar', BODY here is just the file name of the store item.
          ;; We call 'write-file' from here because we know that's the only
          ;; way to avoid building the whole nar in memory, which could
          ;; quickly become a real problem.  As a bonus, we even do
          ;; sendfile(2) directly from the store files to the socket.
          (swallow-zlib-error
           (swallow-EPIPE
            (write-file (utf8->string body) port)))
          (swallow-zlib-error
           (close-port port))
          (values)))))
    (_
     (match (assoc-ref (response-headers response) 'x-raw-file)
       ((? string? file)
        ;; Send a raw file in a separate thread.
        (call-with-new-thread
         (lambda ()
           (set-thread-name "publish file")
           (catch 'system-error
             (lambda ()
               (call-with-input-file file
                 (lambda (input)
                   (let* ((size     (stat:size (stat input)))
                          (response (write-response (with-content-length response
                                                                         size)
                                                    client))
                          (output   (response-port response)))
                     (configure-socket client)
                     (if (file-port? output)
                         (sendfile output input size)
                         (dump-port input output))
                     (close-port output)
                     (values)))))
             (lambda args
               ;; If the file was GC'd behind our back, that's fine.  Likewise if
               ;; the client closes the connection.
               (unless (memv (system-error-errno args)
                             (list ENOENT EPIPE ECONNRESET))
                 (apply throw args))
               (values))))))
       (#f
        ;; Handle other responses sequentially.
        (%http-write server client response body))))))

(define-server-impl concurrent-http-server
  ;; A variant of Guile's built-in HTTP server that offloads possibly long
  ;; responses to a different thread.
  (@@ (web server http) http-open)
  (@@ (web server http) http-read)
  http-write
  (@@ (web server http) http-close))

(define (string->compression-type string)
  "Return a symbol denoting the compression method expressed by STRING; return
#f if STRING doesn't match any supported method."
  (match string
    ("gzip" 'gzip)
    ("lzip" 'lzip)
    ("zstd" 'zstd)
    (_      #f)))

(define (effective-compression requested-type compressions)
  "Given the REQUESTED-TYPE for compression and the set of chosen COMPRESSION
methods, return the applicable compression."
  (or (find (match-lambda
              (($ <compression> type)
               (and (eq? type requested-type)
                    compression)))
            compressions)
      (default-compression requested-type)))

(define* (make-request-handler store
                               #:key
                               cache pool
                               narinfo-ttl
                               (nar-path "nar")
                               (compressions (list %no-compression)))
  (define compression-type?
    string->compression-type)

  (define nar-path?
    (let ((expected (split-and-decode-uri-path nar-path)))
      (cut equal? expected <>)))

  (lambda (request body)
    (format #t "~a ~a~%"
            (request-method request)
            (uri-path (request-uri request)))
    (if (get-request? request)                    ;reject POST, PUT, etc.
        (match (request-path-components request)
          ;; /nix-cache-info
          (("nix-cache-info")
           (render-nix-cache-info))
          ;; /
          ((or () ("index.html"))
           (render-home-page request))
          ;; guix signing-key
          (("signing-key.pub")
           (render-signing-key))
          ;; /<hash>.narinfo
          (((= extract-narinfo-hash (? string? hash)))
           (if cache
               (render-narinfo/cached store request hash
                                      #:cache cache
                                      #:pool pool
                                      #:ttl narinfo-ttl
                                      #:nar-path nar-path
                                      #:compressions compressions)
               (render-narinfo store request hash
                               #:ttl narinfo-ttl
                               #:nar-path nar-path
                               #:compressions compressions)))
          ;; /nar/file/NAME/sha256/HASH
          (("file" name "sha256" hash)
           (guard (c ((invalid-base32-character? c)
                      (not-found request)))
             (let ((hash (nix-base32-string->bytevector hash)))
               (render-content-addressed-file store request
                                              name 'sha256 hash))))

          ;; /log/OUTPUT
          (("log" name)
           (render-log-file store request name))

          ;; Use different URLs depending on the compression type.  This
          ;; guarantees that /nar URLs remain valid even when 'guix publish'
          ;; is restarted with different compression parameters.

          ;; /nar/gzip/<store-item>
          ((components ... (? compression-type? type) store-item)
           (if (nar-path? components)
               (let* ((compression-type (string->compression-type type))
                      (compression (effective-compression compression-type
                                                          compressions)))
                 (if cache
                     (render-nar/cached store cache request store-item
                                        #:ttl narinfo-ttl
                                        #:compression compression)
                     (render-nar store request store-item
                                 #:compression compression)))
               (not-found request)))

          ;; /nar/<store-item>
          ((components ... store-item)
           (if (nar-path? components)
               (if cache
                   (render-nar/cached store cache request store-item
                                      #:ttl narinfo-ttl
                                      #:compression %no-compression)
                   (render-nar store request store-item
                               #:compression %no-compression))
               (not-found request)))

          (x (not-found request)))
        (not-found request))))

(define (service-name)
  "Return the Avahi service name of the server."
  (string-append "guix-publish-" (gethostname)))

(define publish-service-type
  ;; Return the Avahi service type of the server.
  "_guix_publish._tcp")

(define* (run-publish-server socket store
                             #:key
                             advertise? port
                             (compressions (list %no-compression))
                             (nar-path "nar") narinfo-ttl
                             cache pool)
  (when advertise?
    (let ((name (service-name)))
      ;; XXX: Use a callback from Guile-Avahi here, as Avahi can pick a
      ;; different name to avoid name clashes.
      (info (G_ "Advertising ~a~%.") name)
      (avahi-publish-service-thread name
                                    #:type publish-service-type
                                    #:port port)))

  (run-server (make-request-handler store
                                    #:cache cache
                                    #:pool pool
                                    #:nar-path nar-path
                                    #:narinfo-ttl narinfo-ttl
                                    #:compressions compressions)
              concurrent-http-server
              `(#:socket ,socket)))

(define (open-server-socket address)
  "Return a TCP socket bound to ADDRESS, a socket address."
  (let ((sock (socket (sockaddr:fam address) SOCK_STREAM 0)))
    (configure-socket sock #:options (cons (list SO_REUSEADDR 1)
                                           %default-socket-options))
    (bind sock address)
    sock))

(define (gather-user-privileges user)
  "Switch to the identity of USER, a user name."
  (catch 'misc-error
    (lambda ()
      (let ((user (getpw user)))
        (setgroups #())
        (setgid (passwd:gid user))
        (setuid (passwd:uid user))))
    (lambda (key proc message args . rest)
      (leave (G_ "user '~a' not found: ~a~%")
             user (apply format #f message args)))))


;;;
;;; Entry point.
;;;

(define-command (guix-publish . args)
  (category packaging)
  (synopsis "publish build results over HTTP")

  (with-error-handling
    (let* ((opts    (parse-command-line args %options (list %default-options)
                                        #:build-options? #f
                                        #:argument-handler
                                        (lambda (arg result)
                                          (leave (G_ "~A: extraneous argument~%") arg))))
           (advertise?  (assoc-ref opts 'advertise?))
           (user        (assoc-ref opts 'user))
           (port        (assoc-ref opts 'port))
           (ttl         (assoc-ref opts 'narinfo-ttl))
           (compressions (match (filter-map (match-lambda
                                              (('compression . compression)
                                               compression)
                                              (_ #f))
                                            opts)
                           (()
                            ;; Default to fast & low compression.
                            (list %default-gzip-compression))
                           (lst (reverse lst))))
           (address (let ((addr (assoc-ref opts 'address)))
                      (make-socket-address (sockaddr:fam addr)
                                           (sockaddr:addr addr)
                                           port)))
           (socket  (open-server-socket address))
           (nar-path  (assoc-ref opts 'nar-path))
           (repl-port (assoc-ref opts 'repl))
           (cache     (assoc-ref opts 'cache))
           (workers   (assoc-ref opts 'workers))

           ;; Read the key right away so that (1) we fail early on if we can't
           ;; access them, and (2) we can then drop privileges.
           (public-key  (read-file-sexp (assoc-ref opts 'public-key-file)))
           (private-key (read-file-sexp (assoc-ref opts 'private-key-file))))

      (when user
        ;; Now that we've read the key material and opened the socket, we can
        ;; drop privileges.
        (gather-user-privileges user))

      (when (zero? (getuid))
        (warning (G_ "server running as root; \
consider using the '--user' option!~%")))

      (parameterize ((%public-key public-key)
                     (%private-key private-key)
                     (cache-bypass-threshold
                      (or (assoc-ref opts 'cache-bypass-threshold)
                          (cache-bypass-threshold))))
        (info (G_ "publishing ~a on ~a, port ~d~%")
              %store-directory
              (inet-ntop (sockaddr:fam address) (sockaddr:addr address))
              (sockaddr:port address))

        (for-each (lambda (compression)
                    (info (G_ "using '~a' compression method, level ~a~%")
                          (compression-type compression)
                          (compression-level compression)))
                  compressions)

        (when repl-port
          (repl:spawn-server (repl:make-tcp-server-socket #:port repl-port)))

        ;; Set the name of the main thread.
        (set-thread-name "guix publish")

        (with-store store
          (run-publish-server socket store
                              #:advertise? advertise?
                              #:port port
                              #:cache cache
                              #:pool (and cache (make-pool workers
                                                           #:thread-name
                                                           "publish worker"))
                              #:nar-path nar-path
                              #:compressions compressions
                              #:narinfo-ttl ttl))))))

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