Add (guix lzlib).

* guix/lzlib.scm, tests/lzlib.scm: New files.
* Makefile.am (MODULES): Add guix/lzlib.scm.
(SCM_TESTS): Add tests/lzlib.scm.
* m4/guix.m4 (GUIX_LIBLZ_LIBDIR): New macro.
* configure.ac (LIBLZ_LIBDIR): Use it.  Define and substitute
'LIBLZ'.
* guix/config.scm.in (%liblz): New variable.
* guix/self.scm (make-config.scm): Add TODO comment.

Co-authored-by: Ludovic Courtès <ludo@gnu.org>

7 files changed, 777 insertions, 1 deletions

diff --git a/Makefile.am b/Makefile.am
index 0494452386..9539fef1b1 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -103,6 +103,7 @@ MODULES =					\
   guix/cve.scm					\
   guix/workers.scm				\
   guix/zlib.scm					\
+  guix/lzlib.scm				\
   guix/build-system.scm				\
   guix/build-system/android-ndk.scm		\
   guix/build-system/ant.scm			\
@@ -404,6 +405,7 @@ SCM_TESTS =					\
   tests/cve.scm					\
   tests/workers.scm				\
   tests/zlib.scm				\
+  tests/lzlib.scm				\
   tests/file-systems.scm			\
   tests/uuid.scm				\
   tests/system.scm				\
diff --git a/configure.ac b/configure.ac
index 7e7ae02730..3918550a79 100644
--- a/configure.ac
+++ b/configure.ac
@@ -250,6 +250,16 @@ AC_MSG_CHECKING([for zlib's shared library name])
 AC_MSG_RESULT([$LIBZ])
 AC_SUBST([LIBZ])
 
+dnl Library name of lzlib suitable for 'dynamic-link'.
+GUIX_LIBLZ_FILE_NAME([LIBLZ])
+if test "x$LIBLZ" = "x"; then
+  LIBLZ="liblz"
+else
+  # Strip the .so or .so.1 extension since that's what 'dynamic-link' expects.
+  LIBLZ="`echo $LIBLZ | sed -es'/\.so\(\.[[0-9.]]\+\)\?//g'`"
+fi
+AC_SUBST([LIBLZ])
+
 dnl Check for Guile-SSH, for the (guix ssh) module.
 GUIX_CHECK_GUILE_SSH
 AM_CONDITIONAL([HAVE_GUILE_SSH],
diff --git a/guix/config.scm.in b/guix/config.scm.in
index 247b15ed81..0ada0f3c38 100644
--- a/guix/config.scm.in
+++ b/guix/config.scm.in
@@ -34,6 +34,7 @@
 
             %system
             %libz
+            %liblz
             %gzip
             %bzip2
             %xz))
@@ -90,6 +91,9 @@
 (define %libz
   "@LIBZ@")
 
+(define %liblz
+  "@LIBLZ@")
+
 (define %gzip
   "@GZIP@")
 
diff --git a/guix/lzlib.scm b/guix/lzlib.scm
new file mode 100644
index 0000000000..d596f0d95d
--- /dev/null
+++ b/guix/lzlib.scm
@@ -0,0 +1,633 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Pierre Neidhardt <mail@ambrevar.xyz>
+;;;
+;;; 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 lzlib)
+  #:use-module (rnrs bytevectors)
+  #:use-module (rnrs arithmetic bitwise)
+  #:use-module (ice-9 binary-ports)
+  #:use-module (ice-9 match)
+  #:use-module (system foreign)
+  #:use-module (guix config)
+  #:export (lzlib-available?
+            make-lzip-input-port
+            make-lzip-output-port
+            call-with-lzip-input-port
+            call-with-lzip-output-port
+            %default-member-length-limit
+            %default-compression-level))
+
+;;; Commentary:
+;;;
+;;; Bindings to the lzlib / liblz API.  Some convenience functions are also
+;;; provided (see the export).
+;;;
+;;; While the bindings are complete, the convenience functions only support
+;;; single member archives.  To decompress single member archives, we loop
+;;; until lz-decompress-read returns 0.  This is simpler.  To support multiple
+;;; members properly, we need (among others) to call lz-decompress-finish and
+;;; loop over lz-decompress-read until lz-decompress-finished? returns #t.
+;;; Otherwise a multi-member archive starting with an empty member would only
+;;; decompress the empty member and stop there, resulting in truncated output.
+
+;;; Code:
+
+(define %lzlib
+  ;; File name of lzlib's shared library.  When updating via 'guix pull',
+  ;; '%liblz' might be undefined so protect against it.
+  (delay (dynamic-link (if (defined? '%liblz)
+                           %liblz
+                           "liblz"))))
+
+(define (lzlib-available?)
+  "Return true if lzlib is available, #f otherwise."
+  (false-if-exception (force %lzlib)))
+
+(define (lzlib-procedure ret name parameters)
+  "Return a procedure corresponding to C function NAME in liblz, or #f if
+either lzlib or the function could not be found."
+  (match (false-if-exception (dynamic-func name (force %lzlib)))
+    ((? pointer? ptr)
+     (pointer->procedure ret ptr parameters))
+    (#f
+     #f)))
+
+(define-wrapped-pointer-type <lz-decoder>
+  ;; Scheme counterpart of the 'LZ_Decoder' opaque type.
+  lz-decoder?
+  pointer->lz-decoder
+  lz-decoder->pointer
+  (lambda (obj port)
+    (format port "#<lz-decoder ~a>"
+            (number->string (object-address obj) 16))))
+
+(define-wrapped-pointer-type <lz-encoder>
+  ;; Scheme counterpart of the 'LZ_Encoder' opaque type.
+  lz-encoder?
+  pointer->lz-encoder
+  lz-encoder->pointer
+  (lambda (obj port)
+    (format port "#<lz-encoder ~a>"
+            (number->string (object-address obj) 16))))
+
+;; From lzlib.h
+(define %error-number-ok 0)
+(define %error-number-bad-argument 1)
+(define %error-number-mem-error 2)
+(define %error-number-sequence-error 3)
+(define %error-number-header-error 4)
+(define %error-number-unexpected-eof 5)
+(define %error-number-data-error 6)
+(define %error-number-library-error 7)
+
+
+;; Compression bindings.
+
+(define lz-compress-open
+  (let ((proc (lzlib-procedure '* "LZ_compress_open" (list int int uint64)))
+        ;; member-size is an "unsigned long long", and the C standard guarantees
+        ;; a minimum range of 0..2^64-1.
+        (unlimited-size (- (expt 2 64) 1)))
+    (lambda* (dictionary-size match-length-limit #:optional (member-size unlimited-size))
+      "Initialize the internal stream state for compression and returns a
+pointer that can only be used as the encoder argument for the other
+lz-compress functions, or a null pointer if the encoder could not be
+allocated.
+
+See the manual: (lzlib) Compression functions."
+      (let ((encoder-ptr (proc dictionary-size match-length-limit member-size)))
+        (if (not (= (lz-compress-error encoder-ptr) -1))
+            (pointer->lz-encoder encoder-ptr)
+            (throw 'lzlib-error 'lz-compress-open))))))
+
+(define lz-compress-close
+  (let ((proc (lzlib-procedure int "LZ_compress_close" '(*))))
+    (lambda (encoder)
+      "Close encoder.  ENCODER can no longer be used as an argument to any
+lz-compress function. "
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-close ret)
+            ret)))))
+
+(define lz-compress-finish
+  (let ((proc (lzlib-procedure int "LZ_compress_finish" '(*))))
+    (lambda (encoder)
+      "Tell that all the data for this member have already been written (with
+the `lz-compress-write' function).  It is safe to call `lz-compress-finish' as
+many times as needed.  After all the produced compressed data have been read
+with `lz-compress-read' and `lz-compress-member-finished?' returns #t, a new
+member can be started with 'lz-compress-restart-member'."
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-finish (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-restart-member
+  (let ((proc (lzlib-procedure int "LZ_compress_restart_member" (list '* uint64))))
+    (lambda (encoder member-size)
+      "Start a new member in a multimember data stream.
+Call this function only after `lz-compress-member-finished?' indicates that the
+current member has been fully read (with the `lz-compress-read' function)."
+      (let ((ret (proc (lz-encoder->pointer encoder) member-size)))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-restart-member
+                   (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-sync-flush
+  (let ((proc (lzlib-procedure int "LZ_compress_sync_flush" (list '*))))
+    (lambda (encoder)
+      "Make available to `lz-compress-read' all the data already written with
+the `LZ-compress-write' function.  First call `lz-compress-sync-flush'.  Then
+call 'lz-compress-read' until it returns 0.
+
+Repeated use of `LZ-compress-sync-flush' may degrade compression ratio,
+so use it only when needed. "
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-sync-flush
+                   (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-read
+  (let ((proc (lzlib-procedure int "LZ_compress_read" (list '* '* int))))
+    (lambda* (encoder lzfile-bv #:optional (start 0) (count (bytevector-length lzfile-bv)))
+      "Read up to COUNT bytes from the encoder stream, storing the results in LZFILE-BV.
+Return the number of uncompressed bytes written, a strictly positive integer."
+      (let ((ret (proc (lz-encoder->pointer encoder)
+                       (bytevector->pointer lzfile-bv start)
+                       count)))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-read (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-write
+  (let ((proc (lzlib-procedure int "LZ_compress_write" (list '* '* int))))
+    (lambda* (encoder bv #:optional (start 0) (count (bytevector-length bv)))
+      "Write up to COUNT bytes from BV to the encoder stream.  Return the
+number of uncompressed bytes written, a strictly positive integer."
+      (let ((ret (proc (lz-encoder->pointer encoder)
+                       (bytevector->pointer bv start)
+                       count)))
+        (if (< ret 0)
+            (throw 'lzlib-error 'lz-compress-write (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-write-size
+  (let ((proc (lzlib-procedure int "LZ_compress_write_size" '(*))))
+    (lambda (encoder)
+      "The maximum number of bytes that can be immediately written through the
+`lz-compress-write' function.
+
+It is guaranteed that an immediate call to `lz-compress-write' will accept a
+SIZE up to the returned number of bytes. "
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-write-size (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-error
+  (let ((proc (lzlib-procedure int "LZ_compress_errno" '(*))))
+    (lambda (encoder)
+      "ENCODER can be a Scheme object or a pointer."
+      (let* ((error-number (proc (if (lz-encoder? encoder)
+                                     (lz-encoder->pointer encoder)
+                                     encoder))))
+        error-number))))
+
+(define lz-compress-finished?
+  (let ((proc (lzlib-procedure int "LZ_compress_finished" '(*))))
+    (lambda (encoder)
+      "Return #t if all the data have been read and `lz-compress-close' can
+be safely called. Otherwise return #f."
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (match ret
+          (1 #t)
+          (0 #f)
+          (_ (throw 'lzlib-error 'lz-compress-finished? (lz-compress-error encoder))))))))
+
+(define lz-compress-member-finished?
+  (let ((proc (lzlib-procedure int "LZ_compress_member_finished" '(*))))
+    (lambda (encoder)
+      "Return #t if the current member, in a multimember data stream, has
+been fully read and 'lz-compress-restart-member' can be safely called.
+Otherwise return #f."
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (match ret
+          (1 #t)
+          (0 #f)
+          (_ (throw 'lzlib-error 'lz-compress-member-finished? (lz-compress-error encoder))))))))
+
+(define lz-compress-data-position
+  (let ((proc (lzlib-procedure uint64 "LZ_compress_data_position" '(*))))
+    (lambda (encoder)
+      "Return the number of input bytes already compressed in the current
+member."
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-data-position
+                   (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-member-position
+  (let ((proc (lzlib-procedure uint64 "LZ_compress_member_position" '(*))))
+    (lambda (encoder)
+      "Return the number of compressed bytes already produced, but perhaps
+not yet read, in the current member."
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-member-position
+                   (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-total-in-size
+  (let ((proc (lzlib-procedure uint64 "LZ_compress_total_in_size" '(*))))
+    (lambda (encoder)
+      "Return the total number of input bytes already compressed."
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-total-in-size
+                   (lz-compress-error encoder))
+            ret)))))
+
+(define lz-compress-total-out-size
+  (let ((proc (lzlib-procedure uint64 "LZ_compress_total_out_size" '(*))))
+    (lambda (encoder)
+      "Return the total number of compressed bytes already produced, but
+perhaps not yet read."
+      (let ((ret (proc (lz-encoder->pointer encoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-compress-total-out-size
+                   (lz-compress-error encoder))
+            ret)))))
+
+
+;; Decompression bindings.
+
+(define lz-decompress-open
+  (let ((proc (lzlib-procedure '* "LZ_decompress_open" '())))
+    (lambda ()
+      "Initializes the internal stream state for decompression and returns a
+pointer that can only be used as the decoder argument for the other
+lz-decompress functions, or a null pointer if the decoder could not be
+allocated.
+
+See the manual: (lzlib) Decompression functions."
+      (let ((decoder-ptr (proc)))
+        (if (not (= (lz-decompress-error decoder-ptr) -1))
+            (pointer->lz-decoder decoder-ptr)
+            (throw 'lzlib-error 'lz-decompress-open))))))
+
+(define lz-decompress-close
+  (let ((proc (lzlib-procedure int "LZ_decompress_close" '(*))))
+    (lambda (decoder)
+      "Close decoder.  DECODER can no longer be used as an argument to any
+lz-decompress function. "
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-close ret)
+            ret)))))
+
+(define lz-decompress-finish
+  (let ((proc (lzlib-procedure int "LZ_decompress_finish" '(*))))
+    (lambda (decoder)
+      "Tell that all the data for this stream have already been written (with
+the `lz-decompress-write' function).  It is safe to call
+`lz-decompress-finish' as many times as needed."
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-finish (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-reset
+  (let ((proc (lzlib-procedure int "LZ_decompress_reset" '(*))))
+    (lambda (decoder)
+      "Reset the internal state of DECODER as it was just after opening it
+with the `lz-decompress-open' function.  Data stored in the internal buffers
+is discarded.  Position counters are set to 0."
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-reset
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-sync-to-member
+  (let ((proc (lzlib-procedure int "LZ_decompress_sync_to_member" '(*))))
+    (lambda (decoder)
+      "Reset the error state of DECODER and enters a search state that lasts
+until a new member header (or the end of the stream) is found.  After a
+successful call to `lz-decompress-sync-to-member', data written with
+`lz-decompress-write' will be consumed and 'lz-decompress-read' will return 0
+until a header is found.
+
+This function is useful to discard any data preceding the first member, or to
+discard the rest of the current member, for example in case of a data
+error.  If the decoder is already at the beginning of a member, this function
+does nothing."
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-sync-to-member
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-read
+  (let ((proc (lzlib-procedure int "LZ_decompress_read" (list '* '* int))))
+    (lambda* (decoder file-bv #:optional (start 0) (count (bytevector-length file-bv)))
+      "Read up to COUNT bytes from the decoder stream, storing the results in FILE-BV.
+Return the number of uncompressed bytes written, a non-negative positive integer."
+      (let ((ret (proc (lz-decoder->pointer decoder)
+                       (bytevector->pointer file-bv start)
+                       count)))
+        (if (< ret 0)
+            (throw 'lzlib-error 'lz-decompress-read (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-write
+  (let ((proc (lzlib-procedure int "LZ_decompress_write" (list '* '* int))))
+    (lambda* (decoder bv #:optional (start 0) (count (bytevector-length bv)))
+      "Write up to COUNT bytes from BV to the decoder stream.  Return the
+number of uncompressed bytes written, a non-negative integer."
+      (let ((ret (proc (lz-decoder->pointer decoder)
+                       (bytevector->pointer bv start)
+                       count)))
+        (if (< ret 0)
+            (throw 'lzlib-error 'lz-decompress-write (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-write-size
+  (let ((proc (lzlib-procedure int "LZ_decompress_write_size" '(*))))
+    (lambda (decoder)
+      "Return the maximum number of bytes that can be immediately written
+through the `lz-decompress-write' function.
+
+It is guaranteed that an immediate call to `lz-decompress-write' will accept a
+SIZE up to the returned number of bytes. "
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-write-size (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-error
+  (let ((proc (lzlib-procedure int "LZ_decompress_errno" '(*))))
+    (lambda (decoder)
+      "DECODER can be a Scheme object or a pointer."
+      (let* ((error-number (proc (if (lz-decoder? decoder)
+                                     (lz-decoder->pointer decoder)
+                                     decoder))))
+        error-number))))
+
+(define lz-decompress-finished?
+  (let ((proc (lzlib-procedure int "LZ_decompress_finished" '(*))))
+    (lambda (decoder)
+      "Return #t if all the data have been read and `lz-decompress-close' can
+be safely called.  Otherwise return #f."
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (match ret
+          (1 #t)
+          (0 #f)
+          (_ (throw 'lzlib-error 'lz-decompress-finished? (lz-decompress-error decoder))))))))
+
+(define lz-decompress-member-finished?
+  (let ((proc (lzlib-procedure int "LZ_decompress_member_finished" '(*))))
+    (lambda (decoder)
+      "Return #t if the current member, in a multimember data stream, has
+been fully read and `lz-decompress-restart-member' can be safely called.
+Otherwise return #f."
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (match ret
+          (1 #t)
+          (0 #f)
+          (_ (throw 'lzlib-error 'lz-decompress-member-finished? (lz-decompress-error decoder))))))))
+
+(define lz-decompress-member-version
+  (let ((proc (lzlib-procedure int "LZ_decompress_member_version" '(*))))
+    (lambda (decoder)
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        "Return the version of current member from member header."
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-data-position
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-dictionary-size
+  (let ((proc (lzlib-procedure int "LZ_decompress_dictionary_size" '(*))))
+    (lambda (decoder)
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        "Return the dictionary size of current member from member header."
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-member-position
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-data-crc
+  (let ((proc (lzlib-procedure unsigned-int "LZ_decompress_data_crc" '(*))))
+    (lambda (decoder)
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        "Return the 32 bit Cyclic Redundancy Check of the data decompressed
+from the current member.  The returned value is valid only when
+`lz-decompress-member-finished' returns #t. "
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-member-position
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-data-position
+  (let ((proc (lzlib-procedure uint64 "LZ_decompress_data_position" '(*))))
+    (lambda (decoder)
+      "Return the number of decompressed bytes already produced, but perhaps
+not yet read, in the current member."
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-data-position
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-member-position
+  (let ((proc (lzlib-procedure uint64 "LZ_decompress_member_position" '(*))))
+    (lambda (decoder)
+      "Return the number of input bytes already decompressed in the current
+member."
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-member-position
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-total-in-size
+  (let ((proc (lzlib-procedure uint64 "LZ_decompress_total_in_size" '(*))))
+    (lambda (decoder)
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        "Return the total number of input bytes already compressed."
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-total-in-size
+                   (lz-decompress-error decoder))
+            ret)))))
+
+(define lz-decompress-total-out-size
+  (let ((proc (lzlib-procedure uint64 "LZ_decompress_total_out_size" '(*))))
+    (lambda (decoder)
+      (let ((ret (proc (lz-decoder->pointer decoder))))
+        "Return the total number of compressed bytes already produced, but
+perhaps not yet read."
+        (if (= ret -1)
+            (throw 'lzlib-error 'lz-decompress-total-out-size
+                   (lz-decompress-error decoder))
+            ret)))))
+
+
+;; High level functions.
+(define %lz-decompress-input-buffer-size (* 64 1024))
+
+(define* (lzread! decoder file-port bv
+                  #:optional (start 0) (count (bytevector-length bv)))
+  "Read up to COUNT bytes from FILE-PORT into BV at offset START.  Return the
+number of uncompressed bytes actually read; it is zero if COUNT is zero or if
+the end-of-stream has been reached."
+  ;; WARNING: Because we don't alternate between lz-reads and lz-writes, we can't
+  ;; process more than %lz-decompress-input-buffer-size from the file-port.
+  (when (> count %lz-decompress-input-buffer-size)
+    (set! count %lz-decompress-input-buffer-size))
+  (let* ((written 0)
+         (read 0)
+         (file-bv (get-bytevector-n file-port count)))
+    (unless (eof-object? file-bv)
+      (begin
+        (while (and (< 0 (lz-decompress-write-size decoder))
+                    (< written (bytevector-length file-bv)))
+          (set! written (+ written
+                           (lz-decompress-write decoder file-bv written
+                                                (- (bytevector-length file-bv) written)))))))
+    (let loop ((rd 0))
+      (if (< start (bytevector-length bv))
+          (begin
+            (set! rd (lz-decompress-read decoder bv start (- (bytevector-length bv) start)))
+            (set! start (+ start rd))
+            (set! read (+ read rd)))
+          (set! rd 0))
+      (unless (= rd 0)
+        (loop rd)))
+    read))
+
+(define* (lzwrite encoder bv lz-port
+                  #:optional (start 0) (count (bytevector-length bv)))
+  "Write up to COUNT bytes from BV at offset START into LZ-PORT.  Return
+the number of uncompressed bytes written, a non-negative integer."
+  (let ((written 0)
+        (read 0))
+    (while (and (< 0 (lz-compress-write-size encoder))
+                (< written count))
+      (set! written (+ written
+                       (lz-compress-write encoder bv (+ start written) (- count written)))))
+    (when (= written 0)
+      (lz-compress-finish encoder))
+    (let ((lz-bv (make-bytevector written)))
+      (let loop ((rd 0))
+        (set! rd (lz-compress-read encoder lz-bv 0 (bytevector-length lz-bv)))
+        (put-bytevector lz-port lz-bv 0 rd)
+        (set! read (+ read rd))
+        (unless (= rd 0)
+          (loop rd))))
+    ;; `written' is the total byte count of uncompressed data.
+    written))
+
+
+;;;
+;;; Port interface.
+;;;
+
+;; Alist of (levels (dictionary-size match-length-limit)).  0 is the fastest.
+;; See bbexample.c in lzlib's source.
+(define %compression-levels
+  `((0 (65535 16))
+    (1 (,(bitwise-arithmetic-shift-left 1 20) 5))
+    (2 (,(bitwise-arithmetic-shift-left 3 19) 6))
+    (3 (,(bitwise-arithmetic-shift-left 1 21) 8))
+    (4 (,(bitwise-arithmetic-shift-left 3 20) 12))
+    (5 (,(bitwise-arithmetic-shift-left 1 22) 20))
+    (6 (,(bitwise-arithmetic-shift-left 1 23) 36))
+    (7 (,(bitwise-arithmetic-shift-left 1 24) 68))
+    (8 (,(bitwise-arithmetic-shift-left 3 23) 132))
+    (9 (,(bitwise-arithmetic-shift-left 1 25) 273))))
+
+(define %default-compression-level
+  6)
+
+(define* (make-lzip-input-port port)
+  "Return an input port that decompresses data read from PORT, a file port.
+PORT is automatically closed when the resulting port is closed."
+  (define decoder (lz-decompress-open))
+
+  (define (read! bv start count)
+    (lzread! decoder port bv start count))
+
+  (make-custom-binary-input-port "lzip-input" read! #f #f
+                                 (lambda ()
+                                   (lz-decompress-close decoder)
+                                   (close-port port))))
+
+(define* (make-lzip-output-port port
+                                #:key
+                                (level %default-compression-level))
+  "Return an output port that compresses data at the given LEVEL, using PORT,
+a file port, as its sink.  PORT is automatically closed when the resulting
+port is closed."
+  (define encoder (apply lz-compress-open
+                         (car (assoc-ref %compression-levels level))))
+
+  (define (write! bv start count)
+    (lzwrite encoder bv port start count))
+
+  (make-custom-binary-output-port "lzip-output" write! #f #f
+                                  (lambda ()
+                                    (lz-compress-finish encoder)
+                                    ;; "lz-read" the trailing metadata added by `lz-compress-finish'.
+                                    (let ((lz-bv (make-bytevector (* 64 1024))))
+                                      (let loop ((rd 0))
+                                        (set! rd (lz-compress-read encoder lz-bv 0 (bytevector-length lz-bv)))
+                                        (put-bytevector port lz-bv 0 rd)
+                                        (unless (= rd 0)
+                                          (loop rd))))
+                                    (lz-compress-close encoder)
+                                    (close-port port))))
+
+(define* (call-with-lzip-input-port port proc)
+  "Call PROC with a port that wraps PORT and decompresses data read from it.
+PORT is closed upon completion."
+  (let ((lzip (make-lzip-input-port port)))
+    (dynamic-wind
+      (const #t)
+      (lambda ()
+        (proc lzip))
+      (lambda ()
+        (close-port lzip)))))
+
+(define* (call-with-lzip-output-port port proc
+                                     #:key
+                                     (level %default-compression-level))
+  "Call PROC with an output port that wraps PORT and compresses data.  PORT is
+close upon completion."
+  (let ((lzip (make-lzip-output-port port
+                                     #:level level)))
+    (dynamic-wind
+      (const #t)
+      (lambda ()
+        (proc lzip))
+      (lambda ()
+        (close-port lzip)))))
+
+;;; lzlib.scm ends here
diff --git a/guix/self.scm b/guix/self.scm
index 7098e4ea29..74ea65240c 100644
--- a/guix/self.scm
+++ b/guix/self.scm
@@ -925,6 +925,7 @@ Info manual."
                                %store-database-directory
                                %config-directory
                                %libz
+                               ;; TODO: %liblz
                                %gzip
                                %bzip2
                                %xz))
diff --git a/m4/guix.m4 b/m4/guix.m4
index 5c846f7618..d0c5ec0f08 100644
--- a/m4/guix.m4
+++ b/m4/guix.m4
@@ -1,5 +1,5 @@
 dnl GNU Guix --- Functional package management for GNU
-dnl Copyright © 2012, 2013, 2014, 2015, 2016, 2018 Ludovic Courtès <ludo@gnu.org>
+dnl Copyright © 2012, 2013, 2014, 2015, 2016, 2018, 2019 Ludovic Courtès <ludo@gnu.org>
 dnl Copyright © 2014 Mark H Weaver <mhw@netris.org>
 dnl Copyright © 2017 Efraim Flashner <efraim@flashner.co.il>
 dnl
@@ -312,6 +312,21 @@ AC_DEFUN([GUIX_LIBZ_LIBDIR], [
   $1="$guix_cv_libz_libdir"
 ])
 
+dnl GUIX_LIBLZ_FILE_NAME VAR
+dnl
+dnl Attempt to determine liblz's absolute file name; store the result in VAR.
+AC_DEFUN([GUIX_LIBLZ_FILE_NAME], [
+  AC_REQUIRE([PKG_PROG_PKG_CONFIG])
+  AC_CACHE_CHECK([lzlib's file name],
+    [guix_cv_liblz_libdir],
+    [old_LIBS="$LIBS"
+     LIBS="-llz"
+     AC_LINK_IFELSE([AC_LANG_SOURCE([int main () { return LZ_decompress_open(); }])],
+       [guix_cv_liblz_libdir="`ldd conftest$EXEEXT | grep liblz | sed '-es/.*=> \(.*\) .*$/\1/g'`"])
+     LIBS="$old_LIBS"])
+  $1="$guix_cv_liblz_libdir"
+])
+
 dnl GUIX_CURRENT_LOCALSTATEDIR
 dnl
 dnl Determine the localstatedir of an existing Guix installation and set
diff --git a/tests/lzlib.scm b/tests/lzlib.scm
new file mode 100644
index 0000000000..cf53a9417d
--- /dev/null
+++ b/tests/lzlib.scm
@@ -0,0 +1,111 @@
+;;; GNU Guix --- Functional package management for GNU
+;;; Copyright © 2019 Pierre Neidhardt <mail@ambrevar.xyz>
+;;;
+;;; 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 (test-lzlib)
+  #:use-module (guix lzlib)
+  #:use-module (guix tests)
+  #:use-module (srfi srfi-64)
+  #:use-module (rnrs bytevectors)
+  #:use-module (rnrs io ports)
+  #:use-module (ice-9 match))
+
+;; Test the (guix lzlib) module.
+
+(define-syntax-rule (test-assert* description exp)
+  (begin
+    (unless (lzlib-available?)
+      (test-skip 1))
+    (test-assert description exp)))
+
+(test-begin "lzlib")
+
+(define (compress-and-decompress data)
+  "DATA must be a bytevector."
+  (pk "Uncompressed bytes:" (bytevector-length data))
+  (match (pipe)
+    ((parent . child)
+     (match (primitive-fork)
+       (0                               ;compress
+        (dynamic-wind
+          (const #t)
+          (lambda ()
+            (close-port parent)
+            (call-with-lzip-output-port child
+              (lambda (port)
+                (put-bytevector port data))))
+          (lambda ()
+            (primitive-exit 0))))
+       (pid                             ;decompress
+        (begin
+          (close-port child)
+          (let ((received (call-with-lzip-input-port parent
+                            (lambda (port)
+                              (get-bytevector-all port)))))
+            (match (waitpid pid)
+              ((_ . status)
+               (pk "Status" status)
+               (pk "Length data" (bytevector-length data) "received" (bytevector-length received))
+               ;; The following loop is a debug helper.
+               (let loop ((i 0))
+                 (if (and (< i (bytevector-length received))
+                          (= (bytevector-u8-ref received i)
+                             (bytevector-u8-ref data i)))
+                     (loop (+ 1 i))
+                     (pk "First diff at index" i)))
+               (and (zero? status)
+                    (port-closed? parent)
+                    (bytevector=? received data)))))))))))
+
+(test-assert* "null bytevector"
+  (compress-and-decompress (make-bytevector (+ (random 100000)
+                                               (* 20 1024)))))
+
+(test-assert* "random bytevector"
+  (compress-and-decompress (random-bytevector (+ (random 100000)
+                                                 (* 20 1024)))))
+(test-assert* "small bytevector"
+  (compress-and-decompress (random-bytevector 127)))
+
+(test-assert* "1 bytevector"
+  (compress-and-decompress (random-bytevector 1)))
+
+(test-assert* "Bytevector of size relative to Lzip internal buffers (2 * dictionary)"
+  (compress-and-decompress
+   (random-bytevector
+    (* 2 (car (car (assoc-ref (@@ (guix lzlib) %compression-levels)
+                              (@@ (guix lzlib) %default-compression-level))))))))
+
+(test-assert* "Bytevector of size relative to Lzip internal buffers (64KiB)"
+  (compress-and-decompress (random-bytevector (* 64 1024))))
+
+(test-assert* "Bytevector of size relative to Lzip internal buffers (64KiB-1)"
+  (compress-and-decompress (random-bytevector (1- (* 64 1024)))))
+
+(test-assert* "Bytevector of size relative to Lzip internal buffers (64KiB+1)"
+  (compress-and-decompress (random-bytevector (1+ (* 64 1024)))))
+
+(test-assert* "Bytevector of size relative to Lzip internal buffers (1MiB)"
+  (compress-and-decompress (random-bytevector (* 1024 1024))))
+
+(test-assert* "Bytevector of size relative to Lzip internal buffers (1MiB-1)"
+  (compress-and-decompress (random-bytevector (1- (* 1024 1024)))))
+
+(test-assert* "Bytevector of size relative to Lzip internal buffers (1MiB+1)"
+  (compress-and-decompress (random-bytevector (1+ (* 1024 1024)))))
+
+(test-end)