dpkg-deb: Allow to use the same compression for control.tar as data.tar

Add a new --uniform-compression, that allows to use the same compression
parameters on the control.tar member as for the data.tar member.

This is a transitional need, once a dpkg-deb supporting other control.tar
compressions is widely deployed, ideally on stable distribution releases,
then the default could possibly get switched.

debian/changelog

@@ -45,6 +45,8 @@ dpkg (1.17.6) UNRELEASED; urgency=low
     as if -Znone had been passed, as documented. Closes: #718295
   * Add support for .deb archives with a control member not compressed
     (control.tar) or compressed with xz (control.tar.xz).
+  * Add support for creating uniformly compressed .deb archive members,
+    with the new dpkg-deb option --uniform-compression.
 
   [ Updated dpkg translations ]
   * Swedish (Peter Krefting).

dpkg-deb/build.c

@@ -432,6 +432,7 @@ pkg_get_pathname(const char *dir, struct pkginfo *pkg)
 int
 do_build(const char *const *argv)
 {
+  struct compress_params control_compress_params;
   struct dpkg_error err;
   const char *debar, *dir;
   bool subdir;
@@ -516,16 +517,18 @@ do_build(const char *const *argv)
            tfbuf);
   free(tfbuf);
 
-  /* And run gzip to compress our control archive. */
+  /* And run the compressor on our control archive. */
+  if (opt_uniform_compression) {
+    control_compress_params = compress_params;
+  } else {
+    control_compress_params.type = compressor_type_gzip;
+    control_compress_params.strategy = compressor_strategy_none;
+    control_compress_params.level = -1;
+  }
+
   c2 = subproc_fork();
   if (!c2) {
-    struct compress_params params;
-
-    params.type = compressor_type_gzip;
-    params.strategy = compressor_strategy_none;
-    params.level = -1;
-
-    compress_filter(&params, p1[0], gzfd, _("compressing control member"));
+    compress_filter(&control_compress_params, p1[0], gzfd, _("compressing control member"));
     exit(0);
   }
   close(p1[0]);
@@ -555,7 +558,7 @@ do_build(const char *const *argv)
     char adminmember[16 + 1];
 
     sprintf(adminmember, "%s%s", ADMINMEMBER,
-            compressor_get_extension(compressor_type_gzip));
+            compressor_get_extension(control_compress_params.type));
 
     dpkg_ar_put_magic(debar, arfd);
     dpkg_ar_member_put_mem(debar, arfd, DEBMAGIC, deb_magic, strlen(deb_magic));

dpkg-deb/dpkg-deb.h

@@ -36,6 +36,7 @@ action_func do_raw_extract;
 action_func do_fsystarfile;
 
 extern int opt_verbose;
+extern int opt_uniform_compression;
 extern int debugflag, nocheckflag;
 
 extern struct deb_version deb_format;

dpkg-deb/main.c

@@ -107,6 +107,7 @@ usage(const struct cmdinfo *cip, const char *value)
 "      --new                        Legacy alias for '--deb-format=2.0'.\n"
 "  --nocheck                        Suppress control file check (build bad\n"
 "                                     packages).\n"
+"      --uniform-compression        Use the compression params on all members.\n"
 "  -z#                              Set the compression level when building.\n"
 "  -Z<type>                         Set the compression type used when building.\n"
 "                                     Allowed types: gzip, xz, bzip2, none.\n"
@@ -142,6 +143,7 @@ static const char printforhelp[] =
 int debugflag = 0;
 int nocheckflag = 0;
 int opt_verbose = 0;
+int opt_uniform_compression = 0;
 
 struct deb_version deb_format = DEB_VERSION(2, 0);
 
@@ -233,6 +235,7 @@ static const struct cmdinfo cmdinfos[]= {
   { "debug",         'D', 0, &debugflag,     NULL,         NULL,          1 },
   { "verbose",       'v', 0, &opt_verbose,   NULL,         NULL,          1 },
   { "nocheck",       0,   0, &nocheckflag,   NULL,         NULL,          1 },
+  { "uniform-compression", 0, 0, &opt_uniform_compression, NULL, NULL,    1 },
   { NULL,            'z', 1, NULL,           NULL,         set_compress_level },
   { NULL,            'Z', 1, NULL,           NULL,         set_compress_type  },
   { NULL,            'S', 1, NULL,           NULL,         set_compress_strategy },
@@ -255,6 +258,13 @@ int main(int argc, const char *const *argv) {
   if (!compressor_check_params(&compress_params, &err))
     badusage(_("invalid compressor parameters: %s"), err.str);
 
+  if (opt_uniform_compression &&
+      (compress_params.type != compressor_type_none &&
+       compress_params.type != compressor_type_gzip &&
+       compress_params.type != compressor_type_xz))
+    badusage(_("unsupported compression type '%s' with uniform compression"),
+             compressor_get_name(compress_params.type));
+
   ret = cipaction->action(argv);
 
   dpkg_program_done();

man/dpkg-deb.1

@@ -232,6 +232,13 @@ Specify which compression type to use when building a package. Allowed
 values are \fIgzip\fP, \fIxz\fP, \fIbzip2\fP, \fIlzma\fP, and \fInone\fP
 (default is \fIxz\fP).
 .TP
+.B \-\-uniform\-compression
+Specify that the same compression parameters should be used for all archive
+members (i.e. \fBcontrol.tar\fP and \fBdata.tar\fP). Otherwise only the
+\fBdata.tar\fP member will use those parameters. The only supported
+compression types allowed to be uniformly used are \fInone\fP, \fIgzip\fP
+and \fIxz\fP.
+.TP
 .BI \-\-deb\-format= format
 Set the archive format version used when building (since dpkg 1.17.0).
 Allowed values are \fI2.0\fP for the new format, and \fI0.939000\fP