Add --compression option

* doc/wget.texi: Add --compression documentation.
* src/init.c (cmd_spec_compression): New function.
(commands[]): Add opt.compression.
(defaults): Set default opt.compression value.
* src/main.c (option_data[]): Add struct for --compression.
(print_help, help[]): Add description for --compression.
(main): Add incompatibility checks for --compression.
* src/options.h (struct options): Add compression enum and field.

doc/wget.texi

@@ -1535,6 +1535,20 @@ wget --header="Host: foo.bar" http://localhost/
 In versions of Wget prior to 1.10 such use of @samp{--header} caused
 sending of duplicate headers.
 
+@cindex Content-Encoding, choose
+@item --compression=@var{type}
+Choose the type of compression to be used.  Legal values are
+@samp{auto}, @samp{gzip} and @samp{none}.
+
+If @samp{auto} or @samp{gzip} are specified, Wget asks the server to
+compress the file using the gzip compression format. If the server
+compresses the file and responds with the @code{Content-Encoding}
+header field set appropriately, the file will be decompressed
+automatically. This is the default.
+
+If @samp{none} is specified, wget will not ask the server to compress
+the file and will not decompress any server responses.
+
 @cindex redirect
 @item --max-redirect=@var{number}
 Specifies the maximum number of redirections to follow for a resource.
@@ -3368,6 +3382,11 @@ Turn globbing on/off---the same as @samp{--glob} and @samp{--no-glob}.
 Define a header for HTTP downloads, like using
 @samp{--header=@var{string}}.
 
+@item compression = @var{string}
+Choose the compression type to be used.  Legal values are @samp{auto}
+(the default), @samp{gzip}, and @samp{none}.  The same as
+@samp{--compression=@var{string}}.
+
 @item adjust_extension = on/off
 Add a @samp{.html} extension to @samp{text/html} or
 @samp{application/xhtml+xml} files that lack one, a @samp{.css}

src/init.c

@@ -99,6 +99,9 @@ CMD_DECLARE (cmd_vector);
 
 CMD_DECLARE (cmd_use_askpass);
 
+#ifdef HAVE_LIBZ
+CMD_DECLARE (cmd_spec_compression);
+#endif
 CMD_DECLARE (cmd_spec_dirstruct);
 CMD_DECLARE (cmd_spec_header);
 CMD_DECLARE (cmd_spec_warc_header);
@@ -161,6 +164,9 @@ static const struct {
   { "checkcertificate", &opt.check_cert,        cmd_check_cert },
 #endif
   { "chooseconfig",     &opt.choose_config,     cmd_file },
+#ifdef HAVE_LIBZ
+  { "compression",      &opt.compression,       cmd_spec_compression },
+#endif
   { "connecttimeout",   &opt.connect_timeout,   cmd_time },
   { "contentdisposition", &opt.content_disposition, cmd_boolean },
   { "contentonerror",   &opt.content_on_error,  cmd_boolean },
@@ -445,6 +451,10 @@ defaults (void)
   opt.ftps_clear_data_connection = false;
 #endif
 
+#ifdef HAVE_LIBZ
+  opt.compression = compression_auto;
+#endif
+
   /* The default for file name restriction defaults to the OS type. */
 #if defined(WINDOWS) || defined(MSDOS) || defined(__CYGWIN__)
   opt.restrict_files_os = restrict_windows;
@@ -1445,6 +1455,25 @@ cmd_cert_type (const char *com, const char *val, void *place)
 
 static bool check_user_specified_header (const char *);
 
+#ifdef HAVE_LIBZ
+static bool
+cmd_spec_compression (const char *com, const char *val, void *place)
+{
+  static const struct decode_item choices[] = {
+    { "auto", compression_auto },
+    { "gzip", compression_gzip },
+    { "none", compression_none },
+  };
+  int ok = decode_string (val, choices, countof (choices), place);
+  if (!ok)
+    {
+      fprintf (stderr, _("%s: %s: Invalid value %s.\n"), exec_name, com,
+               quote (val));
+    }
+  return ok;
+}
+#endif
+
 static bool
 cmd_spec_dirstruct (const char *com, const char *val, void *place_ignored _GL_UNUSED)
 {

src/main.c

@@ -275,6 +275,9 @@ static struct cmdline_option option_data[] =
     { IF_SSL ("certificate-type"), 0, OPT_VALUE, "certificatetype", -1 },
     { IF_SSL ("check-certificate"), 0, OPT_BOOLEAN, "checkcertificate", -1 },
     { "clobber", 0, OPT__CLOBBER, NULL, optional_argument },
+#ifdef HAVE_LIBZ
+    { "compression", 0, OPT_VALUE, "compression", -1 },
+#endif
     { "config", 0, OPT_VALUE, "chooseconfig", -1 },
     { "connect-timeout", 0, OPT_VALUE, "connecttimeout", -1 },
     { "continue", 'c', OPT_BOOLEAN, "continue", -1 },
@@ -763,6 +766,10 @@ HTTP options:\n"),
        --ignore-length             ignore 'Content-Length' header field\n"),
     N_("\
        --header=STRING             insert STRING among the headers\n"),
+#ifdef HAVE_LIBZ
+    N_("\
+       --compression=TYPE          choose compression, one of auto, gzip and none\n"),
+#endif
     N_("\
        --max-redirect              maximum redirections allowed per page\n"),
     N_("\
@@ -1675,6 +1682,26 @@ for details.\n\n"));
         }
     }
 
+#ifdef HAVE_LIBZ
+  if (opt.always_rest || opt.start_pos >= 0)
+    {
+      if (opt.compression == compression_auto)
+        {
+          /* Compression does not work with --continue or --start-pos.
+             Since compression was not explicitly set, it will be disabled. */
+          opt.compression = compression_none;
+        }
+      else if (opt.compression != compression_none)
+        {
+          fprintf (stderr,
+                   _("Compression does not work with --continue or"
+                     " --start-pos, they will be disabled.\n"));
+          opt.always_rest = false;
+          opt.start_pos = -1;
+        }
+    }
+#endif
+
   if (opt.ask_passwd && opt.passwd)
     {
       fprintf (stderr,

src/options.h

@@ -326,6 +326,14 @@ struct options
                                    name. */
   bool report_bps;              /*Output bandwidth in bits format*/
 
+#ifdef HAVE_LIBZ
+  enum compression_options {
+    compression_auto,
+    compression_gzip,
+    compression_none
+  } compression;                /* type of HTTP compression to use */
+#endif
+
   char *rejected_log;           /* The file to log rejected URLS to. */
 
 #ifdef HAVE_HSTS