apt-helper: cat-file: Add -C/--compress option

This allows passing compressing the output. The compressor must
be a compressor name, extension, or an extension without the
leading dot.

apt-private/private-cmndline.cc

@@ -156,8 +156,12 @@ static bool addArgumentsAPTInternalSolver(std::vector<CommandLine::Args> &, char
    return true;
 }
 									/*}}}*/
-static bool addArgumentsAPTHelper(std::vector<CommandLine::Args> &, char const * const)/*{{{*/
+static bool addArgumentsAPTHelper(std::vector<CommandLine::Args> &Args, char const * const Cmd)/*{{{*/
 {
+   if (CmdMatches("cat-file"))
+   {
+      addArg('C', "compress", "Apt-Helper::Cat-File::Compress",CommandLine::HasArg);
+   }
    return true;
 }
 									/*}}}*/

cmdline/apt-helper.cc

@@ -107,13 +107,42 @@ static bool DoSrvLookup(CommandLine &CmdL)				/*{{{*/
    return true;
 }
 									/*}}}*/
+static const APT::Configuration::Compressor *FindCompressor(std::vector<APT::Configuration::Compressor> const & compressors, std::string name)				/*{{{*/
+{
+   APT::Configuration::Compressor const * compressor = NULL;
+   for (auto const & c : compressors)
+   {
+      if (compressor != NULL && c.Cost >= compressor->Cost)
+         continue;
+      if (c.Name == name || c.Extension == name || (!c.Extension.empty() && c.Extension.substr(1) == name))
+         compressor = &c;
+   }
+
+   return compressor;
+}
+									/*}}}*/
 static bool DoCatFile(CommandLine &CmdL)				/*{{{*/
 {
    FileFd fd;
    FileFd out;
+   std::string const compressorName = _config->Find("Apt-Helper::Cat-File::Compress", "");
+
+   if (compressorName.empty() == false)
+   {
+
+      auto const compressors = APT::Configuration::getCompressors();
+      auto const compressor = FindCompressor(compressors, compressorName);
 
-   if (out.OpenDescriptor(STDOUT_FILENO, FileFd::WriteOnly) == false)
-      return false;
+      if (compressor == NULL)
+         return _error->Error("Could not find compressor: %s", compressorName.c_str());
+
+      if (out.OpenDescriptor(STDOUT_FILENO, FileFd::WriteOnly, *compressor) == false)
+         return false;
+   } else
+   {
+      if (out.OpenDescriptor(STDOUT_FILENO, FileFd::WriteOnly) == false)
+         return false;
+   }
 
    if (CmdL.FileSize() <= 1)
       return _error->Error("Must specify at least one file name");