Guess compressor only if no AR nember with exact name exists

Explicitly opening a tar member is a bit harder than it needs to be as
you have to remove the compressor extension so that it can be guessed
here gain potentially choosing the wrong member.

Doesn't really matter for deb packages of course as the member count is
pretty low and strongly defined, but testing is easier this way.

It also finally fixes an incorrectly formatted error message.

1 files changed, 34 insertions, 25 deletions

diff --git a/apt-pkg/deb/debfile.cc b/apt-pkg/deb/debfile.cc
index bef0cd0d8..645a579ef 100644
--- a/apt-pkg/deb/debfile.cc
+++ b/apt-pkg/deb/debfile.cc
@@ -24,9 +24,12 @@
 #include <apt-pkg/error.h>
 #include <apt-pkg/extracttar.h>
 #include <apt-pkg/fileutl.h>
+#include <apt-pkg/strutl.h>
 #include <apt-pkg/tagfile.h>
 
+#include <algorithm>
 #include <string>
+#include <sstream>
 #include <vector>
 #include <string.h>
 #include <sys/stat.h>
@@ -105,42 +108,48 @@ const ARArchive::Member *debDebFile::GotoMember(const char *Name)
 /* Simple wrapper around tar.. */
 bool debDebFile::ExtractTarMember(pkgDirStream &Stream,const char *Name)
 {
-   // Get the archive member
-   const ARArchive::Member *Member = NULL;
    std::string Compressor;
+   auto const Compressors = APT::Configuration::getCompressors();
 
-   std::vector<APT::Configuration::Compressor> compressor = APT::Configuration::getCompressors();
-   for (std::vector<APT::Configuration::Compressor>::const_iterator c = compressor.begin();
-	c != compressor.end(); ++c)
+   ARArchive::Member const *Member = AR.FindMember(Name);
+   if (Member != nullptr)
    {
-      Member = AR.FindMember(std::string(Name).append(c->Extension).c_str());
-      if (Member == NULL)
-	 continue;
-      Compressor = c->Name;
-      break;
+      auto const found = std::find_if(Compressors.cbegin(), Compressors.cend(), [&](auto const &c) {
+	 return not c.Extension.empty() && APT::String::Endswith(Name, c.Extension);
+      });
+      if (found != Compressors.cend())
+	 Compressor = found->Name;
    }
-
-   if (Member == NULL)
-      Member = AR.FindMember(std::string(Name).c_str());
-
-   if (Member == NULL)
+   else
    {
-      std::string ext = std::string(Name) + ".{";
-      for (std::vector<APT::Configuration::Compressor>::const_iterator c = compressor.begin();
-	   c != compressor.end(); ++c) {
-	 if (!c->Extension.empty())
-	    ext.append(c->Extension.substr(1));
+      for (auto const &c : Compressors)
+      {
+	 if (c.Extension.empty())
+	    continue;
+	 Member = AR.FindMember(std::string(Name).append(c.Extension).c_str());
+	 if (Member == nullptr)
+	    continue;
+	 Compressor = c.Name;
+	 break;
       }
-      ext.append("}");
-      return _error->Error(_("Internal error, could not locate member %s"), ext.c_str());
    }
 
-   if (File.Seek(Member->Start) == false)
+   if (Member == nullptr)
+   {
+      std::ostringstream ext;
+      ext << Name << '{';
+      for (auto const &c : Compressors)
+	 if (not c.Extension.empty())
+	    ext << c.Extension << ',';
+      ext << '}';
+      return _error->Error(_("Internal error, could not locate member %s"), ext.str().c_str());
+   }
+
+   if (not File.Seek(Member->Start))
       return false;
 
-   // Prepare Tar
    ExtractTar Tar(File,Member->Size,Compressor);
-   if (_error->PendingError() == true)
+   if (_error->PendingError())
       return false;
    return Tar.Go(Stream);
 }