provide a public interface for acquiring changelogs

Provided is a specialized acquire item which given a version can figure
out the correct URI to try by itself and if not provides an error
message alongside with static methods to get just the URI it would try
to download if it should just be displayed or similar such.

The URI is constructed as follows:
Release files can provide an URI template in the "Changelogs" field,
otherwise we lookup a configuration item based on the "Label" or
"Origin" of the Release file to get a (hopefully known) default value
for now. This template should contain the string CHANGEPATH which is
replaced with the information about the version we want the changelog
for (e.g.  main/a/apt/apt_1.1). This middleway was choosen as this path
part was consistent over the three known implementations (+1 defunct),
while the rest of the URI varies widely between them.

The benefit of this construct is that it is now easy to get changelogs
for Debian packages on Ubuntu and vice versa – even at the moment where
the Changelogs field is present nowhere. Strictly better than what
apt-get had before as it would even fail to get changelogs from
security… Now it will notice that security identifies as Origin: Debian
and pick this setting (assuming again that no Changelogs field exists).
If on the other hand security would ship its changelogs in a different
location we could set it via the Label option overruling Origin.

Closes: 687147, 739854, 784027, 787190

1 files changed, 211 insertions, 0 deletions

diff --git a/apt-pkg/acquire-item.cc b/apt-pkg/acquire-item.cc
index d6e9ccbe0..4bf4e62f8 100644
--- a/apt-pkg/acquire-item.cc
+++ b/apt-pkg/acquire-item.cc
@@ -31,6 +31,7 @@
 #include <apt-pkg/pkgcache.h>
 #include <apt-pkg/cacheiterators.h>
 #include <apt-pkg/pkgrecords.h>
+#include <apt-pkg/gpgv.h>
 
 #include <stddef.h>
 #include <stdlib.h>
@@ -2836,6 +2837,216 @@ std::string pkgAcqArchive::ShortDesc() const				/*{{{*/
 }
 									/*}}}*/
 
+// AcqChangelog::pkgAcqChangelog - Constructors				/*{{{*/
+pkgAcqChangelog::pkgAcqChangelog(pkgAcquire * const Owner, pkgCache::VerIterator const &Ver,
+      std::string const &DestDir, std::string const &DestFilename) :
+   pkgAcquire::Item(Owner), d(NULL), SrcName(Ver.SourcePkgName()), SrcVersion(Ver.SourceVerStr())
+{
+   Desc.URI = URI(Ver);
+   Init(DestDir, DestFilename);
+}
+// some parameters are char* here as they come likely from char* interfaces – which can also return NULL
+pkgAcqChangelog::pkgAcqChangelog(pkgAcquire * const Owner, pkgCache::RlsFileIterator const &RlsFile,
+      char const * const Component, char const * const SrcName, char const * const SrcVersion,
+      const string &DestDir, const string &DestFilename) :
+   pkgAcquire::Item(Owner), d(NULL), SrcName(SrcName), SrcVersion(SrcVersion)
+{
+   Desc.URI = URI(RlsFile, Component, SrcName, SrcVersion);
+   Init(DestDir, DestFilename);
+}
+pkgAcqChangelog::pkgAcqChangelog(pkgAcquire * const Owner,
+      std::string const &URI, char const * const SrcName, char const * const SrcVersion,
+      const string &DestDir, const string &DestFilename) :
+   pkgAcquire::Item(Owner), d(NULL), SrcName(SrcName), SrcVersion(SrcVersion)
+{
+   Desc.URI = URI;
+   Init(DestDir, DestFilename);
+}
+void pkgAcqChangelog::Init(std::string const &DestDir, std::string const &DestFilename)
+{
+   if (Desc.URI.empty())
+   {
+      Status = StatError;
+      // TRANSLATOR: %s=%s is sourcename=sourceversion, e.g. apt=1.1
+      strprintf(ErrorText, _("Changelog unavailable for %s=%s"), SrcName.c_str(), SrcVersion.c_str());
+      // Let the error message print something sensible rather than "Failed to fetch /"
+      if (DestFilename.empty())
+	 DestFile = SrcName + ".changelog";
+      else
+	 DestFile = DestFilename;
+      Desc.URI = "changelog:/" + DestFile;
+      return;
+   }
+
+   if (DestDir.empty())
+   {
+      std::string const systemTemp = GetTempDir();
+      char tmpname[100];
+      snprintf(tmpname, sizeof(tmpname), "%s/apt-changelog-XXXXXX", systemTemp.c_str());
+      if (NULL == mkdtemp(tmpname))
+      {
+	 _error->Errno("mkdtemp", "mkdtemp failed in changelog acquire of %s %s", SrcName.c_str(), SrcVersion.c_str());
+	 Status = StatError;
+	 return;
+      }
+      DestFile = TemporaryDirectory = tmpname;
+   }
+   else
+      DestFile = DestDir;
+
+   if (DestFilename.empty())
+      DestFile = flCombine(DestFile, SrcName + ".changelog");
+   else
+      DestFile = flCombine(DestFile, DestFilename);
+
+   Desc.ShortDesc = "Changelog";
+   strprintf(Desc.Description, "%s %s %s Changelog", URI::SiteOnly(Desc.URI).c_str(), SrcName.c_str(), SrcVersion.c_str());
+   Desc.Owner = this;
+   QueueURI(Desc);
+
+   if (Status == StatDone) // this happens if we queue the same changelog two times
+   {
+      Complete = true;
+      for (pkgAcquire::UriIterator I = Owner->UriBegin(); I != Owner->UriEnd(); ++I)
+	 if (I->URI == Desc.URI)
+	    if (DestFile != I->Owner->DestFile)
+	       if (symlink(I->Owner->DestFile.c_str(), DestFile.c_str()) != 0)
+	       {
+		  ; // ignore error, there isn't anthing we could do to handle the edgecase of an edgecase
+	       }
+   }
+}
+									/*}}}*/
+std::string pkgAcqChangelog::URI(pkgCache::VerIterator const &Ver)	/*{{{*/
+{
+   char const * const SrcName = Ver.SourcePkgName();
+   char const * const SrcVersion = Ver.SourceVerStr();
+   pkgCache::PkgFileIterator PkgFile;
+   // find the first source for this version which promises a changelog
+   for (pkgCache::VerFileIterator VF = Ver.FileList(); VF.end() == false; ++VF)
+   {
+      pkgCache::PkgFileIterator const PF = VF.File();
+      if (PF.Flagged(pkgCache::Flag::NotSource) || PF->Release == 0)
+	 continue;
+      PkgFile = PF;
+      pkgCache::RlsFileIterator const RF = PF.ReleaseFile();
+      std::string const uri = URI(RF, PF.Component(), SrcName, SrcVersion);
+      if (uri.empty())
+	 continue;
+      return uri;
+   }
+   return "";
+}
+std::string pkgAcqChangelog::URITemplate(pkgCache::RlsFileIterator const &Rls)
+{
+   if (Rls.end() == true || (Rls->Label == 0 && Rls->Origin == 0))
+      return "";
+   std::string const serverConfig = "Acquire::Changelogs::URI";
+   std::string server;
+#define APT_EMPTY_SERVER \
+   if (server.empty() == false) \
+   { \
+      if (server != "no") \
+	 return server; \
+      return ""; \
+   }
+#define APT_CHECK_SERVER(X, Y) \
+   if (Rls->X != 0) \
+   { \
+      std::string const specialServerConfig = serverConfig + "::" + Y + #X + "::" + Rls.X(); \
+      server = _config->Find(specialServerConfig); \
+      APT_EMPTY_SERVER \
+   }
+   // this way e.g. Debian-Security can fallback to Debian
+   APT_CHECK_SERVER(Label, "Override::")
+   APT_CHECK_SERVER(Origin, "Override::")
+
+   if (RealFileExists(Rls.FileName()))
+   {
+      _error->PushToStack();
+      FileFd rf;
+      /* This can be costly. A caller wanting to get millions of URIs might
+	 want to do this on its own once and use Override settings.
+	 We don't do this here as Origin/Label are not as unique as they
+	 should be so this could produce request order-dependent anomalies */
+      if (OpenMaybeClearSignedFile(Rls.FileName(), rf) == true)
+      {
+	 pkgTagFile TagFile(&rf, rf.Size());
+	 pkgTagSection Section;
+	 if (TagFile.Step(Section) == true)
+	    server = Section.FindS("Changelogs");
+      }
+      _error->RevertToStack();
+      APT_EMPTY_SERVER
+   }
+
+   APT_CHECK_SERVER(Label, "")
+   APT_CHECK_SERVER(Origin, "")
+#undef APT_CHECK_SERVER
+#undef APT_EMPTY_SERVER
+   return "";
+}
+std::string pkgAcqChangelog::URI(pkgCache::RlsFileIterator const &Rls,
+	 char const * const Component, char const * const SrcName,
+	 char const * const SrcVersion)
+{
+   return URI(URITemplate(Rls), Component, SrcName, SrcVersion);
+}
+std::string pkgAcqChangelog::URI(std::string const &Template,
+	 char const * const Component, char const * const SrcName,
+	 char const * const SrcVersion)
+{
+   if (Template.find("CHANGEPATH") == std::string::npos)
+      return "";
+
+   // the path is: COMPONENT/SRC/SRCNAME/SRCNAME_SRCVER, e.g. main/a/apt/1.1 or contrib/liba/libapt/2.0
+   std::string Src = SrcName;
+   std::string path = APT::String::Startswith(SrcName, "lib") ? Src.substr(0, 4) : Src.substr(0,1);
+   path.append("/").append(Src).append("/");
+   path.append(Src).append("_").append(StripEpoch(SrcVersion));
+   // we omit component for releases without one (= flat-style repositories)
+   if (Component != NULL && strlen(Component) != 0)
+      path = std::string(Component) + "/" + path;
+
+   return SubstVar(Template, "CHANGEPATH", path);
+}
+									/*}}}*/
+// AcqChangelog::Failed - Failure handler				/*{{{*/
+void pkgAcqChangelog::Failed(string const &Message, pkgAcquire::MethodConfig const * const Cnf)
+{
+   Item::Failed(Message,Cnf);
+
+   std::string errText;
+   // TRANSLATOR: %s=%s is sourcename=sourceversion, e.g. apt=1.1
+   strprintf(errText, _("Changelog unavailable for %s=%s"), SrcName.c_str(), SrcVersion.c_str());
+
+   // Error is probably something techy like 404 Not Found
+   if (ErrorText.empty())
+      ErrorText = errText;
+   else
+      ErrorText = errText + " (" + ErrorText + ")";
+   return;
+}
+									/*}}}*/
+// AcqChangelog::Done - Item downloaded OK				/*{{{*/
+void pkgAcqChangelog::Done(string const &Message,HashStringList const &CalcHashes,
+		      pkgAcquire::MethodConfig const * const Cnf)
+{
+   Item::Done(Message,CalcHashes,Cnf);
+
+   Complete = true;
+}
+									/*}}}*/
+pkgAcqChangelog::~pkgAcqChangelog()					/*{{{*/
+{
+   if (TemporaryDirectory.empty() == false)
+   {
+      unlink(DestFile.c_str());
+      rmdir(TemporaryDirectory.c_str());
+   }
+}
+									/*}}}*/
+
 // AcqFile::pkgAcqFile - Constructor					/*{{{*/
 pkgAcqFile::pkgAcqFile(pkgAcquire * const Owner,string const &URI, HashStringList const &Hashes,
 		       unsigned long long const Size,string const &Dsc,string const &ShortDesc,