Merge branch 'fix/tagfilekeys' into 'main'

Consistently dealing with fields via pkgTagSection::Key

See merge request apt-team/apt!233

26 files changed, 289 insertions, 252 deletions

diff --git a/apt-pkg/CMakeLists.txt b/apt-pkg/CMakeLists.txt
index 5c97493af..a40b041b8 100644
--- a/apt-pkg/CMakeLists.txt
+++ b/apt-pkg/CMakeLists.txt
@@ -2,7 +2,8 @@
 include_directories(${PROJECT_BINARY_DIR}/include/apt-pkg)
 
 file(MAKE_DIRECTORY ${PROJECT_BINARY_DIR}/include/apt-pkg/)
-execute_process(COMMAND ${TRIEHASH_EXECUTABLE}
+execute_process(COMMAND grep -v "^#" "${CMAKE_CURRENT_SOURCE_DIR}/tagfile-keys.list"
+                COMMAND ${TRIEHASH_EXECUTABLE}
                         --ignore-case
                          --header ${PROJECT_BINARY_DIR}/include/apt-pkg/tagfile-keys.h
                          --code ${CMAKE_CURRENT_BINARY_DIR}/tagfile-keys.cc
@@ -10,8 +11,10 @@ execute_process(COMMAND ${TRIEHASH_EXECUTABLE}
                          --enum-name pkgTagSection::Key
                          --function-name pkgTagHash
                          --include "<apt-pkg/tagfile.h>"
-                         ${CMAKE_CURRENT_SOURCE_DIR}/tagfile-keys.list)
+                         --include "<apt-pkg/header-is-private.h>"
+                         /dev/stdin )
 set_property(DIRECTORY APPEND PROPERTY CMAKE_CONFIGURE_DEPENDS "tagfile-keys.list")
+set_source_files_properties("${CMAKE_CURRENT_BINARY_DIR}/tagfile-keys.cc" PROPERTIES COMPILE_DEFINITIONS APT_COMPILING_APT)
 
 
 # Set the version of the library
diff --git a/apt-pkg/acquire-item.cc b/apt-pkg/acquire-item.cc
index f9362b0d5..d9e1e516b 100644
--- a/apt-pkg/acquire-item.cc
+++ b/apt-pkg/acquire-item.cc
@@ -2371,13 +2371,13 @@ bool pkgAcqDiffIndex::ParseDiffIndex(string const &IndexDiffFile)	/*{{{*/
    {
       std::string tagname = *type;
       tagname.append("-Current");
-      std::string const tmp = Tags.FindS(tagname.c_str());
+      auto const tmp = Tags.Find(tagname);
       if (tmp.empty() == true)
 	 continue;
 
       string hash;
       unsigned long long size;
-      std::stringstream ss(tmp);
+      std::stringstream ss(tmp.to_string());
       ss.imbue(posix);
       ss >> hash >> size;
       if (unlikely(hash.empty() == true))
@@ -2441,13 +2441,13 @@ bool pkgAcqDiffIndex::ParseDiffIndex(string const &IndexDiffFile)	/*{{{*/
 
       std::string tagname = *type;
       tagname.append("-History");
-      std::string const tmp = Tags.FindS(tagname.c_str());
+      auto const tmp = Tags.Find(tagname);
       if (tmp.empty() == true)
 	 continue;
 
       string hash, filename;
       unsigned long long size;
-      std::stringstream ss(tmp);
+      std::stringstream ss(tmp.to_string());
       ss.imbue(posix);
 
       while (ss >> hash >> size >> filename)
@@ -2498,13 +2498,13 @@ bool pkgAcqDiffIndex::ParseDiffIndex(string const &IndexDiffFile)	/*{{{*/
 
       std::string tagname = *type;
       tagname.append("-Patches");
-      std::string const tmp = Tags.FindS(tagname.c_str());
+      auto const tmp = Tags.Find(tagname);
       if (tmp.empty() == true)
 	 continue;
 
       string hash, filename;
       unsigned long long size;
-      std::stringstream ss(tmp);
+      std::stringstream ss(tmp.to_string());
       ss.imbue(posix);
 
       while (ss >> hash >> size >> filename)
@@ -2536,13 +2536,13 @@ bool pkgAcqDiffIndex::ParseDiffIndex(string const &IndexDiffFile)	/*{{{*/
    {
       std::string tagname = *type;
       tagname.append("-Download");
-      std::string const tmp = Tags.FindS(tagname.c_str());
+      auto const tmp = Tags.Find(tagname);
       if (tmp.empty() == true)
 	 continue;
 
       string hash, filename;
       unsigned long long size;
-      std::stringstream ss(tmp);
+      std::stringstream ss(tmp.to_string());
       ss.imbue(posix);
 
       // FIXME: all of pdiff supports only .gz compressed patches
@@ -2613,7 +2613,7 @@ bool pkgAcqDiffIndex::ParseDiffIndex(string const &IndexDiffFile)	/*{{{*/
    if (pdiff_merge == true)
    {
       // reprepro and dak add this flag if they merge patches on the server
-      std::string const precedence = Tags.FindS("X-Patch-Precedence");
+      auto const precedence = Tags.Find("X-Patch-Precedence");
       pdiff_merge = (precedence != "merged");
    }
 
diff --git a/apt-pkg/cachefilter-patterns.h b/apt-pkg/cachefilter-patterns.h
index e6ea16c68..284fcc1cf 100644
--- a/apt-pkg/cachefilter-patterns.h
+++ b/apt-pkg/cachefilter-patterns.h
@@ -11,6 +11,7 @@
 #include <apt-pkg/cachefile.h>
 #include <apt-pkg/cachefilter.h>
 #include <apt-pkg/error.h>
+#include <apt-pkg/header-is-private.h>
 #include <apt-pkg/string_view.h>
 #include <apt-pkg/strutl.h>
 #include <iostream>
@@ -20,10 +21,6 @@
 #include <vector>
 #include <assert.h>
 
-#ifndef APT_COMPILING_APT
-#error Internal header
-#endif
-
 namespace APT
 {
 
diff --git a/apt-pkg/contrib/hashes.cc b/apt-pkg/contrib/hashes.cc
index 267e2679a..313b1d37d 100644
--- a/apt-pkg/contrib/hashes.cc
+++ b/apt-pkg/contrib/hashes.cc
@@ -17,6 +17,8 @@
 #include <apt-pkg/hashes.h>
 #include <apt-pkg/macros.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
+#include <apt-pkg/tagfile.h>
 
 #include <algorithm>
 #include <iostream>
@@ -45,6 +47,15 @@ const char * HashString::_SupportedHashes[] =
 {
    "SHA512", "SHA256", "SHA1", "MD5Sum", "Checksum-FileSize", NULL
 };
+std::vector<HashString::HashSupportInfo> HashString::SupportedHashesInfo()
+{
+   return {{
+      { "SHA512",  pkgTagSection::Key::SHA512,"Checksums-Sha512", pkgTagSection::Key::Checksums_Sha512},
+      { "SHA256", pkgTagSection::Key::SHA256, "Checksums-Sha256", pkgTagSection::Key::Checksums_Sha256},
+      { "SHA1", pkgTagSection::Key::SHA1, "Checksums-Sha1", pkgTagSection::Key::Checksums_Sha1 },
+      { "MD5Sum", pkgTagSection::Key::MD5sum, "Files", pkgTagSection::Key::Files },
+   }};
+}
 
 HashString::HashString()
 {
diff --git a/apt-pkg/contrib/hashes.h b/apt-pkg/contrib/hashes.h
index 422c1e023..e259b4e28 100644
--- a/apt-pkg/contrib/hashes.h
+++ b/apt-pkg/contrib/hashes.h
@@ -14,6 +14,11 @@
 
 #include <apt-pkg/macros.h>
 
+#ifdef APT_COMPILING_APT
+#include <apt-pkg/string_view.h>
+#include <apt-pkg/tagfile-keys.h>
+#endif
+
 #include <cstring>
 #include <string>
 #include <vector>
@@ -59,6 +64,15 @@ class APT_PUBLIC HashString
 
    // return the list of hashes we support
    static APT_PURE const char** SupportedHashes();
+#ifdef APT_COMPILING_APT
+   struct APT_HIDDEN HashSupportInfo {
+      APT::StringView name;
+      pkgTagSection::Key namekey;
+      APT::StringView chksumsname;
+      pkgTagSection::Key chksumskey;
+   };
+   APT_HIDDEN static std::vector<HashSupportInfo> SupportedHashesInfo();
+#endif
 };
 
 class APT_PUBLIC HashStringList
diff --git a/apt-pkg/contrib/header-is-private.h b/apt-pkg/contrib/header-is-private.h
new file mode 100644
index 000000000..201a40c62
--- /dev/null
+++ b/apt-pkg/contrib/header-is-private.h
@@ -0,0 +1,3 @@
+#ifndef APT_COMPILING_APT
+#error Internal header without ABI stability. Should only be used by apt itself!
+#endif
diff --git a/apt-pkg/deb/deblistparser.cc b/apt-pkg/deb/deblistparser.cc
index 2f0ebaa7b..6f47053a5 100644
--- a/apt-pkg/deb/deblistparser.cc
+++ b/apt-pkg/deb/deblistparser.cc
@@ -126,7 +126,7 @@ unsigned char debListParser::ParseMultiArch(bool const showErrors)	/*{{{*/
       {
 	 if (showErrors == true)
 	    _error->Warning("Architecture: all package '%s' can't be Multi-Arch: same",
-		  Section.FindS("Package").c_str());
+		  Package().c_str());
 	 MA = pkgCache::Version::No;
       }
       else
@@ -140,7 +140,7 @@ unsigned char debListParser::ParseMultiArch(bool const showErrors)	/*{{{*/
    {
       if (showErrors == true)
 	 _error->Warning("Unknown Multi-Arch type '%s' for package '%s'",
-	       MultiArch.to_string().c_str(), Section.FindS("Package").c_str());
+	       MultiArch.to_string().c_str(), Package().c_str());
       MA = pkgCache::Version::No;
    }
 
@@ -241,10 +241,7 @@ bool debListParser::NewVersion(pkgCache::VerIterator &Ver)
       return false;
    if (ParseDepends(Ver,pkgTagSection::Key::Enhances,pkgCache::Dep::Enhances) == false)
       return false;
-   // Obsolete.
-   if (ParseDepends(Ver,pkgTagSection::Key::Optional,pkgCache::Dep::Suggests) == false)
-      return false;
-   
+
    if (ParseProvides(Ver) == false)
       return false;
    if (not APT::KernelAutoRemoveHelper::getUname(Ver.ParentPkg().Name()).empty())
@@ -259,21 +256,20 @@ bool debListParser::NewVersion(pkgCache::VerIterator &Ver)
 // ListParser::AvailableDescriptionLanguages				/*{{{*/
 std::vector<std::string> debListParser::AvailableDescriptionLanguages()
 {
-   std::vector<std::string> const understood = APT::Configuration::getLanguages(true);
    std::vector<std::string> avail;
    static constexpr int prefixLen = 12;
    char buf[32] = "Description-";
-   if (Section.Exists("Description") == true)
-      avail.push_back("");
-   for (std::vector<std::string>::const_iterator lang = understood.begin(); lang != understood.end(); ++lang)
+   if (Section.Exists(pkgTagSection::Key::Description))
+      avail.emplace_back();
+   for (auto const &lang : APT::Configuration::getLanguages(true))
    {
-      if (unlikely(lang->size() > sizeof(buf) - prefixLen)) {
-	 _error->Warning("Ignoring translated description %s", lang->c_str());
+      if (unlikely(lang.size() > sizeof(buf) - prefixLen)) {
+	 _error->Warning("Ignoring translated description %s", lang.c_str());
 	 continue;
       }
-      memcpy(buf + prefixLen, lang->c_str(), lang->size());
-      if (Section.Exists(StringView(buf, prefixLen + lang->size())) == true)
-	 avail.push_back(*lang);
+      memcpy(buf + prefixLen, lang.c_str(), lang.size());
+      if (Section.Exists(StringView(buf, prefixLen + lang.size())) == true)
+	 avail.push_back(lang);
    }
    return avail;
 }
diff --git a/apt-pkg/deb/debmetaindex.cc b/apt-pkg/deb/debmetaindex.cc
index 32f1fa8db..c6005f1c8 100644
--- a/apt-pkg/deb/debmetaindex.cc
+++ b/apt-pkg/deb/debmetaindex.cc
@@ -515,10 +515,9 @@ bool debReleaseIndex::Load(std::string const &Filename, std::string * const Erro
 
    bool FoundHashSum = false;
    bool FoundStrongHashSum = false;
-   auto const SupportedHashes = HashString::SupportedHashes();
-   for (int i=0; SupportedHashes[i] != NULL; i++)
+   for (auto const hashinfo : HashString::SupportedHashesInfo())
    {
-      if (!Section.Find(SupportedHashes[i], Start, End))
+      if (not Section.Find(hashinfo.namekey, Start, End))
 	 continue;
 
       std::string Name;
@@ -529,7 +528,7 @@ bool debReleaseIndex::Load(std::string const &Filename, std::string * const Erro
 	 if (!parseSumData(Start, End, Name, Hash, Size))
 	    return false;
 
-	 HashString const hs(SupportedHashes[i], Hash);
+	 HashString const hs(hashinfo.name.to_string(), Hash);
          if (Entries.find(Name) == Entries.end())
          {
             metaIndex::checkSum *Sum = new metaIndex::checkSum;
diff --git a/apt-pkg/deb/debrecords.cc b/apt-pkg/deb/debrecords.cc
index 22ac219ba..e2ffaefff 100644
--- a/apt-pkg/deb/debrecords.cc
+++ b/apt-pkg/deb/debrecords.cc
@@ -16,6 +16,7 @@
 #include <apt-pkg/fileutl.h>
 #include <apt-pkg/pkgcache.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 
 #include <algorithm>
@@ -57,13 +58,13 @@ debRecordParserBase::debRecordParserBase() : Parser(), d(NULL) {}
 // RecordParserBase::FileName - Return the archive filename on the site	/*{{{*/
 string debRecordParserBase::FileName()
 {
-   return Section.FindS("Filename");
+   return Section.Find(pkgTagSection::Key::Filename).to_string();
 }
 									/*}}}*/
 // RecordParserBase::Name - Return the package name			/*{{{*/
 string debRecordParserBase::Name()
 {
-   string Result = Section.FindS("Package");
+   auto Result = Section.Find(pkgTagSection::Key::Package).to_string();
 
    // Normalize mixed case package names to lower case, like dpkg does
    // See Bug#807012 for details
@@ -75,7 +76,7 @@ string debRecordParserBase::Name()
 // RecordParserBase::Homepage - Return the package homepage		/*{{{*/
 string debRecordParserBase::Homepage()
 {
-   return Section.FindS("Homepage");
+   return Section.Find(pkgTagSection::Key::Homepage).to_string();
 }
 									/*}}}*/
 // RecordParserBase::Hashes - return the available archive hashes	/*{{{*/
@@ -88,7 +89,7 @@ HashStringList debRecordParserBase::Hashes() const
       if (hash.empty() == false)
 	 hashes.push_back(HashString(*type, hash));
    }
-   auto const size = Section.FindULL("Size", 0);
+   auto const size = Section.FindULL(pkgTagSection::Key::Size, 0);
    if (size != 0)
       hashes.FileSize(size);
    return hashes;
@@ -97,7 +98,7 @@ HashStringList debRecordParserBase::Hashes() const
 // RecordParserBase::Maintainer - Return the maintainer email		/*{{{*/
 string debRecordParserBase::Maintainer()
 {
-   return Section.FindS("Maintainer");
+   return Section.Find(pkgTagSection::Key::Maintainer).to_string();
 }
 									/*}}}*/
 // RecordParserBase::RecordField - Return the value of an arbitrary field	/*{{*/
@@ -129,25 +130,25 @@ string debRecordParserBase::LongDesc(std::string const &lang)
 	    l != lang.end(); ++l)
       {
 	 std::string const tagname = "Description-" + *l;
-	 orig = Section.FindS(tagname.c_str());
+	 orig = Section.FindS(tagname);
 	 if (orig.empty() == false)
 	    break;
 	 else if (*l == "en")
 	 {
-	    orig = Section.FindS("Description");
+	    orig = Section.Find(pkgTagSection::Key::Description).to_string();
 	    if (orig.empty() == false)
 	       break;
 	 }
       }
       if (orig.empty() == true)
-	 orig = Section.FindS("Description");
+	 orig = Section.Find(pkgTagSection::Key::Description).to_string();
    }
    else
    {
       std::string const tagname = "Description-" + lang;
       orig = Section.FindS(tagname.c_str());
       if (orig.empty() == true && lang == "en")
-	 orig = Section.FindS("Description");
+	 orig = Section.Find(pkgTagSection::Key::Description).to_string();
    }
 
    char const * const codeset = nl_langinfo(CODESET);
@@ -165,17 +166,17 @@ static const char * const SourceVerSeparators = " ()";
 // RecordParserBase::SourcePkg - Return the source package name if any	/*{{{*/
 string debRecordParserBase::SourcePkg()
 {
-   string Res = Section.FindS("Source");
-   string::size_type Pos = Res.find_first_of(SourceVerSeparators);
-   if (Pos == string::npos)
-      return Res;
-   return string(Res,0,Pos);
+   auto Res = Section.Find(pkgTagSection::Key::Source).to_string();
+   auto const Pos = Res.find_first_of(SourceVerSeparators);
+   if (Pos != std::string::npos)
+      Res.erase(Pos);
+   return Res;
 }
 									/*}}}*/
 // RecordParserBase::SourceVer - Return the source version number if present	/*{{{*/
 string debRecordParserBase::SourceVer()
 {
-   string Pkg = Section.FindS("Source");
+   auto const Pkg = Section.Find(pkgTagSection::Key::Source).to_string();
    string::size_type Pos = Pkg.find_first_of(SourceVerSeparators);
    if (Pos == string::npos)
       return "";
diff --git a/apt-pkg/deb/debsrcrecords.cc b/apt-pkg/deb/debsrcrecords.cc
index 1fd0fdc12..311bacfdd 100644
--- a/apt-pkg/deb/debsrcrecords.cc
+++ b/apt-pkg/deb/debsrcrecords.cc
@@ -172,26 +172,19 @@ bool debSrcRecordParser::Files(std::vector<pkgSrcRecords::File> &List)
    std::vector<std::string> const compExts = APT::Configuration::getCompressorExtensions();
 
    auto const &posix = std::locale::classic();
-   for (char const * const * type = HashString::SupportedHashes(); *type != NULL; ++type)
+   for (auto const hashinfo : HashString::SupportedHashesInfo())
    {
-      // derive field from checksum type
-      std::string checksumField("Checksums-");
-      if (strcmp(*type, "MD5Sum") == 0)
-	 checksumField = "Files"; // historic name for MD5 checksums
-      else
-	 checksumField.append(*type);
-
-      string const Files = Sect.FindS(checksumField.c_str());
+      auto const Files = Sect.Find(hashinfo.chksumskey);
       if (Files.empty() == true)
 	 continue;
-      std::istringstream ss(Files);
+      std::istringstream ss(Files.to_string());
       ss.imbue(posix);
 
       while (ss.good())
       {
 	 std::string hash, path;
 	 unsigned long long size;
-	 if (iIndex == nullptr && checksumField == "Files")
+	 if (iIndex == nullptr && hashinfo.chksumskey == pkgTagSection::Key::Files)
 	 {
 	    std::string ignore;
 	    ss >> hash >> size >> ignore >> ignore >> path;
@@ -200,9 +193,9 @@ bool debSrcRecordParser::Files(std::vector<pkgSrcRecords::File> &List)
 	    ss >> hash >> size >> path;
 
 	 if (ss.fail() || hash.empty() || path.empty())
-	    return _error->Error("Error parsing file record in %s of source package %s", checksumField.c_str(), Package().c_str());
+	    return _error->Error("Error parsing file record in %s of source package %s", hashinfo.chksumsname.to_string().c_str(), Package().c_str());
 
-	 HashString const hashString(*type, hash);
+	 HashString const hashString(hashinfo.name.to_string(), hash);
 	 if (Base.empty() == false)
 	    path = Base + path;
 
@@ -217,7 +210,7 @@ bool debSrcRecordParser::Files(std::vector<pkgSrcRecords::File> &List)
 	 {
 	    // an error here indicates that we have two different hashes for the same file
 	    if (file->Hashes.push_back(hashString) == false)
-	       return _error->Error("Error parsing checksum in %s of source package %s", checksumField.c_str(), Package().c_str());
+	       return _error->Error("Error parsing checksum in %s of source package %s", hashinfo.chksumsname.to_string().c_str(), Package().c_str());
 	    continue;
 	 }
 
diff --git a/apt-pkg/deb/debsrcrecords.h b/apt-pkg/deb/debsrcrecords.h
index b572d3427..1a0bbe0fd 100644
--- a/apt-pkg/deb/debsrcrecords.h
+++ b/apt-pkg/deb/debsrcrecords.h
@@ -12,6 +12,7 @@
 
 #include <apt-pkg/fileutl.h>
 #include <apt-pkg/srcrecords.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 
 #include <string>
@@ -40,9 +41,9 @@ class APT_HIDDEN debSrcRecordParser : public pkgSrcRecords::Parser
    virtual bool Jump(unsigned long const &Off) APT_OVERRIDE {iOffset = Off; return Tags.Jump(Sect,Off);};
 
    virtual std::string Package() const APT_OVERRIDE;
-   virtual std::string Version() const APT_OVERRIDE {return Sect.FindS("Version");};
-   virtual std::string Maintainer() const APT_OVERRIDE {return Sect.FindS("Maintainer");};
-   virtual std::string Section() const APT_OVERRIDE {return Sect.FindS("Section");};
+   virtual std::string Version() const APT_OVERRIDE {return Sect.Find(pkgTagSection::Key::Version).to_string();};
+   virtual std::string Maintainer() const APT_OVERRIDE {return Sect.Find(pkgTagSection::Key::Maintainer).to_string();};
+   virtual std::string Section() const APT_OVERRIDE {return Sect.Find(pkgTagSection::Key::Section).to_string();};
    virtual const char **Binaries() APT_OVERRIDE;
    virtual bool BuildDepends(std::vector<BuildDepRec> &BuildDeps, bool const &ArchOnly, bool const &StripMultiArch = true) APT_OVERRIDE;
    virtual unsigned long Offset() APT_OVERRIDE {return iOffset;};
diff --git a/apt-pkg/depcache.cc b/apt-pkg/depcache.cc
index f7d9832a0..a5b586f5b 100644
--- a/apt-pkg/depcache.cc
+++ b/apt-pkg/depcache.cc
@@ -23,6 +23,7 @@
 #include <apt-pkg/prettyprinters.h>
 #include <apt-pkg/progress.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 #include <apt-pkg/version.h>
 #include <apt-pkg/versionmatch.h>
@@ -310,8 +311,8 @@ bool pkgDepCache::readStateFile(OpProgress * const Prog)		/*{{{*/
       off_t amt = 0;
       bool const debug_autoremove = _config->FindB("Debug::pkgAutoRemove",false);
       while(tagfile.Step(section)) {
-	 string const pkgname = section.FindS("Package");
-	 string pkgarch = section.FindS("Architecture");
+	 auto const pkgname = section.Find(pkgTagSection::Key::Package);
+	 auto pkgarch = section.Find(pkgTagSection::Key::Architecture);
 	 if (pkgarch.empty() == true)
 	    pkgarch = "any";
 	 pkgCache::PkgIterator pkg = Cache->FindPkg(pkgname, pkgarch);
@@ -379,8 +380,8 @@ bool pkgDepCache::writeStateFile(OpProgress * const /*prog*/, bool const Install
    pkgTagSection section;
    std::set<string> pkgs_seen;
    while(tagfile.Step(section)) {
-	 string const pkgname = section.FindS("Package");
-	 string pkgarch = section.FindS("Architecture");
+	 auto const pkgname = section.Find(pkgTagSection::Key::Package);
+	 auto pkgarch = section.Find(pkgTagSection::Key::Architecture);
 	 if (pkgarch.empty() == true)
 	    pkgarch = "native";
 	 // Silently ignore unknown packages and packages with no actual
diff --git a/apt-pkg/edsp.cc b/apt-pkg/edsp.cc
index b7c0d28d2..6493a4595 100644
--- a/apt-pkg/edsp.cc
+++ b/apt-pkg/edsp.cc
@@ -453,7 +453,7 @@ bool EDSP::ReadResponse(int const input, pkgDepCache &Cache, OpProgress *Progres
 			continue;
 		}
 
-		decltype(VersionCount) const id = section.FindULL(type.c_str(), VersionCount);
+		decltype(VersionCount) const id = section.FindULL(type, VersionCount);
 		if (id == VersionCount) {
 			_error->Warning("Unable to parse %s request with id value '%s'!", type.c_str(), section.FindS(type.c_str()).c_str());
 			continue;
diff --git a/apt-pkg/edsp/edsplistparser.cc b/apt-pkg/edsp/edsplistparser.cc
index 34b9ec934..5419069f2 100644
--- a/apt-pkg/edsp/edsplistparser.cc
+++ b/apt-pkg/edsp/edsplistparser.cc
@@ -19,6 +19,7 @@
 #include <apt-pkg/pkgsystem.h>
 #include <apt-pkg/string_view.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 
 #include <array>
@@ -61,9 +62,7 @@ APT::StringView edspLikeListParser::Description_md5()
 // ListParser::VersionHash - Compute a unique hash for this version	/*{{{*/
 uint32_t edspLikeListParser::VersionHash()
 {
-   if (Section.Exists("APT-Hash") == true)
-      return Section.FindI("APT-Hash");
-   else if (Section.Exists("APT-ID") == true)
+   if (Section.Exists("APT-ID") == true)
       return Section.FindI("APT-ID");
    return 0;
 }
@@ -143,8 +142,8 @@ bool eippListParser::ParseStatus(pkgCache::PkgIterator &Pkg,
       {"triggers-pending",pkgCache::State::TriggersPending},
       {"installed",pkgCache::State::Installed},
    }};
-   auto const status = Section.Find("Status");
-   if (status.empty() == false)
+   auto const status = Section.Find(pkgTagSection::Key::Status);
+   if (not status.empty())
    {
       for (auto && sv: statusvalues)
       {
diff --git a/apt-pkg/indexcopy.cc b/apt-pkg/indexcopy.cc
index 88c2150ff..0d569265d 100644
--- a/apt-pkg/indexcopy.cc
+++ b/apt-pkg/indexcopy.cc
@@ -22,6 +22,7 @@
 #include <apt-pkg/metaindex.h>
 #include <apt-pkg/progress.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 
 #include <iostream>
@@ -413,8 +414,8 @@ bool IndexCopy::GrabFirst(string Path,string &To,unsigned int Depth)
 /* */
 bool PackageCopy::GetFile(string &File,unsigned long long &Size)
 {
-   File = Section->FindS("Filename");
-   Size = Section->FindULL("Size");
+   File = Section->Find(pkgTagSection::Key::Filename).to_string();
+   Size = Section->FindULL(pkgTagSection::Key::Size);
    if (File.empty() || Size == 0)
       return _error->Error("Cannot find filename or size tag");
    return true;
@@ -436,29 +437,16 @@ bool PackageCopy::RewriteEntry(FileFd &Target,string const &File)
 /* */
 bool SourceCopy::GetFile(string &File,unsigned long long &Size)
 {
-   string Files;
-
-   for (char const *const *type = HashString::SupportedHashes(); *type != NULL; ++type)
+   std::string Files;
+   for (auto hashinfo : HashString::SupportedHashesInfo())
    {
-      // derive field from checksum type
-      std::string checksumField("Checksums-");
-      if (strcmp(*type, "MD5Sum") == 0)
-	 checksumField = "Files"; // historic name for MD5 checksums
-      else
-	 checksumField.append(*type);
-
-      Files = Section->FindS(checksumField.c_str());
-      if (Files.empty() == false)
+      Files = Section->Find(hashinfo.chksumskey).to_string();
+      if (not Files.empty())
 	 break;
    }
-   if (Files.empty() == true)
+   if (Files.empty())
       return false;
 
-   // Stash the / terminated directory prefix
-   string Base = Section->FindS("Directory");
-   if (Base.empty() == false && Base[Base.length()-1] != '/')
-      Base += '/';
-   
    // Read the first file triplet
    const char *C = Files.c_str();
    string sSize;
@@ -472,7 +460,8 @@ bool SourceCopy::GetFile(string &File,unsigned long long &Size)
    
    // Parse the size and append the directory
    Size = strtoull(sSize.c_str(), NULL, 10);
-   File = Base + File;
+   auto const Base = Section->Find(pkgTagSection::Key::Directory);
+   File = flCombine(Base.to_string(), File);
    return true;
 }
 									/*}}}*/
diff --git a/apt-pkg/policy.cc b/apt-pkg/policy.cc
index c5328c517..b30eddb37 100644
--- a/apt-pkg/policy.cc
+++ b/apt-pkg/policy.cc
@@ -21,7 +21,9 @@
 #include <apt-pkg/fileutl.h>
 #include <apt-pkg/pkgcache.h>
 #include <apt-pkg/policy.h>
+#include <apt-pkg/string_view.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 #include <apt-pkg/version.h>
 #include <apt-pkg/versionmatch.h>
@@ -425,12 +427,12 @@ bool ReadPinFile(pkgPolicy &Plcy,string File)
       if (Tags.Count() == 0)
          continue;
 
-      string Name = Tags.FindS("Package");
-      if (Name.empty() == true)
+      auto Name = Tags.Find(pkgTagSection::Key::Package);
+      if (Name.empty())
 	 return _error->Error(_("Invalid record in the preferences file %s, no Package header"), File.c_str());
       if (Name == "*")
-	 Name = string();
-      
+	 Name = APT::StringView{};
+
       const char *Start;
       const char *End;
       if (Tags.Find("Pin",Start,End) == false)
@@ -479,7 +481,7 @@ bool ReadPinFile(pkgPolicy &Plcy,string File)
          return _error->Error(_("No priority (or zero) specified for pin"));
       }
 
-      istringstream s(Name);
+      std::istringstream s(Name.to_string());
       string pkg;
       while(!s.eof())
       {
diff --git a/apt-pkg/tagfile-keys.list b/apt-pkg/tagfile-keys.list
index 36da3435e..4b57e46c2 100644
--- a/apt-pkg/tagfile-keys.list
+++ b/apt-pkg/tagfile-keys.list
@@ -1,7 +1,16 @@
+# This file is input for triehash(1) (after stripping comments)
+#
+# The fields listed here are accessible via pkgTagSection::Key::FIELD
+# Do *NOT* edit, remove or insert new fields in the sorted section here
+# as the file forms part of the ABI of the libapt library and is used
+# by our apt tools. External clients are forbidden though, so if really needed
+# we can use libapt Breaks: apt, but always prefer appending only.
+#
+# For Fields used in Packages, Sources and status files, see also tagfile-order.c
 Architecture
+Auto-Built-Package
 Binary
 Breaks
-Bugs
 Build-Conflicts
 Build-Conflicts-Arch
 Build-Conflicts-Indep
@@ -15,7 +24,6 @@ Checksums-Md5
 Checksums-Sha1
 Checksums-Sha256
 Checksums-Sha512
-Class
 Conffiles
 Config-Version
 Conflicts
@@ -23,7 +31,6 @@ Depends
 Description
 Description-md5
 Directory
-Dm-Upload-Allowed
 Enhances
 Essential
 Filename
@@ -32,29 +39,21 @@ Format
 Homepage
 Important
 Installed-Size
-Installer-Menu-Item
-Kernel-Version
 Maintainer
 MD5sum
-MSDOS-Filename
 Multi-Arch
-Optional
 Origin
 Original-Maintainer
 Package
 Package-List
-Package_Revision
-Package-Revision
 Package-Type
 Phased-Update-Percentage
 Pre-Depends
 Priority
 Protected
 Provides
-Recommended
 Recommends
 Replaces
-Revision
 Section
 SHA1
 SHA256
@@ -64,17 +63,13 @@ Source
 Standards-Version
 Static-Built-Using
 Status
-Subarchitecture
 Suggests
 Tag
 Task
 Testsuite
 Testsuite-Triggers
-Triggers-Awaited
-Triggers-Pending
 Uploaders
 Vcs-Arch
-Vcs-Browse
 Vcs-Browser
 Vcs-Bzr
 Vcs-Cvs
@@ -84,3 +79,4 @@ Vcs-Hg
 Vcs-Mtn
 Vcs-Svn
 Version
+### APPEND BELOW, sort in with next ABI break ###
diff --git a/apt-pkg/tagfile-order.c b/apt-pkg/tagfile-order.c
index 79d6992b4..7cf188c51 100644
--- a/apt-pkg/tagfile-order.c
+++ b/apt-pkg/tagfile-order.c
@@ -9,12 +9,12 @@ static const char *iTFRewritePackageOrder[] = {
    "Package",
    "Package-Type",
    "Architecture",
-   "Subarchitecture", // Used only by d-i
+   "Subarchitecture", // NO_KEY: Used only by d-i
    "Version",
-   "Revision",	       // Obsolete (warning in dpkg)
-   "Package-Revision", // Obsolete (warning in dpkg)
-   "Package_Revision", // Obsolete (warning in dpkg)
-   "Kernel-Version",   // Used only by d-i
+// "Revision",         // Obsolete (warning in dpkg)
+// "Package-Revision", // Obsolete (warning in dpkg)
+// "Package_Revision", // Obsolete (warning in dpkg)
+   "Kernel-Version",   // NO_KEY: Used only by d-i
    "Built-Using",
    "Static-Built-Using",
    "Built-For-Profiles",
@@ -22,35 +22,37 @@ static const char *iTFRewritePackageOrder[] = {
    "Multi-Arch",
    "Status",
    "Priority",
-   "Class", // dpkg nickname for Priority
+// "Class", // Obsolete alias for Priority, warning by dpkg
    "Build-Essential",
    "Protected",
+   "Important", // old name of Protected
    "Essential",
-   "Installer-Menu-Item", // Used only by d-i
+   "Installer-Menu-Item", // NO_KEY: Used only by d-i
    "Section",
    "Source",
    "Origin",
+   "Phased-Update-Percentage",
    "Maintainer",
    "Original-Maintainer", // unknown in dpkg order
-   "Bugs",
+   "Bugs", // NO_KEY: very uncommon encounter
    "Config-Version", // Internal of dpkg
    "Conffiles",
-   "Triggers-Awaited",
-   "Triggers-Pending",
+   "Triggers-Awaited", // NO_KEY: Internal of dpkg
+   "Triggers-Pending", // NO_KEY: Internal of dpkg
    "Installed-Size",
    "Provides",
    "Pre-Depends",
    "Depends",
    "Recommends",
-   "Recommended", // dpkg nickname for Recommends
+// "Recommended", // Obsolete alias for Recommends, warning by dpkg
    "Suggests",
-   "Optional", // dpkg nickname for Suggests
+// "Optional", // Obsolete alias for Suggests, warning by dpkg
    "Conflicts",
    "Breaks",
    "Replaces",
    "Enhances",
    "Filename",
-   "MSDOS-Filename", // Obsolete (used by dselect)
+   "MSDOS-Filename", // NO_KEY: Obsolete (used by dselect)
    "Size",
    "MD5sum",
    "SHA1",
@@ -58,6 +60,7 @@ static const char *iTFRewritePackageOrder[] = {
    "SHA512",
    "Homepage",
    "Description",
+   "Description-md5",
    "Tag",
    "Task",
    0,
@@ -70,13 +73,13 @@ static const char *iTFRewriteSourceOrder[] = {
    "Architecture",
    "Version",
    "Priority",
-   "Class", // dpkg nickname for Priority
+// "Class", // Obsolete alias for Priority, warning by dpkg
    "Section",
    "Origin",
    "Maintainer",
    "Original-Maintainer", // unknown in dpkg order
    "Uploaders",
-   "Dm-Upload-Allowed", // Obsolete (ignored by dak)
+   "Dm-Upload-Allowed", // NO_KEY: Obsolete (ignored by dak)
    "Standards-Version",
    "Build-Depends",
    "Build-Depends-Arch",
@@ -89,7 +92,7 @@ static const char *iTFRewriteSourceOrder[] = {
    "Homepage",
    "Description",
    "Vcs-Browser",
-   "Vcs-Browse", // dak only (nickname?)
+   "Vcs-Browse", // NO_KEY: dak only (nickname?)
    "Vcs-Arch",
    "Vcs-Bzr",
    "Vcs-Cvs",
diff --git a/apt-pkg/tagfile.cc b/apt-pkg/tagfile.cc
index 52000c6b9..047f88986 100644
--- a/apt-pkg/tagfile.cc
+++ b/apt-pkg/tagfile.cc
@@ -626,6 +626,11 @@ bool pkgTagSection::Exists(StringView Tag) const
    unsigned int tmp;
    return Find(Tag, tmp);
 }
+bool pkgTagSection::Exists(Key key) const
+{
+   unsigned int tmp;
+   return Find(key, tmp);
+}
 									/*}}}*/
 // TagSection::Find - Locate a tag					/*{{{*/
 // ---------------------------------------------------------------------
@@ -1051,8 +1056,8 @@ bool pkgTagSection::Write(FileFd &File, char const * const * const Order, std::v
    {
       if (R->Action == Tag::REMOVE)
 	 continue;
-      std::string const name = ((R->Action == Tag::RENAME) ? R->Data : R->Name);
-      if (Exists(name.c_str()))
+      auto const name = ((R->Action == Tag::RENAME) ? R->Data : R->Name);
+      if (Exists(name))
 	 continue;
       if (Order != NULL)
       {
diff --git a/apt-pkg/tagfile.h b/apt-pkg/tagfile.h
index f6bdd12c9..54562d07c 100644
--- a/apt-pkg/tagfile.h
+++ b/apt-pkg/tagfile.h
@@ -70,18 +70,21 @@ class APT_PUBLIC pkgTagSection
    std::string FindS(APT::StringView sv) const { return Find(sv).to_string(); }
    std::string FindRawS(APT::StringView sv) const { return FindRaw(sv).to_string(); };
 
+#ifdef APT_COMPILING_APT
    // Functions for lookup with a perfect hash function
    enum class Key;
-   APT_HIDDEN bool Find(Key key,const char *&Start, const char *&End) const;
-   APT_HIDDEN bool Find(Key key,unsigned int &Pos) const;
-   APT_HIDDEN signed int FindI(Key key,signed long Default = 0) const;
-   APT_HIDDEN bool FindB(Key key, bool Default = false) const;
-   APT_HIDDEN unsigned long long FindULL(Key key, unsigned long long const &Default = 0) const;
-   APT_HIDDEN bool FindFlag(Key key,uint8_t &Flags, uint8_t const Flag) const;
-   APT_HIDDEN bool FindFlag(Key key,unsigned long &Flags, unsigned long Flag) const;
-   APT_HIDDEN bool Exists(Key key) const;
-   APT_HIDDEN APT::StringView Find(Key key) const;
-   APT_HIDDEN APT::StringView FindRaw(Key key) const;
+   bool Find(Key key,const char *&Start, const char *&End) const;
+   bool Find(Key key,unsigned int &Pos) const;
+   signed int FindI(Key key,signed long Default = 0) const;
+   bool FindB(Key key, bool Default = false) const;
+   unsigned long long FindULL(Key key, unsigned long long const &Default = 0) const;
+   bool FindFlag(Key key,uint8_t &Flags, uint8_t const Flag) const;
+   bool FindFlag(Key key,unsigned long &Flags, unsigned long Flag) const;
+   bool Exists(Key key) const;
+   APT::StringView Find(Key key) const;
+   APT::StringView FindRaw(Key key) const;
+#endif
+
    bool Find(APT::StringView Tag,const char *&Start, const char *&End) const;
    bool Find(APT::StringView Tag,unsigned int &Pos) const;
    APT::StringView Find(APT::StringView Tag) const;
diff --git a/apt-private/private-show.cc b/apt-private/private-show.cc
index b56b87d67..08a4fe6df 100644
--- a/apt-private/private-show.cc
+++ b/apt-private/private-show.cc
@@ -17,6 +17,7 @@
 #include <apt-pkg/policy.h>
 #include <apt-pkg/sourcelist.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 
 #include <apt-private/private-cacheset.h>
@@ -233,13 +234,15 @@ static bool DisplayRecordV2(pkgCacheFile &CacheFile, pkgRecords &Recs, /*{{{*/
 
    // make size nice
    std::string installed_size;
-   if (Tags.FindULL("Installed-Size") > 0)
-      strprintf(installed_size, "%sB", SizeToStr(Tags.FindULL("Installed-Size") * 1024).c_str());
+   auto const installed_size_field = Tags.FindULL(pkgTagSection::Key::Installed_Size);
+   if (installed_size_field > 0)
+      installed_size = SizeToStr(installed_size_field * 1024).append("B");
    else
       installed_size = _("unknown");
    std::string package_size;
-   if (Tags.FindULL("Size") > 0)
-      strprintf(package_size, "%sB", SizeToStr(Tags.FindULL("Size")).c_str());
+   auto const package_size_field = Tags.FindULL(pkgTagSection::Key::Size);
+   if (package_size_field > 0)
+      package_size = SizeToStr(package_size_field).append("B");
    else
       package_size = _("unknown");
 
@@ -257,10 +260,8 @@ static bool DisplayRecordV2(pkgCacheFile &CacheFile, pkgRecords &Recs, /*{{{*/
    // delete, apt-cache show has this info and most users do not care
    if (not _config->FindB("APT::Cache::ShowFull", false))
    {
-      RW.push_back(pkgTagSection::Tag::Remove("MD5sum"));
-      RW.push_back(pkgTagSection::Tag::Remove("SHA1"));
-      RW.push_back(pkgTagSection::Tag::Remove("SHA256"));
-      RW.push_back(pkgTagSection::Tag::Remove("SHA512"));
+      for (char const * const * type = HashString::SupportedHashes(); *type != nullptr; ++type)
+	 RW.push_back(pkgTagSection::Tag::Remove(*type));
       RW.push_back(pkgTagSection::Tag::Remove("Filename"));
       RW.push_back(pkgTagSection::Tag::Remove("Multi-Arch"));
       RW.push_back(pkgTagSection::Tag::Remove("Conffiles"));
diff --git a/cmdline/apt-extracttemplates.cc b/cmdline/apt-extracttemplates.cc
index 01b5dbb11..88a204110 100644
--- a/cmdline/apt-extracttemplates.cc
+++ b/cmdline/apt-extracttemplates.cc
@@ -28,6 +28,7 @@
 #include <apt-pkg/pkgsystem.h>
 #include <apt-pkg/sourcelist.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 #include <apt-pkg/version.h>
 
@@ -170,11 +171,11 @@ bool DebFile::ParseInfo()
 	if (Section.Scan(Control, ControlLen) == false)
 		return false;
 
-	Package = Section.FindS("Package");
+	Package = Section.Find(pkgTagSection::Key::Package).to_string();
 	Version = GetInstalledVer(Package);
 
 	const char *Start, *Stop;
-	if (Section.Find("Depends", Start, Stop) == true)
+	if (Section.Find(pkgTagSection::Key::Depends, Start, Stop))
 	{
 		while (1)
 		{
@@ -191,8 +192,8 @@ bool DebFile::ParseInfo()
 			if (Start == Stop) break;
 		}
 	}
-	
-	if (Section.Find("Pre-Depends", Start, Stop) == true)
+
+	if (Section.Find(pkgTagSection::Key::Pre_Depends, Start, Stop))
 	{
 		while (1)
 		{
diff --git a/cmdline/apt-sortpkgs.cc b/cmdline/apt-sortpkgs.cc
index da451708f..519825457 100644
--- a/cmdline/apt-sortpkgs.cc
+++ b/cmdline/apt-sortpkgs.cc
@@ -20,6 +20,7 @@
 #include <apt-pkg/init.h>
 #include <apt-pkg/pkgsystem.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 
 #include <apt-private/private-cmndline.h>
@@ -85,9 +86,9 @@ static bool DoIt(string InFile)
       
       /* Fetch the name, auto-detecting if this is a source file or a 
          package file */
-      Tmp.Name = Section.FindS("Package");
-      Tmp.Ver = Section.FindS("Version");
-      Tmp.Arch = Section.FindS("Architecture");
+      Tmp.Name = Section.Find(pkgTagSection::Key::Package).to_string();
+      Tmp.Ver = Section.Find(pkgTagSection::Key::Version).to_string();
+      Tmp.Arch = Section.Find(pkgTagSection::Key::Architecture).to_string();
       
       if (Tmp.Name.empty() == true)
 	 return _error->Error(_("Unknown package record!"));
diff --git a/ftparchive/writer.cc b/ftparchive/writer.cc
index 5dcb98c9c..ae427b120 100644
--- a/ftparchive/writer.cc
+++ b/ftparchive/writer.cc
@@ -21,6 +21,7 @@
 #include <apt-pkg/hashes.h>
 #include <apt-pkg/pkgcache.h>
 #include <apt-pkg/strutl.h>
+#include <apt-pkg/tagfile-keys.h>
 #include <apt-pkg/tagfile.h>
 
 #include <algorithm>
@@ -421,7 +422,7 @@ bool PackagesWriter::DoPackage(string FileName)
    
    // Lookup the override information
    pkgTagSection &Tags = Db.Control.Section;
-   string Package = Tags.FindS("Package");
+   auto const Package = Tags.Find(pkgTagSection::Key::Package).to_string();
    string Architecture;
    // if we generate a Packages file for a given arch, we use it to
    // look for overrides. if we run in "simple" mode without the 
@@ -430,9 +431,9 @@ bool PackagesWriter::DoPackage(string FileName)
    if(Arch != "")
       Architecture = Arch;
    else
-      Architecture = Tags.FindS("Architecture");
-   unique_ptr<Override::Item> OverItem(Over.GetItem(Package,Architecture));
-   
+      Architecture = Tags.Find(pkgTagSection::Key::Architecture).to_string();
+   unique_ptr<Override::Item> OverItem(Over.GetItem(Package, Architecture));
+
    if (Package.empty() == true)
       return _error->Error(_("Archive had no package field"));
 
@@ -444,10 +445,10 @@ bool PackagesWriter::DoPackage(string FileName)
 	 NewLine(1);
 	 ioprintf(c1out, _("  %s has no override entry\n"), Package.c_str());
       }
-      
+
       OverItem = unique_ptr<Override::Item>(new Override::Item);
-      OverItem->FieldOverride["Section"] = Tags.FindS("Section");
-      OverItem->Priority = Tags.FindS("Priority");
+      OverItem->FieldOverride["Section"] = Tags.Find(pkgTagSection::Key::Section).to_string();
+      OverItem->Priority = Tags.Find(pkgTagSection::Key::Priority).to_string();
    }
 
    // Strip the DirStrip prefix from the FileName and add the PathPrefix
@@ -466,7 +467,7 @@ bool PackagesWriter::DoPackage(string FileName)
       in the package file - instead we want to ship a separated file */
    string desc;
    if (LongDescription == false) {
-      desc = Tags.FindS("Description").append("\n");
+      desc = Tags.Find(pkgTagSection::Key::Description).to_string().append("\n");
       OverItem->FieldOverride["Description"] = desc.substr(0, desc.find('\n')).c_str();
    }
 
@@ -486,7 +487,6 @@ bool PackagesWriter::DoPackage(string FileName)
    Changes.push_back(pkgTagSection::Tag::Rewrite("Filename", NewFileName));
    Changes.push_back(pkgTagSection::Tag::Rewrite("Priority", OverItem->Priority));
    Changes.push_back(pkgTagSection::Tag::Remove("Status"));
-   Changes.push_back(pkgTagSection::Tag::Remove("Optional"));
 
    string DescriptionMd5;
    if (LongDescription == false) {
@@ -500,33 +500,20 @@ bool PackagesWriter::DoPackage(string FileName)
 
    // Rewrite the maintainer field if necessary
    bool MaintFailed;
-   string NewMaint = OverItem->SwapMaint(Tags.FindS("Maintainer"),MaintFailed);
+   string NewMaint = OverItem->SwapMaint(Tags.Find(pkgTagSection::Key::Maintainer).to_string(), MaintFailed);
    if (MaintFailed == true)
    {
       if (NoOverride == false)
       {
 	 NewLine(1);
 	 ioprintf(c1out, _("  %s maintainer is %s not %s\n"),
-	       Package.c_str(), Tags.FindS("Maintainer").c_str(), OverItem->OldMaint.c_str());
+	       Package.c_str(), Tags.Find(pkgTagSection::Key::Maintainer).to_string().c_str(), OverItem->OldMaint.c_str());
       }
    }
 
    if (NewMaint.empty() == false)
       Changes.push_back(pkgTagSection::Tag::Rewrite("Maintainer", NewMaint));
 
-   /* Get rid of the Optional tag. This is an ugly, ugly, ugly hack that
-      dpkg-scanpackages does. Well sort of. dpkg-scanpackages just does renaming
-      but dpkg does this append bit. So we do the append bit, at least that way the
-      status file and package file will remain similar. There are other transforms
-      but optional is the only legacy one still in use for some lazy reason. */
-   string OptionalStr = Tags.FindS("Optional");
-   if (OptionalStr.empty() == false)
-   {
-      if (Tags.FindS("Suggests").empty() == false)
-	 OptionalStr = Tags.FindS("Suggests") + ", " + OptionalStr;
-      Changes.push_back(pkgTagSection::Tag::Rewrite("Suggests", OptionalStr));
-   }
-
    for (map<string,string>::const_iterator I = OverItem->FieldOverride.begin();
         I != OverItem->FieldOverride.end(); ++I)
       Changes.push_back(pkgTagSection::Tag::Rewrite(I->first, I->second));
@@ -628,14 +615,14 @@ SourcesWriter::SourcesWriter(FileFd * const GivenOutput, string const &DB, strin
 									/*}}}*/
 // SourcesWriter::DoPackage - Process a single package			/*{{{*/
 static std::string getDscHash(unsigned int const DoHashes,
-      Hashes::SupportedHashes const DoIt, pkgTagSection &Tags, char const * const FieldName,
+      Hashes::SupportedHashes const DoIt, pkgTagSection &Tags, pkgTagSection::Key const FieldKey,
       HashString const * const Hash, unsigned long long Size, std::string const &FileName)
 {
-   if ((DoHashes & DoIt) != DoIt || Tags.Exists(FieldName) == false || Hash == NULL)
+   if ((DoHashes & DoIt) != DoIt || not Tags.Exists(FieldKey) || Hash == nullptr)
       return "";
    std::ostringstream out;
    out << "\n " << Hash->HashValue() << " " << std::to_string(Size) << " " << FileName
-      << "\n " << Tags.FindS(FieldName);
+      << "\n " << Tags.Find(FieldKey).to_string();
    return out.str();
 }
 bool SourcesWriter::DoPackage(string FileName)
@@ -660,19 +647,20 @@ bool SourcesWriter::DoPackage(string FileName)
    if (Tags.Scan(Db.Dsc.Data.c_str(), Db.Dsc.Data.length()) == false)
       return _error->Error("Could not find a record in the DSC '%s'",FileName.c_str());
 
-   if (Tags.Exists("Source") == false)
+   if (not Tags.Exists(pkgTagSection::Key::Source))
       return _error->Error("Could not find a Source entry in the DSC '%s'",FileName.c_str());
    Tags.Trim();
 
    // Lookup the override information, finding first the best priority.
    string BestPrio;
-   string Bins = Tags.FindS("Binary");
+   auto const Bins = Tags.Find(pkgTagSection::Key::Binary);
    char Buffer[Bins.length() + 1];
    unique_ptr<Override::Item> OverItem(nullptr);
    if (Bins.empty() == false)
    {
-      strcpy(Buffer,Bins.c_str());
-      
+      strncpy(Buffer, Bins.data(), Bins.length());
+      Buffer[Bins.length()] = '\0';
+
       // Ignore too-long errors.
       char *BinList[400];
       TokSplitString(',',Buffer,BinList,sizeof(BinList)/sizeof(BinList[0]));
@@ -702,8 +690,8 @@ bool SourcesWriter::DoPackage(string FileName)
    {
       if (NoOverride == false)
       {
-	 NewLine(1);	 
-	 ioprintf(c1out, _("  %s has no override entry\n"), Tags.FindS("Source").c_str());
+	 NewLine(1);
+	 ioprintf(c1out, _("  %s has no override entry\n"), Tags.Find(pkgTagSection::Key::Source).to_string().c_str());
       }
       
       OverItem.reset(new Override::Item);
@@ -713,15 +701,16 @@ bool SourcesWriter::DoPackage(string FileName)
    if (stat(FileName.c_str(), &St) != 0)
       return _error->Errno("fstat","Failed to stat %s",FileName.c_str());
 
-   unique_ptr<Override::Item> SOverItem(SOver.GetItem(Tags.FindS("Source")));
+   auto const Package = Tags.Find(pkgTagSection::Key::Source).to_string();
+   unique_ptr<Override::Item> SOverItem(SOver.GetItem(Package));
    // const unique_ptr<Override::Item> autoSOverItem(SOverItem);
    if (SOverItem.get() == 0)
    {
-      ioprintf(c1out, _("  %s has no source override entry\n"), Tags.FindS("Source").c_str());
-      SOverItem = unique_ptr<Override::Item>(BOver.GetItem(Tags.FindS("Source")));
+      ioprintf(c1out, _("  %s has no source override entry\n"), Package.c_str());
+      SOverItem = unique_ptr<Override::Item>(BOver.GetItem(Package));
       if (SOverItem.get() == 0)
       {
-        ioprintf(c1out, _("  %s has no binary override entry either\n"), Tags.FindS("Source").c_str());
+        ioprintf(c1out, _("  %s has no binary override entry either\n"), Package.c_str());
 	 SOverItem = unique_ptr<Override::Item>(new Override::Item);
 	 *SOverItem = *OverItem;
       }
@@ -729,10 +718,10 @@ bool SourcesWriter::DoPackage(string FileName)
 
    // Add the dsc to the files hash list
    string const strippedName = flNotDir(FileName);
-   std::string const Files = getDscHash(DoHashes, Hashes::MD5SUM, Tags, "Files", Db.HashesList.find("MD5Sum"), St.st_size, strippedName);
-   std::string ChecksumsSha1 = getDscHash(DoHashes, Hashes::SHA1SUM, Tags, "Checksums-Sha1", Db.HashesList.find("SHA1"), St.st_size, strippedName);
-   std::string ChecksumsSha256 = getDscHash(DoHashes, Hashes::SHA256SUM, Tags, "Checksums-Sha256", Db.HashesList.find("SHA256"), St.st_size, strippedName);
-   std::string ChecksumsSha512 = getDscHash(DoHashes, Hashes::SHA512SUM, Tags, "Checksums-Sha512", Db.HashesList.find("SHA512"), St.st_size, strippedName);
+   std::string const Files = getDscHash(DoHashes, Hashes::MD5SUM, Tags, pkgTagSection::Key::Files, Db.HashesList.find("MD5Sum"), St.st_size, strippedName);
+   std::string ChecksumsSha1 = getDscHash(DoHashes, Hashes::SHA1SUM, Tags, pkgTagSection::Key::Checksums_Sha1, Db.HashesList.find("SHA1"), St.st_size, strippedName);
+   std::string ChecksumsSha256 = getDscHash(DoHashes, Hashes::SHA256SUM, Tags, pkgTagSection::Key::Checksums_Sha256, Db.HashesList.find("SHA256"), St.st_size, strippedName);
+   std::string ChecksumsSha512 = getDscHash(DoHashes, Hashes::SHA512SUM, Tags, pkgTagSection::Key::Checksums_Sha512, Db.HashesList.find("SHA512"), St.st_size, strippedName);
 
    // Strip the DirStrip prefix from the FileName and add the PathPrefix
    string NewFileName;
@@ -746,7 +735,6 @@ bool SourcesWriter::DoPackage(string FileName)
       NewFileName = flCombine(PathPrefix,NewFileName);
 
    string Directory = flNotFile(OriginalPath);
-   string Package = Tags.FindS("Source");
 
    // Perform operation over all of the files
    string ParseJnk;
@@ -764,9 +752,9 @@ bool SourcesWriter::DoPackage(string FileName)
       string OriginalPath = Directory + ParseJnk;
 
       // Add missing hashes to source files
-      if (((DoHashes & Hashes::SHA1SUM) == Hashes::SHA1SUM && !Tags.Exists("Checksums-Sha1")) ||
-          ((DoHashes & Hashes::SHA256SUM) == Hashes::SHA256SUM && !Tags.Exists("Checksums-Sha256")) ||
-          ((DoHashes & Hashes::SHA512SUM) == Hashes::SHA512SUM && !Tags.Exists("Checksums-Sha512")))
+      if (((DoHashes & Hashes::SHA1SUM) == Hashes::SHA1SUM && not Tags.Exists(pkgTagSection::Key::Checksums_Sha1)) ||
+          ((DoHashes & Hashes::SHA256SUM) == Hashes::SHA256SUM && not Tags.Exists(pkgTagSection::Key::Checksums_Sha256)) ||
+          ((DoHashes & Hashes::SHA512SUM) == Hashes::SHA512SUM && not Tags.Exists(pkgTagSection::Key::Checksums_Sha512)))
       {
          if (Db.GetFileInfo(OriginalPath,
                             false, /* DoControl */
@@ -783,21 +771,21 @@ bool SourcesWriter::DoPackage(string FileName)
 	 {
 	    if (hs->HashType() == "MD5Sum" || hs->HashType() == "Checksum-FileSize")
 	       continue;
-	    char const * fieldname;
+	    pkgTagSection::Key fieldkey;
 	    std::string * out;
 	    if (hs->HashType() == "SHA1")
 	    {
-	       fieldname = "Checksums-Sha1";
+	       fieldkey = pkgTagSection::Key::Checksums_Sha1;
 	       out = &ChecksumsSha1;
 	    }
 	    else if (hs->HashType() == "SHA256")
 	    {
-	       fieldname = "Checksums-Sha256";
+	       fieldkey = pkgTagSection::Key::Checksums_Sha256;
 	       out = &ChecksumsSha256;
 	    }
 	    else if (hs->HashType() == "SHA512")
 	    {
-	       fieldname = "Checksums-Sha512";
+	       fieldkey = pkgTagSection::Key::Checksums_Sha512;
 	       out = &ChecksumsSha512;
 	    }
 	    else
@@ -805,7 +793,7 @@ bool SourcesWriter::DoPackage(string FileName)
 	       _error->Warning("Ignoring unknown Checksumtype %s in SourcesWriter::DoPackages", hs->HashType().c_str());
 	       continue;
 	    }
-	    if (Tags.Exists(fieldname) == true)
+	    if (Tags.Exists(fieldkey))
 	       continue;
 	    std::ostringstream streamout;
 	    streamout << "\n " << hs->HashValue() << " " << std::to_string(Db.GetFileSize()) << " " << ParseJnk;
@@ -862,14 +850,14 @@ bool SourcesWriter::DoPackage(string FileName)
 
    // Rewrite the maintainer field if necessary
    bool MaintFailed;
-   string NewMaint = OverItem->SwapMaint(Tags.FindS("Maintainer"), MaintFailed);
+   string NewMaint = OverItem->SwapMaint(Tags.Find(pkgTagSection::Key::Maintainer).to_string(), MaintFailed);
    if (MaintFailed == true)
    {
       if (NoOverride == false)
       {
 	 NewLine(1);
 	 ioprintf(c1out, _("  %s maintainer is %s not %s\n"), Package.c_str(),
-	       Tags.FindS("Maintainer").c_str(), OverItem->OldMaint.c_str());
+	       Tags.Find(pkgTagSection::Key::Maintainer).to_string().c_str(), OverItem->OldMaint.c_str());
       }
    }
    if (NewMaint.empty() == false)
@@ -921,7 +909,7 @@ bool ContentsWriter::DoPackage(string FileName, string Package)
    // Parse the package name
    if (Package.empty() == true)
    {
-      Package = Db.Control.Section.FindS("Package");
+      Package = Db.Control.Section.Find(pkgTagSection::Key::Package).to_string();
    }
 
    Db.Contents.Add(Gen,Package);
@@ -951,17 +939,9 @@ bool ContentsWriter::ReadFromPkgs(string const &PkgFile,string const &PkgCompres
    pkgTagSection Section;
    while (Tags.Step(Section) == true)
    {
-      string File = flCombine(Prefix,Section.FindS("FileName"));
-      string Package = Section.FindS("Section");
-      if (Package.empty() == false && Package.end()[-1] != '/')
-      {
-	 Package += '/';
-	 Package += Section.FindS("Package");
-      }
-      else
-	 Package += Section.FindS("Package");
-	 
-      DoPackage(File,Package);
+      auto File = flCombine(Prefix, Section.Find(pkgTagSection::Key::Filename).to_string());
+      auto Package = flCombine(Section.Find(pkgTagSection::Key::Section).to_string(), Section.Find(pkgTagSection::Key::Package).to_string());
+      DoPackage(std::move(File), std::move(Package));
       if (_error->empty() == false)
       {
 	 _error->Error("Errors apply to file '%s'",File.c_str());
diff --git a/test/integration/test-apt-tagfile-fields-order b/test/integration/test-apt-tagfile-fields-order
index 4af58aabb..aa817147d 100755
--- a/test/integration/test-apt-tagfile-fields-order
+++ b/test/integration/test-apt-tagfile-fields-order
@@ -5,13 +5,19 @@ TESTDIR="$(readlink -f "$(dirname "$0")")"
 . "$TESTDIR/framework"
 setupenvironment
 
+DPKG_PERL_VERSION="$(perl -e 'use Dpkg; print "$Dpkg::PROGVERSION";')"
+DPKG_OUTPUT_SORT='sort -u'
+if dpkg --compare-versions "$DPKG_PERL_VERSION" '>=' '1.21.4~'; then
+	DPKG_OUTPUT_SORT='sort'
+fi
+
 dpkg_field_ordered_list() {
 	local FIELDS="$(perl -e "
 use Dpkg::Control;
 use Dpkg::Control::Fields;
 foreach \$f (field_ordered_list(${1})) {
 	print \"\$f\\n\";
-}" | sort -u)"
+}" | $DPKG_OUTPUT_SORT )"
 	if [ -z "$FIELDS" ]; then
 		msgfail 'Could not get fields via libdpkg-perl'
 	fi
@@ -29,9 +35,40 @@ comparelsts() {
 	fi
 }
 
+grep -v '^#' "${SOURCEDIRECTORY}/apt-pkg/tagfile-keys.list" > tagfile-keys.list
+# Hardcoding this is a bit silly, but it might help preventing issues…
+msgtest 'File is append only: do not sort, remove or insert keys in' 'tagfile-keys.list'
+testequal --nomsg 'Version' sed '72q;d' tagfile-keys.list
+
+msgtest 'List has fewer entries than pkgTagSection buckets' 'tagfile-keys.list'
+ENTRIES_LIST="$(wc -l tagfile-keys.list | cut -d' ' -f 1)"
+ENTRIES_BUCKET="$(grep -m 1 'AlphaIndexes\[' "${SOURCEDIRECTORY}/apt-pkg/tagfile.h" | sed -e 's#.*\[\([0-9]\+\)\].*#\1#')"
+if test $ENTRIES_LIST -lt $ENTRIES_BUCKET; then
+	msgpass
+else
+	echo
+	echo "List has $ENTRIES_LIST entries, but pkgTagSection can only store $ENTRIES_BUCKET as AlphaIndexes"
+	msgfail
+fi
+
+msgtest 'Check for duplicates in' 'tagfile-keys.list'
+sort tagfile-keys.list > apt.lst
+testempty --nomsg uniq --repeated 'apt.lst'
+
+msgtest 'Check that apt knows all fields it orders' 'itself'
+grep -v "// NO_KEY: " "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sed -ne 's#^   "\(.*\)",.*$#\1#p' | sort -u > dpkg.lst
+comparelsts
+
+msgtest 'Check tagfile-keys.list does not contain' 'obsoleted and internal fields'
+grep "// NO_KEY: " "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sed -ne 's#^   "\(.*\)",.*$#\1#p' > obsolete.lst
+sed -n -e's#^ *// *"\(.*\)",.*$#\1#p' "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" >> obsolete.lst
+sort -u obsolete.lst > obsolete-sorted.lst
+sort obsolete-sorted.lst tagfile-keys.list > obsolete-keys.lst
+testempty --nomsg uniq --repeat 'obsolete-keys.lst'
+
 msgtest 'Check that apt knows all fields dpkg orders in' 'Packages'
 dpkg_field_ordered_list 'CTRL_INDEX_PKG' > dpkg.lst
-sed -ne 's#^   "\(.*\)",.*$#\1#p' "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sed -n '/^Package$/,/^Package$/ p' | head -n -1 | sort -u > apt.lst
+sed -ne 's#^   "\(.*\)",.*$#\1#p' "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sed -n '/^Package$/,/^Package$/ p' | head -n -1 | sort > apt.lst
 comparelsts
 
 msgtest 'Check that apt knows all fields dpkg orders in' 'status'
@@ -53,30 +90,31 @@ msgtest 'Check that apt knows all fields dpkg orders in' 'dsc'
 dpkg_field_ordered_list 'CTRL_PKG_SRC' > dpkg.lst
 comparelsts
 
-# HACK, but there is no good way to acquire sources in tests and/or to remember to run this regular manually
-if [ "$USER" = 'david' ]; then
-	msgtest 'Check if we have somewhere the sources of' 'dpkg'
-	DPKGSOURCE="$(locate dpkg/lib/dpkg/parse.c  | head -n 1 || true)"
-	if [ -z "$DPKGSOURCE" ]; then
-		msgskip 'Not found'
-	else
-		msgpass
-		msgtest 'Check that apt knows about all fields' 'dpkg parses'
-		sed -n 's#^.*FIELD("\(.*\)").*$#\1#p' "${DPKGSOURCE}" | sort -u > dpkg.lst
-		sed -ne 's#^   "\(.*\)",.*$#\1#p' "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sed -n '/^Package$/,/^Package$/ p' | head -n -1 | sort -u > apt.lst
-		comparelsts
-	fi
+DPKG_SOURCE_PARSE_C="${DPKG_SOURCE_DIRECTORY}/lib/dpkg/parse.c"
+msgtest 'Compare our knowledge with the source code of' 'dpkg'
+if [ -z "$DPKG_SOURCE_DIRECTORY" ]; then
+	msgskip 'source not provided'
+elif [ ! -r "$DPKG_SOURCE_PARSE_C" ]; then
+	msgfail 'source not found'
+else
+	msgpass
+	msgtest 'Check that apt knows about all fields' 'dpkg parses'
+	sed -n 's#^.*FIELD("\(.*\)").*$#\1#p' "${DPKG_SOURCE_PARSE_C}" | sort -u > dpkg.lst
+	sed -n -e's#^ *// *"#   "#' -e 's#^   "\(.*\)",.*$#\1#p' "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sed -n '/^Package$/,/^Package$/ p' | head -n -1 | sort > apt.lst
+	comparelsts
+fi
 
-	msgtest 'Check if we have somewhere the sources of' 'dak'
-	DAKSOURCE="$(locate dak/setup/core-init.d/080_metadatakeys | head -n 1 || true)"
-	if [ -z "$DAKSOURCE" ]; then
-		msgskip 'Not found'
-	else
-		msgpass
-		msgtest 'Check that apt knows about all fields' 'dak knows'
-		# dak mixes both, so we can only check with the mixed one as well
-		sed -ne "s#^.* VALUES ('\(.*\)', \(.*\)).*\$#\1 \2#p" "${DAKSOURCE}" | cut -d ' ' -f 1 | sort -u > dpkg.lst
-		sed -ne 's#^   "\(.*\)",.*$#\1#p' "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sort -u > apt.lst
-		comparelsts
-	fi
+DAK_SOURCE_METADATAKEYS="${DAK_SOURCE_DIRECTORY}/setup/core-init.d/080_metadatakeys"
+msgtest 'Compare our knowledge with the source code of' 'dak'
+if [ -z "$DAK_SOURCE_DIRECTORY" ]; then
+	msgskip 'source not provided'
+elif [ ! -r "$DAK_SOURCE_METADATAKEYS" ]; then
+	msgfail 'source not found'
+else
+	msgpass
+	msgtest 'Check that apt knows about all fields' 'dak knows'
+	# dak mixes both, so we can only check with the mixed one as well
+	sed -ne "s#^.* VALUES ('\(.*\)', \(.*\)).*\$#\1 \2#p" "${DAK_SOURCE_METADATAKEYS}" | cut -d ' ' -f 1 | sort -u > dpkg.lst
+	sed -ne 's#^   "\(.*\)",.*$#\1#p' "${SOURCEDIRECTORY}/apt-pkg/tagfile-order.c" | sort -u > apt.lst
+	comparelsts
 fi
diff --git a/test/integration/test-ubuntu-bug-1098738-apt-get-source-md5sum b/test/integration/test-ubuntu-bug-1098738-apt-get-source-md5sum
index f0a8835a2..6a66094de 100755
--- a/test/integration/test-ubuntu-bug-1098738-apt-get-source-md5sum
+++ b/test/integration/test-ubuntu-bug-1098738-apt-get-source-md5sum
@@ -441,4 +441,4 @@ testnohash pkg-md5-agree
 testfailureequal 'Reading package lists...
 E: Error parsing checksum in Files of source package pkg-md5-disagree' aptget source -d pkg-md5-disagree
 testfailureequal 'Reading package lists...
-E: Error parsing checksum in Checksums-SHA256 of source package pkg-sha256-disagree' aptget source -d pkg-sha256-disagree
+E: Error parsing checksum in Checksums-Sha256 of source package pkg-sha256-disagree' aptget source -d pkg-sha256-disagree