Deal with descriptions embedded in displayed record correctly

The implementation of "apt-cache show" (not "apt show") incorrectly
resets the currently used parser if the record itself and the
description to show come from the same file (as it is the case if no
Translation-* files are available e.g. after debootstrap).

The code is more complex than you would hope to support some rather
unusual setups involving Descriptions and their translations as tested
for by ./test-bug-712435-missing-descriptions as otherwise this could
be a one-line change.

Regression-Of: bf53f39c9a0221b670ffff74053ed36fc502d5a0
Closes: #909155

1 files changed, 58 insertions, 11 deletions

diff --git a/apt-private/private-show.cc b/apt-private/private-show.cc
index 15c05d420..b69008ec9 100644
--- a/apt-private/private-show.cc
+++ b/apt-private/private-show.cc
@@ -42,7 +42,7 @@ pkgRecords::Parser &LookupParser(pkgRecords &Recs, pkgCache::VerIterator const &
    return Recs.Lookup(Vf);
 }
 									/*}}}*/
-static APT_PURE char const *skipDescriptionFields(char const *DescP, size_t const Length) /*{{{*/
+static APT_PURE char const *skipDescription(char const *DescP, size_t const Length, bool fields) /*{{{*/
 {
    auto const backup = DescP;
    char const * const TagName = "\nDescription";
@@ -51,7 +51,7 @@ static APT_PURE char const *skipDescriptionFields(char const *DescP, size_t cons
    {
       if (DescP[1] == ' ')
 	 DescP += 2;
-      else if (strncmp((char*)DescP, TagName, TagLen) == 0)
+      else if (fields && strncmp((char *)DescP, TagName, TagLen) == 0)
 	 DescP += TagLen;
       else
 	 break;
@@ -78,19 +78,43 @@ static APT_PURE char const *findDescriptionField(char const *DescP, size_t const
    return DescP;
 }
 									/*}}}*/
+static APT_PURE char const *skipColonSpaces(char const *Buffer, size_t const Length) /*{{{*/
+{
+   // skipping withspace before and after the field-value separating colon
+   char const *const Start = Buffer;
+   for (; isspace(*Buffer) != 0 && Length - (Buffer - Start) > 0; ++Buffer)
+      ;
+   if (*Buffer != ':')
+      return nullptr;
+   ++Buffer;
+   for (; isspace(*Buffer) != 0 && Length - (Buffer - Start) > 0; ++Buffer)
+      ;
+   if (Length - (Buffer - Start) <= 0)
+      return nullptr;
+   return Buffer;
+}
+									/*}}}*/
 
 bool DisplayRecordV1(pkgCacheFile &, pkgRecords &Recs, /*{{{*/
-		     pkgCache::VerIterator const &V, pkgCache::VerFileIterator const &,
+		     pkgCache::VerIterator const &V, pkgCache::VerFileIterator const &Vf,
 		     char const *Buffer, size_t Length, std::ostream &out)
 {
-   if (unlikely(Length == 0))
+   if (unlikely(Length < 4))
       return false;
 
    auto const Desc = V.TranslatedDescription();
    if (Desc.end())
    {
-      // we have no translation output whatever we have got
-      return FileFd::Write(STDOUT_FILENO, Buffer, Length);
+      /* This handles the unusual case that we have no description whatsoever.
+	 The slightly more common case of only having a short-description embedded
+	 in the record could be handled here, but apt supports also having multiple
+	 descriptions embedded in the record, so we deal with that case later */
+      if (FileFd::Write(STDOUT_FILENO, Buffer, Length) == false)
+	 return false;
+      if (strncmp((Buffer + Length - 4), "\r\n\r\n", 4) != 0 &&
+	  strncmp((Buffer + Length - 2), "\n\n", 2) != 0)
+	 out << std::endl;
+      return true;
    }
 
    // Get a pointer to start of Description field
@@ -111,18 +135,41 @@ bool DisplayRecordV1(pkgCacheFile &, pkgRecords &Recs, /*{{{*/
    else
       snprintf(desctag, sizeof(desctag), "\nDescription-%s", langcode);
 
-   out << desctag + 1 << ": ";
+   out << desctag + 1 << ": " << std::flush;
    auto const Df = Desc.FileList();
    if (Df.end() == false)
    {
-      pkgRecords::Parser &P = Recs.Lookup(Df);
-      out << P.LongDesc();
+      if (Desc.FileList()->File == Vf->File)
+      {
+	 /* If we have the file already open look in the buffer for the
+	    description we want to display. Note that this might not be the
+	    only one we can encounter in this record */
+	 char const *Start = DescP;
+	 do
+	 {
+	    if (strncmp(Start, desctag + 1, strlen(desctag) - 1) != 0)
+	       continue;
+	    Start += strlen(desctag) - 1;
+	    Start = skipColonSpaces(Start, Length - (Start - Buffer));
+	    if (Start == nullptr)
+	       continue;
+	    char const *End = skipDescription(Start, Length - (Start - Buffer), false);
+	    if (likely(End != nullptr))
+	       FileFd::Write(STDOUT_FILENO, Start, End - (Start + 1));
+	    break;
+	 } while ((Start = findDescriptionField(Start, Length - (Start - Buffer))) != nullptr);
+      }
+      else
+      {
+	 pkgRecords::Parser &P = Recs.Lookup(Df);
+	 out << P.LongDesc();
+      }
    }
 
    out << std::endl << "Description-md5: " << Desc.md5() << std::endl;
 
    // Find the first field after the description (if there is any)
-   DescP = skipDescriptionFields(DescP, Length - (DescP - Buffer));
+   DescP = skipDescription(DescP, Length - (DescP - Buffer), true);
 
    // write the rest of the buffer, but skip mixed in Descriptions* fields
    while (DescP != nullptr)
@@ -150,7 +197,7 @@ bool DisplayRecordV1(pkgCacheFile &, pkgRecords &Recs, /*{{{*/
 	 ++End;
       }
       else
-	 DescP = skipDescriptionFields(End + strlen("Description"), Length - (End - Buffer));
+	 DescP = skipDescription(End + strlen("Description"), Length - (End - Buffer), true);
 
       size_t const length = End - Start;
       if (length != 0 && FileFd::Write(STDOUT_FILENO, Start, length) == false)