Sanitize FileEntries iterator behaviour

Only fetch data from iterator when using operator *, or when operator++
if we have not already fetched.

dead.cc

@@ -193,7 +193,6 @@ CoreProcess::getPID() const
 FileEntries::iterator::iterator(const FileEntries &entries, ReaderArray<FileEntry>::iterator pos)
         : entries(entries)
         , entriesIterator(pos) {
-    fetch();
 }
 
 struct NamedEntry {
@@ -205,14 +204,17 @@ struct NamedEntry {
 
 void
 FileEntries::iterator::fetch() {
-   if (entries.names)
+   if (!fetched && entries.names) {
        cur = std::make_pair(entries.names->readString(nameoff), *entriesIterator);
+       fetched = true;
+   }
 }
 
 FileEntries::iterator &FileEntries::iterator::operator++() {
+    fetch();
     ++entriesIterator;
     nameoff += cur.first.size() + 1;
-    fetch();
+    fetched = false;
     return *this;
 }
 

libpstack/proc.h

@@ -435,15 +435,17 @@ class FileEntries {
 
 public:
     class iterator {
+        friend class FileEntries;
         const FileEntries &entries;
         void fetch();
+        bool fetched = false;
         size_t nameoff = 0;
         std::pair<std::string, FileEntry> cur;
         ReaderArray<FileEntry>::iterator entriesIterator;
    public:
         iterator(const FileEntries &entries, ReaderArray<FileEntry>::iterator start);
         iterator &operator++();
-        std::pair<std::string, FileEntry> operator *() { return cur; }
+        std::pair<std::string, FileEntry> operator *() { fetch(); return cur; }
         bool operator != (const iterator &rhs) const { return entriesIterator != rhs.entriesIterator; }
     };
     FileEntries(const Elf::Object &obj) {
@@ -461,8 +463,12 @@ class FileEntries {
            entries = std::make_shared<NullReader>();
         entriesArray = std::make_unique<ReaderArray<FileEntry>>(*entries);
     }
-    iterator begin() const { return iterator(*this, entriesArray->begin()); }
-    iterator end() const { return iterator(*this, entriesArray->end()); }
+    iterator begin() const {
+       return iterator(*this, entriesArray->begin());
+    }
+    iterator end() const {
+       return iterator(*this, entriesArray->end());
+    }
 };