cuke: make File.tail utility more robust

features/support/exceptions.rb

@@ -18,8 +18,15 @@ class OSRMError < StandardError
   private
 
   def log_tail path, n
-    File.open(path) do |f|
-      return f.tail(n).map { |line| "  > #{line}" }.join "\n"
+    Dir.chdir TEST_FOLDER do
+      expanded = File.expand_path path
+      if File.exists? expanded
+        File.open(expanded) do |f|
+          return f.tail(n).map { |line| "    #{line}" }.join "\n"
+        end
+      else
+        return "File '#{expanded} does not exist!"
+      end
     end
   end
 end

features/support/file.rb

@@ -1,24 +1,34 @@
 class File
 
-  #read last n lines of a file. useful for getting last part of a big log file.
+  # read last n lines of a file (trailing newlines are ignored)
   def tail(n)
+    return [] if size==0
     buffer = 1024
-    idx = (size - buffer).abs
-    chunks = []
-    lines = 0
+    str = nil
 
-    begin
-      seek(idx)
-      chunk = read(buffer)
-      lines += chunk.count("\n")
-      chunks.unshift chunk
-      idx -= buffer
-    end while lines < ( n + 1 ) && pos != 0
+    if size>buffer
+      chunks = []
+      lines = 0
+      idx = size
+      begin
+        idx -= buffer     # rewind
+        if idx<0
+          buffer += idx   # adjust last read to avoid negative index
+          idx = 0
+        end
+        seek(idx)
+        chunk = read(buffer)
+        chunk.gsub!(/\n+\Z/,"") if chunks.empty? # strip newlines from end of file (first chunk)
+        lines += chunk.count("\n")  # update total lines found
+        chunks.unshift chunk        # prepend
+      end while lines<(n) && idx>0  # stop when enough lines found or no more to read
+      str = chunks.join('')
+    else
+      str = read(buffer)
+    end
 
-    tail_of_file = chunks.join('')
-    ary = tail_of_file.split(/\n/)
-    lines_to_return = ary[ ary.size - n, ary.size - 1 ]
-  rescue
-    ["Cannot read log file!"]
+    # return last n lines of str
+    lines = str.split("\n")
+    lines.size>=n ? lines[-n,n] : lines
   end
 end