[PATCH 1/2] wbuf_lite: prevent clobbering responses

[Eric Wong <e@80x24.org>]

All of our wbuf code assumes we append to existing buffers
(files) since sendfile cannot deal otherwise.  We also
follow this pattern for StringIO to avoid extra data copies.
---
 lib/yahns/wbuf.rb      | 1 +
 lib/yahns/wbuf_lite.rb | 7 ++++---
 2 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/lib/yahns/wbuf.rb b/lib/yahns/wbuf.rb
index 583df10..3abc5f9 100644
--- a/lib/yahns/wbuf.rb
+++ b/lib/yahns/wbuf.rb
@@ -58,6 +58,7 @@ def wbuf_write(c, buf)
     end until @busy
 
     @tmpio ||= Yahns::TmpIO.new(c.class.output_buffer_tmpdir)
+    # n.b.: we rely on O_APPEND in TmpIO, here
     @sf_count += String === buf ? @tmpio.write(buf) : wbuf_writev(buf)
 
     # we spent some time copying to the FS, try to write to
diff --git a/lib/yahns/wbuf_lite.rb b/lib/yahns/wbuf_lite.rb
index 1902ce7..8a93ad1 100644
--- a/lib/yahns/wbuf_lite.rb
+++ b/lib/yahns/wbuf_lite.rb
@@ -33,6 +33,7 @@ def wbuf_write(c, buf)
     end until @busy
 
     @tmpio ||= StringIO.new(''.dup) # relies on encoding: binary above
+    @tmpio.seek(0, 2) # fake O_APPEND behavior
     @sf_count += @tmpio.write(buf)
 
     # we spent some time copying to the FS, try to write to
@@ -45,12 +46,12 @@ def wbuf_write(c, buf)
       @busy = rv
       return rv
     else
-      raise "BUG: #{rv.nil? ? "EOF" : rv.inspect} on tmpio " \
+      raise "BUG: #{rv.nil? ? 'EOF' : rv.inspect} on "
+            "tmpio.size=#{@tmpio.size} " \
             "sf_offset=#@sf_offset sf_count=#@sf_count"
     end while @sf_count > 0
 
-    # we're all caught up, try to prevent dirty data from getting flushed
-    # to disk if we can help it.
+    # we're all caught up, try to save some memory if we can help it.
     wbuf_abort
     @sf_offset = 0
     @busy = false
-- 
EW