Allocate header table ringbuffer lazily

Previously in inflater we reserve new ringbuffer when table size is
changed.  This may be potentially a problem if new table size is very
large number.  When inflater is not used directly by application, this
is not a problem because application can choose the buffer size.  On
the other hand, if application uses inflater directly and it does not
have control of new buffer size (e.g., protocol dissector), then we
just fail to allocate large buffer in
nghttp2_hd_inflate_change_table_size() without actually use such huge
buffer.  This change defers the actual allocation of buffer when it is
actually needed so that we will fail when it is absolutely needed.

lib/nghttp2_hd.c

@@ -273,12 +273,20 @@ static void hd_ringbuf_free(nghttp2_hd_ringbuf *ringbuf)
   free(ringbuf->buffer);
 }
 
-static size_t hd_ringbuf_push_front(nghttp2_hd_ringbuf *ringbuf,
+static int hd_ringbuf_push_front(nghttp2_hd_ringbuf *ringbuf,
-                                    nghttp2_hd_entry *ent)
+                                 nghttp2_hd_entry *ent)
 {
-  assert(ringbuf->len <= ringbuf->mask);
+  int rv;
+
+  rv = hd_ringbuf_reserve(ringbuf, ringbuf->len + 1);
+
+  if(rv != 0) {
+    return rv;
+  }
+
   ringbuf->buffer[--ringbuf->first & ringbuf->mask] = ent;
   ++ringbuf->len;
+
   return 0;
 }
 
@@ -852,8 +860,17 @@ static nghttp2_hd_entry* add_hd_table_incremental(nghttp2_hd_context *context,
        immediately evicted. */
     --new_ent->ref;
   } else {
+    rv = hd_ringbuf_push_front(&context->hd_table, new_ent);
+
+    if(rv != 0) {
+      --new_ent->ref;
+      nghttp2_hd_entry_free(new_ent);
+      free(new_ent);
+
+      return NULL;
+    }
+
     context->hd_table_bufsize += room;
-    hd_ringbuf_push_front(&context->hd_table, new_ent);
 
     new_ent->flags |= NGHTTP2_HD_FLAG_REFSET;
   }
@@ -950,14 +967,8 @@ static void hd_context_shrink_table_size(nghttp2_hd_context *context)
 int nghttp2_hd_deflate_change_table_size(nghttp2_hd_deflater *deflater,
                                          size_t settings_hd_table_bufsize_max)
 {
-  int rv;
   size_t next_bufsize = nghttp2_min(settings_hd_table_bufsize_max,
                                     deflater->deflate_hd_table_bufsize_max);
-  rv = hd_ringbuf_reserve
-    (&deflater->ctx.hd_table, next_bufsize / NGHTTP2_HD_ENTRY_OVERHEAD);
-  if(rv != 0) {
-    return rv;
-  }
 
   deflater->ctx.hd_table_bufsize_max = next_bufsize;
 
@@ -970,14 +981,6 @@ int nghttp2_hd_deflate_change_table_size(nghttp2_hd_deflater *deflater,
 int nghttp2_hd_inflate_change_table_size(nghttp2_hd_inflater *inflater,
                                          size_t settings_hd_table_bufsize_max)
 {
-  int rv;
-
-  rv = hd_ringbuf_reserve
-    (&inflater->ctx.hd_table,
-     settings_hd_table_bufsize_max / NGHTTP2_HD_ENTRY_OVERHEAD);
-  if(rv != 0) {
-    return rv;
-  }
   inflater->settings_hd_table_bufsize_max = settings_hd_table_bufsize_max;
   inflater->ctx.hd_table_bufsize_max = settings_hd_table_bufsize_max;
   hd_context_shrink_table_size(&inflater->ctx);

tests/main.c

@@ -273,6 +273,8 @@ int main(int argc, char* argv[])
                    test_nghttp2_hd_inflate_clearall_inc) ||
       !CU_add_test(pSuite, "hd_inflate_zero_length_huffman",
                    test_nghttp2_hd_inflate_zero_length_huffman) ||
+      !CU_add_test(pSuite, "hd_ringbuf_reserve",
+                   test_nghttp2_hd_ringbuf_reserve) ||
       !CU_add_test(pSuite, "hd_change_table_size",
                    test_nghttp2_hd_change_table_size) ||
       !CU_add_test(pSuite, "hd_deflate_inflate",

tests/nghttp2_hd_test.c

@@ -641,6 +641,57 @@ void test_nghttp2_hd_inflate_zero_length_huffman(void)
   nghttp2_hd_inflate_free(&inflater);
 }
 
+void test_nghttp2_hd_ringbuf_reserve(void)
+{
+  nghttp2_hd_deflater deflater;
+  nghttp2_hd_inflater inflater;
+  nghttp2_nv nv;
+  nghttp2_bufs bufs;
+  nva_out out;
+  int i;
+  ssize_t rv;
+  ssize_t blocklen;
+
+  frame_pack_bufs_init(&bufs);
+  nva_out_init(&out);
+
+  nv.flags = NGHTTP2_NV_FLAG_NONE;
+  nv.name = (uint8_t*)"a";
+  nv.namelen = strlen((const char*)nv.name);
+  nv.valuelen = 4;
+  nv.value = malloc(nv.valuelen);
+  memset(nv.value, 0, nv.valuelen);
+
+  nghttp2_hd_deflate_init2(&deflater, 8000);
+  nghttp2_hd_inflate_init(&inflater);
+
+  nghttp2_hd_inflate_change_table_size(&inflater, 8000);
+  nghttp2_hd_deflate_change_table_size(&deflater, 8000);
+
+  for(i = 0; i < 150; ++i) {
+    memcpy(nv.value, &i, sizeof(i));
+    rv = nghttp2_hd_deflate_hd_bufs(&deflater, &bufs, &nv, 1);
+    blocklen = nghttp2_bufs_len(&bufs);
+
+    CU_ASSERT(0 == rv);
+    CU_ASSERT(blocklen > 0);
+
+    CU_ASSERT(blocklen == inflate_hd(&inflater, &out, &bufs, 0));
+
+    CU_ASSERT(1 == out.nvlen);
+    assert_nv_equal(&nv, out.nva, 1);
+
+    nva_out_reset(&out);
+    nghttp2_bufs_reset(&bufs);
+  }
+
+  nghttp2_bufs_free(&bufs);
+  nghttp2_hd_inflate_free(&inflater);
+  nghttp2_hd_deflate_free(&deflater);
+
+  free(nv.value);
+}
+
 void test_nghttp2_hd_change_table_size(void)
 {
   nghttp2_hd_deflater deflater;
@@ -663,10 +714,8 @@ void test_nghttp2_hd_change_table_size(void)
   CU_ASSERT(0 == nghttp2_hd_inflate_change_table_size(&inflater, 8000));
   CU_ASSERT(0 == nghttp2_hd_deflate_change_table_size(&deflater, 8000));
 
-  CU_ASSERT(127 == deflater.ctx.hd_table.mask);
   CU_ASSERT(4096 == deflater.ctx.hd_table_bufsize_max);
 
-  CU_ASSERT(255 == inflater.ctx.hd_table.mask);
   CU_ASSERT(8000 == inflater.ctx.hd_table_bufsize_max);
   CU_ASSERT(8000 == inflater.settings_hd_table_bufsize_max);
 
@@ -691,10 +740,8 @@ void test_nghttp2_hd_change_table_size(void)
   CU_ASSERT(0 == nghttp2_hd_inflate_change_table_size(&inflater, 1024));
   CU_ASSERT(0 == nghttp2_hd_deflate_change_table_size(&deflater, 1024));
 
-  CU_ASSERT(127 == deflater.ctx.hd_table.mask);
   CU_ASSERT(1024 == deflater.ctx.hd_table_bufsize_max);
 
-  CU_ASSERT(255 == inflater.ctx.hd_table.mask);
   CU_ASSERT(1024 == inflater.ctx.hd_table_bufsize_max);
   CU_ASSERT(1024 == inflater.settings_hd_table_bufsize_max);
 
@@ -718,11 +765,9 @@ void test_nghttp2_hd_change_table_size(void)
   CU_ASSERT(0 == nghttp2_hd_inflate_change_table_size(&inflater, 0));
   CU_ASSERT(0 == nghttp2_hd_deflate_change_table_size(&deflater, 0));
 
-  CU_ASSERT(127 == deflater.ctx.hd_table.mask);
   CU_ASSERT(0 == deflater.ctx.hd_table.len);
   CU_ASSERT(0 == deflater.ctx.hd_table_bufsize_max);
 
-  CU_ASSERT(255 == inflater.ctx.hd_table.mask);
   CU_ASSERT(0 == inflater.ctx.hd_table.len);
   CU_ASSERT(0 == inflater.ctx.hd_table_bufsize_max);
   CU_ASSERT(0 == inflater.settings_hd_table_bufsize_max);
@@ -757,10 +802,8 @@ void test_nghttp2_hd_change_table_size(void)
   CU_ASSERT(0 == nghttp2_hd_inflate_change_table_size(&inflater, 8000));
   CU_ASSERT(0 == nghttp2_hd_deflate_change_table_size(&deflater, 8000));
 
-  CU_ASSERT(255 == deflater.ctx.hd_table.mask);
   CU_ASSERT(8000 == deflater.ctx.hd_table_bufsize_max);
 
-  CU_ASSERT(255 == inflater.ctx.hd_table.mask);
   CU_ASSERT(8000 == inflater.ctx.hd_table_bufsize_max);
   CU_ASSERT(8000 == inflater.settings_hd_table_bufsize_max);
 
@@ -783,10 +826,8 @@ void test_nghttp2_hd_change_table_size(void)
   CU_ASSERT(0 == nghttp2_hd_inflate_change_table_size(&inflater, 16383));
   CU_ASSERT(0 == nghttp2_hd_deflate_change_table_size(&deflater, 16383));
 
-  CU_ASSERT(255 == deflater.ctx.hd_table.mask);
   CU_ASSERT(8192 == deflater.ctx.hd_table_bufsize_max);
 
-  CU_ASSERT(511 == inflater.ctx.hd_table.mask);
   CU_ASSERT(16383 == inflater.ctx.hd_table_bufsize_max);
   CU_ASSERT(16383 == inflater.settings_hd_table_bufsize_max);
 
@@ -823,7 +864,6 @@ void test_nghttp2_hd_change_table_size(void)
   nghttp2_hd_deflate_init2(&deflater, 1024);
   nghttp2_hd_inflate_init(&inflater);
 
-  CU_ASSERT(127 == deflater.ctx.hd_table.mask);
   CU_ASSERT(1024 == deflater.ctx.hd_table_bufsize_max);
 
   /* This emits context update with buffer size 1024 */

tests/nghttp2_hd_test.h

@@ -37,6 +37,7 @@ void test_nghttp2_hd_inflate_newname_noinc(void);
 void test_nghttp2_hd_inflate_newname_inc(void);
 void test_nghttp2_hd_inflate_clearall_inc(void);
 void test_nghttp2_hd_inflate_zero_length_huffman(void);
+void test_nghttp2_hd_ringbuf_reserve(void);
 void test_nghttp2_hd_change_table_size(void);
 void test_nghttp2_hd_deflate_inflate(void);
 void test_nghttp2_hd_no_index(void);