nghttp2_hd: Avoid nghttp2_hd_huff_decode_count

Huffman decoding is costly. It is faster to do geometric realloc
than calling nghttp2_hd_huff_decode_count to know the length in
advance.

lib/nghttp2_hd.c

@@ -1237,26 +1237,6 @@ static int inflater_post_process_hd_entry(nghttp2_hd_context *inflater,
   return 0;
 }
 
-static ssize_t inflate_decode(uint8_t **dest_ptr, uint8_t *in, size_t inlen,
-                              nghttp2_hd_side side)
-{
-  ssize_t declen;
-  if(inlen == 0) {
-    *dest_ptr = NULL;
-    return 0;
-  }
-  declen = nghttp2_hd_huff_decode_count(in, inlen, side);
-  if(declen == -1) {
-    return NGHTTP2_ERR_HEADER_COMP;
-  }
-  *dest_ptr = malloc(declen);
-  if(*dest_ptr == NULL) {
-    return NGHTTP2_ERR_HEADER_COMP;
-  }
-  nghttp2_hd_huff_decode(*dest_ptr, declen, in, inlen, side);
-  return declen;
-}
-
 ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
                               nghttp2_nv **nva_ptr,
                               uint8_t *in, size_t inlen)
@@ -1341,7 +1321,7 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
         goto fail;
       }
       if(name_huffman) {
-        rv = inflate_decode(&nv.name, in, namelen, inflater->side);
+        rv = nghttp2_hd_huff_decode(&nv.name, in, namelen, inflater->side);
         if(rv < 0) {
           DEBUGF(fprintf(stderr, "Name huffman decoding failed\n"));
           goto fail;
@@ -1369,7 +1349,7 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
         goto fail;
       }
       if(value_huffman) {
-        rv = inflate_decode(&nv.value, in, valuelen, inflater->side);
+        rv = nghttp2_hd_huff_decode(&nv.value, in, valuelen, inflater->side);
         if(rv < 0) {
           DEBUGF(fprintf(stderr, "Value huffman decoding failed\n"));
           free(decoded_huffman_name);
@@ -1453,7 +1433,7 @@ ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_context *inflater,
         goto fail;
       }
       if(value_huffman) {
-        rv = inflate_decode(&value, in, valuelen, inflater->side);
+        rv = nghttp2_hd_huff_decode(&value, in, valuelen, inflater->side);
         if(rv < 0) {
           DEBUGF(fprintf(stderr, "Value huffman decoding failed\n"));
           goto fail;

lib/nghttp2_hd.h

@@ -381,12 +381,11 @@ ssize_t nghttp2_hd_huff_decode_count(const uint8_t *src, size_t srclen,
                                      nghttp2_hd_side side);
 
 /*
- * Decodes the given data |src| with length |srclen| to the given
- * memory location pointed by |dest|, allocated at lest |destlen|
- * bytes. The given input must be padded with the prefix of terminal
- * code. The caller is responsible to specify |destlen| at least the
- * length that nghttp2_hd_huff_decode_count() returns.  If |side| is
- * NGHTTP2_HD_SIDE_REQUEST, the request huffman code table is
+ * Decodes the given data |src| with length |srclen|. This function
+ * allocates memory to store the result and assigns the its pointer to
+ * |*dest_ptr| on success. The caller is responsible to release the
+ * memory pointed by |*dest_ptr| if this function succeeds. If |side|
+ * is NGHTTP2_HD_SIDE_REQUEST, the request huffman code table is
  * used. Otherwise, the response code table is used.
  *
  * This function returns the number of written bytes.  This return
@@ -394,9 +393,15 @@ ssize_t nghttp2_hd_huff_decode_count(const uint8_t *src, size_t srclen,
  * nghttp2_hd_huff_decode_count() if it is given with the same |src|,
  * |srclen|, and |side|.
  *
- * This function returns -1 if it fails.
+ * If this function fails, it returns one of the following negative
+ * return codes:
+ *
+ * NGHTTP2_ERR_NOMEM
+ *     Out of memory.
+ * NGHTTP2_ERR_HEADER_COMP
+ *     Decoding process has failed.
  */
-ssize_t nghttp2_hd_huff_decode(uint8_t *dest, size_t destlen,
+ssize_t nghttp2_hd_huff_decode(uint8_t **dest_ptr,
                                const uint8_t *src, size_t srclen,
                                nghttp2_hd_side side);
 

lib/nghttp2_hd_huffman.c

@@ -213,7 +213,7 @@ ssize_t nghttp2_hd_huff_decode_count(const uint8_t *src, size_t srclen,
   return j;
 }
 
-ssize_t nghttp2_hd_huff_decode(uint8_t *dest, size_t destlen,
+ssize_t nghttp2_hd_huff_decode(uint8_t **dest_ptr,
                                const uint8_t *src, size_t srclen,
                                nghttp2_hd_side side)
 {
@@ -221,6 +221,9 @@ ssize_t nghttp2_hd_huff_decode(uint8_t *dest, size_t destlen,
   size_t i, j;
   const nghttp2_huff_sym *huff_sym_table;
   const huff_decode_table_type *huff_decode_table;
+  uint8_t *dest = NULL;
+  size_t destlen = 0;
+  int rv;
 
   if(side == NGHTTP2_HD_SIDE_REQUEST) {
     huff_sym_table = req_huff_sym_table;
@@ -231,23 +234,39 @@ ssize_t nghttp2_hd_huff_decode(uint8_t *dest, size_t destlen,
   }
   j = 0;
   for(i = 0; i < srclen;) {
-    int rv = huff_decode(src + i, srclen - i, bitoff,
-                         huff_sym_table, huff_decode_table);
+    rv = huff_decode(src + i, srclen - i, bitoff,
+                     huff_sym_table, huff_decode_table);
     if(rv == -1) {
       if(check_last_byte(src, srclen, i, bitoff)) {
         break;
       }
-      return -1;
+      rv = NGHTTP2_ERR_HEADER_COMP;
+      goto fail;
     }
     if(rv == 256) {
       /* 256 is special terminal symbol and it should not encoded in
          byte string. */
-      return -1;
+      rv = NGHTTP2_ERR_HEADER_COMP;
+      goto fail;
+    }
+    if(j == destlen) {
+      size_t new_len = j == 0 ? 32 : j * 2;
+      uint8_t *new_dest = realloc(dest, new_len);
+      if(new_dest == NULL) {
+        rv = NGHTTP2_ERR_NOMEM;
+        goto fail;
+      }
+      dest = new_dest;
+      destlen = new_len;
     }
     dest[j++] = rv;
     bitoff += huff_sym_table[rv].nbits;
     i += bitoff / 8;
     bitoff &= 0x7;
   }
+  *dest_ptr = dest;
   return j;
+ fail:
+  free(dest);
+  return rv;
 }