Create a dissection mode for the deflate function.

This is to be used by protocol analysers which wants to show as much as
possible of the header even if packets are missing. In this case a dummy
header is inserted ":Failed deflate", "Index not seen before".

lib/includes/nghttp2/nghttp2.h

@@ -398,6 +398,11 @@ typedef enum {
    * receives an other type of frame.
    */
   NGHTTP2_ERR_SETTINGS_EXPECTED = -536,
+  /**
+   * Integer exceeded the maximum value
+   */
+  NGHTTP2_ERR_HEADER_COMP_MAX_LEN_EX = -537,
+
   /**
    * The errors < :enum:`NGHTTP2_ERR_FATAL` mean that the library is
    * under unexpected condition and processing was terminated (e.g.,
@@ -5080,7 +5085,12 @@ typedef enum {
   /**
    * Indicates a header was emitted.
    */
-  NGHTTP2_HD_INFLATE_EMIT = 0x02
+  NGHTTP2_HD_INFLATE_EMIT = 0x02,
+  /**
+   * Input value: Indicates that the inflater is run in decode mode
+   * e.g will not stop on unknown indexes.
+   */
+  NGHTTP2_HD_INFLATE_DECODE = 0x04
 } nghttp2_hd_inflate_flag;
 
 /**
@@ -5179,6 +5189,11 @@ NGHTTP2_EXTERN ssize_t nghttp2_hd_inflate_hd(nghttp2_hd_inflater *inflater,
  * and the function returns.  The caller must not free the members of
  * |nv_out|.
  *
+ * If :|*inflate_flags| is set to enum:`NGHTTP2_HD_INFLATE_DECODE` as
+ * an IN parameter the deflater will act as a decoder and atempt to
+ * decode the header even if unknown indexes occure. This is aimed
+ * at analysers such as Wireshark.
+ *
  * The |nv_out| may include pointers to the memory region in the |in|.
  * The caller must retain the |in| while the |nv_out| is used.
  *

lib/nghttp2_hd.c

@@ -109,6 +109,10 @@ static const nghttp2_hd_static_entry static_table[] = {
     MAKE_STATIC_ENT("www-authenticate", "", 60, 779865858u),
 };
 
+static const nghttp2_hd_static_entry dissect_index_table[] = {
+    MAKE_STATIC_ENT(":Failed deflate", "Index not seen before", "", -1, NGHTTP2_NV_FLAG_NONE),
+};
+
 static int memeq(const void *s1, const void *s2, size_t n) {
   return memcmp(s1, s2, n) == 0;
 }
@@ -1654,8 +1658,9 @@ static ssize_t hd_inflate_read_len(nghttp2_hd_inflater *inflater, int *rfin,
   }
 
   if (out > maxlen) {
-    DEBUGF("inflatehd: integer exceeded the maximum value %zu\n", maxlen);
-    return NGHTTP2_ERR_HEADER_COMP;
+    DEBUGF("inflatehd: integer %zu exceeded the maximum value %zu\n", out, maxlen);
+    inflater->left = out;
+    return NGHTTP2_ERR_HEADER_COMP_MAX_LEN_EX;
   }
 
   inflater->left = out;
@@ -1870,6 +1875,12 @@ ssize_t nghttp2_hd_inflate_hd_nv(nghttp2_hd_inflater *inflater,
   int rfin = 0;
   int busy = 0;
   nghttp2_mem *mem;
+  int dissection = 0;
+
+  if (*inflate_flags == NGHTTP2_HD_INFLATE_DECODE) {
+    dissection = 1;
+    DEBUGF("inflatehd: dissection = 1 inflate flag %d\n", *inflate_flags);
+  }
 
   mem = inflater->ctx.mem;
 
@@ -1963,7 +1974,34 @@ ssize_t nghttp2_hd_inflate_hd_nv(nghttp2_hd_inflater *inflater,
       rv = hd_inflate_read_len(inflater, &rfin, in, last, prefixlen,
                                get_max_index(&inflater->ctx));
       if (rv < 0) {
-        goto fail;
+        if ((dissection == 1) && (rv == NGHTTP2_ERR_HEADER_COMP_MAX_LEN_EX)) {
+          /* We recived an index not seen before, make a dissect header entry */
+          rv = 1;
+          in += rv;
+
+          if (!rfin) {
+            goto almost_ok;
+          }
+
+          if (inflater->left == 0) {
+            rv = NGHTTP2_ERR_HEADER_COMP;
+            goto fail;
+          }
+          const nghttp2_hd_static_entry *ent = &dissect_index_table[0];
+          nghttp2_hd_nv nv = {(nghttp2_rcbuf *)&ent->name,
+                              (nghttp2_rcbuf *)&ent->value, ent->token,
+                              NGHTTP2_NV_FLAG_NONE};
+
+          emit_header(nv_out, &nv);
+          DEBUGF("inflatehd dissect: index=%zu\n", inflater->left);
+          inflater->index = inflater->left;
+          --inflater->index;
+          inflater->state = NGHTTP2_HD_STATE_OPCODE;
+          *inflate_flags |= NGHTTP2_HD_INFLATE_EMIT;
+          return (ssize_t)(in - first);
+        } else {
+          goto fail;
+        }
       }
 
       in += rv;
@@ -2223,7 +2261,7 @@ almost_ok:
   return (ssize_t)(in - first);
 
 fail:
-  DEBUGF("inflatehd: error return %zd\n", rv);
+  DEBUGF("inflatehd: error return %d\n", rv);
 
   inflater->ctx.bad = 1;
   return rv;