diff --git a/deps/nghttp2/lib/includes/nghttp2/nghttp2ver.h b/deps/nghttp2/lib/includes/nghttp2/nghttp2ver.h
index fba310c7888d0c..7f5251a6243e41 100644
--- a/deps/nghttp2/lib/includes/nghttp2/nghttp2ver.h
+++ b/deps/nghttp2/lib/includes/nghttp2/nghttp2ver.h
@@ -29,7 +29,7 @@
  * @macro
  * Version number of the nghttp2 library release
  */
-#define NGHTTP2_VERSION "1.55.1"
+#define NGHTTP2_VERSION "1.56.0"
 
 /**
  * @macro
@@ -37,6 +37,6 @@
  * release. This is a 24 bit number with 8 bits for major number, 8 bits
  * for minor and 8 bits for patch. Version 1.2.3 becomes 0x010203.
  */
-#define NGHTTP2_VERSION_NUM 0x013701
+#define NGHTTP2_VERSION_NUM 0x013800
 
 #endif /* NGHTTP2VER_H */
diff --git a/deps/nghttp2/lib/nghttp2_frame.c b/deps/nghttp2/lib/nghttp2_frame.c
index 35072c15fc18e6..77cb463df5441f 100644
--- a/deps/nghttp2/lib/nghttp2_frame.c
+++ b/deps/nghttp2/lib/nghttp2_frame.c
@@ -418,8 +418,8 @@ void nghttp2_frame_unpack_priority_spec(nghttp2_priority_spec *pri_spec,
   nghttp2_priority_spec_init(pri_spec, dep_stream_id, weight, exclusive);
 }
 
-int nghttp2_frame_unpack_headers_payload(nghttp2_headers *frame,
-                                         const uint8_t *payload) {
+void nghttp2_frame_unpack_headers_payload(nghttp2_headers *frame,
+                                          const uint8_t *payload) {
   if (frame->hd.flags & NGHTTP2_FLAG_PRIORITY) {
     nghttp2_frame_unpack_priority_spec(&frame->pri_spec, payload);
   } else {
@@ -428,11 +428,9 @@ int nghttp2_frame_unpack_headers_payload(nghttp2_headers *frame,
 
   frame->nva = NULL;
   frame->nvlen = 0;
-
-  return 0;
 }
 
-int nghttp2_frame_pack_priority(nghttp2_bufs *bufs, nghttp2_priority *frame) {
+void nghttp2_frame_pack_priority(nghttp2_bufs *bufs, nghttp2_priority *frame) {
   nghttp2_buf *buf;
 
   assert(bufs->head == bufs->cur);
@@ -448,8 +446,6 @@ int nghttp2_frame_pack_priority(nghttp2_bufs *bufs, nghttp2_priority *frame) {
   nghttp2_frame_pack_priority_spec(buf->last, &frame->pri_spec);
 
   buf->last += NGHTTP2_PRIORITY_SPECLEN;
-
-  return 0;
 }
 
 void nghttp2_frame_unpack_priority_payload(nghttp2_priority *frame,
@@ -457,8 +453,8 @@ void nghttp2_frame_unpack_priority_payload(nghttp2_priority *frame,
   nghttp2_frame_unpack_priority_spec(&frame->pri_spec, payload);
 }
 
-int nghttp2_frame_pack_rst_stream(nghttp2_bufs *bufs,
-                                  nghttp2_rst_stream *frame) {
+void nghttp2_frame_pack_rst_stream(nghttp2_bufs *bufs,
+                                   nghttp2_rst_stream *frame) {
   nghttp2_buf *buf;
 
   assert(bufs->head == bufs->cur);
@@ -473,8 +469,6 @@ int nghttp2_frame_pack_rst_stream(nghttp2_bufs *bufs,
 
   nghttp2_put_uint32be(buf->last, frame->error_code);
   buf->last += 4;
-
-  return 0;
 }
 
 void nghttp2_frame_unpack_rst_stream_payload(nghttp2_rst_stream *frame,
@@ -592,16 +586,15 @@ int nghttp2_frame_pack_push_promise(nghttp2_bufs *bufs,
   return frame_pack_headers_shared(bufs, &frame->hd);
 }
 
-int nghttp2_frame_unpack_push_promise_payload(nghttp2_push_promise *frame,
-                                              const uint8_t *payload) {
+void nghttp2_frame_unpack_push_promise_payload(nghttp2_push_promise *frame,
+                                               const uint8_t *payload) {
   frame->promised_stream_id =
       nghttp2_get_uint32(payload) & NGHTTP2_STREAM_ID_MASK;
   frame->nva = NULL;
   frame->nvlen = 0;
-  return 0;
 }
 
-int nghttp2_frame_pack_ping(nghttp2_bufs *bufs, nghttp2_ping *frame) {
+void nghttp2_frame_pack_ping(nghttp2_bufs *bufs, nghttp2_ping *frame) {
   nghttp2_buf *buf;
 
   assert(bufs->head == bufs->cur);
@@ -616,8 +609,6 @@ int nghttp2_frame_pack_ping(nghttp2_bufs *bufs, nghttp2_ping *frame) {
 
   buf->last =
       nghttp2_cpymem(buf->last, frame->opaque_data, sizeof(frame->opaque_data));
-
-  return 0;
 }
 
 void nghttp2_frame_unpack_ping_payload(nghttp2_ping *frame,
@@ -697,8 +688,8 @@ int nghttp2_frame_unpack_goaway_payload2(nghttp2_goaway *frame,
   return 0;
 }
 
-int nghttp2_frame_pack_window_update(nghttp2_bufs *bufs,
-                                     nghttp2_window_update *frame) {
+void nghttp2_frame_pack_window_update(nghttp2_bufs *bufs,
+                                      nghttp2_window_update *frame) {
   nghttp2_buf *buf;
 
   assert(bufs->head == bufs->cur);
@@ -713,8 +704,6 @@ int nghttp2_frame_pack_window_update(nghttp2_bufs *bufs,
 
   nghttp2_put_uint32be(buf->last, (uint32_t)frame->window_size_increment);
   buf->last += 4;
-
-  return 0;
 }
 
 void nghttp2_frame_unpack_window_update_payload(nghttp2_window_update *frame,
@@ -723,7 +712,7 @@ void nghttp2_frame_unpack_window_update_payload(nghttp2_window_update *frame,
       nghttp2_get_uint32(payload) & NGHTTP2_WINDOW_SIZE_INCREMENT_MASK;
 }
 
-int nghttp2_frame_pack_altsvc(nghttp2_bufs *bufs, nghttp2_extension *frame) {
+void nghttp2_frame_pack_altsvc(nghttp2_bufs *bufs, nghttp2_extension *frame) {
   int rv;
   nghttp2_buf *buf;
   nghttp2_ext_altsvc *altsvc;
@@ -752,8 +741,6 @@ int nghttp2_frame_pack_altsvc(nghttp2_bufs *bufs, nghttp2_extension *frame) {
   rv = nghttp2_bufs_add(bufs, altsvc->field_value, altsvc->field_value_len);
 
   assert(rv == 0);
-
-  return 0;
 }
 
 void nghttp2_frame_unpack_altsvc_payload(nghttp2_extension *frame,
@@ -901,8 +888,8 @@ int nghttp2_frame_unpack_origin_payload(nghttp2_extension *frame,
   return 0;
 }
 
-int nghttp2_frame_pack_priority_update(nghttp2_bufs *bufs,
-                                       nghttp2_extension *frame) {
+void nghttp2_frame_pack_priority_update(nghttp2_bufs *bufs,
+                                        nghttp2_extension *frame) {
   int rv;
   nghttp2_buf *buf;
   nghttp2_ext_priority_update *priority_update;
@@ -927,8 +914,6 @@ int nghttp2_frame_pack_priority_update(nghttp2_bufs *bufs,
                         priority_update->field_value_len);
 
   assert(rv == 0);
-
-  return 0;
 }
 
 void nghttp2_frame_unpack_priority_update_payload(nghttp2_extension *frame,
@@ -1186,14 +1171,14 @@ static void frame_set_pad(nghttp2_buf *buf, size_t padlen, int framehd_only) {
   buf->last += trail_padlen;
 }
 
-int nghttp2_frame_add_pad(nghttp2_bufs *bufs, nghttp2_frame_hd *hd,
-                          size_t padlen, int framehd_only) {
+void nghttp2_frame_add_pad(nghttp2_bufs *bufs, nghttp2_frame_hd *hd,
+                           size_t padlen, int framehd_only) {
   nghttp2_buf *buf;
 
   if (padlen == 0) {
     DEBUGF("send: padlen = 0, nothing to do\n");
 
-    return 0;
+    return;
   }
 
   /*
@@ -1226,6 +1211,4 @@ int nghttp2_frame_add_pad(nghttp2_bufs *bufs, nghttp2_frame_hd *hd,
   hd->flags |= NGHTTP2_FLAG_PADDED;
 
   DEBUGF("send: final payloadlen=%zu, padlen=%zu\n", hd->length, padlen);
-
-  return 0;
 }
diff --git a/deps/nghttp2/lib/nghttp2_frame.h b/deps/nghttp2/lib/nghttp2_frame.h
index 5f6152b74587ae..d58668806c432a 100644
--- a/deps/nghttp2/lib/nghttp2_frame.h
+++ b/deps/nghttp2/lib/nghttp2_frame.h
@@ -143,11 +143,9 @@ int nghttp2_frame_pack_headers(nghttp2_bufs *bufs, nghttp2_headers *frame,
  * Unpacks HEADERS frame byte sequence into |frame|.  This function
  * only unapcks bytes that come before name/value header block and
  * after possible Pad Length field.
- *
- * This function always succeeds and returns 0.
  */
-int nghttp2_frame_unpack_headers_payload(nghttp2_headers *frame,
-                                         const uint8_t *payload);
+void nghttp2_frame_unpack_headers_payload(nghttp2_headers *frame,
+                                          const uint8_t *payload);
 
 /*
  * Packs PRIORITY frame |frame| in wire format and store it in
@@ -155,10 +153,8 @@ int nghttp2_frame_unpack_headers_payload(nghttp2_headers *frame,
  *
  * The caller must make sure that nghttp2_bufs_reset(bufs) is called
  * before calling this function.
- *
- * This function always succeeds and returns 0.
  */
-int nghttp2_frame_pack_priority(nghttp2_bufs *bufs, nghttp2_priority *frame);
+void nghttp2_frame_pack_priority(nghttp2_bufs *bufs, nghttp2_priority *frame);
 
 /*
  * Unpacks PRIORITY wire format into |frame|.
@@ -172,11 +168,9 @@ void nghttp2_frame_unpack_priority_payload(nghttp2_priority *frame,
  *
  * The caller must make sure that nghttp2_bufs_reset(bufs) is called
  * before calling this function.
- *
- * This function always succeeds and returns 0.
  */
-int nghttp2_frame_pack_rst_stream(nghttp2_bufs *bufs,
-                                  nghttp2_rst_stream *frame);
+void nghttp2_frame_pack_rst_stream(nghttp2_bufs *bufs,
+                                   nghttp2_rst_stream *frame);
 
 /*
  * Unpacks RST_STREAM frame byte sequence into |frame|.
@@ -265,15 +259,9 @@ int nghttp2_frame_pack_push_promise(nghttp2_bufs *bufs,
  * Unpacks PUSH_PROMISE frame byte sequence into |frame|.  This
  * function only unapcks bytes that come before name/value header
  * block and after possible Pad Length field.
- *
- * This function returns 0 if it succeeds or one of the following
- * negative error codes:
- *
- * NGHTTP2_ERR_PROTO
- *     TODO END_HEADERS flag is not set
  */
-int nghttp2_frame_unpack_push_promise_payload(nghttp2_push_promise *frame,
-                                              const uint8_t *payload);
+void nghttp2_frame_unpack_push_promise_payload(nghttp2_push_promise *frame,
+                                               const uint8_t *payload);
 
 /*
  * Packs PING frame |frame| in wire format and store it in
@@ -281,10 +269,8 @@ int nghttp2_frame_unpack_push_promise_payload(nghttp2_push_promise *frame,
  *
  * The caller must make sure that nghttp2_bufs_reset(bufs) is called
  * before calling this function.
- *
- * This function always succeeds and returns 0.
  */
-int nghttp2_frame_pack_ping(nghttp2_bufs *bufs, nghttp2_ping *frame);
+void nghttp2_frame_pack_ping(nghttp2_bufs *bufs, nghttp2_ping *frame);
 
 /*
  * Unpacks PING wire format into |frame|.
@@ -343,11 +329,9 @@ int nghttp2_frame_unpack_goaway_payload2(nghttp2_goaway *frame,
  *
  * The caller must make sure that nghttp2_bufs_reset(bufs) is called
  * before calling this function.
- *
- * This function always succeeds and returns 0.
  */
-int nghttp2_frame_pack_window_update(nghttp2_bufs *bufs,
-                                     nghttp2_window_update *frame);
+void nghttp2_frame_pack_window_update(nghttp2_bufs *bufs,
+                                      nghttp2_window_update *frame);
 
 /*
  * Unpacks WINDOW_UPDATE frame byte sequence into |frame|.
@@ -361,17 +345,13 @@ void nghttp2_frame_unpack_window_update_payload(nghttp2_window_update *frame,
  *
  * The caller must make sure that nghttp2_bufs_reset(bufs) is called
  * before calling this function.
- *
- * This function always succeeds and returns 0.
  */
-int nghttp2_frame_pack_altsvc(nghttp2_bufs *bufs, nghttp2_extension *ext);
+void nghttp2_frame_pack_altsvc(nghttp2_bufs *bufs, nghttp2_extension *ext);
 
 /*
  * Unpacks ALTSVC wire format into |frame|.  The |payload| of
  * |payloadlen| bytes contains frame payload.  This function assumes
  * that frame->payload points to the nghttp2_ext_altsvc object.
- *
- * This function always succeeds and returns 0.
  */
 void nghttp2_frame_unpack_altsvc_payload(nghttp2_extension *frame,
                                          size_t origin_len, uint8_t *payload,
@@ -431,19 +411,15 @@ int nghttp2_frame_unpack_origin_payload(nghttp2_extension *frame,
  *
  * The caller must make sure that nghttp2_bufs_reset(bufs) is called
  * before calling this function.
- *
- * This function always succeeds and returns 0.
  */
-int nghttp2_frame_pack_priority_update(nghttp2_bufs *bufs,
-                                       nghttp2_extension *ext);
+void nghttp2_frame_pack_priority_update(nghttp2_bufs *bufs,
+                                        nghttp2_extension *ext);
 
 /*
  * Unpacks PRIORITY_UPDATE wire format into |frame|.  The |payload| of
  * |payloadlen| bytes contains frame payload.  This function assumes
  * that frame->payload points to the nghttp2_ext_priority_update
  * object.
- *
- * This function always succeeds and returns 0.
  */
 void nghttp2_frame_unpack_priority_update_payload(nghttp2_extension *frame,
                                                   uint8_t *payload,
@@ -654,16 +630,8 @@ int nghttp2_iv_check(const nghttp2_settings_entry *iv, size_t niv);
  * |padlen| including Pad Length field.  The |hd| is the frame header
  * for the serialized data.  This function fills zeros padding region
  * unless framehd_only is nonzero.
- *
- * This function returns 0 if it succeeds, or one of the following
- * negative error codes:
- *
- * NGHTTP2_ERR_NOMEM
- *     Out of memory.
- * NGHTTP2_ERR_FRAME_SIZE_ERROR
- *     The length of the resulting frame is too large.
  */
-int nghttp2_frame_add_pad(nghttp2_bufs *bufs, nghttp2_frame_hd *hd,
-                          size_t padlen, int framehd_only);
+void nghttp2_frame_add_pad(nghttp2_bufs *bufs, nghttp2_frame_hd *hd,
+                           size_t padlen, int framehd_only);
 
 #endif /* NGHTTP2_FRAME_H */
diff --git a/deps/nghttp2/lib/nghttp2_session.c b/deps/nghttp2/lib/nghttp2_session.c
index 71858a39e07db7..a45cbeef673108 100644
--- a/deps/nghttp2/lib/nghttp2_session.c
+++ b/deps/nghttp2/lib/nghttp2_session.c
@@ -937,8 +937,8 @@ static int session_ob_data_push(nghttp2_session *session,
   return 0;
 }
 
-static int session_ob_data_remove(nghttp2_session *session,
-                                  nghttp2_stream *stream) {
+static void session_ob_data_remove(nghttp2_session *session,
+                                   nghttp2_stream *stream) {
   uint32_t urgency;
 
   assert(stream->flags & NGHTTP2_STREAM_FLAG_NO_RFC7540_PRIORITIES);
@@ -951,8 +951,6 @@ static int session_ob_data_remove(nghttp2_session *session,
   nghttp2_pq_remove(&session->sched[urgency].ob_data, &stream->pq_entry);
 
   stream->queued = 0;
-
-  return 0;
 }
 
 static int session_attach_stream_item(nghttp2_session *session,
@@ -972,38 +970,28 @@ static int session_attach_stream_item(nghttp2_session *session,
   return session_ob_data_push(session, stream);
 }
 
-static int session_detach_stream_item(nghttp2_session *session,
-                                      nghttp2_stream *stream) {
-  int rv;
-
-  rv = nghttp2_stream_detach_item(stream);
-  if (rv != 0) {
-    return rv;
-  }
+static void session_detach_stream_item(nghttp2_session *session,
+                                       nghttp2_stream *stream) {
+  nghttp2_stream_detach_item(stream);
 
   if (!(stream->flags & NGHTTP2_STREAM_FLAG_NO_RFC7540_PRIORITIES) ||
       !stream->queued) {
-    return 0;
+    return;
   }
 
-  return session_ob_data_remove(session, stream);
+  session_ob_data_remove(session, stream);
 }
 
-static int session_defer_stream_item(nghttp2_session *session,
-                                     nghttp2_stream *stream, uint8_t flags) {
-  int rv;
-
-  rv = nghttp2_stream_defer_item(stream, flags);
-  if (rv != 0) {
-    return rv;
-  }
+static void session_defer_stream_item(nghttp2_session *session,
+                                      nghttp2_stream *stream, uint8_t flags) {
+  nghttp2_stream_defer_item(stream, flags);
 
   if (!(stream->flags & NGHTTP2_STREAM_FLAG_NO_RFC7540_PRIORITIES) ||
       !stream->queued) {
-    return 0;
+    return;
   }
 
-  return session_ob_data_remove(session, stream);
+  session_ob_data_remove(session, stream);
 }
 
 static int session_resume_deferred_stream_item(nghttp2_session *session,
@@ -1476,11 +1464,7 @@ int nghttp2_session_close_stream(nghttp2_session *session, int32_t stream_id,
 
     item = stream->item;
 
-    rv = session_detach_stream_item(session, stream);
-
-    if (rv != 0) {
-      return rv;
-    }
+    session_detach_stream_item(session, stream);
 
     /* If item is queued, it will be deleted when it is popped
        (nghttp2_session_prep_frame() will fail).  If session->aob.item
@@ -2221,7 +2205,6 @@ static ssize_t session_call_select_padding(nghttp2_session *session,
    frame->push_promise has also padlen in the same position. */
 static int session_headers_add_pad(nghttp2_session *session,
                                    nghttp2_frame *frame) {
-  int rv;
   ssize_t padded_payloadlen;
   nghttp2_active_outbound_item *aob;
   nghttp2_bufs *framebufs;
@@ -2246,11 +2229,7 @@ static int session_headers_add_pad(nghttp2_session *session,
   DEBUGF("send: padding selected: payloadlen=%zd, padlen=%zu\n",
          padded_payloadlen, padlen);
 
-  rv = nghttp2_frame_add_pad(framebufs, &frame->hd, padlen, 0);
-
-  if (rv != 0) {
-    return rv;
-  }
+  nghttp2_frame_add_pad(framebufs, &frame->hd, padlen, 0);
 
   frame->headers.padlen = padlen;
 
@@ -2333,13 +2312,7 @@ static int session_prep_frame(nghttp2_session *session,
       // Search stream including closed again.
       stream = nghttp2_session_get_stream_raw(session, frame->hd.stream_id);
       if (stream) {
-        int rv2;
-
-        rv2 = session_detach_stream_item(session, stream);
-
-        if (nghttp2_is_fatal(rv2)) {
-          return rv2;
-        }
+        session_detach_stream_item(session, stream);
       }
 
       return rv;
@@ -2354,12 +2327,8 @@ static int session_prep_frame(nghttp2_session *session,
          queue when session->remote_window_size > 0 */
       assert(session->remote_window_size > 0);
 
-      rv = session_defer_stream_item(session, stream,
-                                     NGHTTP2_STREAM_FLAG_DEFERRED_FLOW_CONTROL);
-
-      if (nghttp2_is_fatal(rv)) {
-        return rv;
-      }
+      session_defer_stream_item(session, stream,
+                                NGHTTP2_STREAM_FLAG_DEFERRED_FLOW_CONTROL);
 
       session->aob.item = NULL;
       active_outbound_item_reset(&session->aob, mem);
@@ -2373,23 +2342,15 @@ static int session_prep_frame(nghttp2_session *session,
       return rv;
     }
     if (rv == NGHTTP2_ERR_DEFERRED) {
-      rv = session_defer_stream_item(session, stream,
-                                     NGHTTP2_STREAM_FLAG_DEFERRED_USER);
-
-      if (nghttp2_is_fatal(rv)) {
-        return rv;
-      }
+      session_defer_stream_item(session, stream,
+                                NGHTTP2_STREAM_FLAG_DEFERRED_USER);
 
       session->aob.item = NULL;
       active_outbound_item_reset(&session->aob, mem);
       return NGHTTP2_ERR_DEFERRED;
     }
     if (rv == NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE) {
-      rv = session_detach_stream_item(session, stream);
-
-      if (nghttp2_is_fatal(rv)) {
-        return rv;
-      }
+      session_detach_stream_item(session, stream);
 
       rv = nghttp2_session_add_rst_stream(session, frame->hd.stream_id,
                                           NGHTTP2_INTERNAL_ERROR);
@@ -2399,13 +2360,7 @@ static int session_prep_frame(nghttp2_session *session,
       return NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE;
     }
     if (rv != 0) {
-      int rv2;
-
-      rv2 = session_detach_stream_item(session, stream);
-
-      if (nghttp2_is_fatal(rv2)) {
-        return rv2;
-      }
+      session_detach_stream_item(session, stream);
 
       return rv;
     }
@@ -2907,10 +2862,7 @@ static int session_after_frame_sent1(nghttp2_session *session) {
     }
 
     if (stream && aux_data->eof) {
-      rv = session_detach_stream_item(session, stream);
-      if (nghttp2_is_fatal(rv)) {
-        return rv;
-      }
+      session_detach_stream_item(session, stream);
 
       /* Call on_frame_send_callback after
          nghttp2_stream_detach_item(), so that application can issue
@@ -3143,17 +3095,8 @@ static int session_after_frame_sent1(nghttp2_session *session) {
 /*
  * Called after a frame is sent and session_after_frame_sent1.  This
  * function is responsible to reset session->aob.
- *
- * This function returns 0 if it succeeds, or one of the following
- * negative error codes:
- *
- * NGHTTP2_ERR_NOMEM
- *     Out of memory.
- * NGHTTP2_ERR_CALLBACK_FAILURE
- *     The callback function failed.
  */
-static int session_after_frame_sent2(nghttp2_session *session) {
-  int rv;
+static void session_after_frame_sent2(nghttp2_session *session) {
   nghttp2_active_outbound_item *aob = &session->aob;
   nghttp2_outbound_item *item = aob->item;
   nghttp2_bufs *framebufs = &aob->framebufs;
@@ -3176,13 +3119,13 @@ static int session_after_frame_sent2(nghttp2_session *session) {
         DEBUGF("send: next CONTINUATION frame, %zu bytes\n",
                nghttp2_buf_len(&framebufs->cur->buf));
 
-        return 0;
+        return;
       }
     }
 
     active_outbound_item_reset(&session->aob, mem);
 
-    return 0;
+    return;
   }
 
   /* DATA frame */
@@ -3196,7 +3139,7 @@ static int session_after_frame_sent2(nghttp2_session *session) {
   if (aux_data->eof) {
     active_outbound_item_reset(aob, mem);
 
-    return 0;
+    return;
   }
 
   /* Reset no_copy here because next write may not use this. */
@@ -3208,22 +3151,18 @@ static int session_after_frame_sent2(nghttp2_session *session) {
      further data. */
   if (nghttp2_session_predicate_data_send(session, stream) != 0) {
     if (stream) {
-      rv = session_detach_stream_item(session, stream);
-
-      if (nghttp2_is_fatal(rv)) {
-        return rv;
-      }
+      session_detach_stream_item(session, stream);
     }
 
     active_outbound_item_reset(aob, mem);
 
-    return 0;
+    return;
   }
 
   aob->item = NULL;
   active_outbound_item_reset(&session->aob, mem);
 
-  return 0;
+  return;
 }
 
 static int session_call_send_data(nghttp2_session *session,
@@ -3454,7 +3393,7 @@ static ssize_t nghttp2_session_mem_send_internal(nghttp2_session *session,
 
         /* Frame has completely sent */
         if (fast_cb) {
-          rv = session_after_frame_sent2(session);
+          session_after_frame_sent2(session);
         } else {
           rv = session_after_frame_sent1(session);
           if (rv < 0) {
@@ -3462,12 +3401,7 @@ static ssize_t nghttp2_session_mem_send_internal(nghttp2_session *session,
             assert(nghttp2_is_fatal(rv));
             return rv;
           }
-          rv = session_after_frame_sent2(session);
-        }
-        if (rv < 0) {
-          /* FATAL */
-          assert(nghttp2_is_fatal(rv));
-          return rv;
+          session_after_frame_sent2(session);
         }
         /* We have already adjusted the next state */
         break;
@@ -3506,11 +3440,7 @@ static ssize_t nghttp2_session_mem_send_internal(nghttp2_session *session,
       }
 
       if (rv == NGHTTP2_ERR_TEMPORAL_CALLBACK_FAILURE) {
-        rv = session_detach_stream_item(session, stream);
-
-        if (nghttp2_is_fatal(rv)) {
-          return rv;
-        }
+        session_detach_stream_item(session, stream);
 
         rv = nghttp2_session_add_rst_stream(session, frame->hd.stream_id,
                                             NGHTTP2_INTERNAL_ERROR);
@@ -3534,11 +3464,7 @@ static ssize_t nghttp2_session_mem_send_internal(nghttp2_session *session,
         assert(nghttp2_is_fatal(rv));
         return rv;
       }
-      rv = session_after_frame_sent2(session);
-      if (rv < 0) {
-        assert(nghttp2_is_fatal(rv));
-        return rv;
-      }
+      session_after_frame_sent2(session);
 
       /* We have already adjusted the next state */
 
@@ -4424,17 +4350,12 @@ int nghttp2_session_on_headers_received(nghttp2_session *session,
 }
 
 static int session_process_headers_frame(nghttp2_session *session) {
-  int rv;
   nghttp2_inbound_frame *iframe = &session->iframe;
   nghttp2_frame *frame = &iframe->frame;
   nghttp2_stream *stream;
 
-  rv = nghttp2_frame_unpack_headers_payload(&frame->headers, iframe->sbuf.pos);
+  nghttp2_frame_unpack_headers_payload(&frame->headers, iframe->sbuf.pos);
 
-  if (rv != 0) {
-    return nghttp2_session_terminate_session_with_reason(
-        session, NGHTTP2_PROTOCOL_ERROR, "HEADERS: could not unpack");
-  }
   stream = nghttp2_session_get_stream(session, frame->hd.stream_id);
   if (!stream) {
     frame->headers.cat = NGHTTP2_HCAT_REQUEST;
@@ -5097,17 +5018,11 @@ int nghttp2_session_on_push_promise_received(nghttp2_session *session,
 }
 
 static int session_process_push_promise_frame(nghttp2_session *session) {
-  int rv;
   nghttp2_inbound_frame *iframe = &session->iframe;
   nghttp2_frame *frame = &iframe->frame;
 
-  rv = nghttp2_frame_unpack_push_promise_payload(&frame->push_promise,
-                                                 iframe->sbuf.pos);
-
-  if (rv != 0) {
-    return nghttp2_session_terminate_session_with_reason(
-        session, NGHTTP2_PROTOCOL_ERROR, "PUSH_PROMISE: could not unpack");
-  }
+  nghttp2_frame_unpack_push_promise_payload(&frame->push_promise,
+                                            iframe->sbuf.pos);
 
   return nghttp2_session_on_push_promise_received(session, frame);
 }
@@ -7808,11 +7723,8 @@ int nghttp2_session_pack_data(nghttp2_session *session, nghttp2_bufs *bufs,
 
   nghttp2_frame_pack_frame_hd(buf->pos, &frame->hd);
 
-  rv = nghttp2_frame_add_pad(bufs, &frame->hd, frame->data.padlen,
-                             aux_data->no_copy);
-  if (rv != 0) {
-    return rv;
-  }
+  nghttp2_frame_add_pad(bufs, &frame->hd, frame->data.padlen,
+                        aux_data->no_copy);
 
   session_reschedule_stream(session, stream);
 
diff --git a/deps/nghttp2/lib/nghttp2_stream.c b/deps/nghttp2/lib/nghttp2_stream.c
index b3614a0b02761e..f1951f879d7927 100644
--- a/deps/nghttp2/lib/nghttp2_stream.c
+++ b/deps/nghttp2/lib/nghttp2_stream.c
@@ -465,14 +465,12 @@ static int stream_update_dep_on_attach_item(nghttp2_stream *stream) {
   return 0;
 }
 
-static int stream_update_dep_on_detach_item(nghttp2_stream *stream) {
+static void stream_update_dep_on_detach_item(nghttp2_stream *stream) {
   if (nghttp2_pq_empty(&stream->obq)) {
     stream_obq_remove(stream);
   }
 
   validate_tree(stream);
-
-  return 0;
 }
 
 int nghttp2_stream_attach_item(nghttp2_stream *stream,
@@ -503,20 +501,20 @@ int nghttp2_stream_attach_item(nghttp2_stream *stream,
   return 0;
 }
 
-int nghttp2_stream_detach_item(nghttp2_stream *stream) {
+void nghttp2_stream_detach_item(nghttp2_stream *stream) {
   DEBUGF("stream: stream=%d detach item=%p\n", stream->stream_id, stream->item);
 
   stream->item = NULL;
   stream->flags = (uint8_t)(stream->flags & ~NGHTTP2_STREAM_FLAG_DEFERRED_ALL);
 
   if (stream->flags & NGHTTP2_STREAM_FLAG_NO_RFC7540_PRIORITIES) {
-    return 0;
+    return;
   }
 
-  return stream_update_dep_on_detach_item(stream);
+  stream_update_dep_on_detach_item(stream);
 }
 
-int nghttp2_stream_defer_item(nghttp2_stream *stream, uint8_t flags) {
+void nghttp2_stream_defer_item(nghttp2_stream *stream, uint8_t flags) {
   assert(stream->item);
 
   DEBUGF("stream: stream=%d defer item=%p cause=%02x\n", stream->stream_id,
@@ -525,10 +523,10 @@ int nghttp2_stream_defer_item(nghttp2_stream *stream, uint8_t flags) {
   stream->flags |= flags;
 
   if (stream->flags & NGHTTP2_STREAM_FLAG_NO_RFC7540_PRIORITIES) {
-    return 0;
+    return;
   }
 
-  return stream_update_dep_on_detach_item(stream);
+  stream_update_dep_on_detach_item(stream);
 }
 
 int nghttp2_stream_resume_deferred_item(nghttp2_stream *stream, uint8_t flags) {
diff --git a/deps/nghttp2/lib/nghttp2_stream.h b/deps/nghttp2/lib/nghttp2_stream.h
index 7a8e4c6c1ddb08..71b9fb1140c932 100644
--- a/deps/nghttp2/lib/nghttp2_stream.h
+++ b/deps/nghttp2/lib/nghttp2_stream.h
@@ -258,14 +258,8 @@ void nghttp2_stream_shutdown(nghttp2_stream *stream, nghttp2_shut_flag flag);
  * more of NGHTTP2_STREAM_FLAG_DEFERRED_USER and
  * NGHTTP2_STREAM_FLAG_DEFERRED_FLOW_CONTROL.  The |flags| indicates
  * the reason of this action.
- *
- * This function returns 0 if it succeeds, or one of the following
- * negative error codes:
- *
- * NGHTTP2_ERR_NOMEM
- *     Out of memory
  */
-int nghttp2_stream_defer_item(nghttp2_stream *stream, uint8_t flags);
+void nghttp2_stream_defer_item(nghttp2_stream *stream, uint8_t flags);
 
 /*
  * Put back deferred data in this stream to active state.  The |flags|
@@ -379,14 +373,8 @@ int nghttp2_stream_attach_item(nghttp2_stream *stream,
 /*
  * Detaches |stream->item|.  This function does not free
  * |stream->item|.  The caller must free it.
- *
- * This function returns 0 if it succeeds, or one of the following
- * negative error codes:
- *
- * NGHTTP2_ERR_NOMEM
- *     Out of memory
  */
-int nghttp2_stream_detach_item(nghttp2_stream *stream);
+void nghttp2_stream_detach_item(nghttp2_stream *stream);
 
 /*
  * Makes the |stream| depend on the |dep_stream|.  This dependency is
diff --git a/doc/contributing/maintaining/maintaining-dependencies.md b/doc/contributing/maintaining/maintaining-dependencies.md
index 321020a29670a1..c8f2b1a7ec1110 100644
--- a/doc/contributing/maintaining/maintaining-dependencies.md
+++ b/doc/contributing/maintaining/maintaining-dependencies.md
@@ -21,7 +21,7 @@ This a list of all the dependencies:
 * [libuv 1.46.0][]
 * [llhttp 8.1.0][]
 * [minimatch 9.0.3][]
-* [nghttp2 1.55.1][]
+* [nghttp2 1.56.0][]
 * [nghttp3 0.7.0][]
 * [ngtcp2 0.8.1][]
 * [npm 9.6.7][]
@@ -223,7 +223,7 @@ See [maintaining-http][] for more informations.
 The [minimatch](https://github.com/isaacs/minimatch) dependency is a
 minimal matching utility.
 
-### nghttp2 1.55.1
+### nghttp2 1.56.0
 
 The [nghttp2](https://github.com/nghttp2/nghttp2) dependency is a C library
 implementing HTTP/2 protocol.
@@ -338,7 +338,7 @@ performance improvements not currently available in standard zlib.
 [maintaining-openssl]: ./maintaining-openssl.md
 [maintaining-web-assembly]: ./maintaining-web-assembly.md
 [minimatch 9.0.3]: #minimatch-903
-[nghttp2 1.55.1]: #nghttp2-1551
+[nghttp2 1.56.0]: #nghttp2-1560
 [nghttp3 0.7.0]: #nghttp3-070
 [ngtcp2 0.8.1]: #ngtcp2-081
 [npm 9.6.7]: #npm-967