From 9b6332c359590ae4dcb1d95c217cd003de9c42b7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?J=C5=8Dshin?= <git@wholezero.org>
Date: Sat, 11 Dec 2021 04:54:06 +0000
Subject: [PATCH] newt: change framing to tag byte + 32-bit length

---
 pkg/urbit/include/vere/vere.h |  2 +-
 pkg/urbit/vere/newt.c         | 49 ++++++++++++++++-------------------
 2 files changed, 23 insertions(+), 28 deletions(-)

diff --git a/pkg/urbit/include/vere/vere.h b/pkg/urbit/include/vere/vere.h
index e3c24ea65d..9db525be09 100644
--- a/pkg/urbit/include/vere/vere.h
+++ b/pkg/urbit/include/vere/vere.h
@@ -67,7 +67,7 @@
         u3_mess_type     sat_e;             //  msg type
         union {                             //
           struct {                          //  awaiting header:
-            c3_y         len_y[8];          //    header bytes
+            c3_y         hed_y[5];          //    header bytes
             c3_y         has_y;             //    length
           } hed_u;                          //
           struct {                          //  awaiting body
diff --git a/pkg/urbit/vere/newt.c b/pkg/urbit/vere/newt.c
index e501c5e7d4..7cfc18c133 100644
--- a/pkg/urbit/vere/newt.c
+++ b/pkg/urbit/vere/newt.c
@@ -2,9 +2,11 @@
 **
 **  implements noun blob messages with trivial framing.
 **
-**  a message is a 64-bit little-endian byte count, followed
-**  by the indicated number of bytes.  the bytes are the
-**  the +jam of of a noun.
+**  framing is 5 bytes long. first byte is a version tag; a
+**  character that should never otherwise appear in a message
+**  intended for urbit. right now we use 0x9, horizontal tab.
+**  next 32 bits are little-endian byte count. after that is the
+**  indicated number of bytes, which are the +jam of a noun.
 **
 **  the implementation is relatively inefficient and could
 **  lose a few copies, mallocs, etc.
@@ -117,15 +119,15 @@ u3_newt_decode(u3_moat* mot_u, c3_y* buf_y, c3_d len_d)
   while ( len_d ) {
     switch( mes_u->sat_e ) {
 
-      //  read up to 8 length bytes as needed
+      //  read up to 5 bytes as needed
       //
       case u3_mess_head: {
-        c3_y* len_y = mes_u->hed_u.len_y;
+        c3_y* hed_y = mes_u->hed_u.hed_y;
         c3_y  has_y = mes_u->hed_u.has_y;
-        c3_y  ned_y = 8 - has_y;
+        c3_y  ned_y = sizeof(mes_u->hed_u.hed_y) - has_y;
         c3_y  cop_y = c3_min(ned_y, len_d);
 
-        memcpy(len_y + has_y, buf_y, cop_y);
+        memcpy(hed_y + has_y, buf_y, cop_y);
         buf_y += cop_y;
         len_d -= cop_y;
         ned_y -= cop_y;
@@ -138,18 +140,14 @@ u3_newt_decode(u3_moat* mot_u, c3_y* buf_y, c3_d len_d)
         //  length known, allocate message
         //
         else {
-          c3_d met_d = (((c3_d)len_y[0]) <<  0)
-                     | (((c3_d)len_y[1]) <<  8)
-                     | (((c3_d)len_y[2]) << 16)
-                     | (((c3_d)len_y[3]) << 24)
-                     | (((c3_d)len_y[4]) << 32)
-                     | (((c3_d)len_y[5]) << 40)
-                     | (((c3_d)len_y[6]) << 48)
-                     | (((c3_d)len_y[7]) << 56);
+          c3_d met_d = (((c3_d)hed_y[1]) <<  0)
+                     | (((c3_d)hed_y[2]) <<  8)
+                     | (((c3_d)hed_y[3]) << 16)
+                     | (((c3_d)hed_y[4]) << 24);
 
-          //  must be non-zero, only 32 bits supported
+          //  check for version tag and nonzero length
           //
-          if ( !met_d || !(0xFFFFFFFFULL > met_d) ) {
+          if ( 0x9 != hed_y[0] || !met_d ) {
             return c3n;
           }
 
@@ -379,7 +377,7 @@ typedef struct _n_req {
   uv_write_t wri_u;
   u3_mojo*   moj_u;
   c3_y*      buf_y;
-  c3_y       len_y[8];
+  c3_y       hed_y[5];
 } n_req;
 
 /* _newt_write_cb(): generic write callback.
@@ -438,18 +436,15 @@ u3_newt_send(u3_mojo* moj_u, c3_d len_d, c3_y* byt_y)
 
   //  write header
   //
-  req_u->len_y[0] = ( len_d        & 0xff);
-  req_u->len_y[1] = ((len_d >>  8) & 0xff);
-  req_u->len_y[2] = ((len_d >> 16) & 0xff);
-  req_u->len_y[3] = ((len_d >> 24) & 0xff);
-  req_u->len_y[4] = ((len_d >> 32) & 0xff);
-  req_u->len_y[5] = ((len_d >> 40) & 0xff);
-  req_u->len_y[6] = ((len_d >> 48) & 0xff);
-  req_u->len_y[7] = ((len_d >> 56) & 0xff);
+  req_u->hed_y[0] = 0x9;
+  req_u->hed_y[1] = ( len_d        & 0xff);
+  req_u->hed_y[2] = ((len_d >>  8) & 0xff);
+  req_u->hed_y[3] = ((len_d >> 16) & 0xff);
+  req_u->hed_y[4] = ((len_d >> 24) & 0xff);
 
   {
     uv_buf_t buf_u[2] = {
-      uv_buf_init((c3_c*)req_u->len_y, 8),
+      uv_buf_init((c3_c*)req_u->hed_y, sizeof(req_u->hed_y)),
       uv_buf_init((c3_c*)req_u->buf_y, len_d)
     };