notcurses_stop_minimal: use reliable I/O

fflush(), so far as i can tell, cannot be reliably used
in glibc. after it fails once, subsequent calls return 0
and do not set errno -- only the persistent ferror() serves
to indicate that flushing is not going on. instead, write
into the render state's memstream, and then use reliable
blocking_write() to dump it to stdout. closes #1872.

src/lib/direct.c

@@ -1250,12 +1250,7 @@ bool ncdirect_canutf8(const ncdirect* n){
 }
 
 int ncdirect_flush(const ncdirect* nc){
-  while(fflush(nc->ttyfp) == EOF){
-    if(errno != EAGAIN){
-      return -1;
-    }
-  }
-  return 0;
+  return ncflush(nc->ttyfp);
 }
 
 int ncdirect_check_pixel_support(const ncdirect* n){

src/lib/internal.h

@@ -1204,14 +1204,24 @@ tty_emit(const char* seq, int fd){
   return 0;
 }
 
-// reliably flush a FILE*
+int set_fd_nonblocking(int fd, unsigned state, unsigned* oldstate);
+
+// reliably flush a FILE*...except you can't, so far as i can tell. at least
+// on glibc, a single fflush() error latches the FILE* error, but ceases to
+// perform any work (even following a clearerr()), despite returning 0 from
+// that point on. thus, after a fflush() error, even on EAGAIN and friends,
+// you can't use the stream any further. doesn't this make fflush() pretty
+// much useless? it sure would seem to, which is why we use a memstream for
+// all our important I/O, which we then blit with blocking_write(). if you
+// care about your data, you'll do the same.
 static inline int
 ncflush(FILE* out){
-  while(fflush(out) == EOF){
-    if(errno != EAGAIN && errno != EINTR && errno != EBUSY){
-      logerror("Unrecoverable error flushing io (%s)\n", strerror(errno));
-      return -1;
-    }
+  if(ferror(out)){
+    logerror("Not attempting a flush following error\n");
+  }
+  if(fflush(out) == EOF){
+    logerror("Unrecoverable error flushing io (%s)\n", strerror(errno));
+    return -1;
   }
   return 0;
 }
@@ -1304,6 +1314,24 @@ coerce_styles(FILE* out, const tinfo* ti, uint16_t* curstyle,
   return ret;
 }
 
+#define SET_BTN_EVENT_MOUSE   "1002"
+#define SET_FOCUS_EVENT_MOUSE "1004"
+#define SET_SGR_MODE_MOUSE    "1006"
+
+static inline int
+mouse_enable(FILE* out){
+  return term_emit("\x1b[?" SET_BTN_EVENT_MOUSE ";"
+                   /*SET_FOCUS_EVENT_MOUSE ";" */SET_SGR_MODE_MOUSE "h",
+                   out, false);
+}
+
+static inline int
+mouse_disable(FILE* out){
+  return term_emit("\x1b[?" SET_BTN_EVENT_MOUSE ";"
+                   /*SET_FOCUS_EVENT_MOUSE ";" */SET_SGR_MODE_MOUSE "l",
+                   out, false);
+}
+
 // how many edges need touch a corner for it to be printed?
 static inline unsigned
 box_corner_needs(unsigned ctlword){
@@ -1591,8 +1619,6 @@ cellcmp_and_dupfar(egcpool* dampool, nccell* damcell,
   return 1;
 }
 
-int set_fd_nonblocking(int fd, unsigned state, unsigned* oldstate);
-
 int get_tty_fd(FILE* ttyfp);
 
 // Given the four channels arguments, verify that:

src/lib/notcurses.c

@@ -53,7 +53,12 @@ int reset_term_attributes(const tinfo* ti, FILE* fp){
 static int
 notcurses_stop_minimal(void* vnc){
   notcurses* nc = vnc;
+  // collect output into the memstream buffer, and then dump it directly using
+  // blocking_write(), to avoid problems with unreliable fflush().
+  FILE* out = nc->rstate.mstreamfp;
+  fseeko(out, 0, SEEK_SET);
   int ret = 0;
+  ret |= drop_signals(nc);
   // be sure to write the restoration sequences *prior* to running rmcup, as
   // they apply to the screen (alternate or otherwise) we're actually using.
   const char* esc;
@@ -61,35 +66,32 @@ notcurses_stop_minimal(void* vnc){
   // byte. if we leave an active escape open, it can lock up the terminal.
   // we only want to do it when in the middle of a rasterization, though. FIXME
   if(nc->tcache.pixel_shutdown){
-    ret |= nc->tcache.pixel_shutdown(nc->ttyfp);
+    ret |= nc->tcache.pixel_shutdown(out);
   }
-  ret |= notcurses_mouse_disable(nc);
-  ret |= reset_term_attributes(&nc->tcache, nc->ttyfp);
+  ret |= mouse_disable(out);
+  ret |= reset_term_attributes(&nc->tcache, out);
   if(nc->ttyfd >= 0){
     if((esc = get_escape(&nc->tcache, ESCAPE_RMCUP))){
-      if(sprite_clear_all(&nc->tcache, nc->ttyfp)){
+      if(sprite_clear_all(&nc->tcache, out)){
         ret = -1;
       }
-      if(term_emit(esc, nc->ttyfp, false)){
+      if(term_emit(esc, out, false)){
         ret = -1;
       }
     }
     ret |= tcsetattr(nc->ttyfd, TCSANOW, &nc->tcache.tpreserved);
   }
-  if((esc = get_escape(&nc->tcache, ESCAPE_RMKX)) && term_emit(esc, nc->ttyfp, false)){
+  if((esc = get_escape(&nc->tcache, ESCAPE_RMKX)) && term_emit(esc, out, false)){
     ret = -1;
   }
   const char* cnorm = get_escape(&nc->tcache, ESCAPE_CNORM);
-  if(cnorm && term_emit(cnorm, nc->ttyfp, false)){
+  if(cnorm && term_emit(cnorm, out, false)){
     ret = -1;
   }
-  if(ncflush(nc->ttyfp)){
-    ret = -1;
+  if(fflush(out)){
+    return -1;
   }
-  // see #1872; without keeping this at the end, we run into mysterious,
-  // poorly-understood issues during shutdown =[. cowardly. FIXME
-  ret |= drop_signals(nc);
-  return ret;
+  return blocking_write(fileno(nc->ttyfp), nc->rstate.mstream, nc->rstate.mstrsize);
 }
 
 // make a heap-allocated wchar_t expansion of the multibyte string at s
@@ -2159,14 +2161,8 @@ ncplane* ncplane_above(ncplane* n){
   return n->above;
 }
 
-#define SET_BTN_EVENT_MOUSE   "1002"
-#define SET_FOCUS_EVENT_MOUSE "1004"
-#define SET_SGR_MODE_MOUSE    "1006"
 int notcurses_mouse_enable(notcurses* n){
   if(n->ttyfd >= 0){
-    return term_emit(ESC "[?" SET_BTN_EVENT_MOUSE ";"
-                     /*SET_FOCUS_EVENT_MOUSE ";" */SET_SGR_MODE_MOUSE "h",
-                     n->ttyfp, false);
   }
   return 0;
 }
@@ -2175,9 +2171,6 @@ int notcurses_mouse_enable(notcurses* n){
 // the sequences 1000 etc?
 int notcurses_mouse_disable(notcurses* n){
   if(n->ttyfd >= 0){
-    return term_emit(ESC "[?" SET_BTN_EVENT_MOUSE ";"
-                     /*SET_FOCUS_EVENT_MOUSE ";" */SET_SGR_MODE_MOUSE "l",
-                     n->ttyfp, false);
   }
   return 0;
 }