detect sixel using device attributes request #200

src/lib/internal.h

@@ -282,7 +282,7 @@ typedef struct tinfo {
   uint32_t bg_collides_default;
   bool sextants;  // do we have (good, vetted) Unicode 13 sextant support?
   bool braille;   // do we have Braille support? (linux console does not)
-  bool libsixel;  // do we have Sixel support?
+  bool sixel;     // do we have Sixel support?
 } tinfo;
 
 typedef struct ncinputlayer {
@@ -373,8 +373,16 @@ void sigwinch_handler(int signo);
 
 void init_lang(notcurses* nc); // nc may be NULL, only used for logging
 int terminfostr(char** gseq, const char* name);
+
+// load |ti| from the terminfo database, which must already have been
+// initialized. set |utf8| if we've verified UTF8 output encoding.
 int interrogate_terminfo(tinfo* ti, const char* termname, unsigned utf8);
 
+// perform queries that require writing to the terminal, and reading a
+// response, rather than simply reading the terminfo database. can result
+// in a lengthy delay or even block if the terminal doesn't respond.
+int query_term(tinfo* ti, int fd);
+
 // if there were missing elements we wanted from terminfo, bitch about them here
 void warn_terminfo(const notcurses* nc, const tinfo* ti);
 
@@ -507,26 +515,30 @@ rgb_greyscale(int r, int g, int b){
   return fg * 255;
 }
 
+// write(2) with retry on partial write or interrupted write
+static inline ssize_t
+writen(int fd, const void* buf, size_t len){
+  ssize_t r;
+  size_t w = 0;
+  while(w < len){
+    if((r = write(fd, (const char*)buf + w, len - w)) < 0){
+      if(errno == EAGAIN || errno == EBUSY || errno == EINTR){
+        continue;
+      }
+      return -1;
+    }
+    w += r;
+  }
+  return w;
+}
+
 static inline int
 tty_emit(const char* seq, int fd){
   if(!seq){
     return -1;
   }
   size_t slen = strlen(seq);
-  size_t written = 0;
-  do{
-    ssize_t ret = write(fd, seq, slen);
-    if(ret > 0){
-      written += ret;
-    }
-    if(ret < 0){
-      if(errno != EAGAIN){
-        break;
-      }
-    }
-  }while(written < slen);
-  if(written < slen){
-//fprintf(stderr, "Error emitting %zub escape (%s)\n", strlen(seq), strerror(errno));
+  if(writen(fd, seq, slen) < 0){
     return -1;
   }
   return 0;

src/lib/notcurses.c

@@ -1018,9 +1018,6 @@ notcurses* notcurses_core_init(const notcurses_options* opts, FILE* outfp){
   if(ncinputlayer_init(&ret->input, stdin)){
     goto err;
   }
-  if(make_nonblocking(ret->input.ttyinfd)){
-    goto err;
-  }
   // Neither of these is supported on e.g. the "linux" virtual console.
   if(!(opts->flags & NCOPTION_NO_ALTERNATE_SCREEN)){
     terminfostr(&ret->tcache.smcup, "smcup");
@@ -1034,6 +1031,12 @@ notcurses* notcurses_core_init(const notcurses_options* opts, FILE* outfp){
     goto err;
   }
   if(ret->ttyfd >= 0){
+    if(opts->flags & NCOPTION_VERIFY_SIXEL){
+      if(query_term(&ret->tcache, ret->ttyfd)){
+        free_plane(ret->stdplane);
+        goto err;
+      }
+    }
     if(ret->tcache.smkx && tty_emit(ret->tcache.smkx, ret->ttyfd)){
       free_plane(ret->stdplane);
       goto err;
@@ -1044,6 +1047,9 @@ notcurses* notcurses_core_init(const notcurses_options* opts, FILE* outfp){
     }
     reset_term_attributes(ret);
   }
+  if(make_nonblocking(ret->input.ttyinfd)){
+    goto err;
+  }
   if((ret->rstate.mstreamfp = open_memstream(&ret->rstate.mstream, &ret->rstate.mstrsize)) == NULL){
     free_plane(ret->stdplane);
     goto err;
@@ -2065,7 +2071,7 @@ bool notcurses_canchangecolor(const notcurses* nc){
 }
 
 bool notcurses_cansixel(const notcurses* nc){
-  return nc->tcache.libsixel;
+  return nc->tcache.sixel;
 }
 
 palette256* palette256_new(notcurses* nc){

src/lib/terminfo.c

@@ -189,3 +189,59 @@ int interrogate_terminfo(tinfo* ti, const char* termname, unsigned utf8){
   }
   return 0;
 }
+
+static int
+query_sixel(tinfo* ti, int fd){
+  if(writen(fd, "\033[c", 3) != 3){
+    return -1;
+  }
+  char in;
+  enum {
+    WANT_CSI,
+    WANT_QMARK,
+    WANT_SEMI,
+    WANT_C,
+    DONE
+  } state = WANT_CSI;
+  while(read(fd, &in, 1) == 1){
+    switch(state){
+      case WANT_CSI:
+        if(in == NCKEY_ESC){
+          state = WANT_QMARK;
+        }
+        break;
+      case WANT_QMARK:
+        if(in == '?'){
+          state = WANT_SEMI;
+        }
+        break;
+      case WANT_SEMI:
+        if(in == ';'){
+          state = WANT_C;
+        }
+        break;
+      case WANT_C:
+        if(in == 'c'){
+          state = DONE;
+        }else if(in == '4'){
+          ti->sixel = true;
+        }
+        break;
+      case DONE:
+      default:
+        break;
+    }
+    if(state == DONE){
+      break;
+    }
+  }
+  return 0;
+}
+
+// fd must be a real terminal, and must not be in nonblocking mode
+int query_term(tinfo* ti, int fd){
+  if(query_sixel(ti, fd)){
+    return -1;
+  }
+  return 0;
+}

src/player/play.cpp

@@ -303,6 +303,7 @@ auto main(int argc, char** argv) -> int {
   float timescale, displaytime;
   ncscale_e scalemode;
   notcurses_options ncopts{};
+  ncopts.flags = NCOPTION_VERIFY_SIXEL;
   ncblitter_e blitter = NCBLIT_DEFAULT;
   bool quiet = false;
   bool loop = false;