notcurses-info: be reliable in the face of output EAGAIN

src/info/main.c

@@ -1,7 +1,32 @@
+#include <errno.h>
+#include <unistd.h>
 #include <stdlib.h>
 #include <notcurses/notcurses.h>
 
+// 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;
+}
+
 int main(void){
+  char* mbuf = NULL;
+  size_t len = 0;
+  FILE* mstream;
+  if((mstream = open_memstream(&mbuf, &len)) == NULL){
+    return EXIT_FAILURE;
+  }
   notcurses_options nopts = {
     .flags = NCOPTION_NO_ALTERNATE_SCREEN,
   };
@@ -10,6 +35,17 @@ int main(void){
     return EXIT_FAILURE;
   }
   notcurses_check_pixel_support(nc);
-  notcurses_debug_caps(nc, stdout);
+  notcurses_debug_caps(nc, mstream);
+  if(fclose(mstream)){
+    notcurses_stop(nc);
+    fprintf(stderr, "Error closing memstream after %zuB\n", len);
+    return EXIT_FAILURE;
+  }
+  if(writen(fileno(stdout), mbuf, len) < 0){
+    notcurses_stop(nc);
+    fprintf(stderr, "Error writing %zuB memstream\n", len);
+    return EXIT_FAILURE;
+  }
+  free(mbuf);
   return notcurses_stop(nc) ? EXIT_FAILURE : EXIT_SUCCESS;
 }