+
+const char *pollbadbit(int revents)
+{
+#define BADBIT(b) \
+ if ((revents & b)) return #b
+ BADBIT(POLLERR);
+ BADBIT(POLLHUP);
+ /* POLLNVAL is handled by the event loop - see afterpoll_fn comment */
+#undef BADBIT
+ return 0;
+}
+
+enum async_linebuf_result
+async_linebuf_read(struct pollfd *pfd, struct buffer_if *buf,
+ const char **emsg_out)
+{
+ int revents=pfd->revents;
+
+#define BAD(m) do{ *emsg_out=(m); return async_linebuf_broken; }while(0)
+
+ const char *badbit=pollbadbit(revents);
+ if (badbit) BAD(badbit);
+
+ if (!(revents & POLLIN))
+ return async_linebuf_nothing;
+
+ /*
+ * Data structure: A line which has been returned to the user is
+ * stored in buf at base before start. But we retain the usual
+ * buffer meaning of size. So:
+ *
+ * | returned : | input read, | unused |
+ * | to user : \0 | awaiting | buffer |
+ * | : | processing | space |
+ * | : | | |
+ * ^base ^start ^start+size ^base+alloclen
+ */
+
+ BUF_ASSERT_USED(buf);
+
+ /* firstly, eat any previous */
+ if (buf->start != buf->base) {
+ memmove(buf->base,buf->start,buf->size);
+ buf->start=buf->base;
+ }
+
+ uint8_t *searched=buf->base;
+
+ /*
+ * During the workings here we do not use start. We set start
+ * when we return some actual data. So we have this:
+ *
+ * | searched | read, might | unused |
+ * | for \n | contain \n | buffer |
+ * | none found | but not \0 | space |
+ * | | | |
+ * ^base ^searched ^base+size ^base+alloclen
+ * [^start] ^dataend
+ *
+ */
+ for (;;) {
+ uint8_t *dataend=buf->base+buf->size;
+ char *newline=memchr(searched,'\n',dataend-searched);
+ if (newline) {
+ *newline=0;
+ buf->start=newline+1;
+ buf->size=dataend-buf->start;
+ return async_linebuf_ok;
+ }
+ searched=dataend;
+ ssize_t space=(buf->base+buf->alloclen)-dataend;
+ if (!space) BAD("input line too long");
+ ssize_t r=read(pfd->fd,searched,space);
+ if (r==0) {
+ *searched=0;
+ *emsg_out=buf->size?"no newline at eof":0;
+ buf->start=searched+1;
+ buf->size=0;
+ return async_linebuf_eof;
+ }
+ if (r<0) {
+ if (errno==EINTR)
+ continue;
+ if (iswouldblock(errno))
+ return async_linebuf_nothing;
+ BAD(strerror(errno));
+ }
+ assert(r<=space);
+ if (memchr(searched,0,r)) BAD("nul in input data");
+ buf->size+=r;
+ }
+
+#undef BAD
+}