lib: eliminate `conn->cselect_bits`

- use `data->state.dselect_bits` everywhere instead
- remove `bool *comeback` parameter as non-zero
  `data->state.dselect_bits` will indicate that IO is
  incomplete.

Closes #12512

lib/cf-h2-proxy.c

@@ -221,10 +221,10 @@ static void drain_tunnel(struct Curl_cfilter *cf,
   bits = CURL_CSELECT_IN;
   if(!tunnel->closed && !tunnel->reset && tunnel->upload_blocked_len)
     bits |= CURL_CSELECT_OUT;
-  if(data->state.dselect_bits != bits) {
-    CURL_TRC_CF(data, cf, "[%d] DRAIN dselect_bits=%x",
+  if(data->state.select_bits != bits) {
+    CURL_TRC_CF(data, cf, "[%d] DRAIN select_bits=%x",
                 tunnel->stream_id, bits);
-    data->state.dselect_bits = bits;
+    data->state.select_bits = bits;
     Curl_expire(data, 0, EXPIRE_RUN_NOW);
   }
 }

lib/easy.c

@@ -1111,7 +1111,7 @@ CURLcode curl_easy_pause(struct Curl_easy *data, int action)
     if(!data->state.tempcount)
       /* if not pausing again, force a recv/send check of this connection as
          the data might've been read off the socket already */
-      data->conn->cselect_bits = CURL_CSELECT_IN | CURL_CSELECT_OUT;
+      data->state.select_bits = CURL_CSELECT_IN | CURL_CSELECT_OUT;
     if(data->multi) {
       if(Curl_update_timer(data->multi))
         return CURLE_ABORTED_BY_CALLBACK;

lib/http2.c

@@ -219,10 +219,10 @@ static void drain_stream(struct Curl_cfilter *cf,
   if(!stream->send_closed &&
      (stream->upload_left || stream->upload_blocked_len))
     bits |= CURL_CSELECT_OUT;
-  if(data->state.dselect_bits != bits) {
-    CURL_TRC_CF(data, cf, "[%d] DRAIN dselect_bits=%x",
+  if(data->state.select_bits != bits) {
+    CURL_TRC_CF(data, cf, "[%d] DRAIN select_bits=%x",
                 stream->id, bits);
-    data->state.dselect_bits = bits;
+    data->state.select_bits = bits;
     Curl_expire(data, 0, EXPIRE_RUN_NOW);
   }
 }

lib/imap.c

@@ -1220,7 +1220,7 @@ static CURLcode imap_state_fetch_resp(struct Curl_easy *data,
       data->req.maxdownload = size;
       /* force a recv/send check of this connection, as the data might've been
        read off the socket already */
-      data->conn->cselect_bits = CURL_CSELECT_IN;
+      data->state.select_bits = CURL_CSELECT_IN;
       Curl_setup_transfer(data, FIRSTSOCKET, size, FALSE, -1);
     }
   }

lib/multi.c

@@ -2371,7 +2371,6 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
     {
       char *newurl = NULL;
       bool retry = FALSE;
-      bool comeback = FALSE;
       DEBUGASSERT(data->state.buffer);
       /* check if over send speed */
       send_timeout_ms = 0;
@@ -2402,7 +2401,7 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
       }
 
       /* read/write data if it is ready to do so */
-      result = Curl_readwrite(data->conn, data, &done, &comeback);
+      result = Curl_readwrite(data->conn, data, &done);
 
       if(done || (result == CURLE_RECV_ERROR)) {
         /* If CURLE_RECV_ERROR happens early enough, we assume it was a race
@@ -2512,7 +2511,7 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
           }
         }
       }
-      else if(comeback) {
+      else if(data->state.select_bits) {
         /* This avoids CURLM_CALL_MULTI_PERFORM so that a very fast transfer
            won't get stuck on this transfer at the expense of other concurrent
            transfers */
@@ -3164,7 +3163,7 @@ static CURLMcode multi_socket(struct Curl_multi *multi,
 
         if(data->conn && !(data->conn->handler->flags & PROTOPT_DIRLOCK))
           /* set socket event bitmask if they're not locked */
-          data->conn->cselect_bits = (unsigned char)ev_bitmask;
+          data->state.select_bits = (unsigned char)ev_bitmask;
 
         Curl_expire(data, 0, EXPIRE_RUN_NOW);
       }

lib/transfer.c

@@ -417,15 +417,11 @@ bool Curl_meets_timecondition(struct Curl_easy *data, time_t timeofdoc)
  * Go ahead and do a read if we have a readable socket or if
  * the stream was rewound (in which case we have data in a
  * buffer)
- *
- * return '*comeback' TRUE if we didn't properly drain the socket so this
- * function should get called again without select() or similar in between!
  */
 static CURLcode readwrite_data(struct Curl_easy *data,
                                struct connectdata *conn,
                                struct SingleRequest *k,
-                               int *didwhat, bool *done,
-                               bool *comeback)
+                               int *didwhat, bool *done)
 {
   CURLcode result = CURLE_OK;
   char *buf;
@@ -438,7 +434,6 @@ static CURLcode readwrite_data(struct Curl_easy *data,
 
   DEBUGASSERT(data->state.buffer);
   *done = FALSE;
-  *comeback = FALSE;
 
   /* This is where we loop until we have read everything there is to
      read or we get a CURLE_AGAIN */
@@ -722,8 +717,7 @@ static CURLcode readwrite_data(struct Curl_easy *data,
 
   if(maxloops <= 0 || max_recv <= 0) {
     /* we mark it as read-again-please */
-    data->state.dselect_bits = CURL_CSELECT_IN;
-    *comeback = TRUE;
+    data->state.select_bits = CURL_CSELECT_IN;
   }
 
   if(((k->keepon & (KEEP_RECV|KEEP_SEND)) == KEEP_SEND) &&
@@ -1032,14 +1026,10 @@ static int select_bits_paused(struct Curl_easy *data, int select_bits)
 /*
  * Curl_readwrite() is the low-level function to be called when data is to
  * be read and written to/from the connection.
- *
- * return '*comeback' TRUE if we didn't properly drain the socket so this
- * function should get called again without select() or similar in between!
  */
 CURLcode Curl_readwrite(struct connectdata *conn,
                         struct Curl_easy *data,
-                        bool *done,
-                        bool *comeback)
+                        bool *done)
 {
   struct SingleRequest *k = &data->req;
   CURLcode result;
@@ -1047,22 +1037,16 @@ CURLcode Curl_readwrite(struct connectdata *conn,
   int didwhat = 0;
   int select_bits;
 
-  if(data->state.dselect_bits) {
-    if(select_bits_paused(data, data->state.dselect_bits)) {
+  if(data->state.select_bits) {
+    if(select_bits_paused(data, data->state.select_bits)) {
       /* leave the bits unchanged, so they'll tell us what to do when
        * this transfer gets unpaused. */
-      DEBUGF(infof(data, "readwrite, dselect_bits, early return on PAUSED"));
+      DEBUGF(infof(data, "readwrite, select_bits, early return on PAUSED"));
       result = CURLE_OK;
       goto out;
     }
-    select_bits = data->state.dselect_bits;
-    data->state.dselect_bits = 0;
-  }
-  else if(conn->cselect_bits) {
-    /* CAVEAT: adding `select_bits_paused()` check here makes test640 hang
-     * (among others). Which hints at strange state handling in FTP land... */
-    select_bits = conn->cselect_bits;
-    conn->cselect_bits = 0;
+    select_bits = data->state.select_bits;
+    data->state.select_bits = 0;
   }
   else {
     curl_socket_t fd_read;
@@ -1100,7 +1084,7 @@ CURLcode Curl_readwrite(struct connectdata *conn,
      the stream was rewound (in which case we have data in a
      buffer) */
   if((k->keepon & KEEP_RECV) && (select_bits & CURL_CSELECT_IN)) {
-    result = readwrite_data(data, conn, k, &didwhat, done, comeback);
+    result = readwrite_data(data, conn, k, &didwhat, done);
     if(result || *done)
       goto out;
   }

lib/transfer.h

@@ -46,8 +46,7 @@ typedef enum {
 CURLcode Curl_follow(struct Curl_easy *data, char *newurl,
                      followtype type);
 CURLcode Curl_readwrite(struct connectdata *conn,
-                        struct Curl_easy *data, bool *done,
-                        bool *comeback);
+                        struct Curl_easy *data, bool *done);
 int Curl_single_getsock(struct Curl_easy *data,
                         struct connectdata *conn, curl_socket_t *socks);
 CURLcode Curl_fillreadbuffer(struct Curl_easy *data, size_t bytes,

lib/urldata.h

@@ -1103,7 +1103,6 @@ struct connectdata {
   unsigned short localport;
   unsigned short secondary_port; /* secondary socket remote port to connect to
                                     (ftp) */
-  unsigned char cselect_bits; /* bitmask of socket events */
   unsigned char alpn; /* APLN TLS negotiated protocol, a CURL_HTTP_VERSION*
                          value */
 #ifndef CURL_DISABLE_PROXY
@@ -1479,7 +1478,7 @@ struct UrlState {
                                 server involved in this request */
   unsigned char httpreq; /* Curl_HttpReq; what kind of HTTP request (if any)
                             is this */
-  unsigned char dselect_bits; /* != 0 -> bitmask of socket events for this
+  unsigned char select_bits; /* != 0 -> bitmask of socket events for this
                                  transfer overriding anything the socket may
                                  report */
 #ifdef CURLDEBUG

lib/vquic/curl_msh3.c

@@ -204,8 +204,8 @@ static void drain_stream_from_other_thread(struct Curl_easy *data,
   bits = CURL_CSELECT_IN;
   if(stream && !stream->upload_done)
     bits |= CURL_CSELECT_OUT;
-  if(data->state.dselect_bits != bits) {
-    data->state.dselect_bits = bits;
+  if(data->state.select_bits != bits) {
+    data->state.select_bits = bits;
     /* cannot expire from other thread */
   }
 }
@@ -220,8 +220,8 @@ static void drain_stream(struct Curl_cfilter *cf,
   bits = CURL_CSELECT_IN;
   if(stream && !stream->upload_done)
     bits |= CURL_CSELECT_OUT;
-  if(data->state.dselect_bits != bits) {
-    data->state.dselect_bits = bits;
+  if(data->state.select_bits != bits) {
+    data->state.select_bits = bits;
     Curl_expire(data, 0, EXPIRE_RUN_NOW);
   }
 }

lib/vquic/curl_ngtcp2.c

@@ -292,8 +292,8 @@ static void h3_drain_stream(struct Curl_cfilter *cf,
   bits = CURL_CSELECT_IN;
   if(stream && stream->upload_left && !stream->send_closed)
     bits |= CURL_CSELECT_OUT;
-  if(data->state.dselect_bits != bits) {
-    data->state.dselect_bits = bits;
+  if(data->state.select_bits != bits) {
+    data->state.select_bits = bits;
     Curl_expire(data, 0, EXPIRE_RUN_NOW);
   }
 }

lib/vquic/curl_quiche.c

@@ -337,8 +337,8 @@ static void drain_stream(struct Curl_cfilter *cf,
   bits = CURL_CSELECT_IN;
   if(stream && !stream->send_closed && stream->upload_left)
     bits |= CURL_CSELECT_OUT;
-  if(data->state.dselect_bits != bits) {
-    data->state.dselect_bits = bits;
+  if(data->state.select_bits != bits) {
+    data->state.select_bits = bits;
     Curl_expire(data, 0, EXPIRE_RUN_NOW);
   }
 }

lib/vssh/libssh.c

@@ -1370,7 +1370,7 @@ static CURLcode myssh_statemach_act(struct Curl_easy *data, bool *block)
       /* we want to use the _sending_ function even when the socket turns
          out readable as the underlying libssh sftp send function will deal
          with both accordingly */
-      conn->cselect_bits = CURL_CSELECT_OUT;
+      data->state.select_bits = CURL_CSELECT_OUT;
 
       /* since we don't really wait for anything at this point, we want the
          state machine to move on as soon as possible so we set a very short
@@ -1740,7 +1740,7 @@ static CURLcode myssh_statemach_act(struct Curl_easy *data, bool *block)
     /* we want to use the _receiving_ function even when the socket turns
        out writableable as the underlying libssh recv function will deal
        with both accordingly */
-    conn->cselect_bits = CURL_CSELECT_IN;
+    data->state.select_bits = CURL_CSELECT_IN;
 
     if(result) {
       /* this should never occur; the close state should be entered
@@ -1868,7 +1868,7 @@ static CURLcode myssh_statemach_act(struct Curl_easy *data, bool *block)
       /* we want to use the _sending_ function even when the socket turns
          out readable as the underlying libssh scp send function will deal
          with both accordingly */
-      conn->cselect_bits = CURL_CSELECT_OUT;
+      data->state.select_bits = CURL_CSELECT_OUT;
 
       state(data, SSH_STOP);
 
@@ -1908,7 +1908,7 @@ static CURLcode myssh_statemach_act(struct Curl_easy *data, bool *block)
         /* we want to use the _receiving_ function even when the socket turns
            out writableable as the underlying libssh recv function will deal
            with both accordingly */
-        conn->cselect_bits = CURL_CSELECT_IN;
+        data->state.select_bits = CURL_CSELECT_IN;
 
         state(data, SSH_STOP);
         break;

lib/vssh/libssh2.c

@@ -2213,7 +2213,7 @@ static CURLcode ssh_statemach_act(struct Curl_easy *data, bool *block)
         /* we want to use the _sending_ function even when the socket turns
            out readable as the underlying libssh2 sftp send function will deal
            with both accordingly */
-        conn->cselect_bits = CURL_CSELECT_OUT;
+        data->state.select_bits = CURL_CSELECT_OUT;
 
         /* since we don't really wait for anything at this point, we want the
            state machine to move on as soon as possible so we set a very short
@@ -2602,7 +2602,7 @@ static CURLcode ssh_statemach_act(struct Curl_easy *data, bool *block)
     /* we want to use the _receiving_ function even when the socket turns
        out writableable as the underlying libssh2 recv function will deal
        with both accordingly */
-    conn->cselect_bits = CURL_CSELECT_IN;
+    data->state.select_bits = CURL_CSELECT_IN;
 
     if(result) {
       /* this should never occur; the close state should be entered
@@ -2757,7 +2757,7 @@ static CURLcode ssh_statemach_act(struct Curl_easy *data, bool *block)
         /* we want to use the _sending_ function even when the socket turns
            out readable as the underlying libssh2 scp send function will deal
            with both accordingly */
-        conn->cselect_bits = CURL_CSELECT_OUT;
+        data->state.select_bits = CURL_CSELECT_OUT;
 
         state(data, SSH_STOP);
       }
@@ -2819,7 +2819,7 @@ static CURLcode ssh_statemach_act(struct Curl_easy *data, bool *block)
       /* we want to use the _receiving_ function even when the socket turns
          out writableable as the underlying libssh2 recv function will deal
          with both accordingly */
-      conn->cselect_bits = CURL_CSELECT_IN;
+      data->state.select_bits = CURL_CSELECT_IN;
 
       if(result) {
         state(data, SSH_SCP_CHANNEL_FREE);

lib/vssh/wolfssh.c

@@ -694,7 +694,7 @@ static CURLcode wssh_statemach_act(struct Curl_easy *data, bool *block)
         /* we want to use the _sending_ function even when the socket turns
            out readable as the underlying libssh2 sftp send function will deal
            with both accordingly */
-        conn->cselect_bits = CURL_CSELECT_OUT;
+        data->state.select_bits = CURL_CSELECT_OUT;
 
         /* since we don't really wait for anything at this point, we want the
            state machine to move on as soon as possible so we set a very short
@@ -790,7 +790,7 @@ static CURLcode wssh_statemach_act(struct Curl_easy *data, bool *block)
       /* we want to use the _receiving_ function even when the socket turns
          out writableable as the underlying libssh2 recv function will deal
          with both accordingly */
-      conn->cselect_bits = CURL_CSELECT_IN;
+      data->state.select_bits = CURL_CSELECT_IN;
 
       if(result) {
         /* this should never occur; the close state should be entered