Enforce the invariant that each socket is only ever expected to be read from or written to, never both

3 files changed, 16 insertions, 25 deletions

diff --git a/opentracker.c b/opentracker.c
index b54327a..27b2570 100644
--- a/opentracker.c
+++ b/opentracker.c
@@ -180,12 +180,11 @@ static void handle_write(const int64_t sock) {
 
   /* In a chunked transfer, wait for the next piece once everything queued has gone out */
   if (chunked)
-    http_interest_drop(sock, cookie, EVENT_OUT);
+    http_interest_set(sock, cookie, 0);
   else if (keep_alive) {
-    /* The reply is out and the client asked to keep the connection, so stop
-       waiting to write and go back to waiting for the next request */
-    http_interest_drop(sock, cookie, EVENT_OUT);
-    http_interest_add(sock, cookie, EVENT_IN);
+    /* The reply is out and the client asked to keep the connection, so go
+       back to waiting for the next request */
+    http_interest_set(sock, cookie, EVENT_IN);
     fdstate_set_expiry(sock, time_future_seconds(OT_CLIENT_TIMEOUT));
   } else
     http_close(sock);
diff --git a/ot_http.c b/ot_http.c
index e8ba3da..66f0102 100644
--- a/ot_http.c
+++ b/ot_http.c
@@ -118,11 +118,9 @@ static void http_senddata(const int64_t sock, struct ot_workstruct *ws) {
     batch_add(cookie->batch, outbuf, ws->reply_size - written_size);
 
     /* writeable short data sockets just have a tcp timeout */
-    if (!ws->keep_alive) {
+    if (!ws->keep_alive)
       fdstate_set_expiry(sock, 0);
-      http_interest_drop(sock, cookie, EVENT_IN);
-    }
-    http_interest_add(sock, cookie, EVENT_OUT);
+    http_interest_set(sock, cookie, EVENT_OUT);
   }
 }
 
@@ -135,21 +133,16 @@ static void http_senddata(const int64_t sock, struct ot_workstruct *ws) {
 #define HTTPERROR_403_IP         return http_issue_error(sock, ws, CODE_HTTPERROR_403_IP)
 #define HTTPERROR_404            return http_issue_error(sock, ws, CODE_HTTPERROR_404)
 #define HTTPERROR_500            return http_issue_error(sock, ws, CODE_HTTPERROR_500)
-static void http_interest(const int64_t sock, struct http_data *cookie, int what) {
+/* A connection is either being read or being written, never both, so what it
+   waits for is set outright rather than added to and taken away again. The
+   event layer only hears about it when the answer changes. */
+void http_interest_set(const int64_t sock, struct http_data *cookie, int what) {
   if (cookie->interest == what)
     return;
   cookie->interest = what;
   event_modify((int)sock, what, fdstate_generation((int)sock));
 }
 
-void http_interest_add(const int64_t sock, struct http_data *cookie, int what) {
-  http_interest(sock, cookie, cookie->interest | what);
-}
-
-void http_interest_drop(const int64_t sock, struct http_data *cookie, int what) {
-  http_interest(sock, cookie, cookie->interest & ~what);
-}
-
 ssize_t http_issue_error(const int64_t sock, struct ot_workstruct *ws, int code) {
   const char *error_code[] = {"302 Found",      "400 Invalid Request", "400 Invalid Request", "400 Invalid Request",      "402 Payment Required",
                         "403 Not Modest", "403 Access Denied",   "404 Not Found",       "500 Internal Server Error"};
@@ -194,7 +187,7 @@ ssize_t http_sendiovecdata(const int64_t sock, struct ot_workstruct *ws, size_t
 
   /* If we came here, wait for the answer is over */
   if (cookie->flag & STRUCT_HTTP_FLAG_WAITINGFORTASK) {
-    http_interest_drop(sock, cookie, EVENT_IN);
+    http_interest_set(sock, cookie, 0);
     cookie->flag &= ~STRUCT_HTTP_FLAG_WAITINGFORTASK;
   }
 
@@ -245,7 +238,7 @@ ssize_t http_sendiovecdata(const int64_t sock, struct ot_workstruct *ws, size_t
   }
 
   fdstate_set_expiry(sock, time_future_seconds(OT_CLIENT_TIMEOUT_SEND));
-  http_interest_add(sock, cookie, EVENT_OUT);
+  http_interest_set(sock, cookie, EVENT_OUT);
   return 0;
 }
 
@@ -340,7 +333,7 @@ static ssize_t http_handle_stats(const int64_t sock, struct ot_workstruct *ws, c
     /* Clients waiting for us should not easily timeout */
     fdstate_set_expiry(sock, 0);
     fullscrape_deliver(sock, format);
-    http_interest_drop(sock, cookie, EVENT_IN);
+    http_interest_set(sock, cookie, 0);
     return ws->reply_size = -2;
   }
 #endif
@@ -435,7 +428,7 @@ static ssize_t http_handle_fullscrape(const int64_t sock, struct ot_workstruct *
   /* Clients waiting for us should not easily timeout */
   fdstate_set_expiry(sock, 0);
   fullscrape_deliver(sock, format);
-  http_interest_drop(sock, cookie, EVENT_IN);
+  http_interest_set(sock, cookie, 0);
   return ws->reply_size = -2;
 }
 #endif
diff --git a/ot_http.h b/ot_http.h
index 0f351c1..ba16de4 100644
--- a/ot_http.h
+++ b/ot_http.h
@@ -33,9 +33,8 @@ struct http_data {
   STRUCT_HTTP_FLAG flag;
 };
 
-/* Add to or drop from what this connection is waiting to be told about */
-void           http_interest_add(const int64_t s, struct http_data *cookie, int what);
-void           http_interest_drop(const int64_t s, struct http_data *cookie, int what);
+/* What this connection is waiting for: EVENT_IN, EVENT_OUT, or nothing */
+void           http_interest_set(const int64_t s, struct http_data *cookie, int what);
 
 /* Close a connection and release everything that belongs to it */
 void           http_close(const int64_t s);