POP3: fix end of body detection

Curl_pop3_write() now has a state machine that scans for the end of a
POP3 body so that the CR LF '.' CR LF sequence can come in everything
from one up to five subsequent packets.

Test case 810 is modified to use SLOWDOWN which makes the server pause
between each single byte and thus makes the POP3 body get sent to curl
basically one byte at a time.

lib/pop3.c

@@ -1032,34 +1032,68 @@ CURLcode Curl_pop3_write(struct connectdata *conn,
 
   /* Detect the end-of-body marker, which is 5 bytes:
      0d 0a 2e 0d 0a. This marker can of course be spread out
-     over up to 5 different data chunks. Deal with it! */
+     over up to 5 different data chunks.
+  */
   struct pop3_conn *pop3c = &conn->proto.pop3c;
-  size_t checkmax = (nread >= POP3_EOB_LEN?POP3_EOB_LEN:nread);
+  unsigned int i;
-  size_t checkleft = POP3_EOB_LEN-pop3c->eob;
-  size_t check = (checkmax >= checkleft?checkleft:checkmax);
 
-  if(!memcmp(POP3_EOB, &str[nread - check], check)) {
+  /* since the EOB string must be within the last 5 bytes, get the index
-    /* substring match */
+     position of where to start to scan for it */
-    pop3c->eob += check;
+  size_t checkstart = (nread>POP3_EOB_LEN)?nread-POP3_EOB_LEN:0;
-    if(pop3c->eob == POP3_EOB_LEN) {
+
-      /* full match, the transfer is done! */
+  if(checkstart) {
-      str[nread - check] = '\0';
+    /* write out the first piece, if any */
-      nread -= check;
+    result = Curl_client_write(conn, CLIENTWRITE_BODY, str, checkstart);
-      k->keepon &= ~KEEP_RECV;
-      pop3c->eob = 0;
-    }
-  }
-  else if(pop3c->eob) {
-    /* not a match, but we matched a piece before so we must now
-       send that part as body first, before we move on and send
-       this buffer */
-    result = Curl_client_write(conn, CLIENTWRITE_BODY,
-                               (char *)POP3_EOB, pop3c->eob);
     if(result)
       return result;
-    pop3c->eob = 0;
+    pop3c->eob=0;
   }
 
+  for(i=checkstart; i<nread; i++) {
+    size_t prev = pop3c->eob;
+    switch(str[i]) {
+    case 0x0d:
+      if((pop3c->eob == 0) || (pop3c->eob == 3))
+        pop3c->eob++;
+      else
+        /* if it wasn't 0 or 3, it restarts the pattern match again */
+        pop3c->eob=1;
+      break;
+    case 0x0a:
+      if((pop3c->eob == 1) || (pop3c->eob == 4))
+        pop3c->eob++;
+      else
+        pop3c->eob=0;
+      break;
+    case 0x2e:
+      if(pop3c->eob == 2)
+        pop3c->eob++;
+      else
+        pop3c->eob=0;
+      break;
+    default:
+      pop3c->eob=0;
+      break;
+    }
+    if(pop3c->eob == POP3_EOB_LEN) {
+      /* full match, the transfer is done! */
+      k->keepon &= ~KEEP_RECV;
+      pop3c->eob = 0;
+      return CURLE_OK;
+    }
+    else if(prev && (prev >= pop3c->eob)) {
+      /* write out the body part that didn't match */
+      result = Curl_client_write(conn, CLIENTWRITE_BODY, (char*)POP3_EOB,
+                                 prev);
+      if(result)
+        return result;
+    }
+  }
+
+  if(pop3c->eob)
+    /* while EOB is matching, don't output it! */
+    return CURLE_OK;
+
   result = Curl_client_write(conn, CLIENTWRITE_BODY, str, nread);
 
   return result;

tests/data/test810

@@ -9,6 +9,11 @@ LIST
 #
 # Server-side
 <reply>
+# We use SLOWDOWN to really exercise the end-of-body parsing over multiple
+# packets
+<servercmd>
+SLOWDOWN
+</servercmd>
 # When doing LIST, we get the default list output hard-coded in the test
 # POP3 server
 <datacheck>
@@ -25,7 +30,7 @@ LIST
 pop3
 </server>
  <name>
-POP3 LIST messages
+POP3 LIST messages from *SLOW* server
  </name>
  <command>
 pop3://%HOSTIP:%POP3PORT/ -u user:secret