Fix jshPopIOEventOfType when the event to be popped is right at the start

Author: gfwilliams

ChangeLog

@@ -9,6 +9,7 @@
             Date: fix parsing of ISO8601 timezones (+HHMM worked, but +HH:MM and +HH added) (fix #2669)
             Bangle.js1: dump() now doesn't write out interpreter state as JS (saves 1.5kB Flash)
             Espruino Pico: Removed 'tv' library by default to free up flash storage
+            Fix jshPopIOEventOfType when the event to be popped is right at the start
 
      2v28 : Add `E.internal` as a way to access the 'hidden root' containing Espruino internal variables that previously needed `global["\xff"]`
             Bangle.js: Fix back handler not removed when using E.setUI with a back button but without widgets (#2636)

src/jsdevices.c

@@ -570,12 +570,25 @@ void CALLED_FROM_INTERRUPT jshPushIOEvent(
   jshPushEvent(channel, (uint8_t*)&t, 4);
 }
 
+/// Debugging only - prints the IO buffer, one item per line
+void jshDumpIOEvents() {
+  for (int i=ioTail;;i++) {
+    const char *name = "";
+    if (i==ioHead) name = (i==ioLastHead) ? "ioHead + ioLastHead" : "ioHead";
+    else if (i==ioLastHead) name = "ioLastHead";
+    if (i==ioTail) name = "ioTail";
+    jsiConsolePrintf("%d: %d %s\n", i, ioBuffer[i], name);
+    if (i==ioHead) break;
+  }
+}
+
 // pop an IO event, returns EV_NONE on failure
 IOEventFlags jshPopIOEvent(uint8_t *data, unsigned int *length) {
   if (ioHead==ioTail) return EV_NONE;
   if (ioLastHead==ioTail) ioLastHead = ioHead; // if we're processing last head now, reset it
   IOBufferIdx idx = ioTail;
   unsigned int len = (unsigned int)ioBuffer[idx];
+  assert(len <= IOEVENT_MAX_LEN);
   idx = (IOBufferIdx)((idx+1) & IOBUFFERMASK);
   IOEventFlags evt = (IOEventFlags)ioBuffer[idx];
   idx = (IOBufferIdx)((idx+1) & IOBUFFERMASK);
@@ -594,6 +607,7 @@ IOEventFlags jshPopIOEventOfType(IOEventFlags eventType, uint8_t *data, unsigned
   IOBufferIdx i = ioTail;
   while (ioHead!=i) {
     uint32_t len = (uint32_t)ioBuffer[i];
+    assert(len <= IOEVENT_MAX_LEN);
     IOBufferIdx j = (IOBufferIdx)((i+1) & IOBUFFERMASK);
     IOEventFlags evt = (IOEventFlags)ioBuffer[j];
     if (IOEVENTFLAGS_GETTYPE(evt) == eventType) {
@@ -608,19 +622,23 @@ IOEventFlags jshPopIOEventOfType(IOEventFlags eventType, uint8_t *data, unsigned
         if (data) data[n] = ioBuffer[j];
         j = (IOBufferIdx)((j+1) & IOBUFFERMASK);
       }
-      // work backwards and shift all items in queue down
-      IOBufferIdx dst = (IOBufferIdx)((i+len+1) & IOBUFFERMASK); // to: last element of this event
-      IOBufferIdx src = (IOBufferIdx)((i+IOBUFFERMASK) & IOBUFFERMASK); // from: item before current
-      while (true) {
-        ioBuffer[dst] = ioBuffer[src];
-        if (src==ioTail)
-          break;
-        // move backwards
-        src = (IOBufferIdx)((src+IOBUFFERMASK) & IOBUFFERMASK);
-        dst = (IOBufferIdx)((dst+IOBUFFERMASK) & IOBUFFERMASK);
+      if (i==ioTail) { // if we were at the start, just move onwards
+        ioTail = j;
+      } else { // not at the start, must shift back
+        // work backwards and shift all items in queue down
+        IOBufferIdx dst = (IOBufferIdx)((i+len+1) & IOBUFFERMASK); // to: last element of this event
+        IOBufferIdx src = (IOBufferIdx)((i+IOBUFFERMASK) & IOBUFFERMASK); // from: item before current
+        while (true) {
+          ioBuffer[dst] = ioBuffer[src];
+          if (src==ioTail)
+            break;
+          // move backwards
+          src = (IOBufferIdx)((src+IOBUFFERMASK) & IOBUFFERMASK);
+          dst = (IOBufferIdx)((dst+IOBUFFERMASK) & IOBUFFERMASK);
+        }
+        // finally update the tail pointer, and return
+        ioTail = dst;
       }
-      // finally update the tail pointer, and return
-      ioTail = dst;
       ioLastHead = ioHead; // reset last head - if we're removing stuff in the middle it's easier not to optimise!
       jshInterruptOn();
       return evt;

src/jsdevices.h

@@ -200,6 +200,9 @@ void jshPushIOCharEvent(IOEventFlags channel, char ch);
 /// Push many character events at once (for example USB RX)
 void jshPushIOCharEvents(IOEventFlags channel, char *data, unsigned int count);
 
+/// Debugging only - prints the IO buffer, one item per line
+void jshDumpIOEvents();
+
 /// pop an IO event, returns EV_NONE on failure. data must be IOEVENT_MAX_LEN bytes
 IOEventFlags jshPopIOEvent(uint8_t *data, unsigned int *length);
 // pop an IO event of type eventType, returns event type on success,EV_NONE on failure. data must be IOEVENT_MAX_LEN bytes