enable cancel mid-flight in an HTTPS firmware upload

interface/src/app/status/SystemMonitor.tsx

@@ -145,9 +145,21 @@ const SystemMonitor = () => {
                 {LL.PLEASE_WAIT()}…
               </Typography>
               {isUploading && (
-                <Box sx={{ width: '100%', pl: 2, pr: 2, py: 2 }}>
-                  <LinearProgressWithLabel value={progressValue} />
-                </Box>
+                <>
+                  <Box sx={{ width: '100%', pl: 2, pr: 2, py: 2 }}>
+                    <LinearProgressWithLabel value={progressValue} />
+                  </Box>
+
+                  <Button
+                    sx={{ ml: 2, mt: 2 }}
+                    startIcon={<CancelIcon />}
+                    variant="outlined"
+                    color="secondary"
+                    onClick={onCancel}
+                  >
+                    {LL.CANCEL()}
+                  </Button>
+                </>
               )}
             </>
           )}

src/core/system.cpp

@@ -3149,6 +3149,18 @@ bool System::uploadFirmwareURL(const char * url) {
     int                last_pct   = -1;
 
     while (total_read < (size_t)firmware_size) {
+        // a cancel is signalled by the WebUI dropping the status below UPLOADING (back to NORMAL)
+        // via the systemStatus action, which runs on the AsyncTCP task while we're blocked here
+        if (EMSESP::system_.systemStatus() < SYSTEM_STATUS::SYSTEM_STATUS_UPLOADING) {
+            LOG_WARNING("Firmware upload cancelled at %u of %d bytes", (unsigned)total_read, firmware_size);
+            Update.abort();    // release the OTA partition handle so a later attempt can start cleanly
+            ssl_client.stop(); // drop the connection
+            saved_url.clear(); // prevent it from downloading again
+            EMSESP::system_.systemStatus(SYSTEM_STATUS::SYSTEM_STATUS_NORMAL);
+            Shell::loop_all(); // flush log buffers so the cancel message shows in the console
+            return true;       // not an error - don't trigger the failure/reset path in emsesp.cpp
+        }
+
         // wait for some data or for the connection to drop
         uint32_t wait_start = millis();
         while (!stream->available()) {
@@ -3158,10 +3170,18 @@ bool System::uploadFirmwareURL(const char * url) {
             if (millis() - wait_start > READ_TIMEOUT_MS) {
                 break;
             }
+            // also bail out promptly if a cancel arrives mid-stall
+            if (EMSESP::system_.systemStatus() < SYSTEM_STATUS::SYSTEM_STATUS_UPLOADING) {
+                break;
+            }
             delay(1);
         }
 
         if (!stream->available()) {
+            // if the inner wait broke because of a cancel, loop back so the top-of-loop handler runs
+            if (EMSESP::system_.systemStatus() < SYSTEM_STATUS::SYSTEM_STATUS_UPLOADING) {
+                continue;
+            }
             LOG_ERROR("Firmware upload failed - read stalled at %u of %d bytes", (unsigned)total_read, firmware_size);
             EMSESP::system_.systemStatus(SYSTEM_STATUS::SYSTEM_STATUS_ERROR_UPLOAD);
             return false;

src/core/system.h

@@ -358,7 +358,7 @@ class System {
     static uint32_t heap_mem_;
     static uint32_t min_free_mem_;
 
-    uint8_t systemStatus_; // uses SYSTEM_STATUS enum
+    volatile uint8_t systemStatus_; // uses SYSTEM_STATUS enum - written from the AsyncTCP task (e.g. cancel) and read from the main loop during OTA
 
     void set_partition_install_date();