HttpClientLight: time out reading a body when the server goes silent (#25139)

writeToStreamDataBlock() looped for as long as connected() held, waiting
for the rest of the body with no time limit. A server that stops sending
part way through a body without closing the connection - a computer that
sleeps, a cable pulled, a network that drops between the two ends - leaves
connected() true for ever, so the read never returned. Called from the main
loop, as Berry's webclient get_string() is, it left the device answering
nothing, not even its web page, until it was power-cycled.

Give up after _tcpTimeout without data, returning HTTPC_ERROR_READ_TIMEOUT,
as handleHeaderResponse() already does for the headers. A body that keeps
arriving, however slowly, is unaffected: each piece resets the clock.

lib/libesp32/HttpClientLight/src/HttpClientLight.cpp

@@ -1370,6 +1370,10 @@ int HTTPClientLight::writeToStreamDataBlock(Stream * stream, int size)
     uint8_t * buff = (uint8_t *) malloc(buff_size);
 
     if(buff) {
+        // a server gone silent without closing stays connected(): give up
+        // after _tcpTimeout without data, as handleHeaderResponse() does
+        unsigned long lastDataTime = millis();
+
         // read all data from server
         while(connected() && (len > 0 || len == -1)) {
 
@@ -1442,8 +1446,14 @@ int HTTPClientLight::writeToStreamDataBlock(Stream * stream, int size)
                     len -= readBytes;
                 }
 
+                lastDataTime = millis();
                 delay(0);
             } else {
+                if((millis() - lastDataTime) > _tcpTimeout) {
+                    log_w("read timeout after %d bytes", bytesWritten);
+                    free(buff);
+                    return HTTPC_ERROR_READ_TIMEOUT;
+                }
                 delay(1);
             }
         }