I have a plain old HTTP response stream (WiFiClient *) that I'm passing to HTTPClient::sendRequest(method, Stream *, size_t) over SSL.

The while-loop in ESP8266HTTPClient.cpp for reading from the stream and writing to the _tcp instance only does one iteration.

    while(connected() && stream->available() && (len > 0 || len == -1)) {

shouldn't check stream->available() since it could return 0 over a slow-ish connection. Maybe check for -1?

Similarly, the call here:

           // write it to Stream
            bytesWritten += _tcp->write((const uint8_t *)buff, c);

is returning 0 when _tcp is a WifiClientSecure.

size_t WiFiClientSecure::write(const uint8_t *buf, size_t size) {
    if (!_ssl)
        return 0;

    int rc = ssl_write(*_ssl, buf, size);
    if (rc >= 0)
        return rc;

    return 0;
}

The last return should maybe be a -1 with errno set, or simply just returning rc. If I change this to a -1 then I see that ssl_write is always returning a negative number....

I'm not familiar with the Arduino API enough to submit a patch for these issues.