HTTP READ() instead of GET()

Projects General Guidance
1

I am using the following:

#include <ESP8266HTTPClient.h>
#include <ESP8266httpUpdate.h>

In order to connect to a FOTA server that I have set up.

There I check for a ".bin" file that matches the ESP8266´s own MAC address converted to string. All is well there.

What I´m doing with http.GET() is first to retrieve "Last Modified" header, so I can compare to my current firmware´s saved date and time.

  HTTPClient httpClient;
  httpClient.setTimeout(2000);
  httpClient.begin( cfgVersionURL );
  httpClient.collectHeaders(headerKeys, headerKeysCount);
  int httpCode = httpClient.GET();
  if (httpCode == 200 && httpClient.hasHeader("date") && httpClient.hasHeader("last-modified")) {
    String onlineCurrentDate = UTC2Date(httpClient.header("date"));
    String onlineConfigDate = UTC2Date(httpClient.header("last-modified"));
    String lastConfigUpdate = <value from SPIFF parameter>

    if (onlineConfigDate > lastConfigUpdate) {
      String newConfig = httpClient.getString();

"UTC2Date" simply converts a UTC Date format to YYYYMMDDhhmmss string for easier comparison.

Of course, +99 out of 100 requests do not result in firmware update.

The question is if GET() retrieves the whole file from the server, or the bulk of the file is not currently received until getString() is called.

The .bin files are currently around 400Kb and in some scenarios the ESP8266 will be running on battery, so every kbyte and second turned on counts.

I have read that http.HEAD() sent to the same URL retrieves only headers, which is all I need to compare dates, but I haven´t found a clear way to implement it in my sketch.

Any advice?

2

You do a HEAD request this way:

httpClient.sendRequest("HEAD");

3

Thanks, I know that´s the request. I couldn´t find an operating example of how to use it (if .collectHeaders() is required, how the data is retrieved from the response, etc)... so I was asking for assistance.

4

All that "httpClient.GET()" does is call "httpClient.sendRequest("GET")"

What happens if you replace the line:
int httpCode = httpClient.GET();
with
int httpCode = httpClient.sendRequest("HEAD");
It may just work.