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Add support for ETag header #89

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Add support for ETag header #89

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6688792
Add support for ETag header
jamesthurley Mar 11, 2025
b989d35
Further work on ETag support after testing on device
jamesthurley Mar 11, 2025
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1 change: 1 addition & 0 deletions include/config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -22,6 +22,7 @@
#define PREFERENCES_LAST_SLEEP_TIME "last_sleep"
#define PREFERENCES_CONNECT_API_RETRY_COUNT "retry_count"
#define PREFERENCES_CONNECT_WIFI_RETRY_COUNT "wifi_retry"
#define PREFERENCES_ETAG_KEY "etag"

#define WIFI_CONNECTION_RSSI (-100)

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34 changes: 34 additions & 0 deletions src/bl.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -207,7 +207,12 @@ void bl_init(void)
need_to_refresh_display = 1;
preferences.putBool(PREFERENCES_DEVICE_REGISTRED_KEY, false);
Log.info("%s [%d]: Display TRMNL logo end\r\n", __FILE__, __LINE__);

// We're displaying the logo on the screen, so we reset the
// two preferences specifying the previous filename and the previous ETag
// to ensure we refresh this time to remove the logo.
preferences.putString(PREFERENCES_FILENAME_KEY, "");
preferences.putString(PREFERENCES_ETAG_KEY, "");
}

// Mount SPIFFS
Expand Down Expand Up @@ -1058,8 +1063,20 @@ static https_request_err_e downloadAndShow()

return HTTPS_UNABLE_TO_CONNECT;
}

// If we have an ETag, add it to the request.
String currentEtag = preferences.getString(PREFERENCES_ETAG_KEY, "");
if (currentEtag.length() > 0) {
https.addHeader("If-None-Match", currentEtag);
}

Log.info("%s [%d]: [HTTPS] GET..\r\n", __FILE__, __LINE__);
Log.info("%s [%d]: RSSI: %d\r\n", __FILE__, __LINE__, WiFi.RSSI());

// Ensure we look for the ETag header in the response.
const char* headerKeys[] = {"ETag", "Content-Type"};
https.collectHeaders(headerKeys, 2);

// start connection and send HTTP header
int httpCode = https.GET();

Expand All @@ -1076,6 +1093,23 @@ static https_request_err_e downloadAndShow()
// HTTP header has been send and Server response header has been handled
Log.error("%s [%d]: [HTTPS] GET... code: %d\r\n", __FILE__, __LINE__, httpCode);
Log.info("%s [%d]: RSSI: %d\r\n", __FILE__, __LINE__, WiFi.RSSI());

if (httpCode == HTTP_CODE_NOT_MODIFIED)
{
// The server used the ETag to determine that the content hasn't changed
// for this device and so returned a 304 Not Modified response.
// We don't need to update the screen.
Log.info("%s [%d]: Not modified. No need to download\r\n", __FILE__, __LINE__);
return HTTPS_SUCCES;
}

if (https.hasHeader("ETag")) {
// The server sent back an ETag header. Save it to include in the next request.
String etag = https.header("ETag");
Log.info("%s [%d]: ETag: %s\r\n", __FILE__, __LINE__, etag.c_str());
preferences.putString(PREFERENCES_ETAG_KEY, etag);
}

// file found at server
if (httpCode != HTTP_CODE_OK && httpCode != HTTP_CODE_MOVED_PERMANENTLY)
{
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