feat(ESP8266): Add Max Fragment Length Negotiation for TLS connection

CHANGELOG.md

@@ -1,4 +1,10 @@
 # Changelog
+## Version 3.4.0 (in progres)
+### Features
+ - [#88](https://github.com/tobiasschuerg/InfluxDB-Client-for-Arduino/pull/88) - ESP8266 only - Added Max Fragment Length Negotiation for TLS communicaton to reduce memory allocation. If server supports MFLN, it saves ~15kB. Standalone InfluxDB OSS server doesn't support MFLN, Cloud yes. To leverage MFLN for standalone OSS, a reverse proxy needs to be used. 
+
+ ### Documentation
+ - [#87](https://github.com/tobiasschuerg/InfluxDB-Client-for-Arduino/pull/87) - Fixed include file name in the Readme
 
 ## Version 3.3.0 (2020-07-07)
  - [NEW] Added possibility skip server certification validation (`setInsecure()` method)

README.md

@@ -103,7 +103,7 @@ InfluxDBCloud uses secure communication (https) and we need to tell the client t
 Connection parameters are almost the same as above, the only difference is that server URL now points to the InfluxDB Cloud 2, where you've got after you've finished creating InfluxDB Cloud 2 subscription. You will find correct server URL in  `InfluxDB UI -> Load Data -> Client Libraries`.
 ```cpp
 //Include also InfluxClould 2 CA certificate
-#include <InfluxCloud.h>
+#include <InfluxDbCloud.h>
 // InfluxDB 2 server or cloud url, e.g. https://eu-central-1-1.aws.cloud2.influxdata.com (Use: InfluxDB UI -> Load Data -> Client Libraries)
 #define INFLUXDB_URL "influxdb-url"
 // InfluxDB 2 server or cloud API authentication token (Use: InfluxDB UI -> Load Data -> Tokens -> <select token>)

src/InfluxDbClient.cpp

@@ -50,7 +50,9 @@ static const char RetryAfter[] = "Retry-After";
 static const char TransferEnconding[] = "Transfer-Encoding";
 
 static String escapeJSONString(String &value);
-
+#if defined(ESP8266)  
+bool checkMFLN(BearSSL::WiFiClientSecure *client, String url);
+#endif
 static String precisionToString(WritePrecision precision, uint8_t version = 2) {
     switch(precision) {
         case WritePrecision::US:
@@ -220,6 +222,7 @@ bool InfluxDBClient::init() {
         if (_insecure) {
             wifiClientSec->setInsecure();
         }
+        checkMFLN(wifiClientSec, _serverUrl);
 #elif defined(ESP32)
         WiFiClientSecure *wifiClientSec = new WiFiClientSecure;  
         if(_certInfo && strlen_P(_certInfo) > 0) { 
@@ -236,6 +239,52 @@ bool InfluxDBClient::init() {
     return true;
 }
 
+// parse URL for host and port and call probeMaxFragmentLength
+#if defined(ESP8266)         
+bool checkMFLN(BearSSL::WiFiClientSecure  *client, String url) {
+    int index = url.indexOf(':');
+     if(index < 0) {
+        return false;
+    }
+    String protocol = url.substring(0, index);
+    int port = -1;
+    url.remove(0, (index + 3)); // remove http:// or https://
+
+    if (protocol == "http") {
+        // set default port for 'http'
+        port = 80;
+    } else if (protocol == "https") {
+        // set default port for 'https'
+        port = 443;
+    } else {
+        return false;
+    }
+    index = url.indexOf('/');
+    String host = url.substring(0, index);
+    url.remove(0, index); // remove host 
+    // check Authorization
+    index = host.indexOf('@');
+    if(index >= 0) {
+        host.remove(0, index + 1); // remove auth part including @
+    }
+    // get port
+    index = host.indexOf(':');
+    if(index >= 0) {
+        String portS = host;
+        host = host.substring(0, index); // hostname
+        portS.remove(0, (index + 1)); // remove hostname + :
+        port = portS.toInt(); // get port
+    }
+    INFLUXDB_CLIENT_DEBUG("probeMaxFragmentLength to %s:%d\n", host.c_str(), port);
+    bool mfln = client->probeMaxFragmentLength(host, port, 1024);
+    INFLUXDB_CLIENT_DEBUG("  MFLN:%s\n", mfln ? "yes" : "no");
+    if (mfln) {
+        client->setBufferSizes(1024, 1024);
+    } 
+    return mfln;
+}
+#endif //ESP8266
+
 InfluxDBClient::~InfluxDBClient() {
      if(_pointsBuffer) {
         delete [] _pointsBuffer;
@@ -248,10 +297,6 @@ InfluxDBClient::~InfluxDBClient() {
 }
 
 void InfluxDBClient::clean() {
-    // if(_wifiClient) {
-    //     delete _wifiClient;
-    //     _wifiClient = nullptr;
-    // }
      _wifiClient = nullptr;
 #if defined(ESP8266)     
     if(_cert) {