.h

HttpClient& client;
    int bytesWritten;
public:
    int contentLength;
    char* client_ID;
    char* api_Key;


    ParamSender(HttpClient& _client) : client(_client) {
        bytesWritten = 0;
        contentLength = 0;
    }

    bool start(int _contentLength);
    bool sendParam(const char* name, char* value);
    bool sendParam(const __FlashStringHelper *ifsh, char* value);
    bool end();
};




.cpp

#include "ParamSender.h"
#include "GSMmodem.h"

#define HTTP_PARAMS_PATH "/client/parameter"


bool ParamSender::start(int _contentLength) {
#ifdef USE_SSL
    client.connectionKeepAlive();
#endif // USE_SSL

    client.beginRequest();
    int err = client.post(HTTP_PARAMS_PATH);
    if (err == 0) {
        client.sendHeader(HTTP_HEADER_CONTENT_TYPE, HTTP_URLENCODED);
        client.sendHeader(HTTP_HEADER_CONTENT_LENGTH, contentLength);
        client.sendHeader(HTTP_HEADER_CLIENT_GUID, client_ID);
        client.sendHeader(HTTP_HEADER_API_KEY, api_Key);
        client.endRequest();
        return true;
    }
    else {
        DBGS("ParamSend START failed");
        client.stop();
        return false;
    }
}

bool ParamSender::sendParam(const char* name, char* value) {
    int written = 0;
    written += client.write(name);
    written += client.write("=");
    written += client.write(value);
    written += client.write("\n");
    if (written < strlen(name) + strlen(value) + 3) {
        client.stop();
        return false;
    }
    bytesWritten += written;
    return true;
}

bool ParamSender::sendParam(const __FlashStringHelper *ifsh, char* value) {
    int written = 0;
    int namelength = 0;
    //written += client.print(name);

    PGM_P p = reinterpret_cast<PGM_P>(ifsh);
    p = reinterpret_cast<PGM_P>(ifsh);
    while (1) {
        unsigned char c = pgm_read_byte(p++);
        if (c == 0) break;
        if (client.write(c)) written++;
        else break;
    }
    namelength = written;
    written += client.write("=");
    written += client.write(value);
    written += client.write("\n");
    if (written < namelength + strlen(value) + 3) {
        client.stop();
        return false;
    }
    bytesWritten += written;
    return true;
}

bool ParamSender::end() {
    //char buff[16] = { '.','.','.','.','.','.','.','.','.','.','.','.','.','.','.','.' };
    char buff[8] = { '.','.','.','.','.','.','.','.'};
    while (bytesWritten < contentLength) {
        int toWrite = contentLength - bytesWritten;
        if (toWrite > 8) toWrite = 8;

        int written = client.write(buff, toWrite);
        if (written < toWrite) {
            client.stop();
            return false;
        }
        bytesWritten += written;
    }

    int status = client.responseStatusCode();
    client.skipResponseHeaders();
    if (!status) {
        client.stop();
        return false;
    }

    client.stop();
    return true;
}