Catch spotify song and display it on an esp98266 OLED

spotify_catcher.ino

/*
  Spotify catcher

  Functions as a "man in the middle" for the Spotify Client scrobbles that
  go to post.audioscrobbler.com (last.fm).
  
  Works on an esp8266 (Arduino IDE). Connect an oled to pin 3 (SDA) and
  pin4 (SCL) to show the currently playing song. 
  
  Make sure you put the IP of the esp9266 into /etc/hosts with the name 
  post.audioscrobbler.com. 

 */
#include <ESP8266WiFi.h>
#include <ESP8266mDNS.h>
#include <WiFiClient.h>
#include <Credentials.h>
#include "SSD1306.h"

const char* ssid = WIFI;
const char* password = WIFIPW;

// TCP server at port 80 will respond to HTTP requests
WiFiServer server(80);

// SDA on GPIO4, SDC on GPIO5
SSD1306  display(0x3c, 4, 5);

char *req = (char *)malloc(256);
char *path = (char *)malloc(64);

void get_param(char * str, char * value, char p) {
  int start, length;

  for (int i=0; i<(strlen(str)-2); i++) {
    if ( str[i] == p && str[i+1] == '=' ) {
      start = i + 2;
      i=strlen(str);
    }
  }

  length = 0;
  if ( start > 0 ) {
    for ( int i=start; i<strlen(str); i++ ) {
      if ( str[i] == '&' )
        break;
      length++;
    }
  }

  if ( length > 0 )
    memcpy(value, &str[start], length);

  value[length] = '\0';
  return;
}

void update_lastfm( char *req, char *str, char *feedback ) {
  WiFiClient client;

  const char* host = "post.audioscrobbler.com";
  const int httpPort = 80;

  if (!client.connect(host, httpPort)) {
    Serial.println("last.fm unreachable");
  }
  char *post = req;
  // char *replace = (char *)"Host: post.audioscrobbler.com";

  // First find "Host:"
  // char *rest = strstr(str, "Host:");
  // Determine where to start replacing
  // int s = (int)(rest - str);
  // The rest of the string starts after \n
  // rest = strstr(rest, "\n");

  // Determine how long the replacement text is.
  // int l = 0;
  // while ( rest[l] != '\n' ) { l++; };

  // Allocate memory
  // char *output = (char *)malloc(strlen(post)+strlen(str)+strlen(replace)-l);
  char *output = (char *)malloc(strlen(post)+strlen(str));
  memcpy(output, post, strlen(post));
  memcpy(output+strlen(post), str, strlen(str));
  output[strlen(output)+strlen(post)] = '\0';
  // memcpy(output+strlen(post), str, s);
  // memcpy(output+strlen(post)+s, replace, strlen(replace));
  // memcpy(output+strlen(post)+s+strlen(replace), rest, strlen(rest));
  // output[strlen(post)+s+strlen(replace)+strlen(rest)] = '\0';

  // Send the new output to last.fm
  client.print(output);

  delay(10);

  // catch the feedback
  int i=0;
  while(client.available()) {
    feedback[i++] = client.read();
  }
  feedback[i] = '\0';

  delay(10);

  free(output);

  client.flush();
}

int url_decode(char *str, char *dst) {
    unsigned int i;
    char *ptr = dst;

    for (i=0; i < strlen(str); i++) {
      if (str[i] == '+') {
        *ptr++ = ' ';
        continue;
      }
      if (str[i] != '%') {
        *ptr++ = str[i];
        continue;
      }

      if (!isdigit(str[i+1]) || !isdigit(str[i+2])) {
        *ptr++ = str[i];
        continue;
      }

      *ptr++ = ((str[i+1] - '0') << 4) | (str[i+2] - '0');
      i += 2;
    }
    *ptr = '\0';

    return 0;
}

void setup(void)
{
  Serial.begin(115200);

  // Connect to WiFi network
  WiFi.begin(ssid, password);
  Serial.println("");

  // Wait for connection
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");
  Serial.print("Connected to ");
  Serial.println(ssid);
  Serial.print("IP address: ");
  Serial.println(WiFi.localIP());

  // Set up mDNS responder:
  // - first argument is the domain name, in this example
  //   the fully-qualified domain name is "esp8266.local"
  // - second argument is the IP address to advertise
  //   we send our IP address on the WiFi network
  if (!MDNS.begin("esp8266")) {
    Serial.println("Error setting up MDNS responder!");
    while(1) {
      delay(1000);
    }
  }

  // Start TCP (HTTP) server
  server.begin();

  // Add service to MDNS-SD
  MDNS.addService("http", "tcp", 80);

  display.init();
  display.clear();
  display.setFont(ArialMT_Plain_16);
  display.drawString(0, 0, "Spotify catcher");
  display.display();

}

void loop(void)
{
  // Check if a client has connected
  WiFiClient client = server.available();
  if (!client) {
    return;
  }
  Serial.println("New client");

  // Wait for data from client to become available
  while(client.connected() && !client.available()){
    delay(1);
  }

  // Read the first line of HTTP request

  client.readBytesUntil('\r', req, 255);

  // Serial.print("req = ["); Serial.print(req); Serial.println("]");

  // Get the path from the request (we are only interested in responding to
  // /?hs=tr and /np_1.2 requests)

  path = strchr(req, ' ');
  path++;

  if (path == NULL) {
    Serial.print("Invalid request: ");
    Serial.println(req);
    return;
  }

  char feedback[512];

  // Spotify still uses the deprecated API of last.fm...
  if ( strncmp(path, "/np_1.2", 7) == 0  ) {
    Serial.println("searching track");
    char *artist;
    char *track;
    char data[512];

    // First we need to read all of the data that is comming from the spotify
    // client
    int i=0;
    while(client.available()) {
      data[i++] = client.read();
    }
    data[i] = '\0';
    // The interesting part is in the posted data. That contains the first = of
    // the whole package, so search for the '='.
    char *s;
    s = strchr(data, '=');

    // first url decode
    char *d = (char*)malloc(strlen(s));
    url_decode(s, d);

    artist = (char*)malloc(strlen(s));
    get_param(d, artist, 'a');
    Serial.print("artist=");
    Serial.println(artist);

    track = (char*)malloc(strlen(s));
    get_param(d, track, 't');
    Serial.print("track=");
    Serial.println(track);

    // update last.fm and get feedback
    update_lastfm(req, data, feedback);

    // Now output the band and track to the oled screen.
    display.clear();
    display.drawString(0, 0, artist);
    display.drawString(0,32, track);
    display.display();

  } else if ( strncmp(path, "/?hs=tr", 7) == 0  ) {
    // Serial.println("Authentication.. leave that to last.fm");
    char data[512];

    // First we need to read all of the data that is comming from the spotify
    // client
    int i=0;
    while(client.available()) {
      data[i++] = client.read();
    }
    data[i] = '\0';

    update_lastfm(req, data, feedback);

  }

  client.flush();

  String s;
  if ( strncmp(path, "/np_1.2", 7) == 0  ) {
    s = feedback;
  }
  else if ( strncmp(path, "/?hs=tr", 7) == 0 ) {
    s = feedback;
  }
  else
  {
    s = "HTTP/1.1 404 Not Found\r\n\r\n";
    Serial.println("Sending 404");
  }
  client.print(s);


}