Arduino_Ethernet(3)

看了一下如何用Arduino跟Server要求資料的部分，筆記一下

1. Stream:
依照官網分類，Stream是被分類在Function的部分，和Serial一樣，主要是用來Communication

按照官網的敘述:
Stream is the base class for character and binary based streams. It is not called directly, but invoked whenever you use a function that relies on it.

Stream defines the reading functions in Arduino. When using any core functionality that uses a read() or similar method, you can safely assume it calls on the Stream class. For functions like print(), Stream inherits from the Print class.

Stream Function沒辦法直接像C language的方式直接使用，使用的方法比較接近OOP使用method的方式(ex: client.fine(str))。在官網的敘述中描述"invoked whenever you use a function that relies on it."指可以被依賴Stream的object所調用 -> 想成被繼承Stream的object使用。

2. Some of the libraries that rely on Stream include:
   |- Serial
   |- Wire
   |- Ethernet Client
   |- Ethernet Server
   |- SD

3. 包含的Function:
   |- available()
   |- read() -> 用來讀取data
   |- flush()
   |- find() -> 搜尋目前list中是否有指定的String
   |- findUntil()
   |- peek()
   |- readBytes()
   |- readBytesUntil()
   |- parseInt() -> 用來parse目前list中的Int
   |- parseFloat() -> 用來parse目前list中的Float
   |- setTimeout()

4. 這次比較需要注意的是網站response，以下是在瀏覽器用Google搜尋的結果:
   a.在搜尋的text field打上50 miles
     (注意網址列:因為是用GET的方式來要求response，所以在網址列的後方會出現search?q=50+miles)
     
   b.注意搜尋到結果:
     下圖中框起來的部分是用粗體字 -> 在HTML語法中，粗體字是<b>tag，因此我們要利用此tag來得到我們要求的資料
     

5. Sample Code:
   在Sample Code中用到Stream中的find和parseFloat

#include 
#include 

byte mac[] = {0xDE,0xAD,0xBE,0xEF,0xFE,0xED};
char serverName[] = "www.google.com";
EthernetClient client;

void setup(){
  Serial.begin(9600);
  if(Ethernet.begin(mac)==0){
    Serial.println("Failed configure Ethernet using DHCP!");
    while(1);
  }
  delay(1000);
  Serial.println("connecting...");
}

void loop(){
  if(client.connect(serverName,80)>0){
    Serial.println("connected...");
    client.println("GET /search?q=50+km+in+miles HTTP/1.0");
    client.println();
  }
  else{
    Serial.println("connection failed");
  }
  
  if(client.connected()){
    if(client.find("<b>50 km")){  //find data
      if(client.find(" = ")){
        Serial.print("50 km is ");
        Serial.print(client.parseFloat());  //parse float
        Serial.println(" miles");
      }
    }
    else{
      Serial.println("result not found");
    }
    client.stop();
    delay(10000);  //after 10 second search again!
  }
  else{
    Serial.println();
    Serial.println("not connected");
    client.stop();
    delay(1000);
  }
}

6. run的結果: