I couldn't find anything like this posted so I thought I'd throw it out here. I wanted the Arduino to get XML formatted weather data from a NOAA web site.
This kind of thing definitely isn't Arduino's strong suite but it seems to work great. As I'm no C lang guru, any hints for improvement appreciated.
//////////////////////////////////////////////
// Get XML formatted data from the web.
// 1/6/08 Bob S. - Created
//
// Assumptions: single XML line looks like:
// <tag>data</tag> or <tag>data
//
// Get current weather observation for Raleigh from weather.gov in XML format
//
//////////////////////////////////////////////
// Include description files for other libraries used (if any)
#include <string.h>
#include <Ethernet.h>
// Define Constants
// Max string length may have to be adjusted depending on data to be extracted
#define MAX_STRING_LEN 20
// Setup vars
char tagStr[MAX_STRING_LEN] = "";
char dataStr[MAX_STRING_LEN] = "";
char tmpStr[MAX_STRING_LEN] = "";
char endTag[3] = {'<', '/', '\0'};
int len;
// Flags to differentiate XML tags from document elements (ie. data)
boolean tagFlag = false;
boolean dataFlag = false;
// Ethernet vars
byte mac[] = { 0xDE, 0xAD, 0xBE, 0xEF, 0xFE, 0xED };
byte ip[] = { 192, 168, 0, 41 };
byte server[] = { 140, 90, 113, 200 }; // www.weather.gov
// Start ethernet client
Client client(server, 80);
void setup()
{
Serial.begin(9600);
Serial.println("Starting WebWx");
Serial.println("connecting...");
Ethernet.begin(mac, ip);
delay(1000);
if (client.connect()) {
Serial.println("connected");
client.println("GET /xml/current_obs/KRDU.xml HTTP/1.0");
client.println();
delay(2000);
} else {
Serial.println("connection failed");
}
}
void loop() {
// Read serial data in from web:
while (client.available()) {
serialEvent();
}
if (!client.connected()) {
//Serial.println();
//Serial.println("Disconnected");
client.stop();
// Time until next update
//Serial.println("Waiting");
for (int t = 1; t <= 15; t++) {
delay(60000); // 1 minute
}
if (client.connect()) {
//Serial.println("Reconnected");
client.println("GET /xml/current_obs/KRDU.xml HTTP/1.0");
client.println();
delay(2000);
} else {
Serial.println("Reconnect failed");
}
}
}
// Process each char from web
void serialEvent() {
// Read a char
char inChar = client.read();
//Serial.print(".");
if (inChar == '<') {
addChar(inChar, tmpStr);
tagFlag = true;
dataFlag = false;
} else if (inChar == '>') {
addChar(inChar, tmpStr);
if (tagFlag) {
strncpy(tagStr, tmpStr, strlen(tmpStr)+1);
}
// Clear tmp
clearStr(tmpStr);
tagFlag = false;
dataFlag = true;
} else if (inChar != 10) {
if (tagFlag) {
// Add tag char to string
addChar(inChar, tmpStr);
// Check for </XML> end tag, ignore it
if ( tagFlag && strcmp(tmpStr, endTag) == 0 ) {
clearStr(tmpStr);
tagFlag = false;
dataFlag = false;
}
}
if (dataFlag) {
// Add data char to string
addChar(inChar, dataStr);
}
}
// If a LF, process the line
if (inChar == 10 ) {
/*
Serial.print("tagStr: ");
Serial.println(tagStr);
Serial.print("dataStr: ");
Serial.println(dataStr);
*/
// Find specific tags and print data
if (matchTag("<temp_f>")) {
Serial.print("Temp: ");
Serial.print(dataStr);
}
if (matchTag("<relative_humidity>")) {
Serial.print(", Humidity: ");
Serial.print(dataStr);
}
if (matchTag("<pressure_in>")) {
Serial.print(", Pressure: ");
Serial.print(dataStr);
Serial.println("");
}
// Clear all strings
clearStr(tmpStr);
clearStr(tagStr);
clearStr(dataStr);
// Clear Flags
tagFlag = false;
dataFlag = false;
}
}
/////////////////////
// Other Functions //
/////////////////////
// Function to clear a string
void clearStr (char* str) {
int len = strlen(str);
for (int c = 0; c < len; c++) {
str[c] = 0;
}
}
//Function to add a char to a string and check its length
void addChar (char ch, char* str) {
char *tagMsg = "<TRUNCATED_TAG>";
char *dataMsg = "-TRUNCATED_DATA-";
// Check the max size of the string to make sure it doesn't grow too
// big. If string is beyond MAX_STRING_LEN assume it is unimportant
// and replace it with a warning message.
if (strlen(str) > MAX_STRING_LEN - 2) {
if (tagFlag) {
clearStr(tagStr);
strcpy(tagStr,tagMsg);
}
if (dataFlag) {
clearStr(dataStr);
strcpy(dataStr,dataMsg);
}
// Clear the temp buffer and flags to stop current processing
clearStr(tmpStr);
tagFlag = false;
dataFlag = false;
} else {
// Add char to string
str[strlen(str)] = ch;
}
}
// Function to check the current tag for a specific string
boolean matchTag (char* searchTag) {
if ( strcmp(tagStr, searchTag) == 0 ) {
return true;
} else {
return false;
}
}