String manipulation of a http response using Arduino

arduino

I will like to separate into different vars some information from a HTTP response, at the moment I'm just printing to the serial port the raw data, using:

Serial.print((const char*) Ethernet::buffer + off);

And that prints:

HTTP/1.1 200 OK
Date: Wed, 21 Nov 2012 22:47:21 GMT
Server: Apache
Vary: Accept-Encoding
Connection: close
Content-Type: text/html

Temp = 28...

I wonder how can I extract the information I need for later analysis, like the HTTP response code (200), the date, and the value of Temp, how can I extract this values into variables?

Best Answer

I had a look at the documentation, and it seems that you get the HTTP response from the Ethernet library, but you need to extract the information by other means.

I see two possibilities: (a) you parse the answer using C/C++ standard functions, or (b) you use a library created by somebody else. I found two libraries that may help you: this and this. Have a look at them and tell us how it goes with them.

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Extracting ints from a string on Arduino

FYI, a question about parsing strings is more suitable for Stack Overflow. But I'll try anyways.

It is unclear to me where the time starts in that string, is it 1819CET? Where 18 is the hour in 24-hour clock format and 19 is minutes? Why is there a 3 after the date? I will assume 1819CET is the time here in HHMM{TIMEZONE} format since you've indicated that the starting index is 19 in your code, since 18 would've landed on the 3 in the string.

I am unfamiliar with the arduino library, so I will read their documentation first. Doing so reveals the following. An excerpt from here: http://arduino.cc/en/Reference/StringSubstring

Get a substring of a String. The starting index is inclusive (the corresponding character is included in the substring), but the optional ending index is exclusive (the corresponding character is not included in the substring). If the ending index is omitted, the substring continues to the end of the String.

This:

time.substring(19,20)

Will not include index 20. It will only return a string of 1 character.

To be safe, try these sizes for your char arrays: char h_str[3]; and char m_str[3];

And try calling like this:

char h_str[3];
char m_str[3];
time.substring(19,21).toCharArray(h_str, sizeof(h_str));
time.substring(21,24).toCharArray(m_str, sizeof(m_str));

I'm using sizeof() here because toCharArray() asks for the size of the buffer being passed in as specified here.

Which String methods got changed with Arduino 1.0

I would suggest looking trough the source code of WString.cpp of the current version... That way you'll get up to date informations from the first hand...

Best Answer

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Which String methods got changed with Arduino 1.0

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