URL encode char*

Projects Programming
1

I have the following function which sends text to a php script. But the php script only gets the first word of the sentence.

How do I convert the LogTxt to something that the php will receive as a sentence ?

eg : sending : this is a line, of data, 1,2,3

void LogItWebC(char* LogTxt){

  if (client.connect(myserver, 80)) {
    Serial.println("connected");
    client.print("GET http://www.AAA.co.za/serveit.php?data=");
    client.print(LogTxt);
    client.println(" HTTP/1.1");
    client.println("Host: www.AAA.co.za");
    client.println();
    delay(250);
    client.stop();
    Serial.println(LogTxt);
    Serial.println("disconnected");
    Serial.println("==================");
  } 
  else {
    Serial.println("connection failed");
    Serial.println("==================");
  }
}
2

You need to replace certain characters, like space, with different characters. Space becomes %20. You can look at how php encodes URLs and have the Arduino encode the same characters the same way.

3

do you know if there is an available function that can do this without me needing to write code for it ?

4

do you know if there is an available function that can do this without me needing to write code for it ?

Not that I know of.

5

Feeling lazy today, are we? :grin:

unsigned char specials[] = " "; /* String containing chars you want encoded */

static unsigned char hex_digit(unsigned char c)
{  return "01234567890ABCDEF"[c & 0x0F];
}

unsigned char *urlencode(unsigned char *dst,unsigned char *src)
{  unsigned char c,*d = dst;
   while (c = *src++)
   {  if (strchr(specials,c))
      {  *d++ = '%';
         *d++ = hex_digit(c >> 4);
         *d++ = hex_digit(c);
      }
      else *d++ = c;
   }
   return dst;
}

Edit: added declaration of c

6

OK. So if I get this right, I add the code sample you kindly supplied below my existing function, and change the specials value to :

unsigned char specials[] = "§_DISCOURSE_HOISTED_CODE_0_§+,/:;=?@ <>#%{}|\^~[]`"; /* String containing chars you want encoded */

static unsigned char hex_digit(unsigned char c)
{  return "01234567890ABCDEF"[c & 0x0F];
}

unsigned char *urlencode(unsigned char *dst,unsigned char *src)

and in my function I add :

void LogItWebC(char* LogTxt){

  char URLed = urlencode(LogTxt);

then I get an error on compile :

Invalid conversion from 'char*' to 'unsigned char*'

I have only a basic understanding of why this is happening, but not of how to solve it.

Also, the urlencode function appears to require 2 variables passed to it ( dst and src ). What are they ? I only have 1 char ( LogTxt ) that I want encoded.

7

Invalid conversion from 'char*' to 'unsigned char*'

I have only a basic understanding of why this is happening, but not of how to solve it.

Change all the unsigned chars to signed chars. That is, simply removed the unsigned keyword.

I only have 1 char ( LogTxt ) that I want encoded.

The encoded string will be longer than the original string, so you need to define and supply a place to store the encoded string.

8 
char specials[] = "§_DISCOURSE_HOISTED_CODE_0_§+,/:;=?@ <>#%{}|~[]`"; ///* String containing chars you want encoded */

static char hex_digit(char c)
{  return "01234567890ABCDEF"[c & 0x0F];
}

char* urlencode(char* dst,char* src)
{  char *d = dst;
   while (c = *src++)
   {  if (strchr(specials,c))
      {  *d++ = '%';
         *d++ = hex_digit(c >> 4);
         *d++ = hex_digit(c);
      }
      else *d++ = c;
   }
   return dst;
}

'c' was not declared in this scope

9

char* urlencode(char* dst,char* src)
{ char *d = dst;
char c;

10

Many Thanks

Now the (hopefully) last issue is : what should be passed to :

char* urlencode(char* dst,char* src)

as it looks like it is expecting 2 variables to be passed to it.

11 
void LogItWebC(char* LogTxt)
{
  char encodedTxt[120];
  urlencode(encodedTxt, LogTxt);
.
.
.
  //     client.print(LogTxt);
  client.print(encodedTxt);
.
.
.
}
12

PaulS first: Yuppers, I should have caught that before posting and you spotted it before I could correct. Thank you.

Dave next: You'll want a buffer to convert into and output from. For sake of discussion, let's call it 'buffer' and make it 80 chars wide:

char buffer[80];

will probably do the job. Now all that's needed is to recode to

client.print(urlencode(buffer,LogTxt));

to output that line in a urlencoded form.

13

Many Thanks all. ALMOST there.

now the line :

client.print(urlencode(buffer,LogTxt));

gives the error : invalid conversion from 'char*' to 'unsigned char*'

Should I just remove all the 'unsigned' keywords ?

14

That's what Paul suggested - it'll work. You'll also need to add

#include <string.h>

to your headers to get a prototype for strchr().

15

couldn't add :
#include <string.h>
as it doesn't exist in my libraries.

I ran the code without it and working well, except for a few odd characters appearing :

2012-04-02---20:01:32 Setup Completed - System OperationalÝ
2012-04-02---20:01:34 Doors OpenN!

and the = converting to < in this line :
2012-04-02---20:01:33 EEProm < 0 (sms OFF+ Home)0state

I added the following to the variable :

char specials[] = "§_DISCOURSE_HOISTED_CODE_0_§+,/:;=?@ <>#%{}|~[]`";
16

My bad (trying to carry on too many conversations at once) - I forgot to terminate the output string.

Let's try:

char specials[] = "§_DISCOURSE_HOISTED_CODE_0_§+,/:;=?@ <>#%{}|~[]`";

static char hex_digit(c)
{  return "01234567890ABCDEF"[c & 0x0F];
}
char *urlencode(char *dst,char *src)
{  char c,*d = dst;
   while (c = *src++)
   {  if (strchr(specials,c))
      {  *d++ = '%';
         *d++ = hex_digit(c >> 4);
         c = hex_digit(c);
      }
      *d++ = c;
   }
   *d = '\0';
   return dst;
}

It's strange to me that there's no string.h header file, but it'd appear not to have been needed. My ignorance knows no bounds! :grin:

Edit: Removed #include and simplified

17

Thanks Morris

Working like a dream now !!

Thank You so very much.

Lastly, I just have a question about this function, so that I can hopefully understand it properly :

static char hex_digit(char c)
{  return "01234567890ABCDEF"[c & 0x0F];
}

Is the purpose of this function to return either the character found in the string 01234567890ABCDEF, or if not found, then return the Hex of the 'char c' ?

If so, shouldn't the line 01234567890ABCDEF contain all 26 alpha letters, both upper and lower case ?

18

It converts the binary value of the low-order four bits of its argument to a hexadecimal digit character. By convention, the digits after 9 are A, B, C, D, E. and F. The number after F, as you might guess, is 10 - decimal 16.

19

Nice little thread! :slight_smile:

I'm currently having a similar problem -- but the other way around: I'm reading in strings from a POST HTTP response and have to decode the form variable's values. Unfortunately, a string value of "0,255,128" get's sent to the web server (running on the Arduino) as "0%2C255%2C128" because the comma character from the form's 'value=0,255,128' gets urlencoded to %2C.

Sooo, I have to decode HTML entities and was looking for a built-in (in some Arduino lib) function. To no avail.
The search function beamed me to this thread here.

Anybody who has a urldecode() function at hand that'll work on the Arduino?

Thanks so much!
Stefan.

20

Never mind!

Found something here: Google Code Archive - Long-term storage for Google Code Project Hosting.

Copy & pasted the two functions h2int() and urldecode() into my sketch and they work! :slight_smile: