I have used a fifo pipe to read in some data (weather data) into a char variable. The console will display this variable correctly. However, when I try to display it through HTML on the CGI page, it simply does not display. Code below -
int main(void) {
int fd;
char *myfifo = "pressure.txt";
char buff[BUFFER];
long fTemp;
//open and read message
fd = open(myfifo, O_RDONLY);
read(fd, buff, BUFFER);
printf("Received: %s\n", buff);
close(fd);
printf("Content-type: text/html\n\n");
puts("<HTML>");
puts("<BODY>");
printf("Data is: %s", buff);
puts("</BODY>");
puts("</HTML>");
return EXIT_SUCCESS;
}
As you can see in the console is displays correctly -
Received: 2014-08-13 16:54:57
25.0 DegC, 1018.7 mBar
Content-type: text/html
<HTML>
<BODY>
Data is 2014-08-13 16:54:57
25.0 DegC, 1018.7 mBar
</BODY>
</HTML>
logout
But on the CGI webpage it does not display the weather data, but it does display "data is".
Two important things when writing a CGI program:
the program will be run by the webserver, which is normally
started as a different user (the 'www' user for example).
it's possible that the program is started from within another
directory, which can cause different behaviour if you don't
specify the full path of a file you want to open.
Since both these things can cause problems, it can be helpful
to add some debug information. Of course, it's always a good idea
to check return values of functions you use.
To make it easier to display debug or error messages, I'd first
move the following code up, so that all output that comes after
it will be rendered by the browser:
printf("Content-type: text/html\r\n\r\n");
puts("<HTML>");
puts("<BODY>");
It may be useful to know what the webserver uses as the directory
from which the program is started. The getcwd
call can help here. Let's use a buffer of size BUFFER to store
the result in, and check if it worked:
char curpath[BUFFER];
if (getcwd(curpath, BUFFER) == NULL)
printf("Can't get current path: %s<BR>\n", strerror(errno));
else
printf("Current path is: %s<BR>\n", curpath);
The getcwd function returns NULL in case of an error, and sets the value
of errno to a number which indicates what went wrong. To convert this
value to something readable, the strerror
function is used. For example, if BUFFER was not large enough to be
able to store the path, you'll see something like
Can't get current path: Numerical result out of range
The open call returns a negative number
if it didn't work, and sets errno again. So, to check if this worked:
fd = open(myfifo, O_RDONLY);
if (fd < 0)
printf("Can't open file: %s<BR>\n", strerror(errno));
In case the file can be found, but the webserver does not have permission
to open it, you'll see
Can't open file: Permission denied
If the program is started from another directory than you think, and
it's unable to locate the file, you would get:
Can't open file: No such file or directory
Adding such debug info should make it more clear what's going on, and more
importantly, what's going wrong.
To make sure the actual data is read without problems as well, the return
value of the read function should be
checked and appropriate actions should be taken. If read fails,
a negative number is returned. To handle this:
numread = read(fd, buff, BUFFER);
if (numread < 0)
printf("Error reading from file: %s<BR>\n", strerror(errno));
Another value indicates success, and returns the number of bytes that were
read. If really BUFFER bytes were read, it's not at all certain that the
last byte in buff is a 0, which is needed for printf to know when the
string ended. To make sure it is in fact null-terminated, the last byte in
buff is set to 0:
if (numread == BUFFER)
buff[BUFFER-1] = 0;
Note that this actually overwrites one of the bytes that were read in this
case.
If fewer bytes were read, it's still not certain that the last byte that was
read was a 0, but now we can place our own 0 after the bytes that were read
so none of them are overwritten:
else
buff[numread] = 0;
To make everything work, you may need the following additional include files:
#include <unistd.h>
#include <string.h>
#include <errno.h>
The complete code of what I described is shown below:
int main(void)
{
int fd, numread;
char *myfifo = "pressure.txt";
char buff[BUFFER];
char curpath[BUFFER];
long fTemp;
// Let's make sure all text output (even error/debug messages)
// will be visible in the web page
printf("Content-type: text/html\r\n\r\n");
puts("<HTML>");
puts("<BODY>");
// Some debug info: print the current path
if (getcwd(curpath, BUFFER) == NULL)
printf("Can't get current path: %s<BR>\n", strerror(errno));
else
printf("Current path is: %s<BR>\n", curpath);
// Open the file
fd = open(myfifo, O_RDONLY);
if (fd < 0)
{
// An error occurs, let's see what it is
printf("Can't open file: %s<BR>\n", strerror(errno));
}
else
{
// Try to read 'BUFFER' bytes from the file
numread = read(fd, buff, BUFFER);
if (numread < 0)
{
printf("Error reading from file: %s<BR>\n", strerror(errno));
}
else
{
if (numread == BUFFER)
{
// Make sure the last byte in 'buff' is 0, so that the
// string is null-terminated
buff[BUFFER-1] = 0;
}
else
{
// Fewer bytes were read, make sure a 0 is placed after
// them
buff[numread] = 0;
}
printf("Data is: %s<BR>\n", buff);
}
close(fd);
}
puts("</BODY>");
puts("</HTML>");
return EXIT_SUCCESS;
}
Related
Im new to C and very new to network programming. I wrote some code that would read an HTML file chunk by chunk. Everything works great until the last chunk which gets read in twice and Im not inertly sure why.
char request[] = "GET /~kkredo/file.html HTTP/1.0\r\n\r\n";
char response[10000];
int bytes, p_count = 0;
int res_code = 1;
send(sock, request, sizeof(request), 0);
while(res_code != 0) {
res_code = recv(sock, &response, chunk, 0);
printf("%s",response);
bytes += res_code;
}
That's the code for the loop, it prints out each chunk until the last chunk which prints twice. Ive put an If statement to double check what the loop is checking, and even though res_code = 0, it still prints. I think it has something to do with the char buffer but Im not sure.
<p> that's it for this page </p>
</body>
</html>
</body>
</html>
That would be an example of the duplication. The second html and body tags are duplicated and dependent on if the chunk size is larger, then it would duplicate more of the document. Thanks for the help.
you call
printf("%s",response);
without regarding res_code, thus if recv() doesn't receive anymore data and returns 0, you print whatever still is in response. Furthermore: response isn't necessarily NUL terminated, so your printf() invokes UB. And, as a third point, your code doesn't handle that recv() might return -1.
So you should change yout loop to:
while(res_code > 0) {
res_code = recv(sock, response, chunk, 0); // '&' isn't necessary here
if(res_code > 0) {
printf("%.*s",res_code,response);
bytes += res_code;
}
}
I've set up a webserver running on ESP8266 thats currently hosting 7 sites. The sites is written in plain HTML in each diffrent tab in the arduino ide. I have installed the library Pagebuilder to help with making everything look nice and run.
Except one thing. I have a button connected to my ESP8266 which by the time being imitates a sensor input. basicly when the button is pressed my integer "x" increments with 1. I also managed to make a string that replicates "x" and increments with the same value.
I also have a problem with Printing the IPadresse of the server, but thats not as important as the other.
My plan then was writing the string "score" (which contains x) into the HTML tab where it should be output. this obviously didnt work.
Things I've tried:
Splitting up the HTML code where I want the string to be printed and using client.println("");
This didnt work because the two libraries does not cooperate and WiFiClient does not find Pagebuilders server. (basicly, the client.println does nothing when I used it with Pagebuilder).
Reconstructing the HTML page as a literal really long string, and adding in the String with x like this: "html"+score+"html" and adding it into where the HTML page const char were. (basicly replacing the variable with the text that were in the variable).
This did neighter work because the argument "PageElement" from Pagebuilder does only expect one string, and errors out because theres an additional string inside the HTML string.
I've tried sending it as a post req. but this did not output the value either.
I have run out of Ideas to try.
//root page
#if defined(ARDUINO_ARCH_ESP8266)
#include <ESP8266WiFi.h>
#include <ESP8266WebServer.h>
#include <WiFiClient.h>
#elif defined(ARDUINO_ARCH_ESP32)
#include <WiFi.h>
#include <WebServer.h>
#endif
#include "PageBuilder.h"
#include "currentGame.h" //tab 1
#if defined(ARDUINO_ARCH_ESP8266)
ESP8266WebServer Server;
ESP8266WebServer server;
#endif
int sensorPin = 2; // button input
int sensorValue = 0;
int x = 0; // the int x
String score=""; //the string x will be in
PageElement CURRENT_GAME_ELEMENT(htmlPage1);
PageBuilder CURRENT_GAME("/current-game", {CURRENT_GAME_ELEMENT}); // this //only showes on href /current-game
void button() {
sensorValue = analogRead(sensorPin); //read the voltage
score="Team 1: "+String((int)x+1); //"make" x a string
if (sensorValue <= 10) { // check if button is pressed
x++; // increment x
Serial.println(x);
Serial.println(score);
delay(100);
}
}
void setup() {
Serial.begin(115200);
pinMode(2, INPUT);
WiFi.softAP("SSID", "PASS");
delay(100);
CURRENT_GAME.insert(Server);
Server.begin();
}
void loop() {
Server.handleClient();
button();
}
// tab 1
const char htmlPage1[] PROGMEM = R"=====(
/*
alot of HTML, basicly the whole website...
..............................................
*/
<div class="jumbotron">
<div align="center">
<h1 class="display-4"> score </h1> // <--- this is where
//I want to print the
//string:
</div>
</div>
)=====";
what I want to do is getting the value of the string score displayed on the website. If I put "score" directly into the HTML, the word score will be displayed, not the value. I want the value displayed.
Edit:
I have figured out how to make the string(score) be printed in the HTML code, thus, I only have to convert the HTML code string back to a char. explanation is in comment below.
Edit 2: (-------------------------solution-------------------------)
Many thanks for the help I've gotten and sorry for being so ignorant, its just so hard being so close and that thing doesnt work. but anyways, What I did was following Pagebuilders example, and making another element to print in current game..
String test(PageArgument& args) {
return score;
}
const char html[] = "<div class=\"jumbotron\"><div align=\"center\"><h1 class=\"display-4\">{{NAME}}</h1></div></div>";
PageElement FRAMEWORK_PAGE_ELEMENT(htmlPage0);
PageBuilder FRAMEWORK_PAGE("/", {FRAMEWORK_PAGE_ELEMENT});
PageElement body_elem(html, { {"NAME", test} });
PageElement CURRENT_GAME_ELEMENT(htmlPage1);
PageBuilder CURRENT_GAME("/current-game", { CURRENT_GAME_ELEMENT, body_elem});
suprisingly easy when I first understood it.. Thanks again.
You could try building your string first, then converting it to a const char
like this: const char * c = str.c_str();
if you can't use a pointer you could try this:
string s = "yourHTML" + score + "moreHTML";
int n = s.length();
char char_array[n + 1];
strcpy(char_array, s.c_str());
additionally you could try the stringstream standard library
This sort of thing is often done using magic tags in your markup that are detected by the server code before it serves the HTML and filled in by executing some sort of callback or filling in a variable, or whatever.
So with this in mind and hoping for the best, I nipped over to: PageBuilder on github and looked to see if there was something similar here. Good news! In one of the examples:
const char html[] = "hello <b>{{NAME}}</b>, <br>Good {{DAYTIME}}.";
...
PageElement body_elem(html, { {"NAME", AsName}, {"DAYTIME", AsDayTime} });
Where {{NAME}} and {{DAYTIME}} are magic tokens. AsName and AsDayTime are functions to be called when the respective tag is encountered while the page is being served.
EDIT: in response to a request to explain differently, I'm not convinced I can do a better job of explaining the code than the example on the library's own github page, so I'll try a wordy description instead:
When you want to serve a webpage to a client, the code needs to know what you want to serve. In the simplest case, it's a static page: the same every time. You can just write the HTML, stick it in a string an be done.
whole_page = "<html>My fixed content</html>";
webserver.serve(whole_page);
But you want some dynamic element(s). As noted, you can do it in a few ways, such as serving some static HTML, then the dynamic bit, then some more static HTML. It seems you've not had much luck like this, and it's rather clunky anyway.
Or you can pre-build a new string out of the three bits and serve that in one chunk, but that's also pretty clunky.
(Aside: taking big strings and adding them together is likely to be slow and memory intensive, two things you really don't want on a little CPU like the ESP8266).
So instead, you allow 'magic' markers in the HTML, using a marker in place of the dynamic content, and serve that instead.
whole_page = "<html>My dynamic content. Value is {{my_value}}</html>";
webserver.serve(whole_page, ...);
The clever bit is that as the page is being served, the webserver is watching the text go by, and when it sees a magic tag, it stops and asks you to fill in the blank, then carries on as before.
Obviously, there is some processing overhead with watching for tags, and some programming overhead with telling it what tags to watch for and how to ask you for the data it needs.
I got advice from a friend who told me I should make a unique argument where I wanted the string(x) and then using some syntax to replace it. I also took inspiration from you Jelle..
what I did was make a unique argument "VAR_CURRENT_SCORE" put that into the HTML where I want the score output, then convert htmlPage1 from a char to a string, use string.replace() and replace "VAR_CURRENT_SCORE" with the string(x) score. this workes as I can see in the serial monitor output.
This is what I did:
//root page
String HTMLstring(htmlstringPage);
delay(100);
HTMLstring.replace("VAR_CURRENT_SCORE", score);
delay(50);
Serial.println("string:");
Serial.println(HTMLstring);
//tab 1 char htmlstringPage[] PROGMEM = R"=====(
<div class="jumbotron">
<div align="center">
<h1 class="display-4">VAR_CURRENT_SCORE</h1>
</div>
</div>
)=====";
However, I still have a small problem left which is converting the string back to char to post it to the website.
To convert the string back:
request->send_P(200, "text/html", HTMLstring.c_str());
I have a problem with converting a UTF-8 encoded string to a UTF-16 encoded CStringW.
Here is my source code:
CStringW ConvertUTF8ToUTF16( __in const CHAR * pszTextUTF8 )
{
_wsetlocale( LC_ALL, L"Korean" );
if ( (pszTextUTF8 == NULL) || (*pszTextUTF8 == '\0') )
{
return L"";
}
const size_t cchUTF8Max = INT_MAX - 1;
size_t cchUTF8;
HRESULT hr = ::StringCbLengthA( pszTextUTF8, cchUTF8Max, &cchUTF8 );
if ( FAILED( hr ) )
{
AtlThrow( hr );
}
++cchUTF8;
int cbUTF8 = static_cast<int>( cchUTF8 );
int cchUTF16 = ::MultiByteToWideChar(
CP_UTF8,
MB_ERR_INVALID_CHARS,
pszTextUTF8,
-1,
NULL,
0
);
CString strUTF16;
strUTF16.GetBufferSetLength(cbUTF8);
WCHAR * pszUTF16 = new WCHAR[cchUTF16];
int result = ::MultiByteToWideChar(
CP_UTF8,
0,
pszTextUTF8,
cbUTF8,
pszUTF16,
cchUTF16
);
ATLASSERT( result != 0 );
if ( result == 0 )
{
AtlThrowLastWin32();
}
strUTF16.Format(_T("%s"), pszUTF16);
return strUTF16;
}
pszTextUTF8 is htm file's content in UTF-8.
When htm file's volume is less than 500kb, this code works well.
but, when converting over 500kb htm file, (ex 648KB htm file that I have.)
pszUTF16 has all content of file, but strUTF16 is not. (about half)
I guess File open is not wrong.
In strUTF16 m_pszData has all content how to I get that?
strUTF16.Getbuffer(); dosen't work.
The code in the question is stock full of bugs, somewhere in the order of 1 bug per 1-2 lines of code.
Here is a short summary:
_wsetlocale( LC_ALL, L"Korean" );
Changing a global setting in a conversion function is unexpected, and will break code calling that. It's not even necessary either; you aren't using the locale for the encoding conversion.
HRESULT hr = ::StringCbLengthA( pszTextUTF8, cchUTF8Max, &cchUTF8 );
This is passing the wrong cchUTF8Max value (according to the documentation), and counts the number of bytes (vs. the number of characters, i.e. code units). Besides all that, you do not even need to know the number of code units, as you never use it (well, you are, but that is just another bug).
int cbUTF8 = static_cast<int>( cchUTF8 );
While that fixes the prefix (count of bytes as opposed to count of characters), it won't save you from using it later on for something that has an unrelated value.
strUTF16.GetBufferSetLength(cbUTF8);
This resizes the string object that should eventually hold the UTF-16 encoded characters. But it doesn't use the correct number of characters (the previous call to MultiByteToWideChar would have provided that value), but rather chooses a completely unrelated value: The number of bytes in the UTF-8 encoded source string.
But it doesn't just stop there, that line of code also throws away the pointer to the internal buffer, that was ready to be written to. Failure to call ReleaseBuffer is only a natural consequence, since you decided against reading the documentation.
WCHAR * pszUTF16 = new WCHAR[cchUTF16];
While not a bug in itself, it needlessly allocates another buffer (this time passing the correct size). You already allocated a buffer of the required size (albeit wrong) in the previous call to GetBufferSetLength. Just use that, that's what the member function is for.
strUTF16.Format(_T("%s"), pszUTF16);
That is probably the anti-pattern associated with the printf family of functions. It is the convoluted way to write CopyChars (or Append).
Now that that's cleared up, here is the correct way to write that function (or at least one way to do it):
CStringW ConvertUTF8ToUTF16( __in const CHAR * pszTextUTF8 ) {
// Allocate return value immediately, so that (N)RVO can be applied
CStringW strUTF16;
if ( (pszTextUTF8 == NULL) || (*pszTextUTF8 == '\0') ) {
return strUTF16;
}
// Calculate the required destination buffer size
int cchUTF16 = ::MultiByteToWideChar( CP_UTF8,
MB_ERR_INVALID_CHARS,
pszTextUTF8,
-1,
nullptr,
0 );
// Perform error checking
if ( cchUTF16 == 0 ) {
throw std::runtime_error( "MultiByteToWideChar failed." );
}
// Resize the output string size and use the pointer to the internal buffer
wchar_t* const pszUTF16 = strUTF16.GetBufferSetLength( cchUTF16 );
// Perform conversion (return value ignored, since we just checked for success)
::MultiByteToWideChar( CP_UTF8,
MB_ERR_INVALID_CHARS, // Use identical flags
pszTextUTF8,
-1,
pszUTF16,
cchUTF16 );
// Perform required cleanup
strUTF16.ReleaseBuffer();
// Return converted string
return strUTF16;
}
I'm working on a server/client assignment. My server should pass down to Client HTML, .txt, .jpg, .gif, and .xbm files to open up on a web browser when I go the localhost:8080/some address... my HTML and .txt files open like a charm! however the .jpg and .gif wont display at all. the server does locate the file but when it comes to reading or displaying the .jpg or .gif it cannot be display because it contains errors, but when I open it in a regular browser it works good. Our instructions are "When you open an image file for reading, make sure to open it in binary mode, since an image file contains binary data." so I did just that but since the image is not displaying I wonder if I'm doing it correctly. Here is my code in c to read a file that I use for html, txt, and image formats.
void file_read(char *filename){
//filename is actually the path
size_in = strlen(filename);
//this is test display to see how the path was being read and since getting a
//from a web browser contains an extra character '/' in the beginning we need to
//to ignore it,
printf("printf in file_read function %d\n", size_in);
wtg = filename + 1;
printf("printf in file_read function %s\n", wtg);
//file open and transfer in binary 'rb'
fp= fopen (wtg, "rb");
if (fp == NULL){
printf("Could not open the file\n");
exit(0);
}
fseek(fp , 0, SEEK_END);
len = ftell (fp);
rewind (fp);
//allocate memory to contain the whole file:
linehtml = calloc(1, len + 1);
if (linehtml == NULL){fputs("Memory Error", stderr);
exit(2);}
//copy the file into the buffer:
if(1!=fread(linehtml, len, 1, fp)){
fputs("entire read fails",stderr),exit(1);
}
fclose(fp);
/*if (result != len) {
printf("file lenght is %d\n\n", len);
fputs ("Reading Error",stderr);
exit(3);
};*/
}
Is there something wrong? is the buffer not long enough? any ideas?
If I take a swf, and run it through swfdump
swfdump.exe -abc file.swf > ABC.txt
One the first run I may get some output in ABC.txt like this
ObjectConfig.as$60
And on a subsequent run of the same SWF get a different output
ObjectConfig.as$61
What is the meaning of the number after the $ ?
This is part of the debug metadata that the mxmlc compiler adds to the bytecode when you do a debug compile, debug=true. If you do a normal release compile, this info is omitted.
This metadata stores filenames and line numbers so that you can see the location in your source while debugging. Although I'm not sure on the exact meaning of these particular numbers, they seem to be a unique identifier or index of that file for the debugger, perhaps in case of two classes with the same name.
The best I can see is in the source code for swfdump, it calls swf_GetString. Somewhere in this chain it adds what looks like a debugLine or a scopeDepth to the end of the class name:
char* swf_GetString(TAG*t)
{
int pos = t->pos;
while(t->pos < t->len && swf_GetU8(t));
/* make sure we always have a trailing zero byte */
if(t->pos == t->len) {
if(t->len == t->memsize) {
swf_ResetWriteBits(t);
swf_SetU8(t, 0);
t->len = t->pos;
}
t->data[t->len] = 0;
}
return (char*)&(t->data[pos]);
}