Pset6 server.c Error 403

Question

server.c is giving error(403) inside transfer function (written by default)

lookup function :

const char* lookup(const char* path)
{
    char* s=(char*)calloc(20,1);
    strcpy(s,"");

    char *path1=(char*)calloc((strlen(path)+1),1);
    for(int i=0;i<strlen(path);i++)
    {
        path1[i]=tolower(path[i]);
    }
    printf("path1 : %s",path1);
    for(int i=0;i<strlen(path1);i++)
    {  
        if(path1[i]=='.')
            {
                s[0]=path1[i];
                s[1]=path1[i+1];
                s[2]=path1[i+2];
                s[3]='\0';
                break;
            }


    }

   // s[3]='\0';
    if(!strcmp(s,".cs"))
    {
        strcpy(s,"text/css");
        return(s);
    }
    if(!strcmp(s,".ht"))
    {
        strcpy(s,"text/html");
        return(s);
    }if(!strcmp(s,".gi"))
    {
        strcpy(s,"image/gif");
        return(s);
    }if(!strcmp(s,".ic"))
    {
        strcpy(s,"image/x-icon");
        return(s);
    }if(!strcmp(s,".jp"))
    {
        strcpy(s,"image/.jpeg");
        return(s);
    }if(!strcmp(s,".js"))
    {
        strcpy(s,"text/javascript");
        return(s);
    }if(!strcmp(s,".ph"))
    {
        strcpy(s,"text/x-php");
        return(s);
    }if(!strcmp(s,".pn"))
    {

        strcpy(s,"image/png");
        return(s);
    }

    return NULL;


}

parse function :

bool parse(const char* line, char* abs_path, char* query)
{


    for(int i=0;i<strlen(line);i++)
    {
        if(line[i]==34)
        {
            error(400);
            return false;
        }
    }
    if(line[0]!='G'||line[1]!='E'||line[2]!='T'||line[3]!=32)
    {
        error(405);
        return false;
    }
    if(line[4]!='/')
    {
        printf("*Here");
        error(501);
        return false;
    }
  //  int f=0;


    for(int i=0;i<strlen(line);i++)
    {
        int flag=0,j=0,q=0;
        if(line[i]==' ')
        {   
            flag=0;
            q++;

        }
        if(line[i]=='/')
        {
            flag=1;

        }
        if(flag)
        {
            abs_path[j]=line[i];
            j++;
        }

        if(q==2)
        {
            abs_path[j]='\0';
            break;
        }

        if(line[i]=='?')
        {
          abs_path[j]='\0';
          j=0;
          for(int e=i+1;line[e]!=' ';e++)
          {
              query[j]=line[e];
              j++;
          }
          query[j]='\0';
          break;  
        }
    }
 int f=0;
    for(int i=0;i<strlen(line);i++)
    {
        if(line[i]==' ')
            f++;
        if(f==2)
        {
            if(line[i+1]!='H'||line[i+2]!='T'||line[i+3]!='T'||line[i+4]!='P'||line[i+5]!='/'||line[i+6]!='1'||line[i+7]!='.'||line[i+8]!='1')
            {
                f++;
                printf("%c %c %c %c %c %c %c %c",line[i+1],line[i+2],line[i+3],line[i+4],line[i+5],line[i+6],line[i+7],line[i+8]);
                error(505);
                return false;
            }
            else
            break;
        }
    }   
    return true;
}

My valgrind is giving this error :

==6796== Conditional jump or move depends on uninitialised value(s)
==6796==    at 0x4C2E0F8: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6796==    by 0x4029EA: urldecode (server.c:1178)
==6796==    by 0x4018A3: main (server.c:191)
==6796== 
==6796== Conditional jump or move depends on uninitialised value(s)
==6796==    at 0x4C2E0F8: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6796==    by 0x402A32: urldecode (server.c:1186)
==6796==    by 0x4018A3: main (server.c:191)
==6796== 
==6796== Conditional jump or move depends on uninitialised value(s)
==6796==    at 0x4C2E0F8: strlen (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==6796==    by 0x4019EE: main (server.c:221)
==6796== 

I can't figure out the exact problem but I think it is somewhere related to abs_path and urldecode function. Please Help

Answer 1

strcpy(s,lookup(line));

After gdb: Program received signal SIGSEGV, Segmentation fault. __strcpy_ssse3 () at ../sysdeps/i386/i686/multiarch/strcpy-ssse3.S:84

I would look for another way, for example:

// copy line to new string
    char* temp = malloc(strlen(line) + 1);
    if(temp == NULL)
    {
        free(temp);
        return false;
    }
    strcpy(temp, line);

i don't know how is possible to resolve server without using gdb, this is a fundamental skill that you have to learn. I also do not know what you intend to use lookup, if only returns a string with the MIME type of file, you have to analyze line and see that it fulfills the specifications

EDIT

Come to lookup a pointer question: `const char* lookup(const char* path), means that lookup, receives a constant pointer, really it means that we have a string, which already exists and will not change, there is no need to malloc, calloc or realloc; const char * path means I have a pointer to the start of the string path, but can also access each and every one of his characters. We stopped for a moment before writing code "I just need to find a characteristic of path, that is useful to me to determine the file extension".

if you look a time all file extensions have a point: '.' and now we see a little problem specifications suggest us use features like strcasecmp, strcpy, and / or strrchr, it is our duty to learn to use them. char * strrchr (const char * s, int c); It is perfect for us, returns a pointer to the last occurrence of the character c in the string s. We have function (strrchr), we have the character we want( a point) and we have a constant string ( const char* path). therefore we can do:

char * point = strrchr (path, '.'); // Returns a pointer to the character point

point is a string (char *), so if exists point we have a chain that begins in that character, ie if path ends with .html point is precisely ".html" exactly what we want. Now we can use a very useful function in this case strcasecmp, our chain point, and a lot of IF conditions, I think this is enough to start.

EDIT 2

if (abs_path[strlen(abs_path) - 1] != '/')                       
  char* index = indexes(path);

Are the lines of code that cause the error because abs_path is not correct, and strlen is 0. Parse does not work, I understand your idea, but not executed correctly.

for(int i=0;i<strlen(line);i++)
    {
        int flag=0,j=0,q=0;

Every time begins FOR, your control variables initialized zero, so not fulfill its function and abs_path is '\' at the end of parse.

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