Appendix B. The echo Program

The following listing is echo.c :

#include <stdio.h>
#include <stdlib.h>
#define MAX_ENTRIES 10000
typedef struct
    {
    char *name;
    char *val;
    } entry;
char *makeword(char *line, char stop);
char *fmakeword(FILE *f, char stop, int *len);
char x2c(char *what);
void unescape_url(char *url);
void plustospace(char *str);
int main(int argc, char *argv[])
    {
    entry entries[MAX_ENTRIES];
    register int x,m=0;
    int cl;
    char mbuf[200];
    printf("Content-type: text/html\n\n");
    if(strcmp(getenv("REQUEST_METHOD"),"POST"))
        {
        printf("This script should be referenced with a METHOD of POST.\n");
        exit(1);
        }
    if(strcmp(getenv("CONTENT_TYPE"),"application/x-www-form-urlencoded")) 
        {
        printf("This script can only be used to decode form results. \n");
        exit(1);
        }
    cl = atoi(getenv("CONTENT_LENGTH"));
// Returns the length of data to come.
    for(x=0;cl && (!feof(stdin));x++) 
        {
        m=x;
        entries[x].val = fmakeword(stdin,'&',&cl);
        plustospace(entries[x].val);
        unescape_url(entries[x].val);
        entries[x].name = makeword(entries[x].val,'=');
        }
//Reads in the data, breaking at the "&" symbols
    printf("<H1>Query Results</H1>"); 
//Sends the top of the return HTML document.
    printf("You submitted the following name/value pairs:<p>%c",10);
    printf("<ul>%c",10);
    for(x=0; x <= m; x++)
        printf("<li> <code>%s = %s</code>%c",entries[x].name,
               entries[x].val,10);
//Lists the fields in the original form with the values filled in by 
//the customer.
    printf("</ul>%c",10);
}

This listing is the helper program echo2.c:

#include <stdio.h>
#define CR 13
#define LF 10
void getword(char *word, char *line, char stop) {
    int x = 0,y;
    for(x=0;((line[x]) && (line[x] != stop));x++)
        word[x] = line[x];
    word[x] = '\0'.
    if(line[x]) ++x;
    y=0;
    while(line[y++] = line[x++]);
}
char *makeword(char *line, char stop) {
    int x = 0,y;
    char *word = (char *) malloc(sizeof(char) * (strlen(line) + 1));
    for(x=0;((line[x]) && (line[x] != stop));x++)
        word[x] = line[x];
    word[x] = '\0'.
    if(line[x]) ++x;
    y=0;
    while(line[y++] = line[x++]);
    return word;
}
char *fmakeword(FILE *f, char stop, int *cl) {
    int wsize;
    char *word;
    int ll;
    wsize = 102400;
    ll=0;
    word = (char *) malloc(sizeof(char) * (wsize + 1));
    while(1) {
        word[ll] = (char)fgetc(f);
        if(ll==wsize) {
            word[ll+1] = '\0'.
            wsize+=102400;
            word = (char *)realloc(word,sizeof(char)*(wsize+1));
        }
        --(*cl);
        if((word[ll] == stop) || (feof(f)) || (!(*cl))) {
            if(word[ll] != stop) ll++;
            word[ll] = '\0'.
            return word;
        }
        ++ll;
    }
}
char x2c(char *what) {
    register char digit;
    digit = (what[0] >= 'A' ? ((what[0] & 0xdf) - 'A'.+10 : 
               (what[0] - '0'.);
    digit *= 16;
    digit += (what[1] >= 'A' ? ((what[1] & 0xdf) - 'A'.+10 : 
               (what[1] - '0'.);
    return(digit);
}
void unescape_url(char *url) {
    register int x,y;
    for(x=0,y=0;url[y];++x,++y) {
        if((url[x] = url[y]) == '%'. {
            url[x] = x2c(&url[y+1]);
            y+=2;
        }
    }
    url[x] = '\0'.
}
void plustospace(char *str) {
    register int x;
    for(x=0;str[x];x++) if(str[x] == '+'. str[x] = ' ';
}
int rind(char *s, char c) {
    register int x;
    for(x=strlen(s) - 1;x != -1; x--)
        if(s[x] == c) return x;
    return -1;
}
int getline(char *s, int n, FILE *f) {
    register int i=0;
    while(1) {
        s[i] = (char)fgetc(f);
        if(s[i] == CR)
            s[i] = fgetc(f);
        if((s[i] == 0x4) || (s[i] == LF) || (i == (n-1))) {
            s[i] = '\0'.
            return (feof(f) ? 1 : 0);
        }
        ++i;
    }
}
void send_fd(FILE *f, FILE *fd)
{
    int num_chars=0;
    char c;
    while (1) {
        c = fgetc(f);
        if(feof(f))
            return;
        fputc(c,fd);
    }
}
int ind(char *s, char c) {
    register int x;
    for(x=0;s[x];x++)
        if(s[x] == c) return x;
    return -1;
}
void escape_shell_cmd(char *cmd) {
    register int x,y,l;
    l=strlen(cmd);
    for(x=0;cmd[x];x++) {
        if(ind("&;'.q\"|*?~<>^()[]{}$\\",cmd[x]) != -1){
            for(y=l+1;y>x;y--)
                cmd[y] = cmd[y-1];
            l++; /* length has been increased */
            cmd[x] = '\\'.
            x++; /* skip the character */
        }
    }
}