There is no package called httpd! httpd is part of busybox functionality. You could either compile busybox with this functionality included, or you could install a second busybox binary with this functionality included.

From https://busybox.net/downloads/BusyBox.html#httpd:

httpd [-ifv[v]] [-c CONFFILE] [-p [IP:]PORT] [-u USER[:GRP]] [-r REALM] [-h HOME] or httpd -d/-e/-m STRING

Listen for incoming HTTP requests

Options:

        -i              Inetd mode
        -f              Do not daemonize
        -v[v]           Verbose
        -c FILE         Configuration file (default httpd.conf)
        -p [IP:]PORT    Bind to ip:port (default *:80)
        -u USER[:GRP]   Set uid/gid after binding to port
        -r REALM        Authentication Realm for Basic Authentication
        -h HOME         Home directory (default .)
        -m STRING       MD5 crypt STRING
        -e STRING       HTML encode STRING
        -d STRING       URL decode STRING

Note that multiple instances of httpd can be run, which would have different .conf files:

root@OpenWrt:~# /usr/sbin/httpd -p 80 -h /www
root@OpenWrt:~# /usr/sbin/httpd -p 8080 -h /www2 -c /etc/httpd2.conf

httpd works without a configuration file. Default is /etc/httpd.conf (there is also some brief uci support for this: httpd):

#
# httpd.conf - BusyBox v1.00 (2005.04.23-22:18+0000) multi-call binary
# Contribute by Dubravko Penezic, dpenezic@gmail.com , 2005-05-15
#

#
# Allow/Deny part
#
# [aA]:from    ip address allow, * for wildcard, network subnet allow
# [dD]:from    ip address deny, * for wildcard, network subnet allow
#
# network subnet definition
#  172.20.                    address from 172.20.0.0/16
#  10.0.0.0/25                address from 10.0.0.0-10.0.0.127
#  10.0.0.0/255.255.255.128   address that previous set
#
#  The Deny/Allow IP logic:
#
#  - Default is to allow all.  No addresses are denied unless
#         denied with a D: rule.
#  - Order of Deny/Allow rules is significant
#  - Deny rules take precedence over allow rules.
#  - If a deny all rule (D:*) is used it acts as a catch-all for unmatched
#       addresses.
#  - Specification of Allow all (A:*) is a no-op
#
# Example:
#   1. Allow only specified addresses
#     A:172.20          # Allow any address that begins with 172.20.
#     A:10.10.          # Allow any address that begins with 10.10.
#     A:127.0.0.1       # Allow local loopback connections
#     D:*               # Deny from other IP connections
#
#   2. Only deny specified addresses
#     D:1.2.3.        # deny from 1.2.3.0 - 1.2.3.255
#     D:2.3.4.        # deny from 2.3.4.0 - 2.3.4.255
#     A:*             # (optional line added for clarity)
#
# Note:
# A:*
# D:*
# Mean deny ALL !!!!
#

A:*

#
# Authentication part
#
# /path:user:pass     username/password
#
# password may be clear text or MD5 cript
#
# Example :
# /cgi-bin:admin:FOO
#
# MD5 crypt password :
# httpd -m "_password_"
# Example :
# httpd -m "astro"  =>  $1$$e6xMPuPW0w8dESCuffefU.
# /work:toor:$1$$e6xMPuPW0w8dESCuffefU.
#

#
# MIME type part
#
# .ext:mime/type   new mime type not compiled into httpd
#
# Example :
# .ipk:application/octet-stream
#
# MIME type compiled into httpd
#
# .htm:text/html
# .html:text/html
# .jpg:image/jpeg
# .jpeg:image/jpeg
# .gif:image/gif
# .png:image/png
# .txt:text/plain
# .h:text/plain
# .c:text/plain
# .cc:text/plain
# .cpp:text/plain
# .css:text/css
# .wav:audio/wav
# .avi:video/x-msvideo
# .qt:video/quicktime
# .mov:video/quicktime
# .mpe:video/mpeg
# .mpeg:video/mpeg
# .mid:audio/midi
# .midi:audio/midi
# .mp3:audio/mpeg
#
# Default MIME type is application/octet-stream if extension isnt set
#

See Common Gateway Interface. httpd expects it's CGI script files to be in the subdirectory cgi-bin under main web directory set by options -h (default is /www, so /www/cgi-bin). The CGI script files must also have permission to be executed (min mode 700).

Standard set of Comon Gateway Interface environment variable are :

CONTENT_TYPE=application/x-www-form-urlencoded
GATEWAY_INTERFACE=CGI/1.1
REMOTE_ADDR=192.168.1.180
QUERY_STRING=Zbr=1234567&SrceMB=&ime=jhkjhlkh+klhlkjhlk+%A9%D0%C6%AE%C6%AE&prezime=&sektor=OP
REMOTE_PORT=2292
CONTENT_LENGTH=128
REQUEST_URI=/cgi-bin/test
SERVER_SOFTWARE=busybox httpd/1.35 6-Oct-2004
PATH=/bin:/sbin:/usr/bin:/usr/sbin
HTTP_REFERER=http://192.168.1.1/index1.html
SERVER_PROTOCOL=HTTP/1.0
PATH_INFO=
REQUEST_METHOD=POST
PWD=/www/cgi-bin
SERVER_PORT=80
SCRIPT_NAME=/cgi-bin/test
REMOTE_USER=[http basic auth username]

/cgi-bin/test

#!/bin/sh
echo "Content-type: text/html"
echo ""
echo "Sample CGI Output"
echo ""
echo ""
env
echo ""
echo ""

Environment variables are set up and the script is invoked with pipes for stdin/stdout.

If a post is being done the script is fed the POST data in addition to setting the QUERY_STRING variable (for GETs or POSTs).

The preferred way to do forms in CGI is POST.

Example how to use POST in form:

/www/form-post.html

CGI Test
  Text field
 
  Radio button  
  
     1
  
  
     2
  
  
     3
  
  Some text 
 
   
   
   

/www/cgi-bin/test-post:

#!/bin/sh
echo "Content-type: text/html"
echo ""
echo "Sample CGI Output"
echo ""
echo ""
echo "Environment variables"
echo ""
env
echo ""
echo "========================================================="
echo ""
echo "Form variables :"
echo ""
read QUERY_STRING
eval $(echo "$QUERY_STRING"|awk -F'&' '{for(i=1;i<=NF;i++){print $i}}')
tmp=`httpd -d $Text_Field`
echo "Text_Field=$tmp"
tmp=`httpd -d $Radio_Button`
echo "Radio_Button=$tmp"
tmp=`httpd -d $Text_Area`
echo "Text_Area=$tmp"
echo ""
echo ""

Text area fields (and any other field that may contain \n are very hard to menage). Example how to use GET in form:

/www/form-get.html:

CGI Test




  Text field
    
  
  Radio button  
  
     1
  
  
     2
  
  
     3
  
   
  
    
    
  
   
   

/www/cgi-bin/test-get:

#!/bin/sh
echo "Content-type: text/html"
echo ""
echo "Sample CGI Output"
echo ""
echo ""
echo "Environment variables"
echo ""
env
echo ""
echo "========================================================="
echo ""
echo "Form variables :"
echo ""
eval $(echo "$QUERY_STRING"|awk -F'&' '{for(i=1;i<=NF;i++){print $i}}')
tmp=`httpd -d $Text_Field`
echo "Text_Field=$tmp"
tmp=`httpd -d $Radio_Button`
echo "Radio_Button=$tmp"
echo ""
echo ""