BusyBox HTTP Daemon (httpd) webserver

BusyBox is a toolbox with tiny replacements of essential Linux programs. One of them is a tiny HTTP server httpd (HTTP Daemon). Early versions of OpenWrt before Attitude Adjustment 12.0 release used the httpd server but then switched to own uHTTPd which has a built-in Lua interpreter so can serve Luci faster. But Luci still works fine with plain BB httpd. In the same time BB httpd can be compiled with only basic features like CGI and ETag and will have only 8Kb against 32Kb of stock uhttpd.

It's is a single threaded daemon with most needed features:

• ETag to avoid re-downloading of files cached in browser
• CGI to execute server side request processing
• Basic authentication to limit access by a password
• Serving pre-compressed gzip files with Content-Encoding: gzip
• Range requests to get only part of a file.
• ACL by IP to allow or deny access
• Reverse proxy
• Custom error pages e.g. 404.html

But it doesn't support Keep Alive, TLS (HTTPS), Virtual Hosting, FastCGI and many other features so it's often replaced in embedded systems with Lighttpd

There is no package called httpd that you can install with opkg. The 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 may work without a configuration file. But by default it will try to read config from /etc/httpd.conf. There were also some brief uci support for this: httpd.

The httpd documented itself directly in source code

Example of config file:

/etc/httpd.conf

H:/serverroot     # define the server root. It will override -h
# 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 isn't set

Example of BB httpd options and their analogues in Apache HTTPD:

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). If directory URL is given, no index.html is found and CGI support is enabled, then cgi-bin/index.cgi will be executed.

BusyBox sources contains two useful CGI programs:

• httpd_indexcgi.c generates a directory listing i.e. list of files. Other Web Servers has this as built-in feature but for BB http this is delegated to a CGI program.
• httpd_ssi.c processes Server Side Includes

Use httpd_helpers.sh to compile them. Also there is and example of shell script to process File Upload httpd_post_upload.cgi

Check more CGI shell samples.

Standard set of Common Gateway Interface environment variables are described in RFC3875. For example:

CONTENT_TYPE=application/x-www-form-urlencoded
CONTENT_LENGTH=128
REQUEST_METHOD=POST
REQUEST_URI=/cgi-bin/printenvs
QUERY_STRING=param1=12345&param2=&param3=some%20text
REMOTE_USER=[http basic auth username]
HTTP_HOST: "example.com"
HTTP_USER_AGENT: "Chrome"
HTTP_ACCEPT: "*/*"
HTTP_REFERER=http://192.168.1.1/index1.html
REMOTE_ADDR=192.168.1.180
REMOTE_PORT=2292
SERVER_PORT=80
PATH=/bin:/sbin:/usr/bin:/usr/sbin
PATH_INFO=
PWD=/www/cgi-bin
SCRIPT_NAME=/cgi-bin/printenvs
SERVER_PROTOCOL=HTTP/1.0
GATEWAY_INTERFACE=CGI/1.1
SERVER_SOFTWARE=busybox httpd/1.30.1

Example of CGI script that prints them:

/cgi-bin/printenvs

#!/bin/sh
echo "Content-Type: text/html"
echo ""
echo "Environment variables:"
env

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

All request headers are available with HTTP prefix e.g. Host header will be passed in HTTP_HOST env.

BB httpd doesn't support TLS but you may try to use stunnel.

BB httpd has a very basic reverse proxy support but it's not compiled by default. Use FEATURE_HTTPD_PROXY to enable it.

This option allows you to define URLs that will be forwarded to another HTTP server. To setup add the following line to the configuration file:

P:/url/:http://hostname[:port]/new/path/

Then a request to /url/myfile will be forwarded to http://hostname[:port]/new/path/myfile.

* Using the busybox HTTP server