Merecat ∴ Embedded Web Server

Merecat started out as a pun at Mongoose, but is now useful for actual web serving purposes. It is however not a real Meerkat, merely yet another copycat, forked from the great thttpd created by Jef Poskanzer.

Merecat expands on the features originally offered by thttpd, but still has a limited feature set:

• Virtual hosts
• Basic .htpassd and .htaccess support
• URL-traffic-based throttling
• CGI/1.1
• HTTP/1.1 Keep-alive
• Built-in gzip deflate using zlib
• HTTPS support using OpenSSL/LibreSSL, works with Let's Encrypt!
• Dual server support, both HTTP/HTTPS from one process
• HTTP redirect, to gently redirect from HTTP server to HTTPS
• Native PHP support, using php-cgi if enabled in merecat.conf

The resulting footprint (~140 kiB) makes it quick and suitable for small and embedded systems!

Merecat is available as free/open source software under the simplified 2-clause BSD license. For more information, see the manual page merecat(8), or the FAQ.

Docker

Try out Docker Merecat safely isolated from the rest of the system, with easy deployment.

Authentication

To protect a directory in your ~USERNAME/public_html/, create the file .htpasswd using the included htpasswd tool:

[email protected]:~/> cd public_html/Downloads
[email protected]:~/public_html/Downloads/> htpasswd -c .htpasswd friend
Changing password for user friend
New password: *****
Re-type new password: *****

Enable this feature, and user home directories, with the configure script. See more on this in the Features section below.

Virtual Hosts

Setting up virtual hosts on a server can be a bit of a hassle with other web servers. With Merecat you simply create directories for each host in the web server root:

/var/www/
  |-- icons/
  |-- cgi-bin/
  |-- errors/
  |    `-- err404.html
  |-- ftp.example.com/
   `- www.example.com/

Edit /etc/merecat.conf:

virtual-host = true
cgi "/cgi-bin/*|**.cgi" {
    enabled = true
}

Now the web server root, /var/www/, no longer serves files, only virtual host directories do, execpt for the shared files in icons/, cgi-bin/, and errors/.

On Linux bind mounts can be used to set up FTP and web access to the same files. Example /etc/fstab:

/srv/ftp  /var/www/ftp.example.com  none  defaults,bind  0  0

Optimizing Performance

There are many tricks to optimizing the performance of your web server. One of the most important ones is browser caching. Merecat supports both ETag: and Cache-Control:, however to enable the latter you need to define the max-age setting in /etc/merecat.conf:

max-age = 3600        # One hour

The value is completely site dependent. For an embedded system you might want to set it to the maximum value, whereas for other scenarios you will likely want something else. By default this is disabled (0).

Another trick is to employ gzip compression. Merecat has built-in support for serving HTML, CSS, and other text/* files if there is a .gz version of the same file. Here is an example of how to compress relevant files:

[email protected]:~/> cd /var/www/
[email protected]:/var/www/> for file in `find . -name '*.html' -o -name '*.css'`; do \
      gzip -c $file > $file.gz; done

This approach is more CPU friendly than letting Merecat "deflate" files on the fly, which it otherwise does.

HTTPS Support

If configure finds OpenSSL installed, HTTPS support is enabled, this can be disabled using --without-ssl. However, to gain access to the SSL/TLS settings you also need support for merecat.conf, so you must install libConfuse. See below for all Build Requirements.

The HTTPS support has SSLv2, SSLv3, and TLSv1 disabled (hard coded) by default. Only TLSv2 and later will be enabled and negotiated on a per client basis.

To set up Merecat for HTTPS the following /etc/merecat.conf settings must be enabled:

server secure {
    port = 443
    ssl {
        certfile = /etc/letsencrypt/live/example.com/fullchain.pem
        keyfile  = /etc/letsencrypt/live/example.com/privkey.pem
        dhfile   = /etc/letsencrypt/live/example.com/dhparam.pem
    }
}

Let's Encrypt

Merecat fully supports Let's Encrypt certificates, including HTTP-01 renewals. Use the server location directive:

server default {
        port = 80
        location "/.well-known/acme-challenge/**" {
                 path = "letsencrypt/.well-known/acme-challenge/"
        }
        redirect "/**" {
                 code = 301
                 location = "https://$host$request_uri$args"
        }
}

The path must be relative to the server root directory. Use bind mounts to get /var/lib/letsencrypt into your server root. This way we can ensure certbot only writes to its own directory and cannot write to any file in the server root.

Then run certbot with the following arguments and then add all virtual hosts you want to support from Merecat:

[email protected]:/var/www/> certbot certonly --webroot --webroot-path /var/lib/letsencrypt

For a HowTo see:

• https://troglobit.com/2019/06/HowTo-Set-up-Merecat-with-Lets-Encrypt-certificate/

Self-signed Certificate

To create a self signed certificate and enable perfect forward secrecy, PFS, i.e. Diffie-Helman paramters (optional), use the openssl tool as shown below. Notice the use of a sub-shell with openssl.cnf where most of the certificate settings are, and more importantly notice the use of subjectAltName, or SAN. The latter is required by most browsers today.

[email protected]:/var/www/> mkdir private certs
[email protected]:/var/www/> openssl req -x509 -newkey rsa:4096 -nodes    \
            -keyout private/server.key -new -out certs/server.pem    \
            -subj /CN=www.acme.com -reqexts SAN -extensions SAN      \
            -sha256 -days 3650 -config <(cat /etc/ssl/openssl.cnf    \
             <(printf '[SAN]\nsubjectAltName=DNS:www.acme.com'))
[email protected]:/var/www/> openssl dhparam -out certs/dhparm.pem 4096

HTTP Redirect

For a setup with two servers, the following example can be used to run HTTPS on port 4443, HTTP on port 8080 and redirect to the HTTPS server on any access:

server secure {
    port     = 4443
    ssl {
        certfile = certs/server.pem
        keyfile  = private/server.key
        dhfile   = certs/dhparm.pem
    }
}

server default {
    port = 8080
    redirect "/**" {
        code = 303
        location = "https://$host:4443$request_uri$args"
    }
}

Supported HTTP redirect codes are: 301, 302, 303, and 307.

The location setting supports three nginx style variables as shown in the example. Please note the quotes around the pattern, or the .conf parser will think the pattern is a C-style comment.

Build Requirements

Merecat depends on a few external libraries, if enabled, e.g. OpenSSL, zlib, and libConfuse. On Debian/Ubuntu systems you can install the dependencies with:

[email protected]:~/> sudo apt install pkg-config libconfuse-dev libssl-dev zlib1g-dev

If you build the deps. from source, they may default to use an install prefix of /usr/local. Non Debian/Ubuntu systems rarely support this GNU standard, so here is how you reference it for the Merecat configure script:

[email protected]:~/merecat/> PKG_CONFIG_LIBDIR=/usr/local/lib/pkgconfig ./configure

To build Merecat without support for /etc/merecat.conf:

[email protected]:~/merecat/> ./configure --without-config

If you build from GIT sources and not a released tarball, then remember:

[email protected]:~/merecat/> ./autogen.sh

To install httpd into /usr/sbin/, default index and icons into /var/www, and config file to /etc/merecat.conf:

[email protected]:~/merecat/> ./configure --prefix=/usr --localstatedir=/var --sysconfdir=/etc
[email protected]:~/merecat/> make
[email protected]:~/merecat/> sudo make install

Cross compiling Merecat for an another target is possible by setting the --host flag to the configure script. This is well documented in the GNU Documentation. Note: ususally the --build system is automatically detected.

Merecat builds are silent by default. For detailed compiler output, disable silent mode with configure --disable-silent-rules, or build with make V=1.

Features

Merecat consists of a front-end, merecat.c, and a standalone HTTP library, libhttpd.c, which can be tweaked in various ways and used for embedding a web server in another application if needed.

The most common options are available from the merecat command line and the merecat.conf configuration file. Other, less common options, can be enabled using the configure script:

--enable-builtin-icons  Enable built-in icons for dir listings
--enable-htaccess       Enable .htaccess files for access control
--enable-htpasswd       Enable .htpasswd files for authentication
--enable-public-html    Enable $HOME/public_html as ~USERNAME/
--enable-msie-padding   Add padding to error messages for Internet Explorer
--disable-dirlisting    Disable directory listings when no index file is found
--without-config        Disable /etc/merecat.conf support using libConfuse
--without-ssl           Disable HTTPS support, default: enabled
--without-symlinks      Disable httpd and in.httpd symlinks to merecat
--without-zlib          Disable mod_deflate (gzip) using zlib

The source file merecat.h has even more features that can be tweaked, some of those are mentioned in the man page, but the header file has very useful comments as well.

Origin & References

Merecat is a stiched up fork of sthttpd with lots of lost patches found lying around the web. The sthttpd project in turn is a fork from the original thttpd -- the tiny/turbo/throttling HTTP server.

• thttpd was created by Jef Poskanzer mailto:[email protected]
• sthttpd was spawned by Anthony G. Basile mailto:[email protected]
• Merecat is maintained by Joachim Nilsson mailto:[email protected]