Overview

Trying out the Mosquitto MQTT broker.

Quickstart

Having installed the Mosquitto distribution, either by compiling from source or using one of the binaries, start the broker using the following command

mosquitto -v -c conf/mosquitto.conf

The broker should start listening on port 1883.

In another terminal run the following

mosquitto_sub -t test_topic

And finally, in another terminal run this command

mosquitto_pub -t test_topic -m "Hello World"

This should echo the message into the terminal running mosquitto_sub

Building Mosquitto from source

I have a Mac, I don't like relying on brew or other package managers for MacOS (I'm just being silly and awkward) so I prefer to built code from source.

Prerequisites

• MacOS developer tools - either the command line or XCode
• CMake

OpenSSL

• Clone code from github
• Configure with the following command

./config --prefix=/usr/local

• Build using make

make

• Change to root and install

make install

Configure Mosquitto

• Clone the Mosquitto git repo
• I used the CMake GUI
• Selected the mosquitto source directory as source
• Created a build subdirectory and selected as target
• Added an entry
• Of type filepath
• Name OPENSSL_INCLUDE_PATH
• Value /usr/local/include/openssl
• Clicked the configure button
• Clicked the generate button
• In a terminal, navigate to the build directory
• Make the code by simply running

make all

• Install everything as root by running the following

root# make install

Troubleshooting

CMake

I had some linker issues with OpenSSL/Mosquitto, for example this

[ 33%] Linking C shared library libmosquitto.dylib
Undefined symbols for architecture x86_64:
  "_ASN1_STRING_get0_data", referenced from:
      _mosquitto__verify_certificate_hostname in tls_mosq.c.o
  "_OPENSSL_init_crypto", referenced from:
      _net__init in net_mosq.c.o
  "_OPENSSL_sk_num", referenced from:
      _sk_X509_num in net_mosq_ocsp.c.o
      _sk_GENERAL_NAME_num in tls_mosq.c.o
  "_OPENSSL_sk_pop_free", referenced from:
      _sk_GENERAL_NAME_pop_free in tls_mosq.c.o
  "_OPENSSL_sk_value", referenced from:
      _sk_GENERAL_NAME_value in tls_mosq.c.o
  "_SSL_CTX_set_options", referenced from:
      _net__init_ssl_ctx in net_mosq.c.o
  "_SSL_CTX_set_psk_client_callback", referenced from:
      _net__init_ssl_ctx in net_mosq.c.o
  "_SSL_CTX_up_ref", referenced from:
      _mosquitto_opts_set in options.c.o
      _mosquitto_void_option in options.c.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)
make[2]: *** [lib/libmosquitto.1.6.7.dylib] Error 1
make[1]: *** [lib/CMakeFiles/libmosquitto.dir/all] Error 2
make: *** [all] Error 2

This appears to be because CMake found the /usr/lib/libcrypto.dylib file and used that rather than the copy under /usr/local/lib which matches the OpenSSL headers.

To fix the issue I used File -> Delete Cache and started the process again bu pressing Configure then Generate

Man pages

This needed downloaded copies of XSL files, also the use of XML Catalogs

The man pages didn't seem to get build by default, when I tried to force them to build I got the following

cd man
make 
xsltproc --nonet libmosquitto.3.xml
warning: failed to load external entity "http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl"
compilation error: file manpage.xsl line 3 element import
xsl:import : unable to load http://docbook.sourceforge.net/release/xsl/current/manpages/docbook.xsl
compilation error: file libmosquitto.3.xml line 4 element refentry
xsltParseStylesheetProcess : document is not a stylesheet
make: *** [libmosquitto.3] Error 5

It seems that the --nonet is a common option to avoid files being downloaded randomly.

The solution is to download copies of the needed files and use a catalog file to reference these. The latest DocBook releases can be downloaded from SourceForge specifically the XSL release

An example catalog file is provided under xmlcatalog. This should be referenced by the environment variable as follows

export XML_CATALOG_FILES=/Users/sheila/wd/mosquitto_client_examples/xmlcatalog/catalog.xml

References