According to https://paragonie.com/book/pecl-libsodium/read/00-intro.md#extension-versions libsodium can be installed on PHP versions as low as 5.4. For PHP 5.x you have to use PECL v1.0.6 (as opposed to v2.0.7).
Here's my attempt to get it working on PHP 5.5:
FROM php:5.5
RUN apt-get update \
&& apt-get -y install libsodium-dev \
&& pecl install libsodium-1.0.7 \
&& docker-php-ext-enable libsodium
That gets me the following error:
configure: error: wrong libsodium lib version or lib not found
ERROR: `/tmp/pear/temp/libsodium/configure --with-php-config=/usr/local/bin/php-config' failed
error: /usr/local/lib/php/extensions/no-debug-non-zts-20121212/libsodium does not exist
usage: /usr/local/bin/docker-php-ext-enable [options] module-name [module-name ...]
ie: /usr/local/bin/docker-php-ext-enable gd mysqli
/usr/local/bin/docker-php-ext-enable pdo pdo_mysql
/usr/local/bin/docker-php-ext-enable --ini-name 0-apc.ini apcu apc
Possible values for module-name:
opcache.so
If I replace FROM php:5.5
with FROM php:5.6
it works fine.
Any ideas?