feat: support resolve default value when environment not set

apisix/cli/file.lua

@@ -65,8 +65,16 @@ local function resolve_conf_var(conf)
             local var_used = false
             -- we use '${{var}}' because '$var' and '${var}' are taken
             -- by Nginx
-            local new_val = val:gsub("%$%{%{%s*([%w_]+)%s*%}%}", function(var)
-                local v = getenv(var)
+            local new_val = val:gsub("%$%{%{%s*([%w_]+[%:%=]?.-)%s*%}%}", function(var)
+                local i, j = var:find("%:%=")
+                local default
+                if i and j then
+                    default = var:sub(i + 2, #var)
+                    default = default:gsub('^%s*(.-)%s*$', '%1')
+                    var = var:sub(1, i - 1)
+                end
+
+                local v = getenv(var) or default
                 if v then
                     if not exported_vars then
                         exported_vars = {}

conf/config.yaml

@@ -30,6 +30,16 @@
 # And then run `export ETCD_HOST=$your_host` before `make init`.
 #
 # If the configured environment variable can't be found, an error will be thrown.
+#
+# Also, If you want to use default value when the environment variable not set,
+# Use `${{VAR:=default_value}}` instead. For instance:
+#
+# etcd:
+#     host:
+#       - http://${{ETCD_HOST:=localhost}}:2379
+#
+# This will find environment variable `ETCD_HOST` first, and if it's not exist it will use `localhost` as default value.
+#
 apisix:
   admin_key:
     - name: admin

t/cli/test_main.sh

@@ -310,6 +310,45 @@ fi
 
 echo "pass: support environment variables in local_conf"
 
+# support default value when environment not set
+echo '
+tests:
+    key: ${{TEST_ENV:=1.1.1.1}}
+' > conf/config.yaml
+
+make init
+
+if ! grep "env TEST_ENV=1.1.1.1;" conf/nginx.conf > /dev/null; then
+    echo "failed: should use default value when environment not set"
+    exit 1
+fi
+
+echo '
+tests:
+    key: ${{TEST_ENV:=very-long-domain-with-many-symbols.absolutely-non-exists-123ss.com:1234/path?param1=value1}}
+' > conf/config.yaml
+
+make init
+
+if ! grep "env TEST_ENV=very-long-domain-with-many-symbols.absolutely-non-exists-123ss.com:1234/path?param1=value1;" conf/nginx.conf > /dev/null; then
+    echo "failed: should use default value when environment not set"
+    exit 1
+fi
+
+echo '
+tests:
+    key: ${{TEST_ENV:=192.168.1.1}}
+' > conf/config.yaml
+
+TEST_ENV=127.0.0.1 make init
+
+if ! grep "env TEST_ENV=127.0.0.1;" conf/nginx.conf > /dev/null; then
+    echo "failed: should use environment variable when environment is set"
+    exit 1
+fi
+
+echo "pass: support default value when environment not set"
+
 # support merging worker_processes
 echo '
 nginx_config: