Add support for messageFormat strings containing conditionals

Readme.md

@@ -343,6 +343,14 @@ const levelPrettifier = logLevel => `LEVEL: ${levelColorize(logLevel)}`
 }
 ```
 
+In addition to this, if / end statement blocks can also be specified. Else statements and nested conditions are not supported.
+
+```js
+{
+  messageFormat: '{levelLabel} - {if pid}{pid} - {end}url:{req.url}'
+}
+```
+
 This option can also be defined as a `function` with this prototype:
 
 ```js

lib/utils.js

@@ -42,7 +42,8 @@ module.exports.internals = {
   deleteLogProperty,
   splitPropertyKey,
   createDate,
-  isValidDate
+  isValidDate,
+  interpretConditionals
 }
 
 /**
@@ -263,16 +264,21 @@ function prettifyLevel ({ log, colorizer = defaultColorizer, levelKey = LEVEL_KE
  */
 function prettifyMessage ({ log, messageFormat, messageKey = MESSAGE_KEY, colorizer = defaultColorizer, levelLabel = LEVEL_LABEL, levelKey = LEVEL_KEY, customLevels, useOnlyCustomProps }) {
   if (messageFormat && typeof messageFormat === 'string') {
-    const message = String(messageFormat).replace(/{([^{}]+)}/g, function (match, p1) {
-      // return log level as string instead of int
-      let level
-      if (p1 === levelLabel && (level = getPropertyValue(log, levelKey)) !== undefined) {
-        const condition = useOnlyCustomProps ? customLevels === undefined : customLevels[level] === undefined
-        return condition ? LEVELS[level] : customLevels[level]
-      }
-      // Parse nested key access, e.g. `{keyA.subKeyB}`.
-      return getPropertyValue(log, p1) || ''
-    })
+    const parsedMessageFormat = interpretConditionals(messageFormat, log)
+
+    const message = String(parsedMessageFormat).replace(
+      /{([^{}]+)}/g,
+      function (match, p1) {
+        // return log level as string instead of int
+        let level
+        if (p1 === levelLabel && (level = getPropertyValue(log, levelKey)) !== undefined) {
+          const condition = useOnlyCustomProps ? customLevels === undefined : customLevels[level] === undefined
+          return condition ? LEVELS[level] : customLevels[level]
+        }
+
+        // Parse nested key access, e.g. `{keyA.subKeyB}`.
+        return getPropertyValue(log, p1) || ''
+      })
     return colorizer.message(message)
   }
   if (messageFormat && typeof messageFormat === 'function') {
@@ -383,7 +389,7 @@ function prettifyObject ({
   // Split object keys into two categories: error and non-error
   const { plain, errors } = Object.entries(input).reduce(({ plain, errors }, [k, v]) => {
     if (keysToIgnore.includes(k) === false) {
-      // Pre-apply custom prettifiers, because all 3 cases below will need this
+    // Pre-apply custom prettifiers, because all 3 cases below will need this
       const pretty = typeof customPrettifiers[k] === 'function'
         ? customPrettifiers[k](v, k, input)
         : v
@@ -557,7 +563,7 @@ function splitPropertyKey (key) {
  *
  * @param {object} obj The object to be searched.
  * @param {string|string[]} property A string, or an array of strings, identifying
-  * the property to be retrieved from the object.
+ * the property to be retrieved from the object.
  * Accepts nested properties delimited by a `.`.
  * Delimiter can be escaped to preserve property names that contain the delimiter.
  * e.g. `'prop1.prop2'` or `'prop2\.domain\.corp.prop2'`.
@@ -766,3 +772,34 @@ function handleCustomlevelNamesOpts (cLevels) {
     return {}
   }
 }
+
+/**
+ * Translates all conditional blocks from within the messageFormat. Translates any matching
+ * {if key}{key}{end} statements and returns everything between if and else blocks if the key provided
+ * was found in log.
+ *
+ * @param {string} messageFormat A format string or function that defines how the
+ *  logged message should be conditionally formatted, e.g. `'{if level}{level}{end} - {if req.id}{req.id}{end}'`.
+ * @param {object} log The log object to be modified.
+ *
+ * @returns {string} The parsed messageFormat.
+ */
+function interpretConditionals (messageFormat, log) {
+  messageFormat = messageFormat.replace(/{if (.*?)}(.*?){end}/g, replacer)
+
+  // Remove non-terminated if blocks
+  messageFormat = messageFormat.replace(/{if (.*?)}/g, '')
+  // Remove floating end blocks
+  messageFormat = messageFormat.replace(/{end}/g, '')
+
+  return messageFormat.replace(/\s+/g, ' ').trim()
+
+  function replacer (_, key, value) {
+    const propertyValue = getPropertyValue(log, key)
+    if (propertyValue && value.includes(key)) {
+      return value.replace(new RegExp('{' + key + '}', 'g'), propertyValue)
+    } else {
+      return ''
+    }
+  }
+}

test/lib/utils.internals.test.js

@@ -222,3 +222,70 @@ tap.test('#getPropertyValue', t => {
 
   t.end()
 })
+
+tap.test('#interpretConditionals', t => {
+  const logData = {
+    level: 30,
+    data1: {
+      data2: 'bar'
+    },
+    msg: 'foo'
+  }
+
+  t.test('interpretConditionals translates if / else statement to found property value', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level} - {if data1.data2}{data1.data2}{end}', log), '{level} - bar')
+  })
+
+  t.test('interpretConditionals translates if / else statement to found property value and leave unmatched property key untouched', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level} - {if data1.data2}{data1.data2} ({msg}){end}', log), '{level} - bar ({msg})')
+  })
+
+  t.test('interpretConditionals removes non-terminated if statements', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level} - {if data1.data2}{data1.data2}', log), '{level} - {data1.data2}')
+  })
+
+  t.test('interpretConditionals removes floating end statements', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level} - {data1.data2}{end}', log), '{level} - {data1.data2}')
+  })
+
+  t.test('interpretConditionals removes floating end statements within translated if / end statements', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level} - {if msg}({msg}){end}{end}', log), '{level} - (foo)')
+  })
+
+  t.test('interpretConditionals removes if / end blocks if existent condition key does not match existent property key', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level}{if msg}{data1.data2}{end}', log), '{level}')
+  })
+
+  t.test('interpretConditionals removes if / end blocks if non-existent condition key does not match existent property key', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level}{if foo}{msg}{end}', log), '{level}')
+  })
+
+  t.test('interpretConditionals removes if / end blocks if existent condition key does not match non-existent property key', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level}{if msg}{foo}{end}', log), '{level}')
+  })
+
+  t.test('interpretConditionals removes if / end blocks if non-existent condition key does not match non-existent property key', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level}{if foo}{bar}{end}', log), '{level}')
+  })
+
+  t.test('interpretConditionals removes if / end blocks if nested condition key does not match property key', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{level}{if data1.msg}{data1.data2}{end}', log), '{level}')
+  })
+
+  t.test('interpretConditionals removes nested if / end statement blocks', async t => {
+    const log = fastCopy(logData)
+    t.equal(internals.interpretConditionals('{if msg}{if data1.data2}{msg}{data1.data2}{end}{end}', log), 'foo{data1.data2}')
+  })
+
+  t.end()
+})

test/lib/utils.public.test.js

@@ -141,6 +141,11 @@ tap.test('prettifyMessage', t => {
     t.equal(str, 'localhost/test - param:  - foo')
   })
 
+  t.test('`messageFormat` supports conditional blocks', async t => {
+    const str = prettifyMessage({ log: { level: 30, req: { id: 'foo' } }, messageFormat: '{level} | {if req.id}({req.id}){end}{if msg}{msg}{end}' })
+    t.equal(str, '30 | (foo)')
+  })
+
   t.test('`messageFormat` supports function definition', async t => {
     const str = prettifyMessage({
       log: { level: 30, request: { url: 'localhost/test' }, msg: 'incoming request' },