From aedef32bb9ea8a20011762d03ec24082717dd9af Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Beno=C3=AEt=20Lef=C3=A8vre?= <contact@benoit-lefevre.org>
Date: Mon, 14 Nov 2022 02:13:14 +0100
Subject: [PATCH] feat issue #1341 (Layouts) : support a specifier on %m

---
 lib/layouts.js           |  14 ++++-
 test/tap/layouts-test.js | 116 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 128 insertions(+), 2 deletions(-)

diff --git a/lib/layouts.js b/lib/layouts.js
index 52aef56..2d7c660 100644
--- a/lib/layouts.js
+++ b/lib/layouts.js
@@ -101,6 +101,8 @@ function dummyLayout(loggingEvent) {
  *  - %c log category
  *  - %h hostname
  *  - %m log data
+ *  - %m{l}, where l is an integer : log data.slice(l)
+ *  - %m{l,u}, where l ans u are integers : log data.slice(l,u)
  *  - %d date in constious formats
  *  - %% %
  *  - %n newline
@@ -137,6 +139,8 @@ function patternLayout(pattern, tokens) {
   const regex =
     /%(-?[0-9]+)?(\.?-?[0-9]+)?([[\]cdhmnprzxXyflosCMAF%])(\{([^}]+)\})?|([^%]+)/;
 
+  const mSpecifierRegex = /\s*(-?\d)(\s*,\s*(-?\d))?\w*/;
+
   pattern = pattern || TTCC_CONVERSION_PATTERN;
 
   function categoryName(loggingEvent, specifier) {
@@ -210,8 +214,14 @@ function patternLayout(pattern, tokens) {
     return os.hostname().toString();
   }
 
-  function formatMessage(loggingEvent) {
-    return util.format(...loggingEvent.data);
+  function formatMessage(loggingEvent, specifier) {
+    const match = mSpecifierRegex.exec(specifier);
+
+    const lowerBound = match ? parseInt(match[1], 10) : 0;
+    const upperBound = match && match[3] ? parseInt(match[3], 10) : undefined;
+    const dataSlice = loggingEvent.data.slice(lowerBound, upperBound);
+
+    return util.format(...dataSlice);
   }
 
   function endOfLine() {
diff --git a/test/tap/layouts-test.js b/test/tap/layouts-test.js
index e16b83f..a736e5c 100644
--- a/test/tap/layouts-test.js
+++ b/test/tap/layouts-test.js
@@ -375,6 +375,122 @@ test('log4js layouts', (batch) => {
       assert.end();
     });
 
+    t.test('%m should apply util.format on data', (assert) => {
+      const eventWithSeveralDataEntry = JSON.parse(JSON.stringify(event));
+      eventWithSeveralDataEntry.data = [
+        'This %s a %s like other ones',
+        "isn't",
+        'test',
+      ];
+      testPattern(
+        assert,
+        layout,
+        eventWithSeveralDataEntry,
+        tokens,
+        '%m',
+        "This isn't a test like other ones"
+      );
+      assert.end();
+    });
+
+    t.test(
+      '%m{P}, with P been an integer, shoud only consider data.slice( P )',
+      (assert) => {
+        const eventWithSeveralDataEntry = JSON.parse(JSON.stringify(event));
+        eventWithSeveralDataEntry.data = [
+          'This %s a %s like other ones',
+          "isn't",
+          'test',
+        ];
+        testPattern(
+          assert,
+          layout,
+          eventWithSeveralDataEntry,
+          tokens,
+          '%m{1}',
+          "isn't test"
+        );
+        assert.end();
+      }
+    );
+
+    t.test('%m{0, 1} should behave like a dummy layout', (assert) => {
+      const eventWithSeveralDataEntry = JSON.parse(JSON.stringify(event));
+      eventWithSeveralDataEntry.data = [
+        'This %s a %s like other ones',
+        "isn't",
+        'test',
+      ];
+      testPattern(
+        assert,
+        layout,
+        eventWithSeveralDataEntry,
+        tokens,
+        '%m{0, 1}',
+        'This %s a %s like other ones'
+      );
+      assert.end();
+    });
+
+    t.test('%m{1, 2} shoud only consider data.slice( 1, 2 )', (assert) => {
+      const eventWithSeveralDataEntry = JSON.parse(JSON.stringify(event));
+      eventWithSeveralDataEntry.data = [
+        'This %s a %s like other ones',
+        "isn't",
+        'test',
+      ];
+      testPattern(
+        assert,
+        layout,
+        eventWithSeveralDataEntry,
+        tokens,
+        '%m{1,2}',
+        "isn't"
+      );
+      assert.end();
+    });
+
+    t.test('%m{1, 2} shoud only consider data.slice( 1, 2 )', (assert) => {
+      const eventWithSeveralDataEntry = JSON.parse(JSON.stringify(event));
+      eventWithSeveralDataEntry.data = [
+        'This %s a %s like other ones',
+        "isn't",
+        'test',
+      ];
+      testPattern(
+        assert,
+        layout,
+        eventWithSeveralDataEntry,
+        tokens,
+        '%m{1,2}',
+        "isn't"
+      );
+      assert.end();
+    });
+
+    t.test(
+      '%m{0, -1} should consider the whole data except the last element',
+      (assert) => {
+        const eventWithSeveralDataEntry = JSON.parse(JSON.stringify(event));
+        eventWithSeveralDataEntry.data = [
+          'This %s a %s like %s ones',
+          "isn't",
+          'test',
+          'other',
+          "won't be considered in call to util.format",
+        ];
+        testPattern(
+          assert,
+          layout,
+          eventWithSeveralDataEntry,
+          tokens,
+          '%m{0,-1}',
+          "This isn't a test like other ones"
+        );
+        assert.end();
+      }
+    );
+
     t.test('%n should output a new line', (assert) => {
       testPattern(assert, layout, event, tokens, '%n', EOL);
       assert.end();