add "alignLeft" and "alignRight" functions (#9672)

Fixes https://github.com/grafana/loki/issues/9667

CHANGELOG.md

@@ -34,6 +34,7 @@
 * [8684](https://github.com/grafana/loki/pull/8684) **oleksii-boiko-ua**: Helm: Add hpa templates for read, write and backend components.
 * [9535](https://github.com/grafana/loki/pull/9535) **salvacorts** Index stats cache can be configured independently of the results cache. If it's not configured, but it's enabled, it will use the results cache configuration.
 * [9604](https://github.com/grafana/loki/pull/9604) **dannykopping**: Querier: configurable writeback queue bytes size
+* [9672](https://github.com/grafana/loki/pull/9672) **zeitlinger**: Add `alignLeft` and `alignRight` line formatting functions.
 
 ##### Fixes
 

docs/sources/query/template_functions.md

@@ -234,6 +234,32 @@ Examples:
 {{ trimPrefix "-" "-hello" }} // output: hello
 ```
 
+## alignLeft
+
+Use this function to format a string to a fixed with, aligning the content to the left.
+
+Signature: `alignLeft(count int, src string) string`
+
+Examples:
+
+```template
+`{{ alignLeft 5 "hello world"}}` // output: "hello"
+`{{ alignLeft 5 "hi"}}`          // output: "hi   "
+```
+
+## alignRight
+
+Use this function to format a string to a fixed with, aligning the content to the right.
+
+Signature: `alignRight(count int, src string) string`
+
+Examples:
+
+```template
+`{{ alignRight 5 "hello world"}}` // output: "world"
+`{{ alignRight 5 "hi"}}`          // output: "   hi"
+```
+
 ## indent
 
 The indent function indents every line in a given string to the specified indent width. This is useful when aligning multi-line strings.
@@ -672,7 +698,7 @@ Examples:
 
 ```template
 {{ default "-" "" }} // output: -
-{{ default "-" "foo" }} // output: foo
+{{ default "" "foo" }} // output: foo
 ```
 
 Example of a query to print a `-` if the `http_request_headers_x_forwarded_for` label is empty:

pkg/logql/log/fmt.go

@@ -67,6 +67,8 @@ var (
 		"unixEpochMillis":  unixEpochMillis,
 		"unixEpochNanos":   unixEpochNanos,
 		"toDateInZone":     toDateInZone,
+		"alignLeft":        alignLeft,
+		"alignRight":       alignRight,
 	}
 
 	// sprig template functions
@@ -396,6 +398,32 @@ func trunc(c int, s string) string {
 	return s
 }
 
+func alignLeft(count int, src string) string {
+	runes := []rune(src)
+	l := len(runes)
+	if count < 0 || count == l {
+		return src
+	}
+	pad := count - l
+	if pad > 0 {
+		return src + strings.Repeat(" ", pad)
+	}
+	return string(runes[:count])
+}
+
+func alignRight(count int, src string) string {
+	runes := []rune(src)
+	l := len(runes)
+	if count < 0 || count == l {
+		return src
+	}
+	pad := count - l
+	if pad > 0 {
+		return strings.Repeat(" ", pad) + src
+	}
+	return string(runes[l-count:])
+}
+
 type Decolorizer struct{}
 
 // RegExp to select ANSI characters courtesy of https://github.com/acarl005/stripansi

pkg/logql/log/fmt_test.go

@@ -459,6 +459,24 @@ func Test_lineFormatter_Format(t *testing.T) {
 			labels.FromStrings("foo", "aSdtIGEgc3RyaW5nLCBlbmNvZGUgbWUh"),
 			[]byte("1"),
 		},
+		{
+			"alignLeft",
+			newMustLineFormatter("{{ alignLeft 4 .foo }}"),
+			labels.FromStrings("foo", "hello"),
+			1656353124120000000,
+			[]byte("hell"),
+			labels.FromStrings("foo", "hello"),
+			[]byte("1"),
+		},
+		{
+			"alignRight",
+			newMustLineFormatter("{{ alignRight 4 .foo }}"),
+			labels.FromStrings("foo", "hello"),
+			1656353124120000000,
+			[]byte("ello"),
+			labels.FromStrings("foo", "hello"),
+			[]byte("1"),
+		},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
@@ -721,6 +739,48 @@ func Test_trunc(t *testing.T) {
 	}
 }
 
+func Test_AlignLeft(t *testing.T) {
+	tests := []struct {
+		s    string
+		c    int
+		want string
+	}{
+		{"Hello, 世界", -1, "Hello, 世界"},
+		{"Hello, 世界", 0, ""},
+		{"Hello, 世界", 1, "H"},
+		{"Hello, 世界", 8, "Hello, 世"},
+		{"Hello, 世界", 20, "Hello, 世界           "},
+	}
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("%s%d", tt.s, tt.c), func(t *testing.T) {
+			if got := alignLeft(tt.c, tt.s); got != tt.want {
+				t.Errorf("alignLeft() = %q, want %q for %q with %v", got, tt.want, tt.s, tt.c)
+			}
+		})
+	}
+}
+
+func Test_AlignRight(t *testing.T) {
+	tests := []struct {
+		s    string
+		c    int
+		want string
+	}{
+		{"Hello, 世界", -1, "Hello, 世界"},
+		{"Hello, 世界", 0, ""},
+		{"Hello, 世界", 1, "界"},
+		{"Hello, 世界", 2, "世界"},
+		{"Hello, 世界", 20, "           Hello, 世界"},
+	}
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("%s%d", tt.s, tt.c), func(t *testing.T) {
+			if got := alignRight(tt.c, tt.s); got != tt.want {
+				t.Errorf("alignRight() = %q, want %q for %q with %v", got, tt.want, tt.s, tt.c)
+			}
+		})
+	}
+}
+
 func Test_substring(t *testing.T) {
 	tests := []struct {
 		start int