templates: Add `humanize` function (#4767)

Co-authored-by: Francis Lavoie <lavofr@gmail.com>

3 files changed, 112 insertions, 0 deletions

diff --git a/modules/caddyhttp/templates/templates.go b/modules/caddyhttp/templates/templates.go
index b2fe184..85612ba 100644
--- a/modules/caddyhttp/templates/templates.go
+++ b/modules/caddyhttp/templates/templates.go
@@ -238,6 +238,29 @@ func init() {
 // {{stripHTML "Shows <b>only</b> text content"}}
 // ```
 //
+// ##### `humanize`
+//
+// Transforms size and time inputs to a human readable format.
+// This uses the [go-humanize](https://github.com/dustin/go-humanize) library.
+//
+// The first argument must be a format type, and the last argument
+// is the input, or the input can be piped in. The supported format
+// types are:
+// - **size** which turns an integer amount of bytes into a string like `2.3 MB`
+// - **time** which turns a time string into a relative time string like `2 weeks ago`
+//
+// For the `time` format, the layout for parsing the input can be configured
+// by appending a colon `:` followed by the desired time layout. You can
+// find the documentation on time layouts [in Go's docs](https://pkg.go.dev/time#pkg-constants).
+// The default time layout is `RFC1123Z`, i.e. `Mon, 02 Jan 2006 15:04:05 -0700`.
+//
+// ```
+// {{humanize "size" "2048000"}}
+// {{placeholder "http.response.header.Content-Length" | humanize "size"}}
+// {{humanize "time" "Fri, 05 May 2022 15:04:05 +0200"}}
+// {{humanize "time:2006-Jan-02" "2022-May-05"}}
+// ```
+
 type Templates struct {
 	// The root path from which to load files. Required if template functions
 	// accessing the file system are used (such as include). Default is
diff --git a/modules/caddyhttp/templates/tplcontext.go b/modules/caddyhttp/templates/tplcontext.go
index 7843455..bae24ba 100644
--- a/modules/caddyhttp/templates/tplcontext.go
+++ b/modules/caddyhttp/templates/tplcontext.go
@@ -26,11 +26,13 @@ import (
 	"strings"
 	"sync"
 	"text/template"
+	"time"
 
 	"github.com/Masterminds/sprig/v3"
 	"github.com/alecthomas/chroma/formatters/html"
 	"github.com/caddyserver/caddy/v2"
 	"github.com/caddyserver/caddy/v2/modules/caddyhttp"
+	"github.com/dustin/go-humanize"
 	"github.com/yuin/goldmark"
 	highlighting "github.com/yuin/goldmark-highlighting"
 	"github.com/yuin/goldmark/extension"
@@ -81,6 +83,7 @@ func (c *TemplateContext) NewTemplate(tplName string) *template.Template {
 		"placeholder":      c.funcPlaceholder,
 		"fileExists":       c.funcFileExists,
 		"httpError":        c.funcHTTPError,
+		"humanize":         c.funcHumanize,
 	})
 	return c.tpl
 }
@@ -398,6 +401,43 @@ func (c TemplateContext) funcHTTPError(statusCode int) (bool, error) {
 	return false, caddyhttp.Error(statusCode, nil)
 }
 
+// funcHumanize transforms size and time inputs to a human readable format.
+//
+// Size inputs are expected to be integers, and are formatted as a
+// byte size, such as "83 MB".
+//
+// Time inputs are parsed using the given layout (default layout is RFC1123Z)
+// and are formatted as a relative time, such as "2 weeks ago".
+// See https://pkg.go.dev/time#pkg-constants for time layout docs.
+func (c TemplateContext) funcHumanize(formatType, data string) (string, error) {
+	// The format type can optionally be followed
+	// by a colon to provide arguments for the format
+	parts := strings.Split(formatType, ":")
+
+	switch parts[0] {
+	case "size":
+		dataint, dataerr := strconv.ParseUint(data, 10, 64)
+		if dataerr != nil {
+			return "", fmt.Errorf("humanize: size cannot be parsed: %s", dataerr.Error())
+		}
+		return humanize.Bytes(dataint), nil
+
+	case "time":
+		timelayout := time.RFC1123Z
+		if len(parts) > 1 {
+			timelayout = parts[1]
+		}
+
+		dataint, dataerr := time.Parse(timelayout, data)
+		if dataerr != nil {
+			return "", fmt.Errorf("humanize: time cannot be parsed: %s", dataerr.Error())
+		}
+		return humanize.Time(dataint), nil
+	}
+
+	return "", fmt.Errorf("no know function was given")
+}
+
 // WrappedHeader wraps niladic functions so that they
 // can be used in templates. (Template functions must
 // return a value.)
diff --git a/modules/caddyhttp/templates/tplcontext_test.go b/modules/caddyhttp/templates/tplcontext_test.go
index 61fc80c..15a369e 100644
--- a/modules/caddyhttp/templates/tplcontext_test.go
+++ b/modules/caddyhttp/templates/tplcontext_test.go
@@ -606,6 +606,55 @@ title = "Welcome"
 
 }
 
+func TestHumanize(t *testing.T) {
+	tplContext := getContextOrFail(t)
+	for i, test := range []struct {
+		format    string
+		inputData string
+		expect    string
+		errorCase bool
+		verifyErr func(actual_string, substring string) bool
+	}{
+		{
+			format:    "size",
+			inputData: "2048000",
+			expect:    "2.0 MB",
+			errorCase: false,
+			verifyErr: strings.Contains,
+		},
+		{
+			format:    "time",
+			inputData: "Fri, 05 May 2022 15:04:05 +0200",
+			expect:    "ago",
+			errorCase: false,
+			verifyErr: strings.HasSuffix,
+		},
+		{
+			format:    "time:2006-Jan-02",
+			inputData: "2022-May-05",
+			expect:    "ago",
+			errorCase: false,
+			verifyErr: strings.HasSuffix,
+		},
+		{
+			format:    "time",
+			inputData: "Fri, 05 May 2022 15:04:05 GMT+0200",
+			expect:    "error:",
+			errorCase: true,
+			verifyErr: strings.HasPrefix,
+		},
+	} {
+		if actual, err := tplContext.funcHumanize(test.format, test.inputData); !test.verifyErr(actual, test.expect) {
+			if !test.errorCase {
+				t.Errorf("Test %d: Expected '%s' but got '%s'", i, test.expect, actual)
+				if err != nil {
+					t.Errorf("Test %d: error: %s", i, err.Error())
+				}
+			}
+		}
+	}
+}
+
 func getContextOrFail(t *testing.T) TemplateContext {
 	tplContext, err := initTestContext()
 	t.Cleanup(func() {