config: Implement support for postprocess commands

config.go

@@ -1,8 +1,12 @@
 package main
 
 import (
+	"bytes"
+	"log"
 	"os"
+	"os/exec"
 	"path"
+	"strings"
 	"text/template"
 
 	"github.com/BurntSushi/toml"
@@ -27,7 +31,22 @@ type Task struct {
 }
 
 func (t Task) Format(p *Page) (string, []byte) {
-	return path.Join(p.Path, "index"+t.Output), []byte(p.Content)
+	path := path.Join(p.Path, "index"+t.Output)
+
+	// Run a custom command.
+	if t.PostProcess != "" {
+		split := strings.Split(t.PostProcess, " ")
+		cmd := exec.Command(split[0], split[1:]...)
+		buf := new(bytes.Buffer)
+		cmd.Stdin = strings.NewReader(p.Content)
+		cmd.Stdout = buf
+		if err := cmd.Run(); err != nil {
+			log.Fatal(err)
+		}
+		return path, buf.Bytes()
+	}
+
+	return path, []byte(p.Content)
 }
 
 // DefaultConfig returns the default configuration.

example/config.toml

@@ -14,5 +14,5 @@ destination = "public"
 input = ".gmi"
 output = ".html"
 template = ".gmi"
-postprocess = "geminiToHTML"
+postprocess = "geminitohtml"
 destination = "public.html"