gemini: add document rendering function

src/gemini.rs

@@ -1,6 +1,6 @@
 /// This module implements a simple text/gemini parser based on the description
 /// here: https://gemini.circumlunar.space/docs/specification.html
-use std::io::Write;
+use std::io::{self, Write};
 
 /// Build a gemini document up from a series of nodes.
 #[derive(Default)]
@@ -54,6 +54,27 @@ impl Builder {
     }
 }
 
+/// Render a set of nodes as a document to a writer.
+pub fn render(nodes: Vec<Node>, out: &mut impl Write) -> io::Result<()> {
+    use Node::*;
+
+    for node in nodes {
+        match node {
+            Text(body) => write!(out, "{}\n", body)?,
+            Link{to, name} => match name {
+                Some(name) => write!(out, "{} {}\n", to, name)?,
+                None => write!(out, "{}\n", to)?,
+            },
+            Preformatted(body) => write!(out, "```\n{}\n```\n", body)?,
+            Heading { level, body} => write!(out, "{} {}\n", "#".repeat(level as usize), body)?,
+            ListItem(body) => write!(out, "* {}\n", body)?,
+            Quote(body) => write!(out, "> {}\n", body)?,
+        };
+    }
+
+    Ok(())
+}
+
 /// Individual nodes of the document. Each node correlates to a line in the file.
 #[derive(Debug, PartialEq, Eq)]
 pub enum Node {