Made it so the CmdRenderer writes directly to the child's stdin (#544)

Cargo.toml

@@ -32,7 +32,6 @@ open = "1.1"
 regex = "0.2.1"
 tempdir = "0.3.4"
 itertools = "0.7.4"
-tempfile = "2.2.0"
 shlex = "0.1.1"
 toml-query = "0.6"
 

src/lib.rs

@@ -111,7 +111,6 @@ extern crate serde_derive;
 extern crate serde_json;
 extern crate shlex;
 extern crate tempdir;
-extern crate tempfile;
 extern crate toml;
 extern crate toml_query;
 

src/renderer/mod.rs

@@ -17,9 +17,8 @@ mod html_handlebars;
 
 use std::io::Read;
 use std::path::PathBuf;
-use std::process::Command;
+use std::process::{Command, Stdio};
 use serde_json;
-use tempfile;
 use shlex::Shlex;
 
 use errors::*;
@@ -153,21 +152,30 @@ impl Renderer for CmdRenderer {
     fn render(&self, ctx: &RenderContext) -> Result<()> {
         info!("Invoking the \"{}\" renderer", self.cmd);
 
-        // We need to write the RenderContext to a temporary file here instead
+        let mut child = self.compose_command()?
-        // of passing it in via a pipe. This prevents a race condition where
+            .stdin(Stdio::piped())
-        // some quickly executing command (e.g. `/bin/true`) may exit before we
+            .stdout(Stdio::inherit())
-        // finish writing the render context (closing the stdin pipe and
+            .stderr(Stdio::inherit())
-        // throwing a write error).
-        let mut temp = tempfile::tempfile().chain_err(|| "Unable to create a temporary file")?;
-        serde_json::to_writer(&mut temp, &ctx)
-            .chain_err(|| "Unable to serialize the RenderContext")?;
-
-        let status = self.compose_command()?
-            .stdin(temp)
             .current_dir(&ctx.destination)
-            .status()
+            .spawn()
             .chain_err(|| "Unable to start the renderer")?;
 
+        {
+            let mut stdin = child.stdin.take().expect("Child has stdin");
+            if let Err(e) = serde_json::to_writer(&mut stdin, &ctx) {
+                // Looks like the backend hung up before we could finish
+                // sending it the render context. Log the error and keep going
+                warn!("Error writing the RenderContext to the backend, {}", e);
+            }
+
+            // explicitly close the `stdin` file handle
+            drop(stdin);
+        }
+
+        let status = child
+            .wait()
+            .chain_err(|| "Error waiting for the backend to complete")?;
+
         trace!("{} exited with output: {:?}", self.cmd, status);
 
         if !status.success() {

tests/alternate_backends.rs

@@ -3,9 +3,11 @@
 extern crate mdbook;
 extern crate tempdir;
 
+use std::fs::File;
 use tempdir::TempDir;
 use mdbook::config::Config;
 use mdbook::MDBook;
+use mdbook::renderer::RenderContext;
 
 #[test]
 fn passing_alternate_backend() {
@@ -28,6 +30,22 @@ fn alternate_backend_with_arguments() {
     md.build().unwrap();
 }
 
+#[test]
+fn backends_receive_render_context_via_stdin() {
+    let temp = TempDir::new("output").unwrap();
+    let out_file = temp.path().join("out.txt");
+    let cmd = format!("tee {}", out_file.display());
+
+    let (md, _temp) = dummy_book_with_backend("cat-to-file", &cmd);
+
+    assert!(!out_file.exists());
+    md.build().unwrap();
+    assert!(out_file.exists());
+
+    let got = RenderContext::from_json(File::open(&out_file).unwrap());
+    assert!(got.is_ok());
+}
+
 fn dummy_book_with_backend(name: &str, command: &str) -> (MDBook, TempDir) {
     let temp = TempDir::new("mdbook").unwrap();