From 9ab54412ea9d6de5d699b6a9e78088e8943f6ef5 Mon Sep 17 00:00:00 2001
From: Michael Bryan <michaelfbryan@gmail.com>
Date: Sun, 14 Jan 2018 19:14:27 +0800
Subject: [PATCH] Made it so the CmdRenderer writes directly to the child's
 stdin (#544)

---
 Cargo.toml                  |  1 -
 src/lib.rs                  |  1 -
 src/renderer/mod.rs         | 36 ++++++++++++++++++++++--------------
 tests/alternate_backends.rs | 18 ++++++++++++++++++
 4 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/Cargo.toml b/Cargo.toml
index b35d6cb2..27cc0f1e 100644
--- a/Cargo.toml
+++ b/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"
 
diff --git a/src/lib.rs b/src/lib.rs
index fe1c1253..163f3619 100644
--- a/src/lib.rs
+++ b/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;
 
diff --git a/src/renderer/mod.rs b/src/renderer/mod.rs
index 0e145cce..e094b5cd 100644
--- a/src/renderer/mod.rs
+++ b/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
-        // of passing it in via a pipe. This prevents a race condition where
-        // some quickly executing command (e.g. `/bin/true`) may exit before we
-        // finish writing the render context (closing the stdin pipe and
-        // 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)
+        let mut child = self.compose_command()?
+            .stdin(Stdio::piped())
+            .stdout(Stdio::inherit())
+            .stderr(Stdio::inherit())
             .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() {
diff --git a/tests/alternate_backends.rs b/tests/alternate_backends.rs
index 6f69f0ea..c62c7ff7 100644
--- a/tests/alternate_backends.rs
+++ b/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();