Implement the error step which will terminate the pipeline

This isn't yet changing the status of the pipeline however

agent/src/control.rs

@@ -29,7 +29,7 @@ async fn handle_request(mut req: tide::Request<State>) -> tide::Result {
 
 pub async fn run(sender: Sender<Request>) -> tide::Result<()> {
     info!("Starting the agent control server");
-    let sock = "agent.sock";
+    let sock = agent_socket();
     let state = State { sender };
     let mut app = tide::with_state(state);
 
@@ -48,3 +48,22 @@ pub async fn run(sender: Sender<Request>) -> tide::Result<()> {
 
     Ok(())
 }
+
+/**
+ * Return a string representing the absolute path of this agent's control socket
+ */
+pub fn agent_socket() -> String {
+    let path = std::env::current_dir().expect("Failed to get current directory");
+    path.join("agent.sock").to_string_lossy().into_owned()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_agent_sock() {
+        let buf = agent_socket();
+        assert!(buf.ends_with("agent.sock"));
+    }
+}

agent/src/lib.rs

@@ -161,6 +161,9 @@ pub fn run(
 
             let mut file = NamedTempFile::new()?;
             let mut step_args = HashMap::new();
+            // TODO: This is going to be wrong on nested steps
+            let sock = Value::String(control::agent_socket());
+            step_args.insert("control", &sock);
             step_args.insert("parameters", &step.parameters);
 
             serde_yaml::to_writer(&mut file, &step_args)

agent/src/main.rs

@@ -14,7 +14,7 @@ use ottoagent::*;
  * If the number of pending messages exceeds this number, the requests to the
  * control socket will block until the pending messages are cleared out
  */
-const MAX_CONTROl_MSGS: usize = 64;
+const MAX_CONTROL_MSGS: usize = 64;
 
 #[async_std::main]
 async fn main() -> std::io::Result<()> {
@@ -27,7 +27,7 @@ async fn main() -> std::io::Result<()> {
     }
 
     let file = File::open(&args[1])?;
-    let (sender, receiver) = channel(MAX_CONTROl_MSGS);
+    let (sender, receiver) = channel(MAX_CONTROL_MSGS);
 
     match serde_yaml::from_reader::<File, Pipeline>(file) {
         Err(e) => {

stdlib/error/README.adoc

@@ -0,0 +1,3 @@
+= error
+
+The error step will simply abort the pipeline early

stdlib/error/error-step

@@ -0,0 +1,62 @@
+#!/usr/bin/env ruby
+
+require 'net/http'
+require 'json'
+require 'yaml'
+
+data = YAML.load(File.read(ARGV.first))
+control = data['control']
+
+if control.nil?
+  puts "Did not get a control socket! `error` won't work without it!"
+  exit 1
+end
+
+# Originally sourced from https://github.com/puppetlabs/net_http_unix under the
+# Apache 2.0 License
+class HTTPUnix < Net::HTTP
+  BufferedIO = ::Net::BufferedIO
+  UNIX_REGEXP = %r{^unix://}i
+
+  def initialize(address, port=nil)
+    super(address, port)
+    case address
+    when UNIX_REGEXP
+      @socket_type = 'unix'
+      @socket_path = address.sub(UNIX_REGEXP, '')
+      # Address and port are set to localhost so the HTTP client constructs
+      # a HOST request header nginx will accept.
+      @address = 'localhost'
+      @port = 80
+    else
+      @socket_type = 'inet'
+    end
+  end
+
+  def connect
+    if @socket_type == 'unix'
+      connect_unix
+    else
+      super
+    end
+  end
+
+  ##
+  # connect_unix is an alternative implementation of Net::HTTP#connect specific
+  # to the use case of using a Unix Domain Socket.
+  def connect_unix
+    D "opening connection to #{@socket_path}..."
+    s = Timeout.timeout(@open_timeout) { UNIXSocket.open(@socket_path) }
+    D "opened"
+    @socket = BufferedIO.new(s)
+    @socket.read_timeout = @read_timeout
+    @socket.continue_timeout = @continue_timeout
+    @socket.debug_output = @debug_output
+    on_connect
+  end
+end
+
+req = Net::HTTP::Post.new('/control', 'Content-Type' => 'application/json')
+req.body = {:type => :Terminate}.to_json
+client = HTTPUnix.new("unix://#{control}")
+client.request(req)

stdlib/error/manifest.yml

@@ -0,0 +1,19 @@
+---
+symbol: error
+description: |
+  The `error` step is a simple step that exits the pipeline
+
+includes:
+  - name: ./error-step
+  - name: ./README.adoc
+
+entrypoint:
+  path: error-step
+  multiarch: true
+
+parameters:
+  - name: message
+    required: true
+    type: string
+    description: |
+      The message to print when exiting the pipelin