Add better comments about how the daemonization logic works.

cliutils.nimble

@@ -1,6 +1,6 @@
 # Package
 
-version       = "0.7.1"
+version       = "0.8.1"
 author        = "Jonathan Bernard"
 description   = "Helper functions for writing command line interfaces."
 license       = "MIT"

cliutils/config.nim

@@ -1,4 +1,5 @@
-import docopt, json, nre, os, strtabs, strutils
+import std/[json, nre, os, sequtils, strtabs, strutils]
+import docopt
 
 type
   CombinedConfig* = object
@@ -34,6 +35,22 @@ template walkFieldDefs*(t: NimNode, body: untyped) =
 #   cfgType.walkFieldDefs:
 #     let valLookup = quote do: `getVal`(
 
+proc initCombinedConfig*(
+    filename: string,
+    docopt: Table[string, Value] = initTable[string, Value]()
+  ): CombinedConfig =
+
+  result = CombinedConfig(docopt: docopt, json: parseFile(filename))
+
+proc findConfigFile*(name: string, otherLocations: seq[string] = @[]): string =
+  let cfgLocations = @[
+    $getEnv(name.strip(chars = {'.'}).toUpper()),
+    $getEnv("HOME") / name ] & otherLocations
+
+  result = cfgLocations.foldl(if fileExists(b): b else: a, "")
+  if result == "" or not fileExists(result):
+    raise newException(ValueError, "could not find configuration file")
+
 proc getVal*(cfg: CombinedConfig, key: string): string =
   let argKey = "--" & key
   let envKey = key.replace('-', '_').toUpper
@@ -57,6 +74,20 @@ proc getVal*(cfg: CombinedConfig, key, default: string): string =
   try: return getVal(cfg, key)
   except: return default
 
+proc getJson*(cfg: CombinedConfig, key: string): JsonNode =
+  let argKey = "--" & key
+  let envKey = key.replace('-', '_').toUpper
+  let jsonKey = key.replace(re"(-\w)", proc (m: RegexMatch): string = ($m)[1..1].toUpper)
+
+  if cfg.docopt.contains(argKey) and cfg.docopt[argKey]: return parseJson($cfg.docopt[argKey])
+  elif existsEnv(envKey): return parseJson(getEnv(envKey))
+  elif cfg.json.hasKey(jsonKey): return cfg.json[jsonKey]
+  else: raise newException(ValueError, "cannot find a configuration value for \"" & key & "\"")
+
+proc getJson*(cfg: CombinedConfig, key: string, default: JsonNode): JsonNode =
+  try: return getJson(cfg, key)
+  except: return default
+
 proc loadEnv*(): StringTableRef =
   result = newStringTable()
 

cliutils/daemonize.nim

@@ -19,27 +19,50 @@ proc daemonize*(pidfile, si, so, se: string, daemonMain: proc(): void): Pid =
   if fileExists(pidfile):
     raise newException(IOError, "pidfile " & pidfile & " already exists, daemon already running?")
 
+  # We're about to do a little dance to end up with a process that is
+  # disconnected from the calling program's process group and is not a session
+  # leader (a daemon process).
+  #
+  # Remember, after a call to fork the code is now running in two processes,
+  # the parent process and the child process.  So the returned PID will be a
+  # positive value if we are still on the parent process, and represents the
+  # PID of the newly created process. If we are on the newly created process,
+  # the PID returned with be 0.
+
   let pid1 = fork()
 
   # Are we the child process?
   if pid1 == 0:
+    # Yes, so let's get ready to execute the main code given to us. Note that
+    # this child process will not actually live long. As part of our setup,
+    # we're going to create a new process session, resulting in this child
+    # process being the process group owner and session leader. We don't our
+    # daemon process to be a session leader because that allows it to be
+    # connected to a terminal. So after we've setup the new process group we
+    # will fork again and actually run the logic we're daemonizing in the
+    # grandchild process.
 
-    # Yes, so let's get ready to execute the main code given to us.
+    # Ignore whatever the original working directory was.
     discard chdir("/")
+
+    # Create a new session to decouple us from the original terminal.
     discard setsid()
+
+    # Set the process file mode creation mask to 0000
     discard umask(0)
 
-    # Fork again... but I'm not sure why.
+    # Fork again so the grandchild process will not be the session leader.
     let pid2 = fork()
 
-    # We don't need the intermediate process, so if we are not the child this
-    # time, lets just quit
+    # If we're still on the child process, we're done.
     if pid2 > 0: quit(QuitSuccess)
 
-    # If we are the grandchild let's set up our environment.
+    # Otherwise, if we are the grandchild let's finish setting up our
+    # environment.
     flushFile(stdout)
     flushFile(stderr)
 
+    # Setup our STDIN, STDERR, and STDOUT pipes (if given)
     if si.len > 0:
       fi = open(si, fmRead)
       discard dup2(getFileHandle(fi), getFileHandle(stdin))
@@ -52,17 +75,20 @@ proc daemonize*(pidfile, si, so, se: string, daemonMain: proc(): void): Pid =
       fe = open(se, fmAppend)
       discard dup2(getFileHandle(fe), getFileHandle(stderr))
 
+    # Keep a record of the PID filename in our process memory so we can
+    # reference it in our cleanup hooks.
     pidFileInner = pidfile
 
     # Add hooks to cleanup after ourselves when we're asked to die.
     signal(SIGINT, onStop)
     signal(SIGTERM, onStop)
 
-    # Find out what our actual PID is and save it
+    # Find out what our actual PID is and save it to the PID file.
     let childPid = getpid()
     writeFile(pidfile, $childPid)
 
-    # Finally, execute our main
+    # Finally, execute the logic given to us to daemonize
     daemonMain()
 
+  # If we're not the child proces, return the new PID of the daemonized process
   return pid1