Add a feature to provide each process the generated ports from other processes (#194)

* Add a feature to provide each process the generated ports from other processes

- include the ports generated for other processes in each process
  definition
- Add `OVERMIND_PROCESS_<name>_PORT` settings to each process wrapper
  script
- add docs for the feature

* Address PR feedback

- drop the extra command line flag and gate
- add a bit of extra safety to the port environment variable name

* PR feedback: don't carry the other ports around in the procfile

Construct the other service port list as the script is generated

* Explicitly allow only [a-zA-Z0-9_] in the process names

* Precompile the process names

Author: offbyone

README.md

@@ -159,6 +159,17 @@ $ overmind start -N
 $ OVERMIND_NO_PORT=1 overmind start
 ```
 
+#### Referencing the ports of other processes
+
+If overmind is specifying a port, each other process will be provided with environment variables that include them. Those variables will be have the format `OVERMIND_PROCESS_<name>_PORT` where "name" is the name of the process from the procfile, with any characters that are invalid in an environment variable replaced with `_`.
+
+If processes are scaled, those port names will be numbered as well, based on the scaling of the process.
+
+```Procfile
+web: bin/rails server -p $PORT
+proxy: ngrok http --subdomain overmind $OVERMIND_PROCESS_web_PORT
+```
+
 #### Running only the specified processes
 
 You can specify the names of processes you want to run:

start/command.go

@@ -6,6 +6,7 @@ import (
 	"os"
 	"os/signal"
 	"path/filepath"
+	"regexp"
 	"sync"
 	"syscall"
 	"time"
@@ -17,6 +18,11 @@ import (
 
 var defaultColors = []int{2, 3, 4, 5, 6, 42, 130, 103, 129, 108}
 
+// This is a set of characters that are not allowed in a process name.
+// It's expressed as a negation; all character not matching the set of allowed
+// characters will be replaced with an underscore.
+var disallowedProcNameCharacters = regexp.MustCompile(`[^a-zA-Z0-9_]`)
+
 type command struct {
 	title     string
 	timeout   int
@@ -85,7 +91,7 @@ func newCommand(h *Handler) (*command, error) {
 		isIgnored := len(ignoredProcNames) != 0 && utils.StringsContain(ignoredProcNames, e.OrigName)
 
 		if shouldRun && !isIgnored {
-			scriptFilePath := c.createScriptFile(&e, h.Shell, !h.NoPort)
+			scriptFilePath := c.createScriptFile(&e, pf, h.Shell, !h.NoPort)
 
 			c.processes = append(c.processes, newProcess(
 				c.tmux,
@@ -163,14 +169,22 @@ func (c *command) Quit() {
 	c.stopTrig <- syscall.SIGINT
 }
 
-func (c *command) createScriptFile(e *procfileEntry, shell string, setPort bool) string {
+func (c *command) createScriptFile(e *procfileEntry, procFile procfile, shell string, setPort bool) string {
 	scriptFile, err := os.Create(filepath.Join(c.scriptDir, e.Name))
 	utils.FatalOnErr(err)
 
 	fmt.Fprintf(scriptFile, "#!/usr/bin/env %s\n", shell)
 	if setPort {
 		fmt.Fprintf(scriptFile, "export PORT=%d\n", e.Port)
+
+		for _, pf := range procFile {
+			if pf.Name != e.Name {
+				safeProcessName := sanitizeProcName(pf.Name)
+				fmt.Fprintf(scriptFile, "export OVERMIND_PROCESS_%s_PORT=%d\n", safeProcessName, pf.Port)
+			}
+		}
 	}
+
 	fmt.Fprintf(scriptFile, "export PS=%s\n", e.Name)
 	fmt.Fprintln(scriptFile, e.Command)
 
@@ -247,3 +261,7 @@ func (c *command) waitForTimeoutOrStop() {
 	case <-c.stopTrig:
 	}
 }
+
+func sanitizeProcName(name string) string {
+	return disallowedProcNameCharacters.ReplaceAllString(name, "_")
+}