Refactor environment handling logic to separate a server from the environment handler itself

This change makes the environment handling logic execute independent of the server itself and should make it much easier for people to contribute changes and additional environment handlers down the road without polluting the server object even more.

There is still a lot of work to do on this front to make things easier to work with, and there are some questionable design decisions at play I'm sure.

Welcome to additional modifications and cleanup to make this code easier to reason about and work with.

server/configuration.go

@@ -1,41 +1,10 @@
 package server
 
 import (
-	"fmt"
-	"strconv"
+	"github.com/pterodactyl/wings/environment"
 	"sync"
 )
 
-type EnvironmentVariables map[string]interface{}
-
-// Ugly hacky function to handle environment variables that get passed through as not-a-string
-// from the Panel. Ideally we'd just say only pass strings, but that is a fragile idea and if a
-// string wasn't passed through you'd cause a crash or the server to become unavailable. For now
-// try to handle the most likely values from the JSON and hope for the best.
-func (ev EnvironmentVariables) Get(key string) string {
-	val, ok := ev[key]
-	if !ok {
-		return ""
-	}
-
-	switch val.(type) {
-	case int:
-		return strconv.Itoa(val.(int))
-	case int32:
-		return strconv.FormatInt(val.(int64), 10)
-	case int64:
-		return strconv.FormatInt(val.(int64), 10)
-	case float32:
-		return fmt.Sprintf("%f", val.(float32))
-	case float64:
-		return fmt.Sprintf("%f", val.(float64))
-	case bool:
-		return strconv.FormatBool(val.(bool))
-	}
-
-	return val.(string)
-}
-
 type Configuration struct {
 	mu sync.RWMutex
 
@@ -53,20 +22,17 @@ type Configuration struct {
 
 	// An array of environment variables that should be passed along to the running
 	// server process.
-	EnvVars EnvironmentVariables `json:"environment"`
+	EnvVars environment.Variables `json:"environment"`
 
-	Allocations           Allocations   `json:"allocations"`
-	Build                 BuildSettings `json:"build"`
-	CrashDetectionEnabled bool          `default:"true" json:"enabled" yaml:"enabled"`
-	Mounts                []Mount       `json:"mounts"`
-	Resources             ResourceUsage `json:"resources"`
+	Allocations           environment.Allocations `json:"allocations"`
+	Build                 environment.Limits      `json:"build"`
+	CrashDetectionEnabled bool                    `default:"true" json:"enabled" yaml:"enabled"`
+	Mounts                []Mount                 `json:"mounts"`
+	Resources             ResourceUsage           `json:"resources"`
 
 	Container struct {
 		// Defines the Docker image that will be used for this server
 		Image string `json:"image,omitempty"`
-		// If set to true, OOM killer will be disabled on the server's Docker container.
-		// If not present (nil) we will default to disabling it.
-		OomDisabled bool `default:"true" json:"oom_disabled"`
 	} `json:"container,omitempty"`
 }