From ea691f1cf95b6bd223638afa986e136a273aab6b Mon Sep 17 00:00:00 2001
From: Asim Aslam <asim@aslam.me>
Date: Wed, 15 Dec 2021 11:21:48 +0000
Subject: [PATCH] add proxy code

---
 app/proxy/proxy.go | 148 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 148 insertions(+)
 create mode 100644 app/proxy/proxy.go

diff --git a/app/proxy/proxy.go b/app/proxy/proxy.go
new file mode 100644
index 0000000..0708043
--- /dev/null
+++ b/app/proxy/proxy.go
@@ -0,0 +1,148 @@
+package proxy
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"os"
+	"strings"
+	"sync"
+	"time"
+)
+
+var (
+	// API Key
+	APIKey = os.Getenv("MICRO_API_KEY")
+
+	// API Url
+	APIHost = "https://api.m3o.com"
+
+	// host to proxy for Apps
+	AppHost = "m3o.app"
+)
+
+var (
+	mtx sync.RWMutex
+
+	// local cache
+	appMap = map[string]*backend{}
+)
+
+type backend struct {
+	url     *url.URL
+	created time.Time
+}
+
+func Handler(w http.ResponseWriter, r *http.Request) {
+	// no subdomain
+	if r.Host == AppHost {
+		return
+	}
+
+	// lookup the app map
+	mtx.RLock()
+	bk, ok := appMap[r.Host]
+	mtx.RUnlock()
+
+	// check the url map
+	if ok && time.Since(bk.created) < time.Minute {
+		r.Host = bk.url.Host
+		r.Header.Set("Host", r.Host)
+		httputil.NewSingleHostReverseProxy(bk.url).ServeHTTP(w, r)
+		return
+	}
+
+	subdomain := strings.TrimSuffix(r.Host, "."+AppHost)
+
+	// only process one part for now
+	parts := strings.Split(subdomain, ".")
+	if len(parts) > 1 {
+		log.Print("[app/proxy] more parts than expected", parts)
+		return
+	}
+
+	// currently service id is the subdomain
+	id := subdomain
+
+	log.Printf("[app/proxy] resolving host %s to id %s\n", r.Host, id)
+
+	apiURL := APIHost + "/app/resolve"
+
+	// use /v1/
+	if len(APIKey) > 0 {
+		apiURL = APIHost + "/v1/app/resolve"
+	}
+
+	// make new request
+	log.Printf("[app/proxy] Calling: %v", apiURL+"?id="+id)
+	req, err := http.NewRequest("GET", apiURL+"?id="+id, nil)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	if req.Header == nil {
+		req.Header = make(http.Header)
+	}
+
+	// set the api key after we're given the header
+	if len(APIKey) > 0 {
+		req.Header.Set("Authorization", "Bearer "+APIKey)
+	}
+
+	// call the backend for the url
+	rsp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+	defer rsp.Body.Close()
+
+	b, err := ioutil.ReadAll(rsp.Body)
+	if err != nil {
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	if rsp.StatusCode != 200 {
+		log.Printf("[app/proxy] Error calling api: status: %v %v", rsp.StatusCode, string(b))
+		http.Error(w, "unexpected error", 500)
+		return
+	}
+
+	result := map[string]interface{}{}
+
+	if err := json.Unmarshal(b, &result); err != nil {
+		log.Print("[app/proxy] failed to unmarshal response")
+		http.Error(w, err.Error(), 500)
+		return
+	}
+
+	// get the destination url
+	u, _ := result["url"].(string)
+	if len(u) == 0 {
+		log.Print("[app/proxy] no response url")
+		return
+	}
+
+	uri, err := url.Parse(u)
+	if err != nil {
+		log.Print("[app/proxy] failed to parse url", err.Error())
+		return
+	}
+
+	mtx.Lock()
+	appMap[r.Host] = &backend{
+		url:     uri,
+		created: time.Now(),
+	}
+	mtx.Unlock()
+
+	r.Host = uri.Host
+	r.Header.Set("Host", r.Host)
+
+	httputil.NewSingleHostReverseProxy(uri).ServeHTTP(w, r)
+}