reorg: phase 1

cmd/site/html.go

@@ -8,6 +8,8 @@ import (
 	"path/filepath"
 	"time"
 
+	"christine.website/internal"
+	"christine.website/internal/blog"
 	"github.com/prometheus/client_golang/prometheus"
 	"github.com/prometheus/client_golang/prometheus/promauto"
 	"within.website/ln"
@@ -30,7 +32,7 @@ func logTemplateTime(ctx context.Context, name string, f ln.F, from time.Time) {
 func (s *Site) renderTemplatePage(templateFname string, data interface{}) http.Handler {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		ctx := opname.With(r.Context(), "renderTemplatePage")
-		fetag := "W/" + Hash(templateFname, etag) + "-1"
+		fetag := "W/" + internal.Hash(templateFname, etag) + "-1"
 
 		f := ln.F{"etag": fetag, "if_none_match": r.Header.Get("If-None-Match")}
 
@@ -74,14 +76,16 @@ func (s *Site) showPost(w http.ResponseWriter, r *http.Request) {
 	}
 
 	cmp := r.URL.Path[1:]
-	var p *Post
+	var p blog.Post
+	var found bool
 	for _, pst := range s.Posts {
 		if pst.Link == cmp {
 			p = pst
+			found = true
 		}
 	}
 
-	if p == nil {
+	if !found {
 		w.WriteHeader(http.StatusNotFound)
 		s.renderTemplatePage("error.html", "no such post found: "+r.RequestURI).ServeHTTP(w, r)
 		return

cmd/site/main.go

@@ -6,15 +6,12 @@ import (
 	"io/ioutil"
 	"net/http"
 	"os"
-	"path/filepath"
-	"sort"
-	"strings"
 	"sync"
 	"time"
 
-	"christine.website/internal/front"
+	"christine.website/internal/blog"
 	"christine.website/internal/jsonfeed"
-	"github.com/celrenheit/sandflake"
+	"christine.website/internal/middleware"
 	"github.com/gorilla/feeds"
 	"github.com/povilasv/prommod"
 	"github.com/prometheus/client_golang/prometheus"
@@ -29,39 +26,6 @@ import (
 
 var port = os.Getenv("PORT")
 
-var (
-	requestCounter = prometheus.NewCounterVec(
-		prometheus.CounterOpts{
-			Name: "handler_requests_total",
-			Help: "Total number of request/responses by HTTP status code.",
-		}, []string{"handler", "code"})
-
-	requestDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
-		Name: "handler_request_duration",
-		Help: "Handler request duration.",
-	}, []string{"handler", "method"})
-
-	requestInFlight = prometheus.NewGaugeVec(prometheus.GaugeOpts{
-		Name: "handler_requests_in_flight",
-		Help: "Current number of requests being served.",
-	}, []string{"handler"})
-)
-
-func init() {
-	prometheus.Register(requestCounter)
-	prometheus.Register(requestDuration)
-	prometheus.Register(requestInFlight)
-}
-
-func middlewareMetrics(family string, next http.Handler) http.Handler {
-	return promhttp.InstrumentHandlerDuration(
-		requestDuration.MustCurryWith(prometheus.Labels{"handler": family}),
-		promhttp.InstrumentHandlerCounter(requestCounter.MustCurryWith(prometheus.Labels{"handler": family}),
-			promhttp.InstrumentHandlerInFlight(requestInFlight.With(prometheus.Labels{"handler": family}), next),
-		),
-	)
-}
-
 func main() {
 	if port == "" {
 		port = "29384"
@@ -78,30 +42,9 @@ func main() {
 	http.ListenAndServe(":"+port, s)
 }
 
-func requestIDMiddleware(next http.Handler) http.Handler {
-	var g sandflake.Generator
-	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		id := g.Next().String()
-
-		if rid := r.Header.Get("X-Request-Id"); rid != "" {
-			id = rid + "," + id
-		}
-
-		ctx := ln.WithF(r.Context(), ln.F{
-			"request_id": id,
-		})
-		r = r.WithContext(ctx)
-
-		w.Header().Set("X-Request-Id", id)
-		r.Header.Set("X-Request-Id", id)
-
-		next.ServeHTTP(w, r)
-	})
-}
-
 // Site is the parent object for https://christine.website's backend.
 type Site struct {
-	Posts  Posts
+	Posts  blog.Posts
 	Resume template.HTML
 
 	rssFeed  *feeds.Feed
@@ -109,7 +52,7 @@ type Site struct {
 
 	mux     *http.ServeMux
 	sitemap []byte
-	xffmw *xff.XFF
+	xffmw   *xff.XFF
 
 	templates map[string]*template.Template
 	tlock     sync.RWMutex
@@ -117,20 +60,18 @@ type Site struct {
 
 func (s *Site) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	ctx := opname.With(r.Context(), "site.ServeHTTP")
+	ctx = ln.WithF(ctx, ln.F{
+		"user_agent": r.Header.Get("User-Agent"),
+	})
 	r = r.WithContext(ctx)
 
-	requestIDMiddleware(s.xffmw.Handler(ex.HTTPLog(s.mux))).ServeHTTP(w, r)
+	middleware.RequestID(s.xffmw.Handler(ex.HTTPLog(s.mux))).ServeHTTP(w, r)
 }
 
 var arbDate = time.Date(2019, time.March, 21, 18, 0, 0, 0, time.UTC)
 
 // Build creates a new Site instance or fails.
 func Build() (*Site, error) {
-	type postFM struct {
-		Title string
-		Date  string
-	}
-
 	smi := sitemap.New()
 	smi.Add(&sitemap.URL{
 		Loc:        "https://christine.website/resume",
@@ -156,7 +97,6 @@ func Build() (*Site, error) {
 		ChangeFreq: sitemap.Weekly,
 	})
 
-
 	xffmw, err := xff.Default()
 	if err != nil {
 		return nil, err
@@ -185,61 +125,15 @@ func Build() (*Site, error) {
 				Avatar: icon,
 			},
 		},
-		mux:       http.NewServeMux(),
+		mux:   http.NewServeMux(),
 		xffmw: xffmw,
 	}
 
-	err = filepath.Walk("./blog/", func(path string, info os.FileInfo, err error) error {
-		if err != nil {
-			return err
-		}
-
-		if info.IsDir() {
-			return nil
-		}
-
-		fin, err := os.Open(path)
-		if err != nil {
-			return err
-		}
-		defer fin.Close()
-
-		content, err := ioutil.ReadAll(fin)
-		if err != nil {
-			return err
-		}
-
-		var fm postFM
-		remaining, err := front.Unmarshal(content, &fm)
-		if err != nil {
-			return err
-		}
-
-		output := blackfriday.Run(remaining)
-
-		p := &Post{
-			Title:    fm.Title,
-			Date:     fm.Date,
-			Link:     strings.Split(path, ".")[0],
-			Body:     string(remaining),
-			BodyHTML: template.HTML(output),
-		}
-
-		s.Posts = append(s.Posts, p)
-		itime, _ := time.Parse("2006-01-02", p.Date)
-		smi.Add(&sitemap.URL{
-			Loc:        "https://christine.website/" + p.Link,
-			LastMod:    &itime,
-			ChangeFreq: sitemap.Monthly,
-		})
-
-		return nil
-	})
+	posts, err := blog.LoadPosts("./blog/")
 	if err != nil {
 		return nil, err
 	}
-
-	sort.Sort(sort.Reverse(s.Posts))
+	s.Posts = posts
 
 	resumeData, err := ioutil.ReadFile("./static/resume/resume.md")
 	if err != nil {
@@ -249,19 +143,18 @@ func Build() (*Site, error) {
 	s.Resume = template.HTML(blackfriday.Run(resumeData))
 
 	for _, item := range s.Posts {
-		itime, _ := time.Parse("2006-01-02", item.Date)
 		s.rssFeed.Items = append(s.rssFeed.Items, &feeds.Item{
 			Title:       item.Title,
 			Link:        &feeds.Link{Href: "https://christine.website/" + item.Link},
 			Description: item.Summary,
-			Created:     itime,
+			Created:     item.Date,
 		})
 
 		s.jsonFeed.Items = append(s.jsonFeed.Items, jsonfeed.Item{
 			ID:            "https://christine.website/" + item.Link,
 			URL:           "https://christine.website/" + item.Link,
 			Title:         item.Title,
-			DatePublished: itime,
+			DatePublished: item.Date,
 			ContentHTML:   string(item.BodyHTML),
 		})
 	}
@@ -280,13 +173,13 @@ func Build() (*Site, error) {
 		http.Error(w, "OK", http.StatusOK)
 	})
 	s.mux.Handle("/metrics", promhttp.Handler())
-	s.mux.Handle("/resume", middlewareMetrics("resume", s.renderTemplatePage("resume.html", s.Resume)))
-	s.mux.Handle("/blog", middlewareMetrics("blog", s.renderTemplatePage("blogindex.html", s.Posts)))
-	s.mux.Handle("/contact", middlewareMetrics("contact", s.renderTemplatePage("contact.html", nil)))
-	s.mux.Handle("/blog.rss", middlewareMetrics("blog.rss", http.HandlerFunc(s.createFeed)))
-	s.mux.Handle("/blog.atom", middlewareMetrics("blog.atom", http.HandlerFunc(s.createAtom)))
-	s.mux.Handle("/blog.json", middlewareMetrics("blog.json", http.HandlerFunc(s.createJsonFeed)))
-	s.mux.Handle("/blog/", middlewareMetrics("blogpost", http.HandlerFunc(s.showPost)))
+	s.mux.Handle("/resume", middleware.Metrics("resume", s.renderTemplatePage("resume.html", s.Resume)))
+	s.mux.Handle("/blog", middleware.Metrics("blog", s.renderTemplatePage("blogindex.html", s.Posts)))
+	s.mux.Handle("/contact", middleware.Metrics("contact", s.renderTemplatePage("contact.html", nil)))
+	s.mux.Handle("/blog.rss", middleware.Metrics("blog.rss", http.HandlerFunc(s.createFeed)))
+	s.mux.Handle("/blog.atom", middleware.Metrics("blog.atom", http.HandlerFunc(s.createAtom)))
+	s.mux.Handle("/blog.json", middleware.Metrics("blog.json", http.HandlerFunc(s.createJSONFeed)))
+	s.mux.Handle("/blog/", middleware.Metrics("blogpost", http.HandlerFunc(s.showPost)))
 	s.mux.Handle("/css/", http.FileServer(http.Dir(".")))
 	s.mux.Handle("/static/", http.FileServer(http.Dir(".")))
 	s.mux.HandleFunc("/sw.js", func(w http.ResponseWriter, r *http.Request) {
@@ -295,7 +188,7 @@ func Build() (*Site, error) {
 	s.mux.HandleFunc("/robots.txt", func(w http.ResponseWriter, r *http.Request) {
 		http.ServeFile(w, r, "./static/robots.txt")
 	})
-	s.mux.Handle("/sitemap.xml", middlewareMetrics("sitemap", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	s.mux.Handle("/sitemap.xml", middleware.Metrics("sitemap", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Content-Type", "application/xml")
 		smi.WriteTo(w)
 	})))
@@ -304,25 +197,3 @@ func Build() (*Site, error) {
 }
 
 const icon = "https://christine.website/static/img/avatar.png"
-
-// Post is a single blogpost.
-type Post struct {
-	Title    string        `json:"title"`
-	Link     string        `json:"link"`
-	Summary  string        `json:"summary,omitifempty"`
-	Body     string        `json:"-"`
-	BodyHTML template.HTML `json:"body"`
-	Date     string        `json:"date"`
-}
-
-// Posts implements sort.Interface for a slice of Post objects.
-type Posts []*Post
-
-func (p Posts) Len() int { return len(p) }
-func (p Posts) Less(i, j int) bool {
-	iDate, _ := time.Parse("2006-01-02", p[i].Date)
-	jDate, _ := time.Parse("2006-01-02", p[j].Date)
-
-	return iDate.Unix() < jDate.Unix()
-}
-func (p Posts) Swap(i, j int) { p[i], p[j] = p[j], p[i] }

cmd/site/rss.go

@@ -5,19 +5,29 @@ import (
 	"net/http"
 	"time"
 
+	"christine.website/internal"
 	"within.website/ln"
+	"within.website/ln/opname"
 )
 
 var bootTime = time.Now()
-var etag = Hash(bootTime.String(), IncrediblySecureSalt)
+var etag = internal.Hash(bootTime.String(), IncrediblySecureSalt)
 
 // IncrediblySecureSalt *******
 const IncrediblySecureSalt = "hunter2"
 
 func (s *Site) createFeed(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("Content-Type", "application/rss+xml")
-	w.Header().Set("ETag", "W/"+Hash(bootTime.String(), IncrediblySecureSalt))
+	ctx := opname.With(r.Context(), "rss-feed")
+	fetag := "W/" + internal.Hash(bootTime.String(), IncrediblySecureSalt)
+	w.Header().Set("ETag", fetag)
 
+	if r.Header.Get("If-None-Match") == fetag {
+		http.Error(w, "Cached data OK", http.StatusNotModified)
+		ln.Log(ctx, ln.Info("cache hit"))
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/rss+xml")
 	err := s.rssFeed.WriteRss(w)
 	if err != nil {
 		http.Error(w, "Internal server error", http.StatusInternalServerError)
@@ -31,13 +41,21 @@ func (s *Site) createFeed(w http.ResponseWriter, r *http.Request) {
 }
 
 func (s *Site) createAtom(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("Content-Type", "application/atom+xml")
-	w.Header().Set("ETag", "W/"+Hash(bootTime.String(), IncrediblySecureSalt))
+	ctx := opname.With(r.Context(), "atom-feed")
+	fetag := "W/" + internal.Hash(bootTime.String(), IncrediblySecureSalt)
+	w.Header().Set("ETag", fetag)
 
+	if r.Header.Get("If-None-Match") == fetag {
+		http.Error(w, "Cached data OK", http.StatusNotModified)
+		ln.Log(ctx, ln.Info("cache hit"))
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/atom+xml")
 	err := s.rssFeed.WriteAtom(w)
 	if err != nil {
 		http.Error(w, "Internal server error", http.StatusInternalServerError)
-		ln.Error(r.Context(), err, ln.F{
+		ln.Error(ctx, err, ln.F{
 			"remote_addr": r.RemoteAddr,
 			"action":      "generating_atom",
 			"uri":         r.RequestURI,
@@ -46,16 +64,25 @@ func (s *Site) createAtom(w http.ResponseWriter, r *http.Request) {
 	}
 }
 
-func (s *Site) createJsonFeed(w http.ResponseWriter, r *http.Request) {
-	w.Header().Set("Content-Type", "application/json")
-	w.Header().Set("ETag", Hash(bootTime.String(), IncrediblySecureSalt))
+func (s *Site) createJSONFeed(w http.ResponseWriter, r *http.Request) {
+	ctx := opname.With(r.Context(), "atom-feed")
+	fetag := "W/" + internal.Hash(bootTime.String(), IncrediblySecureSalt)
+	w.Header().Set("ETag", fetag)
 
+	if r.Header.Get("If-None-Match") == fetag {
+		http.Error(w, "Cached data OK", http.StatusNotModified)
+		ln.Log(ctx, ln.Info("cache hit"))
+		return
+	}
+
+
+	w.Header().Set("Content-Type", "application/json")
 	e := json.NewEncoder(w)
 	e.SetIndent("", "\t")
 	err := e.Encode(s.jsonFeed)
 	if err != nil {
 		http.Error(w, "Internal server error", http.StatusInternalServerError)
-		ln.Error(r.Context(), err, ln.F{
+		ln.Error(ctx, err, ln.F{
 			"remote_addr": r.RemoteAddr,
 			"action":      "generating_jsonfeed",
 			"uri":         r.RequestURI,

go.mod

@@ -16,9 +16,7 @@ require (
 	github.com/shurcooL/sanitized_anchor_name v1.0.0 // indirect
 	github.com/snabb/sitemap v1.0.0
 	github.com/stretchr/testify v1.3.0
-	github.com/tj/front v0.0.0-20170212063142-739be213b0a1
 	gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 // indirect
-	gopkg.in/yaml.v1 v1.0.0-20140924161607-9f9df34309c0 // indirect
 	gopkg.in/yaml.v2 v2.2.1
 	within.website/ln v0.5.2
 )

go.sum

@@ -69,8 +69,6 @@ github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1
 github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
 github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
 github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
-github.com/tj/front v0.0.0-20170212063142-739be213b0a1 h1:lA+aPRvltlx2fwv/BnxyYSDQo3pIeqzHgMO5GvK0T9E=
-github.com/tj/front v0.0.0-20170212063142-739be213b0a1/go.mod h1:deJrtusCTptAW4EUn5vBLpl3dhNqPqUwEjWJz5UNxpQ=
 golang.org/x/crypto v0.0.0-20180904163835-0709b304e793/go.mod h1:6SG95UA2DQfeDnfUPMdvaQW0Q7yPrPDi9nlGo2tz2b4=
 golang.org/x/net v0.0.0-20180811021610-c39426892332/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
 golang.org/x/net v0.0.0-20181114220301-adae6a3d119a/go.mod h1:mL1N/T3taQHkDXs73rZJwtUhF3w3ftmwwsq0BUmARs4=
@@ -84,8 +82,6 @@ gopkg.in/alecthomas/kingpin.v2 v2.2.6/go.mod h1:FMv+mEhP44yOT+4EoQTLFTRgOQ1FBLks
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127 h1:qIbj1fsPNlZgppZ+VLlY7N33q108Sa+fhmuc+sWQYwY=
 gopkg.in/check.v1 v1.0.0-20180628173108-788fd7840127/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/yaml.v1 v1.0.0-20140924161607-9f9df34309c0 h1:POO/ycCATvegFmVuPpQzZFJ+pGZeX22Ufu6fibxDVjU=
-gopkg.in/yaml.v1 v1.0.0-20140924161607-9f9df34309c0/go.mod h1:WDnlLJ4WF5VGsH/HVa3CI79GS0ol3YnhVnKP89i0kNg=
 gopkg.in/yaml.v2 v2.2.1 h1:mUhvW9EsL+naU5Q3cakzfE91YhliOondGd6ZrsDBHQE=
 gopkg.in/yaml.v2 v2.2.1/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=
 within.website/ln v0.5.2 h1:4pTM2wzpLjeZAputLf2U29HD79vcmdoEI/VPm2QEYgs=

internal/blog/blog.go

@@ -0,0 +1,98 @@
+package blog
+
+import (
+	"html/template"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sort"
+	"strings"
+	"time"
+
+	"christine.website/internal/front"
+	"github.com/russross/blackfriday"
+)
+
+// Post is a single blogpost.
+type Post struct {
+	Title    string        `json:"title"`
+	Link     string        `json:"link"`
+	Summary  string        `json:"summary,omitifempty"`
+	Body     string        `json:"-"`
+	BodyHTML template.HTML `json:"body"`
+	Date     time.Time     `json:"date"`
+}
+
+// Posts implements sort.Interface for a slice of Post objects.
+type Posts []Post
+
+func (p Posts) Len() int { return len(p) }
+func (p Posts) Less(i, j int) bool {
+	iDate := p[i].Date
+	jDate := p[j].Date
+
+	return iDate.Unix() < jDate.Unix()
+}
+func (p Posts) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
+
+// LoadPosts loads posts for a given directory.
+func LoadPosts(path string) (Posts, error) {
+	type postFM struct {
+		Title string
+		Date  string
+	}
+	var result Posts
+
+	err := filepath.Walk(path, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if info.IsDir() {
+			return nil
+		}
+
+		fin, err := os.Open(path)
+		if err != nil {
+			return err
+		}
+		defer fin.Close()
+
+		content, err := ioutil.ReadAll(fin)
+		if err != nil {
+			return err
+		}
+
+		var fm postFM
+		remaining, err := front.Unmarshal(content, &fm)
+		if err != nil {
+			return err
+		}
+
+		output := blackfriday.Run(remaining)
+
+		const timeFormat = `2006-01-02`
+		date, err := time.Parse(timeFormat, fm.Date)
+		if err != nil {
+			return err
+		}
+
+		p := Post{
+			Title:    fm.Title,
+			Date:     date,
+			Link:     strings.Split(path, ".")[0],
+			Body:     string(remaining),
+			BodyHTML: template.HTML(output),
+		}
+		result = append(result, p)
+
+		return nil
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	sort.Sort(sort.Reverse(result))
+
+	return result, nil
+}

internal/blog/blog_test.go

@@ -0,0 +1,12 @@
+package blog
+
+import (
+	"testing"
+)
+
+func TestLoadPosts(t *testing.T) {
+	_, err := LoadPosts("../../blog")
+	if err != nil {
+		t.Fatal(err)
+	}
+}

internal/hash.go

@@ -1,4 +1,4 @@
-package main
+package internal
 
 import (
 	"crypto/md5"

internal/middleware/metrics.go

@@ -0,0 +1,43 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+var (
+	requestCounter = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Name: "handler_requests_total",
+			Help: "Total number of request/responses by HTTP status code.",
+		}, []string{"handler", "code"})
+
+	requestDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
+		Name: "handler_request_duration",
+		Help: "Handler request duration.",
+	}, []string{"handler", "method"})
+
+	requestInFlight = prometheus.NewGaugeVec(prometheus.GaugeOpts{
+		Name: "handler_requests_in_flight",
+		Help: "Current number of requests being served.",
+	}, []string{"handler"})
+)
+
+func init() {
+	prometheus.Register(requestCounter)
+	prometheus.Register(requestDuration)
+	prometheus.Register(requestInFlight)
+}
+
+// Metrics captures request duration, request count and in-flight request count
+// metrics for HTTP handlers. The family field is used to discriminate handlers.
+func Metrics(family string, next http.Handler) http.Handler {
+	return promhttp.InstrumentHandlerDuration(
+		requestDuration.MustCurryWith(prometheus.Labels{"handler": family}),
+		promhttp.InstrumentHandlerCounter(requestCounter.MustCurryWith(prometheus.Labels{"handler": family}),
+			promhttp.InstrumentHandlerInFlight(requestInFlight.With(prometheus.Labels{"handler": family}), next),
+		),
+	)
+}

internal/middleware/requestid.go

@@ -0,0 +1,31 @@
+package middleware
+
+import (
+	"net/http"
+
+	"github.com/celrenheit/sandflake"
+	"within.website/ln"
+)
+
+// RequestID appends a unique (sandflake) request ID to each request's
+// X-Request-Id header field, much like Heroku's router does.
+func RequestID(next http.Handler) http.Handler {
+	var g sandflake.Generator
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		id := g.Next().String()
+
+		if rid := r.Header.Get("X-Request-Id"); rid != "" {
+			id = rid + "," + id
+		}
+
+		ctx := ln.WithF(r.Context(), ln.F{
+			"request_id": id,
+		})
+		r = r.WithContext(ctx)
+
+		w.Header().Set("X-Request-Id", id)
+		r.Header.Set("X-Request-Id", id)
+
+		next.ServeHTTP(w, r)
+	})
+}