Initial version

.gitignore

@@ -0,0 +1 @@
+data/

Dockerfile

@@ -0,0 +1,30 @@
+FROM golang:alpine as builder
+
+COPY . /go/src/github.com/Luzifer/preserve
+WORKDIR /go/src/github.com/Luzifer/preserve
+
+RUN set -ex \
+ && apk add --update git \
+ && go install \
+      -ldflags "-X main.version=$(git describe --tags --always || echo dev)" \
+      -mod=readonly
+
+FROM alpine:latest
+
+LABEL maintainer "Knut Ahlers <knut@ahlers.me>"
+
+ENV STORAGE_DIR=/data
+
+RUN set -ex \
+ && apk --no-cache add \
+      ca-certificates
+
+COPY --from=builder /go/bin/preserve /usr/local/bin/preserve
+
+EXPOSE 3000
+VOLUME ["/data"]
+
+ENTRYPOINT ["/usr/local/bin/preserve"]
+CMD ["--"]
+
+# vim: set ft=Dockerfile:

LICENSE

@@ -0,0 +1,202 @@
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+   1. Definitions.
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+   5. Submission of Contributions. Unless You explicitly state otherwise,
+      any Contribution intentionally submitted for inclusion in the Work
+      by You to the Licensor shall be under the terms and conditions of
+      this License, without any additional terms or conditions.
+      Notwithstanding the above, nothing herein shall supersede or modify
+      the terms of any separate license agreement you may have executed
+      with Licensor regarding such Contributions.
+
+   6. Trademarks. This License does not grant permission to use the trade
+      names, trademarks, service marks, or product names of the Licensor,
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+      origin of the Work and reproducing the content of the NOTICE file.
+
+   7. Disclaimer of Warranty. Unless required by applicable law or
+      agreed to in writing, Licensor provides the Work (and each
+      Contributor provides its Contributions) on an "AS IS" BASIS,
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+      negligent acts) or agreed to in writing, shall any Contributor be
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+   9. Accepting Warranty or Additional Liability. While redistributing
+      the Work or Derivative Works thereof, You may choose to offer,
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+      on Your own behalf and on Your sole responsibility, not on behalf
+      of any other Contributor, and only if You agree to indemnify,
+      defend, and hold each Contributor harmless for any liability
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+      of your accepting any such warranty or additional liability.
+
+   END OF TERMS AND CONDITIONS
+
+   APPENDIX: How to apply the Apache License to your work.
+
+      To apply the Apache License to your work, attach the following
+      boilerplate notice, with the fields enclosed by brackets "[]"
+      replaced with your own identifying information. (Don't include
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+
+   Copyright 2020- Knut Ahlers <knut@ahlers.me>
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+

README.md

@@ -0,0 +1,25 @@
+[![Go Report Card](https://goreportcard.com/badge/github.com/Luzifer/preserve)](https://goreportcard.com/report/github.com/Luzifer/preserve)
+![](https://badges.fyi/github/license/Luzifer/preserve)
+![](https://badges.fyi/github/downloads/Luzifer/preserve)
+![](https://badges.fyi/github/latest-release/Luzifer/preserve)
+![](https://knut.in/project-status/preserve)
+
+# Luzifer / preserve
+
+`preserve` is a little HTTP server to preserve the presence of URLs.
+
+Ever relied on an HTTP resource to be available and it vanished? Happened too often to me so I wrote a little tool to prevent URLs from vanishing: `preserve`.
+
+## Usage
+
+After you've started `preserve` it will by default listen on port 3000 and you can start using it by prefixing the URL of the resource:
+
+Lets say you want to ensure the image `https://example.com/image.png` does not vanish:
+
+- `http://localhost:3000/https://example.com/image.png` will fetch the resource once and then deliver it from the local cache
+- `http://localhost:3000/latest/https://example.com/image.png` will fetch the resource with every request until it gets unavailable and then serve it from local cache
+
+This also works with parameters:
+
+`http://localhost:3000/https://pbs.twimg.com/media/somemediaid?format=jpg&name=4096x4096`
+

cache.go

@@ -0,0 +1,51 @@
+package main
+
+import (
+	"io"
+	"net/http"
+	"os"
+	"path"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+func renewCache(url string) (*meta, error) {
+	var cachePath = urlToCachePath(url)
+
+	resp, err := http.Get(url)
+	if err != nil {
+		return nil, errors.Wrap(err, "Unable to fetch source file")
+	}
+
+	if resp.StatusCode > 299 {
+		return nil, errors.Errorf("HTTP status signaled failure: %d", resp.StatusCode)
+	}
+
+	if err = os.MkdirAll(path.Dir(cachePath), 0700); err != nil {
+		return nil, errors.Wrap(err, "Unable to create cache dir")
+	}
+
+	f, err := os.Create(cachePath)
+	if err != nil {
+		return nil, errors.Wrap(err, "Unable to create cache file")
+	}
+	defer f.Close()
+
+	if _, err := io.Copy(f, resp.Body); err != nil {
+		return nil, errors.Wrap(err, "Unable to write cache file")
+	}
+
+	var lm = time.Now()
+	if t, err := time.Parse(http.TimeFormat, resp.Header.Get("Last-Modified")); err == nil {
+		lm = t
+	}
+
+	metadata := &meta{
+		ContentType:  resp.Header.Get("Content-Type"),
+		LastCached:   time.Now(),
+		LastModified: lm,
+	}
+
+	return metadata, saveMeta(cachePath, *metadata)
+}

go.mod

@@ -0,0 +1,11 @@
+module github.com/Luzifer/preserve
+
+go 1.14
+
+require (
+	github.com/Luzifer/rconfig/v2 v2.2.1
+	github.com/gologme/log v1.2.0
+	github.com/gorilla/mux v1.7.4
+	github.com/pkg/errors v0.9.1
+	github.com/sirupsen/logrus v1.6.0
+)

go.sum

@@ -0,0 +1,25 @@
+github.com/Luzifer/rconfig v1.2.0 h1:waD1sqasGVSQSrExpLrQ9Q1JmMaltrS391VdOjWXP/I=
+github.com/Luzifer/rconfig/v2 v2.2.1 h1:zcDdLQlnlzwcBJ8E0WFzOkQE1pCMn3EbX0dFYkeTczg=
+github.com/Luzifer/rconfig/v2 v2.2.1/go.mod h1:OKIX0/JRZrPJ/ZXXWklQEFXA6tBfWaljZbW37w+sqBw=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/gologme/log v1.2.0 h1:Ya5Ip/KD6FX7uH0S31QO87nCCSucKtF44TLbTtO7V4c=
+github.com/gologme/log v1.2.0/go.mod h1:gq31gQ8wEHkR+WekdWsqDuf8pXTUZA9BnnzTuPz1Y9U=
+github.com/gorilla/mux v1.7.4 h1:VuZ8uybHlWmqV03+zRzdwKL4tUnIp1MAQtp1mIFE1bc=
+github.com/gorilla/mux v1.7.4/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB71So=
+github.com/konsorten/go-windows-terminal-sequences v1.0.3 h1:CE8S1cTafDpPvMhIxNJKvHsGVBgn1xWYf1NbHQhywc8=
+github.com/konsorten/go-windows-terminal-sequences v1.0.3/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
+github.com/pkg/errors v0.9.1 h1:FEBLx1zS214owpjy7qsBeixbURkuhQAwrK5UwLGTwt4=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/sirupsen/logrus v1.6.0 h1:UBcNElsrwanuuMsnGSlYmtmgbb23qDR5dG+6X6Oo89I=
+github.com/sirupsen/logrus v1.6.0/go.mod h1:7uNnSEd1DgxDLC74fIahvMZmmYsHGZGEOFrfsX/uA88=
+github.com/spf13/pflag v1.0.3 h1:zPAT6CGy6wXeQ7NtTnaTerfKOsV6V6F8agHXFiazDkg=
+github.com/spf13/pflag v1.0.3/go.mod h1:DYY7MBk1bdzusC3SYhjObp+wFpr4gzcvqqNjLnInEg4=
+github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
+golang.org/x/sys v0.0.0-20190422165155-953cdadca894 h1:Cz4ceDQGXuKRnVBDTS23GTn/pU5OE2C0WrNTOYK1Uuc=
+golang.org/x/sys v0.0.0-20190422165155-953cdadca894/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/validator.v2 v2.0.0-20180514200540-135c24b11c19 h1:WB265cn5OpO+hK3pikC9hpP1zI/KTwmyMFKloW9eOVc=
+gopkg.in/validator.v2 v2.0.0-20180514200540-135c24b11c19/go.mod h1:o4V0GXN9/CAmCsvJ0oXYZvrZOe7syiDZSN1GWGZTGzc=
+gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
+gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

main.go

@@ -0,0 +1,122 @@
+package main
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"net/http"
+	"net/url"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/gorilla/mux"
+	log "github.com/sirupsen/logrus"
+
+	"github.com/Luzifer/rconfig/v2"
+)
+
+var (
+	cfg = struct {
+		Listen         string `flag:"listen" default:":3000" description:"Port/IP to listen on"`
+		LogLevel       string `flag:"log-level" default:"info" description:"Log level (debug, info, warn, error, fatal)"`
+		StorageDir     string `flag:"storage-dir" default:"./data/" description:"Where to store cached files"`
+		VersionAndExit bool   `flag:"version" default:"false" description:"Prints current version and exits"`
+	}{}
+
+	version = "dev"
+)
+
+func init() {
+	rconfig.AutoEnv(true)
+	if err := rconfig.ParseAndValidate(&cfg); err != nil {
+		log.Fatalf("Unable to parse commandline options: %s", err)
+	}
+
+	if cfg.VersionAndExit {
+		fmt.Printf("preserve %s\n", version)
+		os.Exit(0)
+	}
+
+	if l, err := log.ParseLevel(cfg.LogLevel); err != nil {
+		log.WithError(err).Fatal("Unable to parse log level")
+	} else {
+		log.SetLevel(l)
+	}
+}
+
+func main() {
+	r := mux.NewRouter()
+	r.PathPrefix("/latest/").HandlerFunc(handleCacheLatest)
+	r.PathPrefix("/").HandlerFunc(handleCacheOnce)
+
+	r.SkipClean(true)
+
+	http.ListenAndServe(cfg.Listen, r)
+}
+
+func handleCacheLatest(w http.ResponseWriter, r *http.Request) {
+	handleCache(w, r, strings.TrimPrefix(r.RequestURI, "/latest/"), true)
+}
+
+func handleCacheOnce(w http.ResponseWriter, r *http.Request) {
+	handleCache(w, r, strings.TrimPrefix(r.RequestURI, "/"), false)
+}
+
+func handleCache(w http.ResponseWriter, r *http.Request, uri string, update bool) {
+	var (
+		cachePath   = urlToCachePath(uri)
+		cacheHeader = "HIT"
+		logger      = log.WithFields(log.Fields{
+			"url":  uri,
+			"path": cachePath,
+		})
+	)
+
+	if u, err := url.Parse(uri); err != nil || u.Scheme == "" {
+		http.Error(w, "Unable to parse requested URL", http.StatusBadRequest)
+		return
+	}
+
+	logger.Debug("Received request")
+
+	metadata, err := loadMeta(cachePath)
+	if err != nil && !os.IsNotExist(err) {
+		log.WithError(err).Error("Unable to load meta")
+		http.Error(w, "Unable to access entry metadata", http.StatusInternalServerError)
+		return
+	}
+
+	if update || os.IsNotExist(err) {
+		logger.Debug("Updating cache")
+		cacheHeader = "MISS"
+
+		metadata, err = renewCache(uri)
+		if err != nil {
+			log.WithError(err).Warn("Unable to refresh file")
+		}
+	}
+
+	if metadata == nil {
+		http.NotFound(w, r)
+		return
+	}
+
+	w.Header().Set("Content-Type", metadata.ContentType)
+	w.Header().Set("X-Last-Cached", metadata.LastCached.UTC().Format(http.TimeFormat))
+	w.Header().Set("X-Cache", cacheHeader)
+
+	f, err := os.Open(cachePath)
+	if err != nil {
+		log.WithError(err).Error("Unable to load cached file")
+		http.Error(w, "Unable to access cache entry", http.StatusInternalServerError)
+		return
+	}
+	defer f.Close()
+
+	http.ServeContent(w, r, "", metadata.LastModified, f)
+}
+
+func urlToCachePath(url string) string {
+	h := fmt.Sprintf("%x", sha256.Sum256([]byte(url)))
+	return path.Join(cfg.StorageDir, h[0:2], h)
+}

meta.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"encoding/json"
+	"os"
+	"strings"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+type meta struct {
+	ContentType  string
+	LastCached   time.Time
+	LastModified time.Time
+}
+
+func loadMeta(p string) (*meta, error) {
+	var metaPath = strings.Join([]string{p, "meta"}, ".")
+	if _, err := os.Stat(metaPath); err != nil {
+		return nil, err
+	}
+
+	f, err := os.Open(metaPath)
+	if err != nil {
+		return nil, errors.Wrap(err, "Unable to open metadata file")
+	}
+	defer f.Close()
+
+	var out = new(meta)
+	return out, errors.Wrap(
+		json.NewDecoder(f).Decode(out),
+		"Unable to decode metadata file",
+	)
+}
+
+func saveMeta(p string, m meta) error {
+	f, err := os.Create(strings.Join([]string{p, "meta"}, "."))
+	if err != nil {
+		return errors.Wrap(err, "Unable to create cache meta file")
+	}
+	defer f.Close()
+
+	return errors.Wrap(
+		json.NewEncoder(f).Encode(m),
+		"Unable to write cache meta file",
+	)
+}