Add fileviewer for browsing files via web server

.gitignore

@@ -3,6 +3,7 @@
 *~
 
 # Go binaries
+web/fileviewer/fileviewer
 web/proxy/proxy
 web/server/server
 

WORKSPACE

@@ -56,6 +56,13 @@ go_repository(
     version = "v2.4.0",
 )
 
+go_repository(
+    name = "com_github_gomarkdown_markdown",
+    importpath = "github.com/gomarkdown/markdown",
+    sum = "h1:7dT6mSWxX6R/7sB6FDSade73Q6BVL834Y1wJR/db+5o=",
+    version = "v0.0.0-20230714230225-84ecad09a30a",
+)
+
 go_rules_dependencies()
 
 go_register_toolchains(version = "host")

go.mod

@@ -4,5 +4,6 @@ go 1.12
 
 require (
 	github.com/ghodss/yaml v1.0.0
+	github.com/gomarkdown/markdown v0.0.0-20230714230225-84ecad09a30a
 	gopkg.in/yaml.v2 v2.4.0 // indirect
 )

go.sum

@@ -1,5 +1,7 @@
 github.com/ghodss/yaml v1.0.0 h1:wQHKEahhL6wmXdzwWG11gIVCkOv05bNOh+Rxn0yngAk=
 github.com/ghodss/yaml v1.0.0/go.mod h1:4dBDuWmgqj2HViK6kFavaiC9ZROes6MMH2rRYeMEF04=
+github.com/gomarkdown/markdown v0.0.0-20230714230225-84ecad09a30a h1:7dT6mSWxX6R/7sB6FDSade73Q6BVL834Y1wJR/db+5o=
+github.com/gomarkdown/markdown v0.0.0-20230714230225-84ecad09a30a/go.mod h1:JDGcbDT52eL4fju3sZ4TeHGsQwhG9nbDV21aMyhwPoA=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=

web/fileviewer/BUILD.bazel

@@ -0,0 +1,29 @@
+# Copyright 2023 Google LLC
+#
+# 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.
+
+load("@io_bazel_rules_go//go:def.bzl", "go_binary", "go_library")
+
+go_library(
+    name = "fileviewer_lib",
+    srcs = ["fileviewer.go"],
+    importpath = "github.com/mbrukman/notebook/web/fileviewer",
+    visibility = ["//visibility:private"],
+    deps = ["@com_github_gomarkdown_markdown//:go_default_library"],
+)
+
+go_binary(
+    name = "fileviewer",
+    embed = [":fileviewer_lib"],
+    visibility = ["//visibility:public"],
+)

web/fileviewer/README.md

@@ -0,0 +1,64 @@
+# File viewer
+
+This is a simple web server which renders text files (including HTML, JS, CSS)
+and Markdown files (dynamically rendered to HTML). Some use cases include
+quickly browsing local directories via a web browser, including Markdown files
+with relative links.
+
+This is an early prototype, but you're welcome to play around with it and
+provide feedback, potential new use cases, etc.
+
+## Building
+
+Build in the current directory:
+
+```sh
+$ go build .
+```
+
+Or you can build it from the top of the tree in a local checkout:
+
+```sh
+$ go build ./web/filevewer
+```
+
+Or you can build via Bazel:
+
+```sh
+$ bazel build //web/fileviewer
+```
+
+Or you can build it without having this repo locally:
+
+```sh
+$ go install github.com/mbrukman/notebook/web/fileviewer@latest
+```
+
+# Running
+
+Run locally with a custom web root (only accessible from `localhost` by
+default):
+
+```sh
+$ ./fileviewer -web-root ~/notebook
+```
+
+Expose it to everyone who can access this computer via the network:
+
+```sh
+$ ./fileviewer -web-root ~/notebook -host 0.0.0.0
+```
+
+Get a list of available flags:
+
+```sh
+$ ./fileviewer -help
+```
+
+Running via Bazel (this path is printed when you run the `bazel build ...`
+command above):
+
+```sh
+$ bazel-bin/web/fileviewer/fileviewer_/fileviewer [...flags]
+```
+

web/fileviewer/fileviewer.go

@@ -0,0 +1,166 @@
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"log"
+	"net/http"
+	"os"
+	"path"
+	"strings"
+
+	"github.com/gomarkdown/markdown"
+)
+
+var (
+	cwd, _  = os.Getwd()
+	webRoot = flag.String("web-root", cwd, "Root of the web file tree.")
+	host    = flag.String("host", "127.0.0.1", "By default, the server is only accessible via localhost. "+
+		"Set to 0.0.0.0 or empty string to open to all.")
+	port = flag.String("port", getEnvWithDefault("PORT", "8080"), "Port to listen on; $PORT env var overrides default value.")
+)
+
+func getEnvWithDefault(varName, defaultValue string) string {
+	if value := os.Getenv(varName); value != "" {
+		return value
+	}
+	return defaultValue
+}
+
+func stringHasOneOfSuffixes(str string, suffixes []string) bool {
+	for _, suffix := range suffixes {
+		if strings.HasSuffix(str, suffix) {
+			return true
+		}
+	}
+	return false
+}
+
+type DocHandler struct {
+	webRoot string
+}
+
+func serveFile(rw http.ResponseWriter, mimeType string, fileContents []byte) {
+	rw.WriteHeader(http.StatusOK)
+	rw.Header().Set("Content-Type", fmt.Sprintf("%s; charset=UTF-8", mimeType))
+	rw.Write([]byte(fileContents))
+}
+
+func (handler *DocHandler) DispatchHandler(rw http.ResponseWriter, req *http.Request) {
+	log.Printf("Request: %s", req.URL.Path)
+	var urlPath string = req.URL.Path
+	// Remove any occurrences of `..` in the path to avoid escaping the web root.
+	urlPath = strings.ReplaceAll(urlPath, "..", "")
+	// Replace all multi-sequences of `/` with a single slash.
+	urlPath = strings.ReplaceAll(urlPath, "//", "/")
+	var fsPath string = path.Join(handler.webRoot, "/./", urlPath)
+
+	log.Printf("Local path: %s", fsPath)
+
+	fileInfo, err := os.Stat(fsPath)
+	if err != nil && os.IsNotExist(err) {
+		// File does not exist.
+		rw.WriteHeader(http.StatusNotFound)
+		rw.Header().Set("Content-Type", "text/html; charset=UTF-8")
+		rw.Write([]byte("<!DOCTYPE html>\n"))
+		rw.Write([]byte("<html>"))
+		rw.Write([]byte("<body>"))
+		rw.Write([]byte(fmt.Sprintf("<h1>Error 404: <code>%s</code> not found", urlPath)))
+		rw.Write([]byte("</body>"))
+		rw.Write([]byte("</html>"))
+
+		log.Printf("Path not found: %s", fsPath)
+		return
+	}
+
+	if fileInfo.IsDir() {
+		files, err := ioutil.ReadDir(fsPath)
+		if err != nil {
+			log.Printf("Error listing directory: %s", fsPath)
+			return
+		}
+
+		rw.WriteHeader(http.StatusOK)
+		rw.Header().Set("Content-Type", "text/html; charset=UTF-8")
+		rw.Write([]byte("<!DOCTYPE html>\n"))
+		rw.Write([]byte("<html>"))
+		rw.Write([]byte("<body>"))
+		rw.Write([]byte(fmt.Sprintf("<h1>Directory listing: %s</h1>", urlPath)))
+		rw.Write([]byte("<ul>"))
+		for _, file := range files {
+			// Skip internal files, e.g., `.git` directory, `.gitignore`, other dotfiles, etc.
+			if strings.HasPrefix(file.Name(), ".") {
+				continue
+			}
+			var listItem string
+			if urlPath == "/" {
+				listItem = fmt.Sprintf("<li><a href='%s'>%s</li>\n", file.Name(), file.Name())
+			} else {
+				listItem = fmt.Sprintf("<li><a href='%s/%s'>%s</li>\n", urlPath, file.Name(), file.Name())
+			}
+			rw.Write([]byte(listItem))
+		}
+		rw.Write([]byte("</ul>"))
+		rw.Write([]byte("</body>"))
+		rw.Write([]byte("</html>"))
+		return
+	}
+
+	fileContents, err := ioutil.ReadFile(fsPath)
+	if err != nil {
+		log.Printf("Error reading file (%s): %s", fsPath, err)
+		return
+	}
+
+	if strings.HasSuffix(fsPath, ".html") {
+		serveFile(rw, "text/html", fileContents)
+	} else if strings.HasSuffix(fsPath, ".js") {
+		serveFile(rw, "text/javascript", fileContents)
+	} else if strings.HasSuffix(fsPath, ".ts") {
+		serveFile(rw, "text/typescript", fileContents)
+	} else if strings.HasSuffix(fsPath, ".css") {
+		serveFile(rw, "text/css", fileContents)
+	} else if strings.HasSuffix(fsPath, ".md") {
+		rw.WriteHeader(http.StatusOK)
+		rw.Header().Set("Content-Type", "text/html; charset=UTF-8")
+		rw.Write([]byte(`<!doctype html>
+<html>
+<head>
+  <style>
+    code {
+      background-color: #efefef;
+      margin: 3px;
+      padding: 3px;
+    }
+  </style>
+</head>
+<body>`))
+		rw.Write(markdown.ToHTML(fileContents, nil, nil))
+		rw.Write([]byte(`</body>
+</html>`))
+	} else if stringHasOneOfSuffixes(fsPath, []string{".txt", ".text", ".json", ".sh"}) {
+		rw.Header().Set("Content-Type", "text/plain; charset=UTF-8")
+		rw.Write(fileContents)
+	} else {
+		rw.Header().Set("Content-Type", "text/plain; charset=UTF-8")
+		rw.Write([]byte("Unrecognized file content type or suffix."))
+		log.Printf("Unrecognized file content type or suffix: %s", fsPath)
+	}
+}
+
+func NewDocHandler(webRoot string) *DocHandler {
+	return &DocHandler{webRoot: webRoot}
+}
+
+func main() {
+	flag.Parse()
+
+	handler := NewDocHandler(*webRoot)
+	http.HandleFunc("/", handler.DispatchHandler)
+
+	hostPort := fmt.Sprintf("%s:%s", *host, *port)
+	log.Printf("Listening on http://%s", hostPort)
+	log.Printf("Serving from %s", *webRoot)
+	log.Fatal(http.ListenAndServe(hostPort, nil))
+}