From e1aa19f1e8c4a68b43add79374d6dfeae8bd9921 Mon Sep 17 00:00:00 2001
From: tjpcc <tjp@ctrl-c.club>
Date: Thu, 19 Jan 2023 16:03:52 -0700
Subject: New sharedhost contrib package.

ReplaceTilde simply replaces a leading ~ in the URL.

Fixes #9.
---
 README.gmi                             |  3 +-
 README.md                              |  3 +-
 contrib/sharedhost/replacement.go      | 46 +++++++++++++++++++++++++++
 contrib/sharedhost/replacement_test.go | 57 ++++++++++++++++++++++++++++++++++
 4 files changed, 107 insertions(+), 2 deletions(-)
 create mode 100644 contrib/sharedhost/replacement.go
 create mode 100644 contrib/sharedhost/replacement_test.go

diff --git a/README.gmi b/README.gmi
index a4e9946..9eb12be 100644
--- a/README.gmi
+++ b/README.gmi
@@ -34,10 +34,11 @@ The gemtext package provides a parser and converters for gemtext documents. It e
 
 This is where useful building blocks themselves start to come in. Sub-packages of contrib include Handler and Middleware implementations which accomplish the things your servers actually need to do.
 
-So far there are at least 3 packages:
+So far there are at least 4 packages:
 * log contains a simple request-logging middleware
 * fs has handlers that make file servers possible: serve files, build directory listings, etc
 * cgi includes handlers which can execute CGI programs
+* sharedhost which provides means of handling /~username URLs
 * ...with more to come
 
 ## Get it
diff --git a/README.md b/README.md
index 98a3861..2b4f53b 100644
--- a/README.md
+++ b/README.md
@@ -36,11 +36,12 @@ The gemtext package provides a parser and converters for gemtext documents. It e
 
 This is where useful building blocks themselves start to come in. Sub-packages of contrib include Handler and Middleware implementations which accomplish the things your servers actually need to do.
 
-So far there are at least 3 packages:
+So far there are at least 4 packages:
 
 * log contains a simple request-logging middleware
 * fs has handlers that make file servers possible: serve files, build directory listings, etc
 * cgi includes handlers which can execute CGI programs
+* sharedhost which provides means of handling /~username URLs
 * ...with more to come
 
 ## Get it
diff --git a/contrib/sharedhost/replacement.go b/contrib/sharedhost/replacement.go
new file mode 100644
index 0000000..1fb2a0d
--- /dev/null
+++ b/contrib/sharedhost/replacement.go
@@ -0,0 +1,46 @@
+package sharedhost
+
+import (
+	"context"
+	"crypto/tls"
+	"net/url"
+
+	"tildegit.org/tjp/gus"
+)
+
+// ReplaceTilde builds a middleware which substitutes a leading '~' in the request path.
+//
+// It makes the alteration to a copy of the request which is then passed into the
+// wrapped Handler. This way middlewares outside of this one inspecting the request
+// afterwards will see the original URL.
+//
+// Typically the replacement should end with a "/", so that the ~ ends up mapping to a
+// particular directory on the filesystem. For instance with a replacement string of
+// "users/", "domain.com/~jim/index.gmi" maps to "domain.com/users/jim/index.gmi".
+func ReplaceTilde(replacement string) gus.Middleware {
+	return func(inner gus.Handler) gus.Handler {
+		return func(ctx context.Context, request *gus.Request) *gus.Response {
+			if len(request.Path) > 1 && request.Path[0] == '/' && request.Path[1] == '~' {
+				request = cloneRequest(request)
+				request.Path = "/" + replacement + request.Path[2:]
+			}
+
+			return inner(ctx, request)
+		}
+	}
+}
+
+func cloneRequest(start *gus.Request) *gus.Request {
+	next := &gus.Request{}
+	*next = *start
+
+	next.URL = &url.URL{}
+	*next.URL = *start.URL
+
+	if start.TLSState != nil {
+		next.TLSState = &tls.ConnectionState{}
+		*next.TLSState = *start.TLSState
+	}
+
+	return next
+}
diff --git a/contrib/sharedhost/replacement_test.go b/contrib/sharedhost/replacement_test.go
new file mode 100644
index 0000000..cab80bb
--- /dev/null
+++ b/contrib/sharedhost/replacement_test.go
@@ -0,0 +1,57 @@
+package sharedhost_test
+
+import (
+	"context"
+	"net/url"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"tildegit.org/tjp/gus"
+	"tildegit.org/tjp/gus/contrib/sharedhost"
+)
+
+func TestReplaceTilde(t *testing.T) {
+	tests := []struct {
+		replacement  string
+		inputURL     string
+		replacedPath string
+	}{
+		{
+			replacement:  "users/",
+			inputURL:     "gemini://domain.com/~username/foo/bar",
+			replacedPath: "/users/username/foo/bar",
+		},
+		{
+			replacement:  "people-",
+			inputURL:     "gemini://domain.com/non/match",
+			replacedPath: "/non/match",
+		},
+		{
+			replacement:  "people-",
+			inputURL:     "gemini://domain.com/~someone/dir/file",
+			replacedPath: "/people-someone/dir/file",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.inputURL, func(t *testing.T) {
+			u, err := url.Parse(test.inputURL)
+			assert.Nil(t, err)
+
+			originalPath := u.Path
+
+			replacer := sharedhost.ReplaceTilde(test.replacement)
+			request := &gus.Request{URL: u}
+			handler := replacer(func(_ context.Context, request *gus.Request) *gus.Response {
+				assert.Equal(t, test.replacedPath, request.Path)
+				return &gus.Response{}
+			})
+
+			handler(context.Background(), request)
+
+			// original request was unmodified
+			assert.Equal(t, originalPath, request.Path)
+		})
+	}
+}
-- 
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