Test the generator refusals and a "'" in the source query

Through the router: a source query holding "'" must reach the upstream
as %27. The generator page must answer 400, show the URL pixa would
fetch and make no encrypted URL for a source path holding %2F next to a
space, a "|" or a letter outside ASCII, and for a source URL holding a
user name and password. It must also refuse a source path holding a ".."
segment, as /v1/image/ does. These fail on the branch; the fix follows.

Model: opus-5-5

internal/server/source_url_internal_test.go

@@ -157,10 +157,11 @@ func postGenerate(
 }
 
 // TestImageURLFetchesItsSourcePathAndQuery requests image URLs whose source
-// query holds a space and whose source path holds a "%", each written
-// percent-encoded, and checks the one request the upstream receives: the
-// source path percent-encoded again, and the source query with the space
-// written %20.
+// query holds a space, written percent-encoded, or a "'", and whose source
+// path holds a "%", written percent-encoded, and checks the one request the
+// upstream receives: the source path percent-encoded again, and the source
+// query with the space written %20 and the "'" written %27, as a browser
+// writes them in a query.
 func TestImageURLFetchesItsSourcePathAndQuery(t *testing.T) {
 	t.Parallel()
 
@@ -174,6 +175,8 @@ func TestImageURLFetchesItsSourcePathAndQuery(t *testing.T) {
 	}{
 		{"space in the query", "/photo.png%3Fname=my%20cat",
 			"/photo.png?name=my%20cat"},
+		{"apostrophe in the query", "/photo.png%3Fname=it's",
+			"/photo.png?name=it%27s"},
 		{"percent sign in the path", percentSignPath, percentSignPath},
 	}
 
@@ -305,30 +308,64 @@ func TestGeneratedURLFetchesTheSourceURLAsEntered(t *testing.T) {
 	}
 }
 
-// TestGeneratorRefusesSourceURLItWouldFetchAnotherWay submits a source URL
-// whose path holds %2F. pixa keeps the path decoded and would fetch it with a
-// "/" there, which is another URL, so the generator page answers 400, shows
-// the URL pixa would fetch, and makes no encrypted URL.
-func TestGeneratorRefusesSourceURLItWouldFetchAnotherWay(t *testing.T) {
+// TestGeneratorRefusesSourceURLItCannotFetchAsWritten submits source URLs the
+// generator page must make no encrypted URL for, and checks that it answers
+// 400 and shows why. pixa keeps the source path decoded and fetches it
+// percent-encoded again, so a path holding %2F would be fetched with a "/"
+// there, whatever else the path holds. pixa sends no user name or password,
+// and no "?" with no query after it. For these the page shows the URL pixa
+// would fetch. A source path holding a ".." segment is refused, as
+// /v1/image/ refuses it.
+func TestGeneratorRefusesSourceURLItCannotFetchAsWritten(t *testing.T) {
 	t.Parallel()
 
-	s, _, _ := startImageProxy(t, startRecordingUpstream(t).Server)
-
-	rec := postGenerate(t, s, "https://"+upstreamHost+"/a%2Fb.png")
-	body := rec.Body.String()
-
-	if rec.Code != http.StatusBadRequest {
-		t.Errorf("status = %d, want %d", rec.Code, http.StatusBadRequest)
-	}
-
-	if strings.Contains(body, "/v1/e/") {
-		t.Error("the page shows an encrypted URL")
-	}
-
 	// The test config sets allow_http, so pixa would fetch over plain HTTP
-	fetchURL := "http://" + upstreamHost + "/a/b.png"
-	if !strings.Contains(body, fetchURL) {
-		t.Errorf("the page does not show the URL pixa would fetch, %s; body %s",
-			fetchURL, body)
+	const fetchedFrom = "http://" + upstreamHost
+
+	tests := []struct {
+		name string
+		// sourceURL is the source URL after "https://"
+		sourceURL string
+		// wantShown is what the page must show: the URL pixa would fetch, or
+		// why it makes no encrypted URL
+		wantShown string
+	}{
+		{"encoded slash", upstreamHost + "/a%2Fb.png",
+			fetchedFrom + "/a/b.png"},
+		{"encoded slash and a space", upstreamHost + "/a%2Fb c.png",
+			fetchedFrom + "/a/b%20c.png"},
+		{"encoded slash and a bar", upstreamHost + "/a%2Fb|c.png",
+			fetchedFrom + "/a/b%7Cc.png"},
+		{"encoded slash and a letter outside ASCII", upstreamHost + "/café%2Fx.png",
+			fetchedFrom + "/caf%C3%A9/x.png"},
+		{"user name and password", "user:pass@" + upstreamHost + "/a.png",
+			fetchedFrom + "/a.png"},
+		{"question mark with no query", upstreamHost + "/a.png?",
+			fetchedFrom + "/a.png"},
+		{"two-dot segment", upstreamHost + "/a/../b.png",
+			"cannot hold a .. segment"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			s, _, _ := startImageProxy(t, startRecordingUpstream(t).Server)
+
+			rec := postGenerate(t, s, "https://"+tt.sourceURL)
+			body := rec.Body.String()
+
+			if rec.Code != http.StatusBadRequest {
+				t.Errorf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+			}
+
+			if strings.Contains(body, "/v1/e/") {
+				t.Error("the page shows an encrypted URL")
+			}
+
+			if !strings.Contains(body, tt.wantShown) {
+				t.Errorf("the page does not show %s; body %s", tt.wantShown, body)
+			}
+		})
 	}
 }