feat: enable for operating behind a proxy that modifies the url

Assume the backend is hosted on a server with a proxy that maps requests to `/backend/<routes>` to `/<routes>`, then we need a mechanism so that links still work (the link from the error page to the swagger UI, the links in the swagger UI to the api docs). This solution assumes that `X-forwarded-...` headers are set by the proxy, e.g.: * X-Forwarded-For * X-Forwarded-Proto * X-Forwarded-Prefix
GenSpectrum · Aug 23, 2023 · 78f0231 · 78f0231
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diff --git a/lapis2/README.md b/lapis2/README.md
@@ -34,6 +34,13 @@ Use Docker Compose to run SILO and LAPIS:
 LAPIS_TAG=latest SILO_TAG=latest DATABASE_CONFIG=path/to/config docker compose up
 ```
 
+### Operating LAPIS behind a proxy
+
+When running LAPIS behind a proxy, the proxy needs to set X-Forwarded headers:
+* X-Forwarded-For
+* X-Forwarded-Proto
+* X-Forwarded-Prefix
+
 ## End-to-end tests
 
 There are end-to-end tests in `siloLapisTests/` that test the integration of SILO and LAPIS.

diff --git a/lapis2/src/main/kotlin/org/genspectrum/lapis/controller/ErrorController.kt b/lapis2/src/main/kotlin/org/genspectrum/lapis/controller/ErrorController.kt
@@ -0,0 +1,63 @@
+package org.genspectrum.lapis.controller
+
+import jakarta.servlet.http.HttpServletRequest
+import jakarta.servlet.http.HttpServletResponse
+import mu.KotlinLogging
+import org.springframework.boot.autoconfigure.web.ErrorProperties
+import org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController
+import org.springframework.boot.web.servlet.error.ErrorAttributes
+import org.springframework.http.MediaType
+import org.springframework.stereotype.Component
+import org.springframework.web.bind.annotation.RequestMapping
+import org.springframework.web.servlet.ModelAndView
+import org.springframework.web.servlet.View
+import org.springframework.web.servlet.support.ServletUriComponentsBuilder
+
+private val log = KotlinLogging.logger { }
+
+@Component
+class ErrorController(errorAttributes: ErrorAttributes) :
+    BasicErrorController(errorAttributes, ErrorProperties()) {
+
+    @RequestMapping(produces = [MediaType.TEXT_HTML_VALUE])
+    override fun errorHtml(request: HttpServletRequest, response: HttpServletResponse): ModelAndView {
+        val modelAndView = super.errorHtml(request, response)
+
+        response.addHeader("Content-Type", MediaType.TEXT_HTML_VALUE)
+
+        val urlPrefix = removeErrorSegmentFromUrl(ServletUriComponentsBuilder.fromCurrentRequest().toUriString())
+        val url = "$urlPrefix/swagger-ui/index.html"
+
+        log.debug { "Generated url $url to Swagger UI in 'not found page'" }
+
+        modelAndView.view = NotFoundView(url)
+        return modelAndView
+    }
+
+    fun removeErrorSegmentFromUrl(url: String): String {
+        val lastSlashIndex = url.trimEnd('/').lastIndexOf("error")
+        return url.substring(0, lastSlashIndex).trim('/')
+    }
+}
+
+data class NotFoundView(private val url: String?) : View {
+
+    override fun render(model: MutableMap<String, *>?, request: HttpServletRequest, response: HttpServletResponse) {
+        val html: String = """
+            <!DOCTYPE html>
+            <html lang="en">
+            <head>
+                <meta charset="UTF-8">
+                <title>Error 404</title>
+            </head>
+            <body>
+                <h1>LAPIS</h1>
+                <h3>Page not found!</h3>
+                <a href="$url">Visit our swagger-ui</a>
+            </body>
+            </html>
+        """.trimIndent()
+
+        response.outputStream.write(html.toByteArray())
+    }
+}
diff --git a/lapis2/src/main/resources/public/error/404.html b/lapis2/src/main/resources/public/error/404.html
diff --git a/siloLapisTests/test/unknownUrl.spec.ts b/siloLapisTests/test/unknownUrl.spec.ts
@@ -18,6 +18,6 @@ describe('Error handling: UnknownUrl', () => {
 
     let responseBody = await result.text();
     expect(responseBody).contains('Page not found');
-    expect(responseBody).contains('a href="/swagger-ui/index.html"');
+    expect(responseBody).contains('<a href="http://localhost:8080/swagger-ui/index.html">');
   });
 });