Broken context path override

[mbechto]

Unfortunately, we encountered this issue when upgrading from 4.4.0 to 4.5.6:

java.io.FileNotFoundException: Byte array resource [resource loaded from byte array] cannot be resolved to absolute file path
	at org.springframework.core.io.AbstractResource.getFile(AbstractResource.java:132)
	at org.springframework.core.io.AbstractResource.getFileForLastModifiedCheck(AbstractResource.java:201)
	at org.springframework.core.io.AbstractResource.lastModified(AbstractResource.java:183)
	at org.springframework.web.servlet.resource.ResourceHttpRequestHandler.handleRequest(ResourceHttpRequestHandler.java:601)
	at org.springframework.web.servlet.mvc.HttpRequestHandlerAdapter.handle(HttpRequestHandlerAdapter.java:52)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1089)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:979)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1014)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885)
	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:195)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:140)
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51)

We are not yet sure what the root cause is or how to fix it. Apparently it has to do with the use of ByteArrayResource (probably to the changes introduced in #141).

[DzmitryShylovich]

As a workaround I created custom SpaFallbackMvc like this

class SchedulerUiSpaFallbackMvc(
    private val prefix: String,
    private val patchedIndexHtml: String,
) : SpaFallbackMvc(prefix, patchedIndexHtml) {

    override fun addResourceHandlers(registry: ResourceHandlerRegistry) {
        registry.addResourceHandler("$prefix/db-scheduler", "$prefix/db-scheduler/**")
            .addResourceLocations("classpath:/static/db-scheduler/")
            .resourceChain(true)
            .addResolver(SpaFallbackResolver())
    }

    inner class SpaFallbackResolver : PathResourceResolver() {
        override fun getResource(@NonNull resourcePath: String, location: Resource): Resource {
            val requestedResource = location.createRelative(resourcePath)
            return if (requestedResource.exists() && requestedResource.isReadable) {
                requestedResource
            } else {
                PatchedIndexHtmlResource(ClassPathResource(DEFAULT_STARTING_PAGE))
            }
        }
    }

    /**
     * Custom Resource wrapper that always serves the patched `index.html`.
     *
     * Why do we need this?
     * --------------------
     * Spring's SPA fallback resolver returns a `Resource` when no static file is found.
     * By default, that would just serve the original `index.html` from the classpath.
     *
     * But in our case, we modify the DB Scheduler UI's `index.html` at startup
     * (patching the base path and injecting a `<script>` with the context path).
     * If we simply returned the original `ClassPathResource`, the fallback would
     * ignore our modifications and serve the unpatched file.
     *
     * This wrapper ensures that whenever the SPA fallback kicks in, the response
     * content is our *patched* HTML, while still behaving like a Spring `Resource`
     * in every other way.
     */
    inner class PatchedIndexHtmlResource(
        private val original: Resource,
    ) : Resource by original {

        private val patchedContent: ByteArray by lazy {
            patchedIndexHtml.toByteArray(StandardCharsets.UTF_8)
        }

        override fun getInputStream(): InputStream = patchedContent.inputStream()

        override fun isReadable(): Boolean = original.isReadable

        override fun isOpen(): Boolean = original.isOpen

        override fun isFile(): Boolean = original.isFile

        override fun readableChannel(): ReadableByteChannel = Channels.newChannel(getInputStream())

        override fun getContentAsByteArray(): ByteArray = patchedContent

        override fun getContentAsString(charset: Charset): String = patchedContent.toString(charset)

        override fun contentLength(): Long = patchedContent.size.toLong()
    }
}

[geirsagberg]

@DzmitryShylovich would you be willing to make a PR with this fix?