Refactor DAP4 CDM file reading

Previously, reading datasets via the CDM was reliant upon extracting a
filesystem path from the incoming request through implementation of the
abstract method dap4.servlet.DapController#getResourcePath. This has
been refactored to use dap4.servlet.DapController#getCDMWrap as the
abstract method used to interface the CDM reading code. D4TS continues
to use the getResourcePath code in its implementation of getCDMWrap. The
TDS utilizes TdsRequestedDataset in its implementation, which takes care
of virtual datasets, such as NcML aggregations, object storage based
data, etc., as well as authentication/authorization.

Fixes #568

dap4/d4servlet/src/main/java/dap4/servlet/DapController.java

@@ -130,14 +130,16 @@ public DapController() {}
   abstract protected String getWebContentRoot(DapRequest drq) throws DapException;
 
   /**
-   * Convert a URL path for a dataset into an absolute file path
-   *
-   * @param drq dap request
-   * @param location suffix of url path
-   * @return path in a string builder so caller can extend.
-   * @throws IOException
+   * Obtain a wrapped CDM source (NetcdfDataset) to Provide a DAP4 API
+   * <p>
+   * This method assumes a resource on the local filesystem. Override
+   * this method to provide other request/dataset location mappings. *
+   * </p>
+   * 
+   * @param drq DapRequest
+   * @throws IOException error obtaining the dataset described by the DapRequest
    */
-  abstract protected String getResourcePath(DapRequest drq, String location) throws DapException;
+  abstract protected CDMWrap getCDMWrap(DapRequest drq) throws IOException;
 
   //////////////////////////////////////////////////////////
 
@@ -257,10 +259,8 @@ protected void doDSR(DapRequest drq, DapContext cxt) throws IOException {
    */
 
   protected void doDMR(DapRequest drq, DapContext cxt) throws IOException {
-    // Convert the url to an absolute path
-    String realpath = drq.getResourcePath(drq.getDatasetPath());
 
-    CDMWrap c4 = new CDMWrap().open(realpath); // Create the wrapper
+    CDMWrap c4 = getCDMWrap(drq);
     DapDataset dmr = c4.getDMR();
     CEConstraint ce = constrainDapContext(cxt, dmr);
     ChecksumMode csummode = (ChecksumMode) cxt.get(DapConstants.CHECKSUMTAG);
@@ -310,12 +310,9 @@ protected void doDMR(DapRequest drq, DapContext cxt) throws IOException {
    */
 
   protected void doData(DapRequest drq, DapContext cxt) throws IOException {
-    // Convert the url to an absolute path
-    String realpath = drq.getResourcePath(drq.getDatasetPath());
-
-    CDMWrap c4 = new CDMWrap().open(realpath);
+    CDMWrap c4 = getCDMWrap(drq);
     if (c4 == null)
-      throw new DapException("No such file: " + realpath);
+      throw new DapException("Unknown resource");
 
     DapDataset dmr = c4.getDMR();
     CEConstraint ce = constrainDapContext(cxt, dmr);

dap4/d4servlet/src/main/java/dap4/servlet/DapRequest.java

@@ -205,17 +205,6 @@ public String getServletID() throws DapException {
     return controller.getServletID();
   }
 
-  /**
-   * Convert a URL path for a dataset into an absolute file path
-   *
-   * @param location suffix of url path
-   * @return path in a string builder so caller can extend.
-   * @throws IOException
-   */
-  public String getResourcePath(String location) throws DapException {
-    return controller.getResourcePath(this, location);
-  }
-
   /**
    * Convert a URL path for a web-content related file into an absolute file path
    *

dap4/d4ts/build.gradle

@@ -7,6 +7,7 @@ dependencies {
 
   implementation 'edu.ucar:dap4'
   implementation project(":dap4:d4servlet")
+  implementation 'edu.ucar:cdm-core'
 
   providedCompile "jakarta.servlet:jakarta.servlet-api:${depVersion.jakartaServletApi}"
 

dap4/d4ts/src/main/java/dap4/d4ts/D4TSServlet.java

@@ -69,7 +69,7 @@ protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws Se
   @Override
   protected void doFavicon(String icopath, DapContext cxt) throws IOException {
     DapRequest drq = (DapRequest) cxt.get(DapRequest.class);
-    String favfile = drq.getResourcePath(icopath);
+    String favfile = getResourcePath(drq, icopath);
     if (favfile != null) {
       try (FileInputStream fav = new FileInputStream(favfile);) {
         byte[] content = DapUtil.readbinaryfile(fav);
@@ -113,7 +113,7 @@ protected FrontPage getFrontPage(DapRequest drq, DapContext cxt) throws DapExcep
     if (this.defaultroots == null) {
       // Figure out the directory containing
       // the files to display.
-      String testroot = drq.getResourcePath("/");
+      String testroot = getResourcePath(drq, "/");
       if (testroot == null)
         throw new DapException("Cannot locate dataset  directory");
       this.defaultroots = new ArrayList<>();
@@ -141,6 +141,16 @@ public String getWebContentRoot(DapRequest drq) throws DapException {
     }
   }
 
+  public CDMWrap getCDMWrap(DapRequest drq) throws IOException {
+    // Convert the url to an absolute path
+    String realpath = getResourcePath(drq, drq.getDatasetPath());
+
+    CDMWrap c4 = new CDMWrap().open(realpath); // Create the wrapper
+    if (c4 == null)
+      DapLog.debug("No such file: " + realpath);
+    return c4;
+  }
+
   /**
    * Convert a URL path for a dataset into an absolute file path
    *

tds/src/main/java/thredds/server/dap4/Dap4Controller.java

@@ -9,8 +9,11 @@
 import dap4.core.util.DapException;
 import dap4.core.util.DapUtil;
 import dap4.dap4lib.DapCodes;
+import dap4.servlet.CDMWrap;
 import dap4.servlet.DapController;
 import dap4.servlet.DapRequest;
+import java.util.EnumSet;
+import java.util.Set;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.RequestMapping;
@@ -20,6 +23,9 @@
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
 import java.io.*;
+import ucar.nc2.NetcdfFile;
+import ucar.nc2.dataset.NetcdfDataset;
+import ucar.nc2.dataset.NetcdfDataset.Enhance;
 
 @Controller
 @RequestMapping("/dap4")
@@ -35,7 +41,8 @@ public class Dap4Controller extends DapController {
   static final String SERVICEID = "/dap4";
 
   // NetcdfDataset enhancement to use: need only coord systems
-  // static Set<NetcdfDataset.Enhance> ENHANCEMENT = EnumSet.of(NetcdfDataset.Enhance.CoordSystems);
+  // match dap4.servlet.CDMWrap.ENHANCEMENT
+  static Set<Enhance> ENHANCEMENT = EnumSet.of(NetcdfDataset.Enhance.CoordSystems);
 
   //////////////////////////////////////////////////
   // Instance variables
@@ -104,26 +111,16 @@ public String getWebContentRoot(DapRequest drq) throws DapException {
     return DapUtil.canonicalpath(rootpath);
   }
 
-  /**
-   * Convert a URL path for a dataset into an absolute file path
-   *
-   * @param location suffix of url path
-   * @return path in a string builder so caller can extend.
-   * @throws IOException
-   */
-  public String getResourcePath(DapRequest drq, String location) throws DapException {
-    assert (location.charAt(0) == '/');
-    // Remove the leading service name, if any
-    if (location.startsWith(SERVICEID))
-      location = location.substring(SERVICEID.length());
-    String path = TdsRequestedDataset.getLocationFromRequestPath(location);
-    if (path == null || path.length() == 0)
-      throw new DapException(String.format("getLocationFromRequestPath: location=|%s| path=null", location, path))
-          .setCode(DapCodes.SC_NOT_FOUND);
-    File f = new File(path);
-    if (!f.exists() || !f.canRead() || !f.isFile())
-      throw new DapException("Cannot locate resource: " + location).setCode(DapCodes.SC_NOT_FOUND);
-    return DapUtil.canonicalpath(path);
+  public CDMWrap getCDMWrap(DapRequest drq) throws IOException {
+    String datasetPath = drq.getDatasetPath();
+    String prefix = SERVICEID + "/";
+    if (datasetPath.startsWith(prefix)) {
+      datasetPath = datasetPath.substring(prefix.length());
+    }
+    NetcdfFile ncf = TdsRequestedDataset.getNetcdfFile(drq.getRequest(), drq.getResponse(), datasetPath);
+    NetcdfDataset ncd;
+    ncd = NetcdfDataset.wrap(ncf, ENHANCEMENT);
+    return new CDMWrap().open(ncd);
   }
 
 }