Merge pull request #16188 from calixteman/bug1823296

Use the position of the previous xref stream if any when saving a pdf (bug 1823296)

src/core/worker.js

@@ -660,6 +660,7 @@ class WorkerMessageHandler {
               });
             }
 
+            const lastXRefStreamPos = xref.lastXRefStreamPos;
             newXrefInfo = {
               rootRef: xref.trailer.getRaw("Root") || null,
               encryptRef: xref.trailer.getRaw("Encrypt") || null,
@@ -667,7 +668,8 @@ class WorkerMessageHandler {
               infoRef: xref.trailer.getRaw("Info") || null,
               info: infoObj,
               fileIds: xref.trailer.get("ID") || null,
-              startXRef,
+              startXRef:
+                lastXRefStreamPos === null ? startXRef : lastXRefStreamPos,
               filename,
             };
           }
@@ -836,6 +838,11 @@ class WorkerMessageHandler {
       handler.on("GetXFADatasets", function (data) {
         return pdfManager.ensureDoc("xfaDatasets");
       });
+      handler.on("GetXRefPrevValue", function (data) {
+        return pdfManager
+          .ensureXRef("trailer")
+          .then(trailer => trailer.get("Prev"));
+      });
     }
 
     return workerHandlerName;

src/core/xref.js

@@ -756,6 +756,11 @@ class XRef {
     throw new XRefParseException();
   }
 
+  get lastXRefStreamPos() {
+    const pos = Object.keys(this.xrefstms);
+    return pos.length === 0 ? null : Math.max(...pos);
+  }
+
   getEntry(i) {
     const xrefEntry = this.entries[i];
     if (xrefEntry && !xrefEntry.free && xrefEntry.offset) {

src/display/api.js

@@ -777,6 +777,11 @@ class PDFDocumentProxy {
           return this._transport.getXFADatasets();
         },
       });
+      Object.defineProperty(this, "getXRefPrevValue", {
+        value: () => {
+          return this._transport.getXRefPrevValue();
+        },
+      });
     }
   }
 
@@ -2397,6 +2402,11 @@ class WorkerTransport {
           return this.messageHandler.sendWithPromise("GetXFADatasets", null);
         },
       });
+      Object.defineProperty(this, "getXRefPrevValue", {
+        value: () => {
+          return this.messageHandler.sendWithPromise("GetXRefPrevValue", null);
+        },
+      });
     }
   }