[api-minor] Remove the length parameter from getDocument

This is an old API-parameter that is now unused within the PDF.js project itself, and its description says that it's (partly) being used for "range requests operations".
Note that the `length` API-parameter is used to set the *initial* `contentLength` in various `BasePDFStreamReader` implementations, however it's always overridden by the "Content-Length" header (sent by the server) when that one exists *and* is a valid number. While we currently fallback to the keep the initial `contentLength` otherwise, note however how in that case range requests will always be *disabled* and thus the only spot in the code-base [where `fullReader.contentLength` is necessary](873378b718/src/core/worker.js (L230-L236)) cannot actually be reached.

Hence the only possible reason to use the `length` API-parameter would be for improved progress reporting[1] during streaming of PDF data in rare cases where the "Content-Length" header is missing/invalid, but the user *somehow* has information from another source about the correct `length` of the PDF document.
That situation feels very much like an edge-case, but it's obviously impossible to know if someone is depending on it. However, please note that there's a work-around available for users affected by this removal:
 - Implement a `PDFDataRangeTransport` instance together with custom data-fetching[2], since in that case its `length`-parameter will always be used as-is.

Finally, updates various `BasePDFStreamReader` implementations to only set the `_isRangeSupported` field once the headers are available (since previously we'd just overwrite the "initial" value anyway).

---

[1] I.e. to avoid the "indeterminate" loadingBar being displayed in the viewer.

[2] This is what e.g. the Firefox PDF Viewer uses.

src/core/worker.js

@@ -196,7 +196,6 @@ class WorkerMessageHandler {
       password,
       disableAutoFetch,
       rangeChunkSize,
-      length,
       docBaseUrl,
       enableXfa,
       evaluatorOptions,
@@ -209,7 +208,7 @@ class WorkerMessageHandler {
         enableXfa,
         evaluatorOptions,
         handler,
-        length,
+        length: 0,
         password,
         rangeChunkSize,
       };
@@ -287,14 +286,9 @@ class WorkerMessageHandler {
         }
 
         if (!newPdfManager) {
-          const pdfFile = arrayBuffersToBytes(cachedChunks);
+          pdfManagerArgs.source = arrayBuffersToBytes(cachedChunks);
           cachedChunks = null;
 
-          if (length && pdfFile.length !== length) {
-            warn("reported HTTP length is different from actual");
-          }
-          pdfManagerArgs.source = pdfFile;
-
           newPdfManager = new LocalPdfManager(pdfManagerArgs);
           resolve(newPdfManager);
         }

src/display/api.js

@@ -124,8 +124,6 @@ const RENDERING_CANCELLED_TIMEOUT = 100; // ms
  *   cross-site Access-Control requests should be made using credentials such
  *   as cookies or authorization headers. The default is `false`.
  * @property {string} [password] - For decrypting password-protected PDFs.
- * @property {number} [length] - The PDF file length. It's used for progress
- *   reports and range requests operations.
  * @property {PDFDataRangeTransport} [range] - Allows for using a custom range
  *   transport implementation.
  * @property {number} [rangeChunkSize] - Specify maximum number of bytes fetched
@@ -353,7 +351,6 @@ function getDocument(src = {}) {
   const pagesMapper = src.pagesMapper || new PagesMapper();
 
   // Parameters whose default values depend on other parameters.
-  const length = rangeTransport ? rangeTransport.length : (src.length ?? NaN);
   const useSystemFonts =
     typeof src.useSystemFonts === "boolean"
       ? src.useSystemFonts
@@ -425,7 +422,6 @@ function getDocument(src = {}) {
     password,
     disableAutoFetch,
     rangeChunkSize,
-    length,
     docBaseUrl,
     enableXfa,
     evaluatorOptions: {
@@ -497,7 +493,6 @@ function getDocument(src = {}) {
 
         networkStream = new NetworkStream({
           url,
-          length,
           httpHeaders,
           withCredentials,
           rangeChunkSize,

src/display/fetch_stream.js

@@ -86,15 +86,12 @@ class PDFFetchStreamReader extends BasePDFStreamReader {
     const {
       disableRange,
       disableStream,
-      length,
       rangeChunkSize,
       url,
       withCredentials,
     } = stream._source;
 
-    this._contentLength = length;
     this._isStreamingSupported = !disableStream;
-    this._isRangeSupported = !disableRange;
     // Always create a copy of the headers.
     const headers = new Headers(stream.headers);
 
@@ -114,10 +111,8 @@ class PDFFetchStreamReader extends BasePDFStreamReader {
             rangeChunkSize,
             disableRange,
           });
-
+        this._contentLength = contentLength;
         this._isRangeSupported = isRangeSupported;
-        // Setting right content length.
-        this._contentLength = contentLength || this._contentLength;
 
         this._filename = extractFilenameFromHeader(responseHeaders);
 

src/display/network.js

@@ -187,9 +187,6 @@ class PDFNetworkStreamReader extends BasePDFStreamReader {
 
   constructor(stream) {
     super(stream);
-    const { length } = stream._source;
-
-    this._contentLength = length;
     // Note that `XMLHttpRequest` doesn't support streaming, and range requests
     // will be enabled (if supported) in `this.#onHeadersReceived` below.
 
@@ -229,12 +226,8 @@ class PDFNetworkStreamReader extends BasePDFStreamReader {
         rangeChunkSize,
         disableRange,
       });
-
-    if (isRangeSupported) {
-      this._isRangeSupported = true;
-    }
-    // Setting right content length.
-    this._contentLength = contentLength || this._contentLength;
+    this._contentLength = contentLength;
+    this._isRangeSupported = isRangeSupported;
 
     this._filename = extractFilenameFromHeader(responseHeaders);
 

src/display/network_utils.js

@@ -50,7 +50,7 @@ function validateRangeRequestCapabilities({
     );
   }
   const rv = {
-    contentLength: undefined,
+    contentLength: 0,
     isRangeSupported: false,
   };
 

src/display/node_stream.js

@@ -62,12 +62,9 @@ class PDFNodeStreamReader extends BasePDFStreamReader {
 
   constructor(stream) {
     super(stream);
-    const { disableRange, disableStream, length, rangeChunkSize, url } =
-      stream._source;
+    const { disableRange, disableStream, rangeChunkSize, url } = stream._source;
 
-    this._contentLength = length;
     this._isStreamingSupported = !disableStream;
-    this._isRangeSupported = !disableRange;
 
     const fs = process.getBuiltinModule("fs");
     fs.promises
@@ -79,13 +76,10 @@ class PDFNodeStreamReader extends BasePDFStreamReader {
         this._reader = readableStream.getReader();
 
         const { size } = stat;
-        if (size <= 2 * rangeChunkSize) {
-          // The file size is smaller than the size of two chunks, so it doesn't
-          // make any sense to abort the request and retry with a range request.
-          this._isRangeSupported = false;
-        }
-        // Setting right content length.
         this._contentLength = size;
+        // When the file size is smaller than the size of two chunks, it doesn't
+        // make any sense to abort the request and retry with a range request.
+        this._isRangeSupported = !disableRange && size > 2 * rangeChunkSize;
 
         // We need to stop reading when range is supported and streaming is
         // disabled.

test/unit/network_utils_spec.js

@@ -153,7 +153,7 @@ describe("network_utils", function () {
         })
       ).toEqual({
         isRangeSupported: false,
-        contentLength: undefined,
+        contentLength: 0,
       });
     });