Use response-Headers in the different IPDFStream implementations

Given that the `Headers` functionality is now available in all browsers/environments that we support, [see MDN](https://developer.mozilla.org/en-US/docs/Web/API/Headers#browser_compatibility), we can utilize "proper" `Headers` in the helper functions that are used to parse the response.

src/display/fetch_stream.js

@@ -127,11 +127,11 @@ class PDFFetchStreamReader {
         this._reader = response.body.getReader();
         this._headersCapability.resolve();
 
-        const getResponseHeader = name => response.headers.get(name);
+        const responseHeaders = response.headers;
 
         const { allowRangeRequests, suggestedLength } =
           validateRangeRequestCapabilities({
-            getResponseHeader,
+            responseHeaders,
             isHttp: stream.isHttp,
             rangeChunkSize: this._rangeChunkSize,
             disableRange: this._disableRange,
@@ -141,7 +141,7 @@ class PDFFetchStreamReader {
         // Setting right content length.
         this._contentLength = suggestedLength || this._contentLength;
 
-        this._filename = extractFilenameFromHeader(getResponseHeader);
+        this._filename = extractFilenameFromHeader(responseHeaders);
 
         // We need to stop reading when range is supported and streaming is
         // disabled.

src/display/network.js

@@ -273,11 +273,20 @@ class PDFNetworkStreamFullRequestReader {
     const fullRequestXhrId = this._fullRequestId;
     const fullRequestXhr = this._manager.getRequestXhr(fullRequestXhrId);
 
-    const getResponseHeader = name => fullRequestXhr.getResponseHeader(name);
+    const responseHeaders = new Headers(
+      fullRequestXhr
+        .getAllResponseHeaders()
+        .trim()
+        .split(/[\r\n]+/)
+        .map(x => {
+          const [key, ...val] = x.split(": ");
+          return [key, val.join(": ")];
+        })
+    );
 
     const { allowRangeRequests, suggestedLength } =
       validateRangeRequestCapabilities({
-        getResponseHeader,
+        responseHeaders,
         isHttp: this._manager.isHttp,
         rangeChunkSize: this._rangeChunkSize,
         disableRange: this._disableRange,
@@ -289,7 +298,7 @@ class PDFNetworkStreamFullRequestReader {
     // Setting right content length.
     this._contentLength = suggestedLength || this._contentLength;
 
-    this._filename = extractFilenameFromHeader(getResponseHeader);
+    this._filename = extractFilenameFromHeader(responseHeaders);
 
     if (this._isRangeSupported) {
       // NOTE: by cancelling the full request, and then issuing range

src/display/network_utils.js

@@ -37,7 +37,7 @@ function createHeaders(isHttp, httpHeaders) {
 }
 
 function validateRangeRequestCapabilities({
-  getResponseHeader,
+  responseHeaders,
   isHttp,
   rangeChunkSize,
   disableRange,
@@ -53,7 +53,7 @@ function validateRangeRequestCapabilities({
     suggestedLength: undefined,
   };
 
-  const length = parseInt(getResponseHeader("Content-Length"), 10);
+  const length = parseInt(responseHeaders.get("Content-Length"), 10);
   if (!Number.isInteger(length)) {
     return returnValues;
   }
@@ -69,11 +69,11 @@ function validateRangeRequestCapabilities({
   if (disableRange || !isHttp) {
     return returnValues;
   }
-  if (getResponseHeader("Accept-Ranges") !== "bytes") {
+  if (responseHeaders.get("Accept-Ranges") !== "bytes") {
     return returnValues;
   }
 
-  const contentEncoding = getResponseHeader("Content-Encoding") || "identity";
+  const contentEncoding = responseHeaders.get("Content-Encoding") || "identity";
   if (contentEncoding !== "identity") {
     return returnValues;
   }
@@ -82,8 +82,8 @@ function validateRangeRequestCapabilities({
   return returnValues;
 }
 
-function extractFilenameFromHeader(getResponseHeader) {
-  const contentDisposition = getResponseHeader("Content-Disposition");
+function extractFilenameFromHeader(responseHeaders) {
+  const contentDisposition = responseHeaders.get("Content-Disposition");
   if (contentDisposition) {
     let filename = getFilenameFromContentDispositionHeader(contentDisposition);
     if (filename.includes("%")) {

src/display/node_stream.js

@@ -305,14 +305,11 @@ class PDFNodeStreamFullReader extends BaseFullReader {
       this._headersCapability.resolve();
       this._setReadableStream(response);
 
-      // Make sure that headers name are in lower case, as mentioned
-      // here: https://nodejs.org/api/http.html#http_message_headers.
-      const getResponseHeader = name =>
-        this._readableStream.headers[name.toLowerCase()];
+      const responseHeaders = new Headers(this._readableStream.headers);
 
       const { allowRangeRequests, suggestedLength } =
         validateRangeRequestCapabilities({
-          getResponseHeader,
+          responseHeaders,
           isHttp: stream.isHttp,
           rangeChunkSize: this._rangeChunkSize,
           disableRange: this._disableRange,
@@ -322,7 +319,7 @@ class PDFNodeStreamFullReader extends BaseFullReader {
       // Setting right content length.
       this._contentLength = suggestedLength || this._contentLength;
 
-      this._filename = extractFilenameFromHeader(getResponseHeader);
+      this._filename = extractFilenameFromHeader(responseHeaders);
     };
 
     this._request = createRequest(this._url, headers, handleResponse);