一点背景

我已经在 Chrome 扩展程序上工作了几天，该扩展程序每天多次截取给定网页的屏幕截图。我用过 this作为指南，事情按预期进行。

但是，有一个次要要求扩展无法满足。用户必须有权访问保存图像(屏幕截图)的文件夹，但 Chrome Extensions don't have access to the file system .另一方面，Chrome 应用程序可以。因此，经过多次环顾之后，我得出结论，我必须同时创建 Chrome 扩展程序和 Chrome 应用程序。这个想法是，扩展程序会创建一个截图的 blob，然后将该 blob 发送到应用程序，然后应用程序将其作为图像保存到用户指定的位置。这正是我正在做的——我在扩展端创建一个截图的 blob，然后将它发送到应用程序，要求用户选择保存图像的位置。

问题

直到保存部分，一切都按预期工作。 blob 是在扩展上创建的，发送到应用程序，由应用程序接收，用户被问到在哪里保存，图像被保存......这就是事情分崩离析的地方。 生成的图像无法使用。 当我尝试打开它时，我收到一条消息，显示“无法确定类型”。下面是我正在使用的代码:

 chrome.runtime.sendMessage(
    APP_ID, /* I got this from the app */
    {myMessage: blob}, /* Blob created previously; it's correct */
    function(response) {
      appendLog("response: "+JSON.stringify(response));
    }
 );

// listen for external messages
chrome.runtime.onMessageExternal.addListener(
  function(request, sender, sendResponse) {
    if (sender.id in blacklistedIds) {
      sendResponse({"result":"sorry, could not process your message"});
      return;  // don't allow this extension access
    } else if (request.incomingBlob) {
      appendLog("from "+sender.id+": " + request.incomingBlob);

      // attempt to save blob to choosen location
      if (_folderEntry == null) {
         // get a directory to save in if not yet chosen
         openDirectory();
      }
      saveBlobToFile(request.incomingBlob, "screenshot.png");

      /*
      // inspect object to try to see what's wrong
      var keys = Object.keys(request.incomingBlob);
      var keyString = "";
      for (var key in keys) {
         keyString += " " + key;
      }
      appendLog("Blob object keys:" + keyString);
      */

      sendResponse({"result":"Ok, got your message"});
    } else {
      sendResponse({"result":"Ops, I don't understand this message"});
    }
  }
);

function saveBlobToFile(blob, fileName) {
  appendLog('entering saveBlobToFile function...');
  chrome.fileSystem.getWritableEntry(_folderEntry, function(entry) {         
    entry.getFile(fileName, {create: true}, function(entry) {         
      entry.createWriter(function(writer) {
        //writer.onwrite = function() {
        //   writer.onwrite = null;
        //   writer.truncate(writer.position);
        //};
        appendLog('calling writer.write...');
        writer.write(blob);                       
        // Also tried writer.write(new Blob([blob], {type: 'image/png'}));
      });
    });
  });
}

var worker = new SharedWorker(chrome.runtime.getURL('shared-worker.js'));
worker.port.start();
worker.postMessage('hello from extension'); // Can send blob here too
worker.port.addEventListener("message", function(event) {
   $('h1Title').innerHTML = event.data;
});

var worker = new SharedWorker(chrome.runtime.getURL('shared-worker.js'));
worker.port.start();

worker.port.addEventListener("message",
   function(event) {      
      parent.postMessage(event.data, 'chrome-extension://[extension id]');
   }
);

<script src='proxy.js'></script>

var ports = [];
var count = 0;
onconnect = function(event) {
    count++;
    var port = event.ports[0];
    ports.push(port);
    port.start(); 

    /* 
    On both the extension and the app, I get count = 1 and ports.length = 1
    I'm running them side by side. This is so maddening!!!
    What am I missing?
    */
    var msg = 'Hi, you are connection #' + count + ". ";
    msg += " There are " + ports.length + " ports open so far."
    port.postMessage(msg);

    port.addEventListener("message",       
      function(event) {
        for (var i = 0; i < ports.length; ++i) {
            //if (ports[i] != port) {
                ports[i].postMessage(event.data);
            //}
        }
    });
};

context.addEventListener("message", 
    function(event) {
        appendLog("message from proxy: " + event.data);
    } 
);

最佳答案

感谢您的所有帮助家伙。我发现解决方案是将 blob 转换为扩展程序上的二进制字符串，然后使用 chrome 的消息传递 API 将字符串发送到应用程序。在应用程序上，我按照 Francois 的建议将二进制字符串转换回 blob。我之前尝试过这个解决方案，但我没有工作，因为我在应用程序上使用了以下代码:

blob = new Blob([blobAsBinString], {type: mimeType});

var bytes = new Uint8Array(blobAsBinString.length);
for (var i=0; i<bytes.length; i++) {
   bytes[i] = blobAsBinString.charCodeAt(i);            
}             
blob = new Blob([bytes], {type: mimeString});

function sendBlobToApp() {  

  // read the blob in chunks/chunks and send it to the app
  // Note: I crashed the app using 1 KB chunks. 1 MB chunks work just fine. 
  // I decided to use 256 KB as that seems neither too big nor too small
  var CHUNK_SIZE = 256 * 1024;
  var start = 0;
  var stop = CHUNK_SIZE;      

  var remainder = blob.size % CHUNK_SIZE;
  var chunks = Math.floor(blob.size / CHUNK_SIZE);      

  var chunkIndex = 0;

  if (remainder != 0) chunks = chunks + 1;           

  var fr = new FileReader();
  fr.onload = function() {
      var message = {
          blobAsText: fr.result,
          mimeString: mimeString,                 
          chunks: chunks 
      };          
      // APP_ID was obtained elsewhere
      chrome.runtime.sendMessage(APP_ID, message, function(result) {
          if (chrome.runtime.lastError) {
              // Handle error, e.g. app not installed
              // appendLog is defined elsewhere
              appendLog("could not send message to app");
          } 
      });

      // read the next chunk of bytes
      processChunk();
  };
  fr.onerror = function() { appendLog("An error ocurred while reading file"); };
  processChunk();

  function processChunk() {
     chunkIndex++;         

     // exit if there are no more chunks
     if (chunkIndex > chunks) {
        return;
     }

     if (chunkIndex == chunks && remainder != 0) {
        stop = start + remainder;
     }                           

     var blobChunk = blob.slice(start, stop);

     // prepare for next chunk
     start = stop;
     stop = stop + CHUNK_SIZE;

     // convert chunk as binary string
     fr.readAsBinaryString(blobChunk);
  } 
}

chrome.runtime.onMessageExternal.addListener(
  function(request, sender, sendResponse) {
    if (sender.id in blacklistedIds) {
      return;  // don't allow this extension access
    } else if (request.blobAsText) {                  
       //new chunk received  
      _chunkIndex++;                   

      var bytes = new Uint8Array(request.blobAsText.length);                     
      for (var i=0; i<bytes.length; i++) {
         bytes[i] = request.blobAsText.charCodeAt(i);            
      }         
      // store blob
      _blobs[_chunkIndex-1] = new Blob([bytes], {type: request.mimeString});           

      if (_chunkIndex == request.chunks) {                      
         // merge all blob chunks
         for (j=0; j<_blobs.length; j++) {
            var mergedBlob;
            if (j>0) {                  
               // append blob
               mergedBlob = new Blob([mergedBlob, _blobs[j]], {type: request.mimeString});
            }
            else {                  
               mergedBlob = new Blob([_blobs[j]], {type: request.mimeString});
            }
         }                         

         saveBlobToFile(mergedBlob, "myImage.png", request.mimeString);
      }
    }
 }
);

关于javascript - 如何将 Blob 从 Chrome 扩展程序传递到 Chrome 应用程序，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25668998/