I'm trying to construct an EmailMessage using multiple in-memory streams. However, when I send the e-mail, I get the following error:
"One of the streams has already been used and can't be reset to the origin"
From what I can gather, I think the problem may be that the message is losing context of the memory stream when I try to do the following:
foreach (var att in attachments)
{
doc = fetchDocumentByteArray();
using (MemoryStream ms = new MemoryStream(doc))
{
mailToSend.AddAttachment(new Attachment(ms, att.Filename));
}
}
mailToSend.Send();
I've also tried setting the ms.Position = 0 before the AddAttachment(), but that doesn't work.
After looking around a bit for a scenario like mine, I came across a suggestion to use a List<MemoryStream> - but I'm not sure how I'd implement this or if it's even the correct approach?
When you use "using" keywork, internally, Dispose method is invoked. It will make the MemoryStreams be deallocated.
Remove the using in your inner loop and create a try/finally clause to dispose the memory streams after the e-mail is sent.
The accepted answer did not work for me because you need to keep track of multiple MemoryStreams and dispose of each individually. I took the same approach but implemented it slightly differently adding each MemoryStream to a list and then calling Dispose() on each instance after the email is sent.
var msList = new List<MemoryStream>();
foreach (var attachment in message.Attachments)
{
var ms = new MemoryStream(attachment.Bytes);
msList.Add(ms);
var mailAttachment = new Attachment(ms, attachment.FileName);
mailMessage.Attachments.Add(mailAttachment);
}
smtp.Send(mailMessage);
foreach (var ms in msList)
{
ms.Dispose();
}
Related
Is there a way to take an IEnumerable<T> and emit it as a readable stream kinda like this?
private void DoTheThing(IEnumerable<Foo> foos)
{
using (var myStream = foos.EmitAsStream(f =>
{
var line = JsonConvert.SerializeObject(f);
return line;
}))
using(var streamReader = new StreamReader(myStream))
{
while (!streamReader.EndOfStream)
{
var line = streamReader.ReadLine();
Console.WriteLine(line);
}
}
}
Obviously, there are some problems with this, for example it seems to imply a StreamWriter with none specified, but the idea would be that the stream reader would just yield enumerate through the IEnumerable under the hood, apply the transform delegate, and pull the results without making any new, potentially large objects in memory.
I have some very large enumerable objects in memory, and I need to push them to external places (like Amazon S3) which accepts a stream. I really can't afford to build a MemoryStream with the collection and send that; I can spool to disk and read from disk, but I'd prefer not to if I have the option, since it seems like an extra step.
Is this possible? If it's possible, is it practical?
You can, achieve that by using TakeWhile, if I right understood your problem.
Something like :
while(..end ..)
{
var enumeration = foos.TakeWhile(..line bounds..);
var stream = StreamFromEnum(enumeration ); //custom implementation
// stream --> S3
}
I presume you have some custom definition of "line", which might be some sort of stride/slice of data from the stream.
A lazily-evaluated stream wrapper for IEnumerable is a one possible implementation of IEnumerable<T> -> Stream conversion.
The EnumerableToStream package will do exactly what you ask:
using EnumerableToStream;
using (var myStream = foos.Select(f =>
{
var line = JsonConvert.SerializeObject(f);
return line;
}).ToStream())
That ToStream() method is the one that does the magic. If you are interested in the implementation details, have a look at the source code.
I try to develop an application in C# and have some concerns with MailMessage object:
it implements IDisposable interface, so I use it within using statement. So it implicitly calls Dispose method after. Now, using that object I need to add attachments, which I have converted to byte[] object and I add them as stream. Here's part of code to have better view:
using(MailMessage message = new MailMessage("john.smith#gmail.com"){
MemoryStream stream;
//here I pass byte array to the stream and create an attachemnt
message.Attachments.Add(new Attachment(stream, "name.xyz"));
using(SmtpClient client = new SmtpClient("server.com", port))
{
// send message
}
}
Now, I have one resource unmanaged: Stream object. I can't close it (so can't call Dispose method) right after setting attachments, because I'd get an error when sending message, because it uses the stream while sending.
So, I need to get rid of it later, which I do after sending. That's the code in second using:
try
{
client.Send(messgae);
}
finally
{
if(stream != null)
stream.Dispose();
}
Now the question: Dispose method of MailMesssage frees all resources used by that object. My Stream object is one of the resources, isn't it? So, when using(MailMessage... terminates it should manage also my Stream object, shouldn't it? So I wouldn't need to dispose of my Stream object manually.
EDIT:
Suggested approach:
using(MailMessage message = new MailMessage("john.smith#gmail.com"){
using(MemoryStream stream = ...)
{
//here I pass byte array to the stream and create an attachemnt
message.Attachments.Add(new Attachment(stream, "name.xyz"));
using(SmtpClient client = new SmtpClient("server.com", port))
{
// send message
}
}
}
But the questions stays: MailMessage uses this Stream - so, do we still need to manage Stream on our own?
Why not dispose the stream after the message is sent?
using(MailMessage message = new MailMessage("john.smith#gmail.com"))
{
using(var stream = new MemoryStream())
{
//here I pass byte array to the stream and create an attachemnt
message.Attachments.Add(new Attachment(stream, "name.xyz"));
using(SmtpClient client = new SmtpClient("server.com", port))
{
// send message
}
}
}
From the reference documentation you don't need to when you are using using.
Mail Message disposes Attachment Collection, which then disposes all its attachements.
Regarding, should we take or rely on this approach then I totally agree with Zohar on
Disposing of an IDisposable should be expressed in your code, either by calling Dispose explicitly or with the using statement.
Try this:
using(MailMessage message = new MailMessage("john.smith#gmail.com")
using(MemoryStream stream = new MemoryStream())
using(SmtpClient client = new SmtpClient("server.com", port))
{
message.Attachments.Add(new Attachment(stream, "name.xyz"))
client.Send(messgae);
}
If you put MemoryStream in using block, it will do the same thing as your try/finally block.
I am trying to re-upload a stream that I just retrieved. It shouldn't really matter that I am using AWS I believe... Maybe my understanding of working with streams is just too limited? :-)
I am using the following method straight from the AWS documentation to download and upload streams:
File upload:
public bool UploadFile(string keyName, Stream stream)
{
using (client = new AmazonS3Client(Amazon.RegionEndpoint.USEast1))
{
try
{
TransferUtility fileTransferUtility = new TransferUtility(new AmazonS3Client(Amazon.RegionEndpoint.USEast1));
fileTransferUtility.Upload(stream, bucketName, keyName);
return true;
}
catch (AmazonS3Exception amazonS3Exception)
{
[...]
}
}
}
Getting the file:
public Stream GetFile(string keyName)
{
using (client = new AmazonS3Client(Amazon.RegionEndpoint.USEast2))
{
try
{
GetObjectRequest request = new GetObjectRequest
{
BucketName = bucketName,
Key = keyName
};
GetObjectResponse response = client.GetObject(request);
responseStream = response.ResponseStream;
return responseStream;
}
catch (AmazonS3Exception amazonS3Exception)
{
[...]
}
}
}
Now, I am trying to combine the two methods: I am getting a stream and immediately want to upload it again. However, I am getting the following error message: System.NotSupportedException : HashStream does not support seeking
I am guessing it has something to do that I am getting a stream which is somehow now immediately ready to be uploaded again?
This is how I am trying to get the stream of an existing file (.jpg) and immediately try to upload it with a different filename:
newAWS.UploadFile(newFileName, oldAWS.GetFile(oldFile));
Where newAWS and oldAWS are instances of the AWS class, and newFileName is a string :-)
This is the line I am getting the error message pasted above.
Please let me know if I am missing something obvious here why I would not be able to re-upload a fetched stream. Or could it be that it is related to something else I am not aware of and I am on the wrong track trying to troubleshoot the returned stream?
What I am basically trying to do is to copy one file from an AWS bucket to another using streams. But for some reason I get the error message trying to upload the stream that I just downloaded.
Thank you very much for taking your time digging through my code :-)
As the error indicates, the Hashstream object that Amazon returns does not support seeking.
Something in your code, or a method you're calling, is trying to do seeking on that stream. Most likely it's trying to seek to the beginning of the stream.
So you need to convert Hashstream to a different stream that supports seeking:
using (GetObjectResponse response = client.GetObject(request))
using (Stream responseStream = response.ResponseStream)
using (MemoryStream memStream = new MemoryStream())
{
responseStream.CopyTo(memStream);
memStream.Seek(0, SeekOrigin.Begin);
// now use memStream wherever you were previously using responseStream
}
It looks like that my approach won't work and I am not really sure why it doesn't.
The good news is, that you can simply use the following code to copy from one AWS bucket to another:
static IAmazonS3 client;
client = new AmazonS3Client(Amazon.RegionEndpoint.USEast1);
CopyObjectRequest request = new CopyObjectRequest()
{
SourceBucket = bucketName,
SourceKey = objectKey,
DestinationBucket = bucketName,
DestinationKey = destObjectKey
};
CopyObjectResponse response = client.CopyObject(request);
So I didn't have to try to recreate this functionality using the upload and download methods I wrote but simply use the copy method provided.
HOWEVER, I still would like to know why my approach was failing? I really think I am missing something regarding the streams. Any feedback would be greatly appreciated :-)
I will leave this question as unanswered since I would really like to know what I am missing regarding streams. I would be happy to mark an answer as accepted that explains my missing knowledge :-)
I am trying to use LINQtoCSV to parse out a CSV file into a list of objects and am receiving the error "Stream provided to read is either null, or does not support seek."
The error is happening at foreach(StockQuote sq in stockQuotesStream)
Below is the method that is throwing the error. The .CSV file is being downloaded from the internet and is never stored to disk (only stored to StreamReader).
public List<StockQuote> CreateStockQuotes(string symbol)
{
List<StockQuote> stockQuotes = new List<StockQuote>();
CsvFileDescription inputFileDescription = new CsvFileDescription
{
SeparatorChar = ',',
FirstLineHasColumnNames = false
};
CsvContext cc = new CsvContext();
IEnumerable<StockQuote> stockQuotesStream = cc.Read<StockQuote>(GetCsvData(symbol));
foreach (StockQuote sq in stockQuotesStream)
{
stockQuotes.Add(sq);
}
return stockQuotes;
}
The .CSV file is being downloaded from the internet and is never stored to disk (only stored to StreamReader).
Well presumably that's the problem. It's not quite clear what you mean by this, in that if you have wrapped a StreamReader around it, that's a pain in terms of the underlying stream - but you can't typically seek on a stream being downloaded from the net, and it sounds like the code you're using requires a seekable stream.
One simple option is to download the whole stream into a MemoryStream (use Stream.CopyTo if you're using .NET 4), then rewind the MemoryStream (set Position to 0) and pass that to the Read method.
Using a MemoryStream first and then a StreamReader was the answer, but I went about it a little differently than mentioned.
WebClient client = new WebClient();
using (MemoryStream download = new MemoryStream(client.DownloadData(url)))
{
using (StreamReader dataReader = new StreamReader(download, System.Text.Encoding.Default, true))
{
return dataReader;
}
}
are there any good examples of how to attach multiple files from a database to an e-mail in .NET? I've got a method that returns a Byte[] containing the Image column contents that I am calling in a loop to get each attachment, but I was wondering if there was a "correct"/best-practice way of doing this, especially with the possibility of introducing memory leaks by using MemoryStreams to contain the data? I'm fine creating en e-mail object and attaching the list of attachments to it, once I've got them and can do this fine with a single attachement but it seems to get slightly more complex with multiple files. Considering I wouldn't have thought this was an unusual requirement, there seems to be a dearth of articles/posts about it.
Thx - MH
Here's how to proceed. Let's suppose that you have an array of attachments that you have loaded from your database:
IEnumerable<byte[]> attachments = ... fetch from your database
We could also safely assume that along with those attachments you have loaded the filenames and probably their corresponding MIME type (information that you surely must have persisted along with those byte arrays representing your attachments). So you will probably have fetched IEnumerable<SomeAttachmentType> but that's not important for the purpose of this post.
So now you could send the mail:
using (var client = new SmtpClient("smtp.foo.com"))
using (var message = new MailMessage("from#foo.com", "to#bar.com"))
{
message.Subject = "test subject";
message.Body = "test body";
message.IsBodyHtml = false;
foreach (var attachment in attachments)
{
var attachmentStream = new MemoryStream(attachment);
// TODO: Choose a better name for your attachments and adapt the MIME type
var messageAttachment = new Attachment(attachmentStream, Guid.NewGuid().ToString(), "application/octet-stream");
message.Attachments.Add(messageAttachment);
}
client.Send(message);
}
Here's the deal:
A MailMessage (IDisposable) contains multiple Attachments (IDisposable). Each attachment references a MemoryStream (IDisposable). The MailMessage is wrapped in a using block which ensures that its Dispose method will be called which in turn calls the Dispose method of all attachments which in turn call the Dispose method of the memory streams.
Hi you can have buffered reads directly from the database, MemoryStream does NOT introduce any memory leak if you dispose it after usage. Example using SqlDataReader:
using(var stream = new MemoryStream())
{
byte[] buffer = new byte[4096];
long l, dataOffset = 0;
while ((l = reader.GetBytes(columnIndex, dataOffset, buffer, 0, buffer.Length)) > 0)
{
stream.Write(buffer, 0, buffer.Length);
dataOffset += l;
}
// here you have the whole stream and can attach it to the email...
}
similar question on how to read bytes from database has been asked already countless times, see here for example: What is the most efficient way to read many bytes from SQL Server using SqlDataReader (C#)