使用 REST WebService 和 VB.NET 的附件

Question

我目前正在使用 VB.NET 开发一个应用程序，其中我正在使用 REST WebServices。我已经能够使用 REST 完成基本操作，但是，我无法添加附件（更具体地说，使用附加的 REST 上传文件）。我在网上进行了广泛的研究，但到目前为止，我还没有在 VB.NET 中找到任何工作示例。要实际上传数据，我使用 System.Net.WebClient。下面的 VB.NET 代码完成了重要的工作：

Dim Client As New System.Net.WebClient
Dim postBytes As Byte() = System.Text.Encoding.ASCII.GetBytes(postString)
Client.UploadData(URL, "POST", postBytes)

我的网址的简化版本如下： "../REST/1.0/ticket/" + ticketNumber + "/comment?user=" + userName + "&pass=" + password

最后，我发布的内容的一个例子是：

postString = "content=Text: RT Test" + vbLf + "Action: Comment" + vbLf + "Attachment: examplefile.jpg" + vbLf + "attachment_1="

如您所见，postString 被转换为字节，然后上传到服务器。但是，我不知道应该在哪里或如何发布原始附件本身。我们专门使用状态来使用变量“attachment_1”的服务的文档，我将其添加到 postString 变量中，但我不确定下一步应该是什么。是否应该将文件转换为字节并附加到 postBytes 变量？我尝试了类似的操作，但收到一条错误消息，提示找不到 examplefile.jpg 的附件。

感谢您的帮助！

Answer 1

我们不能使用 Client.UploadData(...) 并且必须将整个帖子转换为字节，从附件之前的 POST 字段开始，然后是附件本身，最后是 POST 字段的其余部分。

Public Sub AddAttachmentToRT(ByVal url As String, ByVal fileName As String, ByVal filePath As String)

    Dim dataBoundary As String = "--xYzZY"
    Dim request As HttpWebRequest
    Dim fileType As String = "image/jpeg" 'Will want to extract this to make it more generic from the uploaded file.

    'Create a POST web request to the REST interface using the passed URL
    request = CType(WebRequest.Create(url), HttpWebRequest)
    request.ContentType = "multipart/form-data; boundary=xYzZY"
    request.Method = "POST"
    request.KeepAlive = True

    'Write the request to the requestStream
    Using requestStream As IO.Stream = request.GetRequestStream()

        'Create a variable "attachment_1" in the POST, specify the file name and file type
        Dim preAttachment As String = dataBoundary + vbCrLf _
        + "Content-Disposition: form-data; name=""attachment_1""; filename=""" + fileName + """" + vbCrLf _
        + "Content-Type: " + fileType + vbCrLf _
        + vbCrLf

        'Convert this preAttachment string to bytes
        Dim preAttachmentBytes As Byte() = System.Text.Encoding.UTF8.GetBytes(preAttachment)

        'Write this preAttachment string to the stream
        requestStream.Write(preAttachmentBytes, 0, preAttachmentBytes.Length)

        'Write the file as bytes to the stream by passing its exact location
        Using fileStream As New IO.FileStream(Server.MapPath(filePath + fileName), IO.FileMode.Open, IO.FileAccess.Read)

            Dim buffer(4096) As Byte
            Dim bytesRead As Int32 = fileStream.Read(buffer, 0, buffer.Length)

            Do While (bytesRead > 0)

                requestStream.Write(buffer, 0, bytesRead)
                bytesRead = fileStream.Read(buffer, 0, buffer.Length)

            Loop

        End Using

        'Create a variable named content in the POST, specify the attachment name and comment text
        Dim postAttachment As String = vbCrLf _
        + dataBoundary + vbCrLf _
        + "Content-Disposition: form-data; name=""content""" + vbCrLf _
        + vbCrLf _
        + "Action: comment" + vbLf _
        + "Attachment: " + fileName + vbCrLf _
        + "Text: Some description" + vbCrLf _
        + vbCrLf _
        + "--xYzZY--"

        'Convert postAttachment string to bytes
        Dim postAttachmentBytes As Byte() = System.Text.Encoding.UTF8.GetBytes(postAttachment)

        'Write the postAttachment string to the stream
        requestStream.Write(postAttachmentBytes, 0, postAttachmentBytes.Length)

    End Using

    Dim response As Net.WebResponse = Nothing

    'Get the response from our REST request to RT
    'Required to capture response, without this Try-Catch attaching will fail
    Try
        response = request.GetResponse()

        Using responseStream As IO.Stream = response.GetResponseStream()

            Using responseReader As New IO.StreamReader(responseStream)

                Dim responseText = responseReader.ReadToEnd()

            End Using

        End Using

    Catch exception As Net.WebException

        response = exception.Response

        If (response IsNot Nothing) Then

            Using reader As New IO.StreamReader(response.GetResponseStream())

                Dim responseText = reader.ReadToEnd()

            End Using

            response.Close()

        End If

    Finally

        request = Nothing

    End Try

End Sub