Parametrising encoded web service requests - web-services

Question

I am trying to parametrise web service requests in a web performance test. Using Fiddler2 I have recorded a sequence of over 60 web service requests for a transaction performed by my desktop application and saved them as a .webtest file. This web test runs without any errors and the responses that I have checked look correct.
When the web service requests are viewed in Visual Studio 2012 they appear in plain text and so I should be able to edit them to parametrise the values in the SOAP requests. For example, most of the requests contain the text <Database>db1a</Database> (actually it has <Database>db1a</Database>) and I want to change them to get the database name from a context parameter. There are several other items to replace with parameters. For this one transaction there are over 60 web service requests and I have other transactions to record. The .webtest file contains XML and the requests looks like:
<Request Method="POST" Version="1.1" Url="http://example.com/somewhere.asmx" ThinkTime="83" Timeout="60" ParseDependentRequests="True" FollowRedirects="True" RecordResult="True" Cache="False" ResponseTimeGoal="0" Encoding="utf-8">
<Headers>
<Header Name="Content-Type" Value="text/xml; charset=utf-8" />
<Header Name="SOAPAction" Value=""http://example.com/webservices/VariousActionNamesHere"" />
</Headers>
<StringHttpBody ContentType="text/xml; charset=utf-8">PAA/AHgAbQBsACAAdg
... lots more characters not shown
+AA==</StringHttpBody>
</Request>
The StringHttpBody field contains an encoded version of the SOAP request. Visual Studio shows it as plain text. What is the encoding of this field and how can I decode and encode it?
I have installed Release 3.0 of the “Web and Load Test Plugins for Visual Studio Team Test” from http://teamtestplugins.codeplex.com/ . They provide a slightly better interface for editing the SOAP requests one at a time. But they do not allow mass changes.
Converting the web test to a coded web test (ie into C#) shows the SOAP requests as simple text and they could be edited there but I would prefer to keep the flexibility of a .webtest file.
Update: I have posted a partial answer to the question. Whilst it works, it feels the wrong way to do the work because it feels too complicated. So I am looking for a better overall approach.

Answer 1

StringHttpBody is base64 encoded. The raw body of the request is converted to a UTF-16 byte array and then base64 encoded, like so:
Convert.ToBase64String(Encoding.Unicode.GetBytes(oSession.GetRequestBodyAsString()));
For a quick view, you can copy/paste this string into Fiddler's Tools > TextWizard screen then use the From Base64 option to decode.

Answer 2

Here is part of an answer to working with the StringHttpBody fields. This is about decoding and encoding the fields to allow easier understanding and modification.
Read the input XML and find the contents of the StringHttpBody fields. Replace each field contents with the result of calling the following routine on the original contents. Write the all the lines to a new intermediate file. The byte array contains UTF-16 characters as high and low bytes. (All the characters I have seen so far have high byte zero.)
private string DecodeBody(string source) {
byte[] outBytes = Convert.FromBase64String(source);
StringBuilder sb = new StringBuilder();
Assert( (outBytes.Length % 2) != 0 );
for (int ix = 0; ix < outBytes.Length; ix += 2) {
Assert(outBytes[ix] != 0);
sb.Append((char)outBytes[ix + 1]);
}
return sb.ToString();
}
Now have a file containing a simple text version of the .webtest file. This file can easily be edited to parameterise fields of the requests. Have an routine used similar to the one above and writing to another intermediate file. The routine has statements such as:
source = source.Replace("<Database>db1a</Database>", "<Database>{{DatabaseName}}</Database>");
The final intermediate file is then reencoded to create a new .webtest file. Just as before the contents of the StringHttpBody fields are found and replaced with the result of calling a routine. The encoding routine is:
private string EncodeBody(string source) {
StringBuilder sb = new StringBuilder();
byte[] outBytes = new byte[2 * source.Length];
for (int ix = 0; ix < source.Length; ix++) {
char ch = source[ix];
outBytes[2 * ix] = (byte)(((int)ch) & 0xFF);
outBytes[2 * ix + 1] = (byte)((((int)ch) / 256) & 0xFF);
}
sb.Append(Convert.ToBase64String(outBytes));
return sb.ToString();
}
The flow of files is thus:
decode original.webtest > intermediate1
parameterise intermediate1 > intermediate2
encode intermediate2 > final.webtest
On the small number of .webtest files I have tried the encode operation is the inverse of the decode operation, the original file from before decoding is identical to the file after encoding. Having the two intermediate files allows easy checking and searching of the contents of the unencoded file and the effect of the parameterise step.

Answer 3

For
[StringHttpBody ContentType="application/json"]
To Decode the body:
var encodedString = childNode.InnerText;
var encodedStringBytes = Convert.FromBase64String(encodedString);
var decodedString = Encoding.Unicode.GetString(encodedStringBytes);
JObject jsonString =JsonConvert.DeserializeObject(decodedString);
To Encode the body:
childNode.InnerText =
Convert.ToBase64String(Encoding.Unicode.GetBytes(JsonConvert.SerializeObject(jsonString)));
I think this might help.