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HttpClient: Add querystring parmas in HttpRequestMessage [duplicate]

If I wish to submit a http get request using System.Net.HttpClient there seems to be no api to add parameters, is this correct?
Is there any simple api available to build the query string that doesn't involve building a name value collection and url encoding those and then finally concatenating them?
I was hoping to use something like RestSharp's api (i.e AddParameter(..))

If I wish to submit a http get request using System.Net.HttpClient
there seems to be no api to add parameters, is this correct?
Yes.
Is there any simple api available to build the query string that
doesn't involve building a name value collection and url encoding
those and then finally concatenating them?
Sure:
var query = HttpUtility.ParseQueryString(string.Empty);
query["foo"] = "bar<>&-baz";
query["bar"] = "bazinga";
string queryString = query.ToString();
will give you the expected result:
foo=bar%3c%3e%26-baz&bar=bazinga
You might also find the UriBuilder class useful:
var builder = new UriBuilder("http://example.com");
builder.Port = -1;
var query = HttpUtility.ParseQueryString(builder.Query);
query["foo"] = "bar<>&-baz";
query["bar"] = "bazinga";
builder.Query = query.ToString();
string url = builder.ToString();
will give you the expected result:
http://example.com/?foo=bar%3c%3e%26-baz&bar=bazinga
that you could more than safely feed to your HttpClient.GetAsync method.

For those who do not want to include System.Web in projects that don't already use it, you can use FormUrlEncodedContent from System.Net.Http and do something like the following:
keyvaluepair version
string query;
using(var content = new FormUrlEncodedContent(new KeyValuePair<string, string>[]{
new KeyValuePair<string, string>("ham", "Glazed?"),
new KeyValuePair<string, string>("x-men", "Wolverine + Logan"),
new KeyValuePair<string, string>("Time", DateTime.UtcNow.ToString()),
})) {
query = content.ReadAsStringAsync().Result;
}
dictionary version
string query;
using(var content = new FormUrlEncodedContent(new Dictionary<string, string>()
{
{ "ham", "Glaced?"},
{ "x-men", "Wolverine + Logan"},
{ "Time", DateTime.UtcNow.ToString() },
})) {
query = content.ReadAsStringAsync().Result;
}

In a ASP.NET Core project you can use the QueryHelpers class, available in the Microsoft.AspNetCore.WebUtilities namespace for ASP.NET Core, or the .NET Standard 2.0 NuGet package for other consumers:
// using Microsoft.AspNetCore.WebUtilities;
var query = new Dictionary<string, string>
{
["foo"] = "bar",
["foo2"] = "bar2",
// ...
};
var response = await client.GetAsync(QueryHelpers.AddQueryString("/api/", query));

TL;DR: do not use accepted version as It's completely broken in relation to handling unicode characters, and never use internal API
I've actually found weird double encoding issue with the accepted solution:
So, If you're dealing with characters which need to be encoded, accepted solution leads to double encoding:
query parameters are auto encoded by using NameValueCollection indexer (and this uses UrlEncodeUnicode, not regular expected UrlEncode(!))
Then, when you call uriBuilder.Uri it creates new Uri using constructor which does encoding one more time (normal url encoding)
That cannot be avoided by doing uriBuilder.ToString() (even though this returns correct Uri which IMO is at least inconsistency, maybe a bug, but that's another question) and then using HttpClient method accepting string - client still creates Uri out of your passed string like this: new Uri(uri, UriKind.RelativeOrAbsolute)
Small, but full repro:
var builder = new UriBuilder
{
Scheme = Uri.UriSchemeHttps,
Port = -1,
Host = "127.0.0.1",
Path = "app"
};
NameValueCollection query = HttpUtility.ParseQueryString(builder.Query);
query["cyrillic"] = "кирилиця";
builder.Query = query.ToString();
Console.WriteLine(builder.Query); //query with cyrillic stuff UrlEncodedUnicode, and that's not what you want
var uri = builder.Uri; // creates new Uri using constructor which does encode and messes cyrillic parameter even more
Console.WriteLine(uri);
// this is still wrong:
var stringUri = builder.ToString(); // returns more 'correct' (still `UrlEncodedUnicode`, but at least once, not twice)
new HttpClient().GetStringAsync(stringUri); // this creates Uri object out of 'stringUri' so we still end up sending double encoded cyrillic text to server. Ouch!
Output:
?cyrillic=%u043a%u0438%u0440%u0438%u043b%u0438%u0446%u044f
https://127.0.0.1/app?cyrillic=%25u043a%25u0438%25u0440%25u0438%25u043b%25u0438%25u0446%25u044f
As you may see, no matter if you do uribuilder.ToString() + httpClient.GetStringAsync(string) or uriBuilder.Uri + httpClient.GetStringAsync(Uri) you end up sending double encoded parameter
Fixed example could be:
var uri = new Uri(builder.ToString(), dontEscape: true);
new HttpClient().GetStringAsync(uri);
But this uses obsolete Uri constructor
P.S on my latest .NET on Windows Server, Uri constructor with bool doc comment says "obsolete, dontEscape is always false", but actually works as expected (skips escaping)
So It looks like another bug...
And even this is plain wrong - it send UrlEncodedUnicode to server, not just UrlEncoded what server expects
Update: one more thing is, NameValueCollection actually does UrlEncodeUnicode, which is not supposed to be used anymore and is incompatible with regular url.encode/decode (see NameValueCollection to URL Query?).
So the bottom line is: never use this hack with NameValueCollection query = HttpUtility.ParseQueryString(builder.Query); as it will mess your unicode query parameters. Just build query manually and assign it to UriBuilder.Query which will do necessary encoding and then get Uri using UriBuilder.Uri.
Prime example of hurting yourself by using code which is not supposed to be used like this

You might want to check out Flurl [disclosure: I'm the author], a fluent URL builder with optional companion lib that extends it into a full-blown REST client.
var result = await "https://api.com"
// basic URL building:
.AppendPathSegment("endpoint")
.SetQueryParams(new {
api_key = ConfigurationManager.AppSettings["SomeApiKey"],
max_results = 20,
q = "Don't worry, I'll get encoded!"
})
.SetQueryParams(myDictionary)
.SetQueryParam("q", "overwrite q!")
// extensions provided by Flurl.Http:
.WithOAuthBearerToken("token")
.GetJsonAsync<TResult>();
Check out the docs for more details. The full package is available on NuGet:
PM> Install-Package Flurl.Http
or just the stand-alone URL builder:
PM> Install-Package Flurl

Along the same lines as Rostov's post, if you do not want to include a reference to System.Web in your project, you can use FormDataCollection from System.Net.Http.Formatting and do something like the following:
Using System.Net.Http.Formatting.FormDataCollection
var parameters = new Dictionary<string, string>()
{
{ "ham", "Glaced?" },
{ "x-men", "Wolverine + Logan" },
{ "Time", DateTime.UtcNow.ToString() },
};
var query = new FormDataCollection(parameters).ReadAsNameValueCollection().ToString();

Since I have to reuse this few time, I came up with this class that simply help to abstract how the query string is composed.
public class UriBuilderExt
{
private NameValueCollection collection;
private UriBuilder builder;
public UriBuilderExt(string uri)
{
builder = new UriBuilder(uri);
collection = System.Web.HttpUtility.ParseQueryString(string.Empty);
}
public void AddParameter(string key, string value) {
collection.Add(key, value);
}
public Uri Uri{
get
{
builder.Query = collection.ToString();
return builder.Uri;
}
}
}
The use will be simplify to something like this:
var builder = new UriBuilderExt("http://example.com/");
builder.AddParameter("foo", "bar<>&-baz");
builder.AddParameter("bar", "second");
var uri = builder.Uri;
that will return the uri:
http://example.com/?foo=bar%3c%3e%26-baz&bar=second

Good part of accepted answer, modified to use UriBuilder.Uri.ParseQueryString() instead of HttpUtility.ParseQueryString():
var builder = new UriBuilder("http://example.com");
var query = builder.Uri.ParseQueryString();
query["foo"] = "bar<>&-baz";
query["bar"] = "bazinga";
builder.Query = query.ToString();
string url = builder.ToString();

Darin offered an interesting and clever solution, and here is something that may be another option:
public class ParameterCollection
{
private Dictionary<string, string> _parms = new Dictionary<string, string>();
public void Add(string key, string val)
{
if (_parms.ContainsKey(key))
{
throw new InvalidOperationException(string.Format("The key {0} already exists.", key));
}
_parms.Add(key, val);
}
public override string ToString()
{
var server = HttpContext.Current.Server;
var sb = new StringBuilder();
foreach (var kvp in _parms)
{
if (sb.Length > 0) { sb.Append("&"); }
sb.AppendFormat("{0}={1}",
server.UrlEncode(kvp.Key),
server.UrlEncode(kvp.Value));
}
return sb.ToString();
}
}
and so when using it, you might do this:
var parms = new ParameterCollection();
parms.Add("key", "value");
var url = ...
url += "?" + parms;

The RFC 6570 URI Template library I'm developing is capable of performing this operation. All encoding is handled for you in accordance with that RFC. At the time of this writing, a beta release is available and the only reason it's not considered a stable 1.0 release is the documentation doesn't fully meet my expectations (see issues #17, #18, #32, #43).
You could either build a query string alone:
UriTemplate template = new UriTemplate("{?params*}");
var parameters = new Dictionary<string, string>
{
{ "param1", "value1" },
{ "param2", "value2" },
};
Uri relativeUri = template.BindByName(parameters);
Or you could build a complete URI:
UriTemplate template = new UriTemplate("path/to/item{?params*}");
var parameters = new Dictionary<string, string>
{
{ "param1", "value1" },
{ "param2", "value2" },
};
Uri baseAddress = new Uri("http://www.example.com");
Uri relativeUri = template.BindByName(baseAddress, parameters);

Or simply using my Uri extension
Code
public static Uri AttachParameters(this Uri uri, NameValueCollection parameters)
{
var stringBuilder = new StringBuilder();
string str = "?";
for (int index = 0; index < parameters.Count; ++index)
{
stringBuilder.Append(str + parameters.AllKeys[index] + "=" + parameters[index]);
str = "&";
}
return new Uri(uri + stringBuilder.ToString());
}
Usage
Uri uri = new Uri("http://www.example.com/index.php").AttachParameters(new NameValueCollection
{
{"Bill", "Gates"},
{"Steve", "Jobs"}
});
Result
http://www.example.com/index.php?Bill=Gates&Steve=Jobs

To avoid double encoding issue described in taras.roshko's answer and to keep possibility to easily work with query parameters, you can use uriBuilder.Uri.ParseQueryString() instead of HttpUtility.ParseQueryString().

Thanks to "Darin Dimitrov", This is the extension methods.
public static partial class Ext
{
public static Uri GetUriWithparameters(this Uri uri,Dictionary<string,string> queryParams = null,int port = -1)
{
var builder = new UriBuilder(uri);
builder.Port = port;
if(null != queryParams && 0 < queryParams.Count)
{
var query = HttpUtility.ParseQueryString(builder.Query);
foreach(var item in queryParams)
{
query[item.Key] = item.Value;
}
builder.Query = query.ToString();
}
return builder.Uri;
}
public static string GetUriWithparameters(string uri,Dictionary<string,string> queryParams = null,int port = -1)
{
var builder = new UriBuilder(uri);
builder.Port = port;
if(null != queryParams && 0 < queryParams.Count)
{
var query = HttpUtility.ParseQueryString(builder.Query);
foreach(var item in queryParams)
{
query[item.Key] = item.Value;
}
builder.Query = query.ToString();
}
return builder.Uri.ToString();
}
}

HttpClient client = new HttpClient();
var uri = Environment.GetEnvironmentVariable("URL of Api");
var requesturi = QueryHelpers.AddQueryString(uri, "parameter_name",parameter_value);
client.BaseAddress = new Uri(requesturi);
And then you can add request headers also eg:
client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
client.DefaultRequestHeaders.Add("x-api-key", secretValue);
response syntax eg:
HttpResponseMessage response = client.GetAsync(requesturi).Result;
Hope it will work for you.

My answer doesn't globally differ from the accepted/other answers. I just tried to create an extension method for the Uri type, which takes variable number of parameters.
public static class UriExtensions
{
public static Uri AddParameter(this Uri url, params (string Name, string Value)[] #params)
{
if (!#params.Any())
{
return url;
}
UriBuilder uriBuilder = new(url);
NameValueCollection query = HttpUtility.ParseQueryString(uriBuilder.Query);
foreach (var param in #params)
{
query[param.Name] = param.Value.Trim();
}
uriBuilder.Query = query.ToString();
return uriBuilder.Uri;
}
}
Usage example:
var uri = new Uri("http://someuri.com")
.AddParameter(
("p1.name", "p1.value"),
("p2.name", "p2.value"),
("p3.name", "p3.value"));

I couldn't find a better solution than creating a extension method to convert a Dictionary to QueryStringFormat. The solution proposed by Waleed A.K. is good as well.
Follow my solution:
Create the extension method:
public static class DictionaryExt
{
public static string ToQueryString<TKey, TValue>(this Dictionary<TKey, TValue> dictionary)
{
return ToQueryString<TKey, TValue>(dictionary, "?");
}
public static string ToQueryString<TKey, TValue>(this Dictionary<TKey, TValue> dictionary, string startupDelimiter)
{
string result = string.Empty;
foreach (var item in dictionary)
{
if (string.IsNullOrEmpty(result))
result += startupDelimiter; // "?";
else
result += "&";
result += string.Format("{0}={1}", item.Key, item.Value);
}
return result;
}
}
And them:
var param = new Dictionary<string, string>
{
{ "param1", "value1" },
{ "param2", "value2" },
};
param.ToQueryString(); //By default will add (?) question mark at begining
//"?param1=value1&param2=value2"
param.ToQueryString("&"); //Will add (&)
//"&param1=value1&param2=value2"
param.ToQueryString(""); //Won't add anything
//"param1=value1&param2=value2"

Find the applicant's current URl

I'm request for get url :
public Uri GetAbsoluteUri()
{
var request = _httpContextAccessor.HttpContext.Request;
UriBuilder uriBuilder = new UriBuilder();
uriBuilder.Scheme = request.Scheme;
uriBuilder.Host = request.Host.Host;
uriBuilder.Path = request.Path.ToString();
uriBuilder.Query = request.QueryString.ToString();
return uriBuilder.Uri;
}
public string RootPath => Path.Combine(WebRootPath, RootFolderName);
public string GetProductPicturePath()
{
return Path.Combine(GetAbsoluteUri().ToString(), RootFolderName, ProductPictureFolder);
}
public string GetProductMainPicturePath()
{
string path = Path.Combine(GetAbsoluteUri().ToString(), RootFolderName, ProductPictureFolder, ProductMainPictureFolder);
return path;
}
public string GetNewPath()
{
string productMainPicturePath = GetProductMainPicturePath();
return Path.Combine(productMainPicturePath);
}
finally i using the GetNewPath().
, but this will give me the address :
https://localhost/api/Product/GetProductList/Upload/ProductPictureFolder/ProductMainPicture/77777.png
but i have 2 problem with this url :
1 - it not contain port in url https://localhost/api but i need return like this : http://localhost:4200/api
2 - This includes the name of the controller and the ActionName, but I need to like this : https://localhost/Upload/ProductPictureFolder/ProductMainPicture/77777.png
but it return for me this : https://localhost/api/Product/GetProductList/Upload/ProductPictureFolder/ProductMainPicture/77777.png
i not need this /api/Product/GetProductList .
Product : Controller Name
GetProductList : ActionName
How Can I Solve This Problem ???

1 - it not contain port in url https://localhost/api but i need return like this
To get port you can use this snippet :
if (request.Host.Port.HasValue)
uriBuilder.Port = request.Host.Port.Value;
2 - This includes the name of the controller and the ActionName, but I
need to like this :
https://localhost/Upload/ProductPictureFolder/ProductMainPicture/77777.png
I suggest you that set UriBuilder Path based on your needs, not from the request. Something like this:
// Make your Upload file path here
var relativePath = Path.Combine(folderName, filename);
var request = _httpContextAccessor.HttpContext.Request;
var uriBuilder = new UriBuilder
{
Host = request.Host.Host,
Scheme = request.Scheme,
Path = relativePath
};
if (request.Host.Port.HasValue)
uriBuilder.Port = request.Host.Port.Value;
var imageUrl = uriBuilder.ToString();

Cosmos DB Azure Table API oData Authentication REST / C#?

I'm trying to access Azure Cosmos DB using Table API.
The challenge is, despite creating SharedKeyLite, server is still returning Unauthorized - seems like SharedKeyLite is not supported or I'm generating the signature or headers wrong.
Here is the code
static readonly string storageAccountName = "accountName";
static readonly string storageAccountKey = "xxxx";
static readonly string uri = "https://accountName.table.cosmosdb.azure.com/Contacts()";
static readonly string utc_date = DateTime.UtcNow.ToString("r");
static void Main(string[] args)
{
Console.WriteLine(GetResult().Result);
}
static async Task<string> GetResult()
{
// Set this to whatever payload you desire. Ours is null because
// we're not passing anything in.
Byte[] requestPayload = null;
var requestDateString = DateTime.UtcNow.ToString("R", CultureInfo.InvariantCulture);
var requestUri = new Uri(uri);
DateTime now = DateTime.UtcNow;
//Instantiate the request message with a null payload.
using (var httpRequestMessage = new HttpRequestMessage(HttpMethod.Get, uri)
{ Content = (requestPayload == null) ? null : new ByteArrayContent(requestPayload) })
{
ConstructHeaders(httpRequestMessage.Headers, requestDateString);
string authorizationHeader = GenerateSharedKeyLite(storageAccountKey, storageAccountName, uri,requestDateString);
httpRequestMessage.Headers.Authorization = new AuthenticationHeaderValue("SharedKeyLite", authorizationHeader);
// Send the request.
using (HttpResponseMessage httpResponseMessage = await new HttpClient().SendAsync(httpRequestMessage))
{
string json = await httpResponseMessage.Content.ReadAsStringAsync();
return json;
}
}
}
These are the headers I"m adding, expansion of ConstructHeaders method.
Refer this link for request parameters
//Construct the headers
static void ConstructHeaders(HttpRequestHeaders headers, string now)
{
headers.Add("x-ms-date", now);
headers.Add("x-ms-version", "2017-04-17");
// If you need any additional headers, add them here before creating
// the authorization header.
headers.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
if (headers.Contains("DataServiceVersion"))
headers.Remove("DataServiceVersion");
headers.Add("DataServiceVersion", "3.0;NetFx");
if (headers.Contains("MaxDataServiceVersion"))
headers.Remove("MaxDataServiceVersion");
headers.Add("MaxDataServiceVersion", "3.0;NetFx");
}
And this is the method that creates the SharedKeyLite
//Created Shared Key Lite
static string GenerateSharedKeyLite(string accessKey, string account, string url, string date)
{
var uri = new Uri(url);
var canonicalizedResourceString = uri.PathAndQuery;
var queryStart = canonicalizedResourceString.IndexOf('?');
if (queryStart > -1)
{
if (queryStart < canonicalizedResourceString.Length - 1)
{
var path = canonicalizedResourceString.Substring(0, queryStart);
var parameters = HttpUtility.ParseQueryString(canonicalizedResourceString.Substring(queryStart + 1));
var sb = new StringBuilder();
foreach (var keyOri in parameters.Keys)
{
var value = parameters[keyOri];
var key = keyOri.ToLowerInvariant();
sb.Append("\n");
sb.Append(key);
sb.Append(":");
sb.Append(value);
}
canonicalizedResourceString = canonicalizedResourceString + sb.ToString();
}
else
{
canonicalizedResourceString = canonicalizedResourceString.Substring(0, canonicalizedResourceString.Length - 1);
}
}
canonicalizedResourceString = $"/{account}{canonicalizedResourceString}";
var stringToSign = $"{date}\n{canonicalizedResourceString}";
var signedSignature = string.Empty;
using (var hmac = new HMACSHA256(Convert.FromBase64String(accessKey)))
{
var outputBytes = hmac.ComputeHash(Encoding.UTF8.GetBytes(stringToSign));
var signature = Convert.ToBase64String(outputBytes);
return $"{account}:{signature}";
}
}
Any Help? Ideally I want to perform the odata query using simple.odata, but first trying to make this work using HttpClient

Just copy your code and it works on my side. If you haven't modified your code, please make sure your storageAccountName and storageAccountKey are correct.
BTW, in method GenerateSharedKeyLite there's no need to add query parameters to canonicalizedResourceString for entity operation. You only need to add comp if you want to operate component info for table or service. See constructing-the-canonicalized-resource-string.
The query string should include the question mark and the comp parameter (for example, ?comp=metadata). No other parameters should be included on the query string.

Check if it is root domain in string

I'm new to C#,
lets say I have a string
string testurl = "http://www.mytestsite.com/hello";
if (test url == root domain) {
// do something
}
I want to check if that string "testurl" is the root domain i.e http://www.mytestsite.com or http://mytestsite.com etc.
Thanks.

Use the Uri class:
var testUrl = new Uri("http://www.mytestsite.com/hello");
if (testUrl.AbsolutePath== "/")
{
Console.WriteLine("At root");
}
else
{
Console.WriteLine("Not at root");
}
Which nicely deals with any normalization issues that may be required (e.g. treating http://www.mytestsite.com and http://www.mytestsite.com/ the same)

You may try like this:
string testurl = "http://www.mytestsite.com/hello"
if ( GetDomain.GetDomainFromUrl(testurl) == rootdomain) {
// do something
}

You can also try using URI.HostName property
The following example writes the host name (www.contoso.com) of the server to the console.
Uri baseUri = new Uri("http://www.contoso.com:8080/");
Uri myUri = new Uri(baseUri, "shownew.htm?date=today");
Console.WriteLine(myUri.Host);
If the hostname returned is equal to "http://mytestsite.com" you are done.

string testurl = "http://www.mytestsite.com/hello";
string prefix = testurl.Split(new String[] { "//" })[0] + "//";
string url = testurl.Replace(prefix, "");
string root = prefix + url.Split("/")[0];
if (testurl == root) {
// do something
}

Combine relative baseUri with relative path

I'm looking for a clean way to combine a relative base Uri with another relative path. I've tried the following, but Uri(Uri, string) and UriBuilder(Uri) require absolute Uris (throwing InvalidOperationException: This operation is not supported for a relative URI).
// where Settings.Default.ImagesPath is "~/path/to/images"
// attempt 1
_imagePath = new Uri(Settings.Default.ImagesPath, image);
// attempt 2
UriBuilder uriBuilder = new UriBuilder(Settings.Default.ImagesPath);
uriBuilder.Path += image;
_imagePath = uriBuilder.Uri;
I don't want to do any ugly string manipulation to make sure the base path ends with a trailing slash, etc.

This is still a bit messier than I'd like, but it works.
public static class UriExtensions
{
public static Uri Combine(this Uri relativeBaseUri, Uri relativeUri)
{
if (relativeBaseUri == null)
{
throw new ArgumentNullException("relativeBaseUri");
}
if (relativeUri == null)
{
throw new ArgumentNullException("relativeUri");
}
string baseUrl = VirtualPathUtility.AppendTrailingSlash(relativeBaseUri.ToString());
string combinedUrl = VirtualPathUtility.Combine(baseUrl, relativeUri.ToString());
return new Uri(combinedUrl, UriKind.Relative);
}
}
Here's an example usage:
Uri imageUrl = new Uri("profile.jpg", UriKind.Relative);
Uri baseImageUrl = new Uri("~/path/to/images", UriKind.Relative);
Uri combinedImageUrl = baseImageUrl.Combine(image);
The combinedImageUrl is
~/path/to/images/profile.jpg

Try:
UriBuilder builder = new UriBuilder();
Uri baseUri = builder.Uri;
builder.Path = Settings.Default.ImagesRealtivePath;
if (!builder.Path.EndsWith("/"))
builder.Path += "/";
_imagePath = baseUri.MakeRelativeUri(new Uri(builder.Uri, image));
This will return the string "~/path/to/images/image.jpg".

First of all, thanks for the response on this post!
I made a simplified version of the method, skipping the "complexity" of using the Uri class. The method only takes strings as parameters and is also return a string.
public static string MakeRelativeUrl(params string[] relativePaths)
{
var res = "~/";
foreach (var relativePath in relativePaths)
{
string baseUrl = VirtualPathUtility.AppendTrailingSlash(res);
res = VirtualPathUtility.Combine(baseUrl, relativePath);
}
return res;
}
Above code might be useful for others who wants to expose a method providing this functionality without being dependent on either Uri or VirtualPathUtility, but only simple strings.
Can of course easily be modified to return Uri - still keeping the benefit of parsing string parameters:
public static Uri MakeRelativeUrl(params string[] relativePaths)
{
var res = "~/";
foreach (var relativePath in relativePaths)
{
string baseUrl = VirtualPathUtility.AppendTrailingSlash(res);
res = VirtualPathUtility.Combine(baseUrl, relativePath);
}
return new Uri(res, UriKind.Relative);
}
Usage of both of above code examples:
Image.ImageUrl = MakeRelativeUrl("path", "to", "images", "image.jpg").ToString();
// Image.ImageUrl == "~/path/to/images/image.jpg"

A slightly more generalized version of jrummell's answer that accepts the first parameter to be either an absolute or a relative Uri is:
/// <summary>
/// Combines two <see cref="Uri"/>s.
/// </summary>
/// <param name="baseUri">Relative or absolute base uri.</param>
/// <param name="relativeUri">Uri to be appended.</param>
public static Uri Combine(this Uri baseUri, Uri relativeUri)
{
if (baseUri == null) throw new ArgumentNullException("baseUri");
if (relativeUri == null) throw new ArgumentNullException("relativeUri");
string baseUrl = VirtualPathUtility.AppendTrailingSlash(baseUri.ToString());
string combinedUrl = VirtualPathUtility.Combine(baseUrl, relativeUri.ToString());
return new Uri(combinedUrl, baseUri.IsAbsoluteUri ? UriKind.Absolute : UriKind.Relative);
}

Try:
UriBuilder uriBuilder = new UriBuilder(Settings.Default.ImagesRealtivePath);
uriBuilder.Path += image;
_imagePath = uriBuilder.Uri;

You can just use Path.Combine(string, string) to achieve this. If it's a relative URL the output will be a little funky, but it would be easy enough to correct- or you could simply ignore the issue and most usages should still work.
Path.Combine("~/path/to/images", "image.jpg");
Output: ~/path/to/images\image.jpg