'Exception: '<' is an invalid start of a value
I have a Blazor Webassembly project with a controller method as follows:
[HttpGet]
public async Task<List<string>> GetStatesForProfile()
{
IConfigurationSection statesSection = configuration.GetSection("SiteSettings:States");
var sections = statesSection.GetChildren();
var states = statesSection.GetChildren().Select(s => s.Key).ToList<string>();
return states;
}
The razor page calls this method:
private async Task<bool> GetStatesModel()
{
try
{
States = await http.GetJsonAsync<List<string>>("api/account/getstatesforprofile");
...
}
catch (Exception ex)
{
Console.WriteLine($"Exception: {ex.Message}, Inner: {ex.InnerException.Message}");
}
I get this Exception:
Exception: '<' is an invalid start of a value.
I read these values from appsettings.json file, And there is no '<' in values.
{
"SiteSettings": {
"States": {
"New York": ["NYC"],
"California": ["Los Angeles", "San Francisco"]
}
}
Also I put a breakpoint in the controller method and it doesn't hit. What is this error? Is it from parsing json? and how to resolve this?
Solution 1:[1]
Most probably the response you re receiving is html instead of actual JSON format for the endpoint you are requesting. Please check that.
An as HTML usually starts with <html> tag, the JSON validator fails on the very first character.
Solution 2:[2]
I had a very similar problem.
In the end it turned out that my browser had cached the HTML error page (I guess I had some problems with the code when I first tried it). And no matter how I tried fixing the code I still only got the error from cache. Clearing my cache also cleared the problem.
Solution 3:[3]
It happens when you're trying to access an API that doesn't exist. You have to check your API project connectionstring under AppSettings and make sure it's correct and running. If it's a Blazor project, you can set it as your default project, execute and see if you get a json response.
Solution 4:[4]
This error indicates a mismatch of the project targeting framework version and installed runtime on the machine. So make sure that the target framework for your project matches an installed runtime - this could be verified by multiple means; one of them is to check out the Individual Components tab of the Visual Studio Installer and lookup the target version.
E.g., there is the TargetFramework attribute in the proj file:
<PropertyGroup>
<TargetFramework>net5.0</TargetFramework>
</PropertyGroup>
The launch the Visual Studio Installer, click Modify, and visit the Individual Components tab:
Install the missing runtime (.NET 5 Runtime in this case) and you're good to go.
Solution 5:[5]
I got the same error. Red herring. use your browser or postman to check your api endpoint is returning the json data and not some HTML. In my case my "api/companytypes" had a typo.
private CompanyType[] companytypesarray;
private List<CompanyType> CompanyTypeList;
private List<CompanyType> CompanyTypeList2;
public async Task<bool> LoadCompanyTypes()
{
//this works
CompanyTypeList = await Http.GetFromJsonAsync<List<CompanyType>>("api/companytype");
//this also works reading the json into an array first
companytypesarray = await Http.GetFromJsonAsync<CompanyType[]>("api/companytype");
CompanyTypeList2 = companytypesarray.ToList();
return true;
}
Solution 6:[6]
I know this is an old question, but it's one of the top results when Googling the error.
I've just spent more time than I care to admit to tracking down this error. I had a straightforward Blazor hosted app, basically unchanged from the template. It worked just fine when run locally, but when published to my web host API calls failed. I finally figured out that the problem was that I was running the publish from the Client project. When I changed to the Server project it worked properly.
Hopefully my long frustration and slight stupidity will save someone else making a similar mistake.
Solution 7:[7]
Seems like your api is not not accessible and its returning error HTML page by default.
You can try below solution:-
I think you are using httpclient to get data to blazor application.
If you have separate projects in solution for blazor and web api,
currently your startup application may set to run blazor project only.
Change startup projects to multiple (blazor and web api app) and give httpClient url in startup of blazor application, as webApi application url, that may solve your issue.
Solution 8:[8]
I had the same issue when passing in an empty string to a controller method. Creating a second controller method that doesn't accept any input variables, and just passing an empty string to the first method helped to fix my problem.
[HttpGet]
[ActionName("GetStuff")]
public async Task<IEnumerable<MyModel>> GetStuff()
{
return await GetStuff("");
}
[HttpGet("{search}")]
[ActionName("GetStuff")]
public async Task<IEnumerable<MyModel>> GetStuff(string search)
{
...
}
Solution 9:[9]
Try to update your packages to old or new version. In my case, system.net.http.json is updated from 6.0 to 5.0
Solution 10:[10]
Likely you are using an Asp.NetCore hosted WASM application. By default the client's App.razor has something similar to:
<CascadingAuthenticationState>
<Router AppAssembly="@typeof(Program).Assembly">
<Found Context="routeData">
<AuthorizeRouteView DefaultLayout="@typeof(MainLayout)"
RouteData="@routeData">
<NotAuthorized>
<RedirectToLogin />
</NotAuthorized>
<Authorizing>
<Loading Caption="Authorizing..."></Loading>
</Authorizing>
</AuthorizeRouteView>
</Found>
<NotFound>
<LayoutView Layout="@typeof(MainLayout)">
<p>Sorry, there's nothing at this address.</p>
</LayoutView>
</NotFound>
</Router>
</CascadingAuthenticationState>
Herein lies the problem. Since the Client and Server share the same base address, when the application cannot find "api/account/getstatesforprofile" it gives you the client's "Sorry, there's nothing at the address" page. Which is of course HTML.
I have not found the solution to this issue, but I am working on it and will reply once I find an issue.
Solution 11:[11]
I was having the same problem, "JsonReaderException: '<' is an invalid start of a value."
In my case the url for the REST service was wrong.
I was using the URL from the client project. Then I looked at the Swagger screen, https://localhost:44322/swagger/index.html and noticed the right URL should start with "44322"... Corrected, worked.
Solution 12:[12]
I know this is an old question, but I had the same problem. It took some searching, but I realized that the return data was in XML instead of JSON.
I'm assuming your "http" variable is of type HttpClient, so here's what I found worked for me.
By setting the "Accept" header to allow only JSON, you avoid a miscommunication between your app and the remote server.
http.DefaultRequestHeaders.Add("Accept", "application/json");
States = await http.GetJsonAsync<List<string>>("api/account/getstatesforprofile");
Solution 13:[13]
In my case, I had a comma (,) written mistakenly at the beginning of the appsettings.json file ... Just check your file and verify
/////// my error details ////// System.FormatException HResult=0x80131537 Message=Could not parse the JSON file. Source=Microsoft.Extensions.Configuration.Json StackTrace: at line 16 This exception was originally thrown at this call stack: [External Code] Inner Exception 1: JsonReaderException: ',' is an invalid start of a value. LineNumber: 0 | BytePositionInLine: 0. ////
Solution 14:[14]
In all these, there is two things that was my issue and realized, first off was that Route[("api/controller")] instead of Route[("api/[controller]")], that is missing square brackets. In the second exercise I was doing, with the first experience in mind, was from the name of the database. The database had a dot in the name (Stock.Inventory). When I change the database name to StockInventory it worked. The second one I am not so sure but it worked for me.
Sources
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