Poper way to make a HTTPClient PostAsync and GetAsync? - xamarin

Question

I want to make a proper HTTPClient request. I have a code but I am always getting so may exceptions like:
Java.IO.IOException: Socket closed
System.OperationCanceledException: The operation was canceled.
Java.Net.SocketException: Connection reset
Java.Net.SocketException: Software caused connection abort
Java.Net.UnknownHostException: android_getaddrinfo failed: EAI_NODATA (No address associated with hostname)
Java.Net.UnknownHostException: Unable to resolve host "tbs.scratchit.ph": No address associated with hostname
Java.IO.IOException: isConnected failed: ETIMEDOUT (Connection timed out)
Java.Net.SocketException: recvfrom failed: ECONNRESET (Connection reset by peer)
I am always getting these kinds of exceptions, errors.
I am starting to wonder how can I create a Post Async and GetAsync properly to avoid these errors in the future?
Here is how I create a HTTP Client:
1. I have a class call Constants, in there I will declare a new HTTP Client so that I only have 1 HTTPClient across my project
public class Constants
{
public static HttpClient client = new HttpClient();
}
2. I have a function(s) that gets data from my server through a PHP API by sending the parameters through JSON.
public async void FirstTimeSyncUser(string host, string database, string contact, string ipaddress)
{
try
{
syncStatus.Text = "Checking internet connection";
string apifile = "first-time-sync-user-api.php";
if (CrossConnectivity.Current.IsConnected)
{
syncStatus.Text = "Initializing first-time user sync";
var db = DependencyService.Get<ISQLiteDB>();
var conn = db.GetConnection();
var getData = conn.QueryAsync<UserTable>("SELECT * FROM tblUser WHERE ContactID = ? AND Deleted != '1'", contact);
var resultCount = getData.Result.Count;
var current_datetime = DateTime.Now.ToString("yyyy-MM-dd HH:mm:ss");
int count = 1;
var settings = new JsonSerializerSettings
{
NullValueHandling = NullValueHandling.Ignore,
MissingMemberHandling = MissingMemberHandling.Ignore
};
if (resultCount == 0)
{
syncStatus.Text = "Getting user data from the server";
var link = "http://" + ipaddress + "/" + Constants.apifolder + "/api/" + apifile;
string contentType = "application/json";
JObject json = new JObject
{
{ "Host", host },
{ "Database", database },
{ "ContactID", contact }
};
Constants.client.DefaultRequestHeaders.ConnectionClose = true;
var response = await Constants.client.PostAsync(link, new StringContent(json.ToString(), Encoding.UTF8, contentType));
if (response.IsSuccessStatusCode)
{
var content = await response.Content.ReadAsStringAsync();
if (!string.IsNullOrEmpty(content))
{
try
{
var dataresult = JsonConvert.DeserializeObject<List<UserData>>(content, settings);
var datacount = dataresult.Count;
for (int i = 0; i < datacount; i++)
{
syncStatus.Text = "Syncing user " + count + " out of " + datacount;
var item = dataresult[i];
var userid = item.UserID;
var usrpassword = item.UsrPassword;
var usertypeid = item.UserTypeID;
var userstatus = item.UserStatus;
var lastsync = DateTime.Parse(current_datetime);
var lastupdated = item.LastUpdated;
var deleted = item.Deleted;
var insertdata = new UserTable
{
UserID = userid,
UsrPassword = usrpassword,
ContactID = contact,
UserTypeID = usertypeid,
UserStatus = userstatus,
LastSync = lastsync,
LastUpdated = lastupdated,
Deleted = deleted
};
await conn.InsertOrReplaceAsync(insertdata);
count++;
}
synccount += "Total synced user: " + count + "\n";
var logType = "App Log";
var log = "Initialized first-time sync (<b>User</b>) <br/>" + "App Version: <b>" + Constants.appversion + "</b><br/> Device ID: <b>" + Constants.deviceID + "</b>";
int logdeleted = 0;
Save_Logs(contact, logType, log, database, logdeleted);
Preferences.Set("userchangeslastcheck", current_datetime, "private_prefs");
FirstTimeSyncSystemSerial(host, database, contact, ipaddress);
}
catch
{
var retry = await DisplayAlert("Application Error", "Syncing failed. Failed to send the data.\n\n Error:\n\n" + content + "\n\n Do you want to retry?", "Yes", "No");
if (retry.Equals(true))
{
FirstTimeSyncUser(host, database, contact, ipaddress);
}
else
{
First_Time_OnSyncFailed();
}
}
}
else
{
Preferences.Set("userchangeslastcheck", current_datetime, "private_prefs");
FirstTimeSyncSystemSerial(host, database, contact, ipaddress);
}
}
else
{
var retry = await DisplayAlert("Application Error", "Syncing failed. Server is unreachable.\n\n Error:\n\n"+ response.StatusCode +" Do you want to retry?", "Yes", "No");
if (retry.Equals(true))
{
FirstTimeSyncUser(host, database, contact, ipaddress);
}
else
{
First_Time_OnSyncFailed();
}
}
}
else
{
SyncUserClientUpdate(host, database, contact, ipaddress);
}
}
else
{
var retry = await DisplayAlert("Application Error", "Syncing failed. Please connect to the internet to sync your data. Do you want to retry?", "Yes", "No");
if (retry.Equals(true))
{
FirstTimeSyncUser(host, database, contact, ipaddress);
}
else
{
First_Time_OnSyncFailed();
}
}
}
catch (Exception ex)
{
Crashes.TrackError(ex);
var retry = await DisplayAlert("Application Error", "Syncing failed. Failed to send the data.\n\n Error:\n\n" + ex.Message.ToString() + "\n\n Do you want to retry?", "Yes", "No");
if (retry.Equals(true))
{
FirstTimeSyncUser(host, database, contact, ipaddress);
}
else
{
First_Time_OnSyncFailed();
}
}
}
3. After getting the data I needed it will execute another function with another POSTASYNC Call. In my code above when I got the user data from my server it will execute the next function which is FirstTimeSyncSystemSerial(host, database, contact, ipaddress);
What am I doing wrong? and How can I improve this so that I can avoid these exceptions?

Answer 1

Debug your code to find out where the exception is thrown.
Put a try catch blocked around that block of code. Then catch all the expected exceptions and try loopback again for a number of time.

Answer 2

You can Make a Generic Custom Service call That Can be Called Anywhere When You Need
public class RestClient : IRestClient
{
private const string TokenHeaderKey = "Any Token Header";
private HttpClient _httpclient = new HttpClient();
public async Task<T> GetAsync<T>(string url, string token) where T : new()
{
var responseContent = await ExecuteRequest(
async () =>
{
try
{
AddTokenToDefaultRequestsHeader(token);
return await _httpclient.GetAsync(url);
}
finally
{
ClearAuthenticationHeader();
}
});
return await Deserialize<T>(responseContent);
}
private void AddTokenToDefaultRequestsHeader(string token)
{
_httpclient.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue(TokenHeaderKey, token);
}
private void ClearAuthenticationHeader()
{
_httpclient.DefaultRequestHeaders.Authorization = null;
}
private static async Task<HttpContent> ExecuteRequest(Func<Task<HttpResponseMessage>> requestFunc)
{
HttpResponseMessage response = null;
try
{
response = await requestFunc();
if (!response.IsSuccessStatusCode)
{
var message = $"Executed HTTP request returned status code {response.StatusCode} and reason phrase {response.ReasonPhrase}";
if (response.StatusCode == HttpStatusCode.Unauthorized)
{
throw new Exception(message);
}
throw new Exception(message);
}
return response.Content;
}
catch (Exception exception)
{
if (exception is HttpRequestException || exception is WebException || exception is TaskCanceledException)
{
throw new Exception(
"Could not connect to service.");
}
throw;
}
}
private static async Task<T> Deserialize<T>(HttpContent responseContent) where T : new()
{
try
{
var responseContentString = await responseContent.ReadAsStringAsync();
return JsonConvert.DeserializeObject<T>(responseContentString);
}
catch (Exception exception)
{
if (exception is TaskCanceledException || exception is JsonException)
{
throw new Exception("Could not deserialize response content.", exception);
}
throw;
}
}
And Add an App settings class
public class AppSettings : IAppSettings
{
public string Server => "server url";
public string ServerEndPoint => "End point";
public string Token => "Token If you Have any";
}
Then Call Like this
public class Servicecall
{
private readonly IRestClient _restClient;
private readonly IAppSettings _appSettings;
public PatientService(IRestClient restClient, IAppSettings appSettings)
{
_restClient = restClient;
_appSettings = appSettings;
}
public async Task<IList<PatientViewModel>> GetPatients()
{
var url = _appSettings.Server + _appSettings.EndPoint ;
var token = _appSettings.Token;
return GetPatientList(await _restClient.GetAsync<List<ListModelClass>>(url, token));
}
public IList<Model> GetPatientList(IList<ListModelClass> List)
{
return List.Select(p => new Model(p)).ToList();
}
}
This way You can Call deferent services without typing a lot of boilercodes
This way You can Call Services with real ease