Synnefo » Pithos MS Client

// -----------------------------------------------------------------------

// <copyright file="RestClient.cs" company="Microsoft">

// TODO: Update copyright text.

// </copyright>

// -----------------------------------------------------------------------

using System.Collections.Specialized;

using System.Diagnostics;

using System.Diagnostics.Contracts;

using System.IO;

using System.Net;

using System.Runtime.Serialization;

using System.Threading.Tasks;

using log4net;

namespace Pithos.Network

{

    using System;

    using System.Collections.Generic;

    using System.Linq;

    using System.Text;

    /// <summary>

    /// TODO: Update summary.

    /// </summary>

    public class RestClient:WebClient

    {

        public int Timeout { get; set; }

        public bool TimedOut { get; set; }

        public HttpStatusCode StatusCode { get; private set; }

        public string StatusDescription { get; set; }

        public long? RangeFrom { get; set; }

        public long? RangeTo { get; set; }

        public int Retries { get; set; }

        private readonly Dictionary<string, string> _parameters=new Dictionary<string, string>();

        public Dictionary<string, string> Parameters

        {

            get

            {

                Contract.Ensures(_parameters!=null);

                return _parameters;

            }            

        }

        private static readonly ILog Log = LogManager.GetLogger("RestClient");

        [ContractInvariantMethod]

        private void Invariants()

        {

            Contract.Invariant(Headers!=null);    

        }

        public RestClient():base()

        {

        }

        public RestClient(RestClient other)

            : base()

        {

            if (other==null)

                throw new ArgumentNullException("other");

            Contract.EndContractBlock();

            CopyHeaders(other);

            Timeout = other.Timeout;

            Retries = other.Retries;

            BaseAddress = other.BaseAddress;             

            foreach (var parameter in other.Parameters)

            {

                Parameters.Add(parameter.Key,parameter.Value);

            }

            this.Proxy = other.Proxy;

        }

        protected override WebRequest GetWebRequest(Uri address)

        {

            TimedOut = false;

            var webRequest = base.GetWebRequest(address);

            var request = (HttpWebRequest)webRequest;

            if (IfModifiedSince.HasValue)

                request.IfModifiedSince = IfModifiedSince.Value;

            request.AutomaticDecompression = DecompressionMethods.Deflate | DecompressionMethods.GZip;

            if(Timeout>0)

                request.Timeout = Timeout;

            if (RangeFrom.HasValue)

            {

                if (RangeTo.HasValue)

                    request.AddRange(RangeFrom.Value, RangeTo.Value);

                else

                    request.AddRange(RangeFrom.Value);

            }

            return request; 

        }

        public DateTime? IfModifiedSince { get; set; }

        protected override WebResponse GetWebResponse(WebRequest request, IAsyncResult result)

        {

            return ProcessResponse(()=>base.GetWebResponse(request, result)); 

        }

        protected override WebResponse GetWebResponse(WebRequest request)

        {

            return ProcessResponse(() => base.GetWebResponse(request));

        }

        private WebResponse ProcessResponse(Func<WebResponse> getResponse)

        {

            try

            {

                var response = (HttpWebResponse)getResponse();

                StatusCode = response.StatusCode;

                LastModified = response.LastModified;

                StatusDescription = response.StatusDescription;

                return response;

            }

            catch (WebException exc)

            {

                if (exc.Response != null)

                {

                    var response = (exc.Response as HttpWebResponse);

                    if (AllowedStatusCodes.Contains(response.StatusCode))

                    {

                        StatusCode = response.StatusCode;

                        LastModified = response.LastModified;

                        StatusDescription = response.StatusDescription;

                        return response;

                    }

                    if (exc.Response.ContentLength > 0)

                    {

                        string content = GetContent(exc.Response);

                        Log.ErrorFormat(content);                        

                    }

                }

                throw;

            }

        }

        private readonly List<HttpStatusCode> _allowedStatusCodes=new List<HttpStatusCode>{HttpStatusCode.NotModified};

        public List<HttpStatusCode> AllowedStatusCodes

        {

            get

            {

                return _allowedStatusCodes;

            }            

        }

        public DateTime LastModified { get; private set; }

        private static string GetContent(WebResponse webResponse)

        {

            if (webResponse == null)

                throw new ArgumentNullException("webResponse");

            Contract.EndContractBlock();

            string content;

            using (var stream = webResponse.GetResponseStream())

            using (var reader = new StreamReader(stream))

            {

                content = reader.ReadToEnd();

            }

            return content;

        }

        public string DownloadStringWithRetry(string address,int retries=0)

        {

            if (address == null)

                throw new ArgumentNullException("address");

            var actualAddress = GetActualAddress(address);

            TraceStart("GET",actualAddress);            

            var actualRetries = (retries == 0) ? Retries : retries;

            var task = Retry(() =>

            {

                var uriString = String.Join("/", BaseAddress.TrimEnd('/'), actualAddress);                

                var content = base.DownloadString(uriString);

                if (StatusCode == HttpStatusCode.NoContent)

                    return String.Empty;

                return content;

            }, actualRetries);

            var result = task.Result;

            return result;

        }

        public void Head(string address,int retries=0)

        {

            AllowedStatusCodes.Add(HttpStatusCode.NotFound);

            RetryWithoutContent(address, retries, "HEAD");

        }

        public void PutWithRetry(string address, int retries = 0)

        {

            RetryWithoutContent(address, retries, "PUT");

        }

        public void DeleteWithRetry(string address,int retries=0)

        {

            RetryWithoutContent(address, retries, "DELETE");

        }

        public string GetHeaderValue(string headerName,bool optional=false)

        {

            if (this.ResponseHeaders==null)

                throw new InvalidOperationException("ResponseHeaders are null");

            Contract.EndContractBlock();

            var values=this.ResponseHeaders.GetValues(headerName);

            if (values != null)

                return values[0];

            if (optional)            

                return null;            

            //A required header was not found

            throw new WebException(String.Format("The {0}  header is missing", headerName));

        }

        public void SetNonEmptyHeaderValue(string headerName, string value)

        {

            if (String.IsNullOrWhiteSpace(value))

                return;

            Headers.Add(headerName,value);

        }

        private void RetryWithoutContent(string address, int retries, string method)

        {

            if (address == null)

                throw new ArgumentNullException("address");

            var actualAddress = GetActualAddress(address);            

            var actualRetries = (retries == 0) ? Retries : retries;

            var task = Retry(() =>

            {

                var uriString = String.Join("/",BaseAddress ,actualAddress);

                var uri = new Uri(uriString);

                var request =  GetWebRequest(uri);

                request.Method = method;

                if (ResponseHeaders!=null)

                    ResponseHeaders.Clear();

                TraceStart(method, uriString);

                if (method == "PUT")

                    request.ContentLength = 0;

                var response = (HttpWebResponse)GetWebResponse(request);

                StatusCode = response.StatusCode;

                StatusDescription = response.StatusDescription;                

                return 0;

            }, actualRetries);

            try

            {

                task.Wait();

            }

            catch (AggregateException ex)

            {

                var exc = ex.InnerException;

                if (exc is RetryException)

                {

                    Log.ErrorFormat("[{0}] RETRY FAILED for {1} after {2} retries",method,address,retries);

                }

                else

                {

                    Log.ErrorFormat("[{0}] FAILED for {1} with \n{2}", method, address, exc);

                }

                throw exc;

            }

            catch(Exception ex)

            {

                Log.ErrorFormat("[{0}] FAILED for {1} with \n{2}", method, address, ex);

                throw;

            }

        }

        private static void TraceStart(string method, string actualAddress)

        {

            Log.InfoFormat("[{0}] {1} {2}", method, DateTime.Now, actualAddress);

        }

        private string GetActualAddress(string address)

        {

            if (Parameters.Count == 0)

                return address;

            var addressBuilder=new StringBuilder(address);            

            bool isFirst = true;

            foreach (var parameter in Parameters)

            {

                if(isFirst)

                    addressBuilder.AppendFormat("?{0}={1}", parameter.Key, parameter.Value);

                else

                    addressBuilder.AppendFormat("&{0}={1}", parameter.Key, parameter.Value);

                isFirst = false;

            }

            return addressBuilder.ToString();

        }

        public string DownloadStringWithRetry(Uri address,int retries=0)

        {

            if (address == null)

                throw new ArgumentNullException("address");

            var actualRetries = (retries == 0) ? Retries : retries;            

            var task = Retry(() =>

            {

                var content = base.DownloadString(address);

                if (StatusCode == HttpStatusCode.NoContent)

                    return String.Empty;

                return content;

            }, actualRetries);

            var result = task.Result;

            return result;

        }

        /// <summary>

        /// Copies headers from another RestClient

        /// </summary>

        /// <param name="source">The RestClient from which the headers are copied</param>

        public void CopyHeaders(RestClient source)

        {

            if (source == null)

                throw new ArgumentNullException("source", "source can't be null");

            Contract.EndContractBlock();

            //The Headers getter initializes the property, it is never null

            Contract.Assume(Headers!=null);

            CopyHeaders(source.Headers,Headers);

        }

        /// <summary>

        /// Copies headers from one header collection to another

        /// </summary>

        /// <param name="source">The source collection from which the headers are copied</param>

        /// <param name="target">The target collection to which the headers are copied</param>

        public static void CopyHeaders(WebHeaderCollection source,WebHeaderCollection target)

        {

            if (source == null)

                throw new ArgumentNullException("source", "source can't be null");

            if (target == null)

                throw new ArgumentNullException("target", "target can't be null");

            Contract.EndContractBlock();

            for (int i = 0; i < source.Count; i++)

            {

                target.Add(source.GetKey(i), source[i]);

            }            

        }

        public void AssertStatusOK(string message)

        {

            if (StatusCode >= HttpStatusCode.BadRequest)

                throw new WebException(String.Format("{0} with code {1} - {2}", message, StatusCode, StatusDescription));

        }

        private Task<T> Retry<T>(Func<T> original, int retryCount, TaskCompletionSource<T> tcs = null)

        {

            if (original==null)

                throw new ArgumentNullException("original");

            Contract.EndContractBlock();

            if (tcs == null)

                tcs = new TaskCompletionSource<T>();

            Task.Factory.StartNew(original).ContinueWith(_original =>

                {

                    if (!_original.IsFaulted)

                        tcs.SetFromTask(_original);

                    else 

                    {

                        var e = _original.Exception.InnerException;

                        var we = (e as WebException);

                        if (we==null)

                            tcs.SetException(e);

                        else

                        {

                            var statusCode = GetStatusCode(we);

                            //Return null for 404

                            if (statusCode == HttpStatusCode.NotFound)

                                tcs.SetResult(default(T));

                            //Retry for timeouts and service unavailable

                            else if (we.Status == WebExceptionStatus.Timeout ||

                                (we.Status == WebExceptionStatus.ProtocolError && statusCode == HttpStatusCode.ServiceUnavailable))

                            {

                                TimedOut = true;

                                if (retryCount == 0)

                                {                                    

                                    Log.ErrorFormat("[ERROR] Timed out too many times. \n{0}\n",e);

                                    tcs.SetException(new RetryException("Timed out too many times.", e));                                    

                                }

                                else

                                {

                                    Log.ErrorFormat(

                                        "[RETRY] Timed out after {0} ms. Will retry {1} more times\n{2}", Timeout,

                                        retryCount, e);

                                    Retry(original, retryCount - 1, tcs);

                                }

                            }

                            else

                                tcs.SetException(e);

                        }

                    };

                });

            return tcs.Task;

        }

        private HttpStatusCode GetStatusCode(WebException we)

        {

            if (we==null)

                throw new ArgumentNullException("we");

            var statusCode = HttpStatusCode.RequestTimeout;

            if (we.Response != null)

            {

                statusCode = ((HttpWebResponse) we.Response).StatusCode;

                this.StatusCode = statusCode;

            }

            return statusCode;

        }

        public UriBuilder GetAddressBuilder(string container, string objectName)

        {

            var builder = new UriBuilder(String.Join("/", BaseAddress, container, objectName));

            return builder;

        }

        public Dictionary<string, string> GetMeta(string metaPrefix)

        {

            if (String.IsNullOrWhiteSpace(metaPrefix))

                throw new ArgumentNullException("metaPrefix");

            Contract.EndContractBlock();

            var keys = ResponseHeaders.AllKeys.AsQueryable();

            var dict = (from key in keys

                        where key.StartsWith(metaPrefix)

                        let name = key.Substring(metaPrefix.Length)

                        select new { Name = name, Value = ResponseHeaders[key] })

                        .ToDictionary(t => t.Name, t => t.Value);

            return dict;

        }

    }

    public class RetryException:Exception

    {

        public RetryException()

            :base()

        {

        }

        public RetryException(string message)

            :base(message)

        {

        }

        public RetryException(string message,Exception innerException)

            :base(message,innerException)

        {

        }

        public RetryException(SerializationInfo info,StreamingContext context)

            :base(info,context)

        {

        }

    }

}