#740 bug: extra space in header values

Test/Flurl.Test/Http/PostTests.cs

@@ -1,4 +1,5 @@
 using System.Net.Http;
+using System.Net.Http.Headers;
 using System.Threading.Tasks;
 using Flurl.Http;
 using NUnit.Framework;
@@ -75,6 +76,15 @@ public async Task can_receive_string() {
 			Assert.AreEqual("good job", data);
 		}
 
+		[Test] // #740
+		public async Task doesnt_add_space_in_content_type_header() {
+			var req = new FlurlRequest("https://fake.com");
+			await req.WithHeader("Content-Type", "application/octet-stream;some=b").PostStringAsync("hello");
+
+			Assert.IsTrue(req.Headers.TryGetFirst("Content-Type", out var val));
+			Assert.AreEqual("application/octet-stream;some=b", val);
+		}
+
 		private class TestData
 		{
 			public int id { get; set; }

src/Flurl.Http/FlurlClient.cs

@@ -147,16 +147,21 @@ public async Task<IFlurlResponse> SendAsync(IFlurlRequest request, HttpCompletio
 
 		private void SyncHeaders(IFlurlRequest req, HttpRequestMessage reqMsg) {
 			// copy any client-level (default) headers to FlurlRequest
-			foreach (var header in this.Headers.Where(h => !req.Headers.Contains(h.Name)).ToList())
-				req.Headers.Add(header.Name, header.Value);
+			foreach (var header in this.Headers.ToList()) {
+				if (!req.Headers.Contains(header.Name))
+					req.Headers.Add(header.Name, header.Value);
+			}
 
 			// copy headers from FlurlRequest to HttpRequestMessage
 			foreach (var header in req.Headers)
 				reqMsg.SetHeader(header.Name, header.Value.Trim(), false);
 
+			if (reqMsg.Content == null)
+				return;
+
 			// copy headers from HttpContent to FlurlRequest
-			if (reqMsg.Content != null) {
-				foreach (var header in reqMsg.Content.Headers)
+			foreach (var header in reqMsg.Content.Headers.ToList()) {
+				if (!req.Headers.Contains(header.Key))
 					req.Headers.AddOrReplace(header.Key, string.Join(",", header.Value));
 			}
 		}