List missing parcels

Bindle.Tests/Integration.cs

@@ -129,5 +129,14 @@ public async Task CanCreateParcel()
             var fetched = await client.GetParcel("mybindle/0.1.0", "460d5965e4d1909e8c7a3748a414956b7038ab5fd79937c9fcb2b214e6b0160a");
             Assert.Equal("The front fell off", await fetched.ReadAsStringAsync());
         }
+
+        [Fact]
+        public async Task CanListMissingParcels()
+        {
+            var client = new BindleClient(DEMO_SERVER_URL);
+            var missing = await client.ListMissingParcels("mybindle/0.3.0");
+            Assert.Contains(missing, (label) => label.Sha256 == "e1706ab0a39ac88094b6d54a3f5cdba41fe5a901");
+            Assert.DoesNotContain(missing, (label) => label.Sha256 == "f7f3b33707fb76d208f5839a40e770452dcf9f348bfd7faf2c524e0fa6710ed6");
+        }
     }
 }

Bindle/BindleClient.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Net;
@@ -18,6 +19,9 @@ string baseUri
         }
 
         private const string INVOICE_PATH = "_i";
+        private const string QUERY_PATH = "_q";
+        private const string RELATIONSHIP_PATH = "_r";
+
         private readonly Uri _baseUri;
 
         public async Task<Invoice> GetInvoice(string invoiceId, GetInvoiceOptions options = GetInvoiceOptions.None)
@@ -113,6 +117,23 @@ public async Task CreateParcel(string invoiceId, string parcelId, HttpContent co
             await httpClient.PostAsync(uri, content);
         }
 
+        public async Task<IEnumerable<Label>> ListMissingParcels(string invoiceId)
+        {
+            var httpClient = new HttpClient();
+            var uri = new Uri(_baseUri, $"{RELATIONSHIP_PATH}/missing/{invoiceId}");
+            var response = await httpClient.GetAsync(uri);
+            if (response == null)
+            {
+                throw new Exception("No response from Bindle server");
+            }
+            if (response.StatusCode != HttpStatusCode.OK)
+            {
+                throw new System.Net.WebException($"Bindle server returned status code {response.StatusCode}");
+            }
+            var toml = await ReadResponseToml(response);
+            return Parser.ParseMissingLabels(toml);
+        }
+
         private static string SlashSafe(string uri)
         {
             if (uri.EndsWith('/'))

Bindle/Parser.cs

@@ -137,6 +137,11 @@ internal static CreateInvoiceResult ParseCreateInvoiceResult(TomlTable toml)
             var missingParcels = (toml.TryGetTomlTables("missing") ?? new TomlTable[0]).Select(ParseLabel);
             return new CreateInvoiceResult(invoice, missingParcels);
         }
+
+        internal static IEnumerable<Label> ParseMissingLabels(TomlTable toml)
+        {
+            return (toml.TryGetTomlTables("missing") ?? new TomlTable[0]).Select(ParseLabel);
+        }
     }
 
     internal static class TomlHelpers