Merge pull request grpc#22743 from JamesNK/jamesnk/metadata-helpers

Add helper methods for getting metadata values

Author: jtattermusch

src/csharp/Grpc.Core.Api/Metadata.cs

@@ -75,7 +75,72 @@ internal Metadata Freeze()
             return this;
         }
 
-        // TODO: add support for access by key
+        /// <summary>
+        /// Gets the last metadata entry with the specified key.
+        /// If there are no matching entries then <c>null</c> is returned.
+        /// </summary>
+        public Entry Get(string key)
+        {
+            for (int i = entries.Count - 1; i >= 0; i--)
+            {
+                if (entries[i].Key == key)
+                {
+                    return entries[i];
+                }
+            }
+
+            return null;
+        }
+
+        /// <summary>
+        /// Gets the string value of the last metadata entry with the specified key.
+        /// If the metadata entry is binary then an exception is thrown.
+        /// If there are no matching entries then <c>null</c> is returned.
+        /// </summary>
+        public string GetValue(string key)
+        {
+            return Get(key)?.Value;
+        }
+
+        /// <summary>
+        /// Gets the bytes value of the last metadata entry with the specified key.
+        /// If the metadata entry is not binary the string value will be returned as ASCII encoded bytes.
+        /// If there are no matching entries then <c>null</c> is returned.
+        /// </summary>
+        public byte[] GetValueBytes(string key)
+        {
+            return Get(key)?.ValueBytes;
+        }
+
+        /// <summary>
+        /// Gets all metadata entries with the specified key.
+        /// </summary>
+        public IEnumerable<Entry> GetAll(string key)
+        {
+            for (int i = 0; i < entries.Count; i++)
+            {
+                if (entries[i].Key == key)
+                {
+                    yield return entries[i];
+                }
+            }
+        }
+
+        /// <summary>
+        /// Adds a new ASCII-valued metadata entry. See <c>Metadata.Entry</c> constructor for params.
+        /// </summary>
+        public void Add(string key, string value)
+        {
+            Add(new Entry(key, value));
+        }
+
+        /// <summary>
+        /// Adds a new binary-valued metadata entry. See <c>Metadata.Entry</c> constructor for params.
+        /// </summary>
+        public void Add(string key, byte[] valueBytes)
+        {
+            Add(new Entry(key, valueBytes));
+        }
 
         #region IList members
 
@@ -135,22 +200,6 @@ public void Add(Metadata.Entry item)
             entries.Add(item);
         }
 
-        /// <summary>
-        /// Adds a new ASCII-valued metadata entry. See <c>Metadata.Entry</c> constructor for params.
-        /// </summary>
-        public void Add(string key, string value)
-        {
-            Add(new Entry(key, value));
-        }
-
-        /// <summary>
-        /// Adds a new binary-valued metadata entry. See <c>Metadata.Entry</c> constructor for params.
-        /// </summary>
-        public void Add(string key, byte[] valueBytes)
-        {
-            Add(new Entry(key, valueBytes));
-        }
-
         /// <summary>
         /// <see cref="T:IList`1"/>
         /// </summary>
@@ -280,6 +329,7 @@ public string Key
 
             /// <summary>
             /// Gets the binary value of this metadata entry.
+            /// If the metadata entry is not binary the string value will be returned as ASCII encoded bytes.
             /// </summary>
             public byte[] ValueBytes
             {
@@ -299,13 +349,14 @@ public byte[] ValueBytes
 
             /// <summary>
             /// Gets the string value of this metadata entry.
+            /// If the metadata entry is binary then an exception is thrown.
             /// </summary>
             public string Value
             {
                 get
                 {
                     GrpcPreconditions.CheckState(!IsBinary, "Cannot access string value of a binary metadata entry");
-                    return value ?? EncodingASCII.GetString(valueBytes);
+                    return value;
                 }
             }
 

src/csharp/Grpc.Core.Tests/MetadataTest.cs

@@ -18,7 +18,9 @@
 
 using System;
 using System.Diagnostics;
+using System.Linq;
 using System.Runtime.InteropServices;
+using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
 using Grpc.Core;
@@ -242,6 +244,110 @@ public void FreezeMakesReadOnly()
             Assert.Throws<InvalidOperationException>(() => metadata.Remove(metadata[0]));
         }
 
+        [Test]
+        public void GetAll()
+        {
+            var metadata = new Metadata
+            {
+                { "abc", "abc-value1" },
+                { "abc", "abc-value2" },
+                { "xyz", "xyz-value1" },
+            };
+
+            var abcEntries = metadata.GetAll("abc").ToList();
+            Assert.AreEqual(2, abcEntries.Count);
+            Assert.AreEqual("abc-value1", abcEntries[0].Value);
+            Assert.AreEqual("abc-value2", abcEntries[1].Value);
+
+            var xyzEntries = metadata.GetAll("xyz").ToList();
+            Assert.AreEqual(1, xyzEntries.Count);
+            Assert.AreEqual("xyz-value1", xyzEntries[0].Value);
+        }
+
+        [Test]
+        public void Get()
+        {
+            var metadata = new Metadata
+            {
+                { "abc", "abc-value1" },
+                { "abc", "abc-value2" },
+                { "xyz", "xyz-value1" },
+            };
+
+            var abcEntry = metadata.Get("abc");
+            Assert.AreEqual("abc-value2", abcEntry.Value);
+
+            var xyzEntry = metadata.Get("xyz");
+            Assert.AreEqual("xyz-value1", xyzEntry.Value);
+
+            var notFound = metadata.Get("not-found");
+            Assert.AreEqual(null, notFound);
+        }
+
+        [Test]
+        public void GetValue()
+        {
+            var metadata = new Metadata
+            {
+                { "abc", "abc-value1" },
+                { "abc", "abc-value2" },
+                { "xyz", "xyz-value1" },
+                { "xyz-bin", Encoding.ASCII.GetBytes("xyz-value1") },
+            };
+
+            var abcValue = metadata.GetValue("abc");
+            Assert.AreEqual("abc-value2", abcValue);
+
+            var xyzValue = metadata.GetValue("xyz");
+            Assert.AreEqual("xyz-value1", xyzValue);
+
+            var notFound = metadata.GetValue("not-found");
+            Assert.AreEqual(null, notFound);
+        }
+
+        [Test]
+        public void GetValue_BytesValue()
+        {
+            var metadata = new Metadata
+            {
+                { "xyz-bin", Encoding.ASCII.GetBytes("xyz-value1") },
+            };
+
+            Assert.Throws<InvalidOperationException>(() => metadata.GetValue("xyz-bin"));
+        }
+
+        [Test]
+        public void GetValueBytes()
+        {
+            var metadata = new Metadata
+            {
+                { "abc-bin", Encoding.ASCII.GetBytes("abc-value1") },
+                { "abc-bin", Encoding.ASCII.GetBytes("abc-value2") },
+                { "xyz-bin", Encoding.ASCII.GetBytes("xyz-value1") },
+            };
+
+            var abcValue = metadata.GetValueBytes("abc-bin");
+            Assert.AreEqual(Encoding.ASCII.GetBytes("abc-value2"), abcValue);
+
+            var xyzValue = metadata.GetValueBytes("xyz-bin");
+            Assert.AreEqual(Encoding.ASCII.GetBytes("xyz-value1"), xyzValue);
+
+            var notFound = metadata.GetValueBytes("not-found");
+            Assert.AreEqual(null, notFound);
+        }
+
+        [Test]
+        public void GetValueBytes_StringValue()
+        {
+            var metadata = new Metadata
+            {
+                { "xyz", "xyz-value1" },
+            };
+
+            var xyzValue = metadata.GetValueBytes("xyz");
+            Assert.AreEqual(Encoding.ASCII.GetBytes("xyz-value1"), xyzValue);
+        }
+
         private Metadata CreateMetadata()
         {
             return new Metadata