diff --git a/packages/grpc-js/src/call-stream.ts b/packages/grpc-js/src/call-stream.ts
index c987d9320..7c06c335c 100644
--- a/packages/grpc-js/src/call-stream.ts
+++ b/packages/grpc-js/src/call-stream.ts
@@ -26,6 +26,7 @@ import {Filter} from './filter';
 import {FilterStackFactory} from './filter-stack';
 import {Metadata} from './metadata';
 import {ObjectDuplex, WriteCallback} from './object-stream';
+import {StreamDecoder} from './stream-decoder';
 
 const {HTTP2_HEADER_STATUS, HTTP2_HEADER_CONTENT_TYPE, NGHTTP2_CANCEL} =
     http2.constants;
@@ -77,12 +78,6 @@ export type Call = {
     EmitterAugmentation1<'status', StatusObject>&
     ObjectDuplex<WriteObject, Buffer>;
 
-enum ReadState {
-  NO_DATA,
-  READING_SIZE,
-  READING_MESSAGE
-}
-
 export class Http2CallStream extends Duplex implements Call {
   credentials: CallCredentials = CallCredentials.createEmpty();
   filterStack: Filter;
@@ -92,13 +87,7 @@ export class Http2CallStream extends Duplex implements Call {
   private pendingWriteCallback: WriteCallback|null = null;
   private pendingFinalCallback: Function|null = null;
 
-  private readState: ReadState = ReadState.NO_DATA;
-  private readCompressFlag: Buffer = Buffer.alloc(1);
-  private readPartialSize: Buffer = Buffer.alloc(4);
-  private readSizeRemaining = 4;
-  private readMessageSize = 0;
-  private readPartialMessage: Buffer[] = [];
-  private readMessageRemaining = 0;
+  private decoder = new StreamDecoder();
 
   private isReadFilterPending = false;
   private canPush = false;
@@ -292,62 +281,10 @@ export class Http2CallStream extends Duplex implements Call {
       });
       stream.on('trailers', this.handleTrailers.bind(this));
       stream.on('data', (data: Buffer) => {
-        let readHead = 0;
-        let toRead: number;
-        while (readHead < data.length) {
-          switch (this.readState) {
-            case ReadState.NO_DATA:
-              this.readCompressFlag = data.slice(readHead, readHead + 1);
-              readHead += 1;
-              this.readState = ReadState.READING_SIZE;
-              this.readPartialSize.fill(0);
-              this.readSizeRemaining = 4;
-              this.readMessageSize = 0;
-              this.readMessageRemaining = 0;
-              this.readPartialMessage = [];
-              break;
-            case ReadState.READING_SIZE:
-              toRead = Math.min(data.length - readHead, this.readSizeRemaining);
-              data.copy(
-                  this.readPartialSize, 4 - this.readSizeRemaining, readHead,
-                  readHead + toRead);
-              this.readSizeRemaining -= toRead;
-              readHead += toRead;
-              // readSizeRemaining >=0 here
-              if (this.readSizeRemaining === 0) {
-                this.readMessageSize = this.readPartialSize.readUInt32BE(0);
-                this.readMessageRemaining = this.readMessageSize;
-                if (this.readMessageRemaining > 0) {
-                  this.readState = ReadState.READING_MESSAGE;
-                } else {
-                  this.tryPush(Buffer.concat(
-                      [this.readCompressFlag, this.readPartialSize]));
-                  this.readState = ReadState.NO_DATA;
-                }
-              }
-              break;
-            case ReadState.READING_MESSAGE:
-              toRead =
-                  Math.min(data.length - readHead, this.readMessageRemaining);
-              this.readPartialMessage.push(
-                  data.slice(readHead, readHead + toRead));
-              this.readMessageRemaining -= toRead;
-              readHead += toRead;
-              // readMessageRemaining >=0 here
-              if (this.readMessageRemaining === 0) {
-                // At this point, we have read a full message
-                const framedMessageBuffers = [
-                  this.readCompressFlag, this.readPartialSize
-                ].concat(this.readPartialMessage);
-                const framedMessage = Buffer.concat(
-                    framedMessageBuffers, this.readMessageSize + 5);
-                this.tryPush(framedMessage);
-                this.readState = ReadState.NO_DATA;
-              }
-              break;
-            default:
-              throw new Error('This should never happen');
-          }
+        const message = this.decoder.write(data);
+
+        if (message !== null) {
+          this.tryPush(message);
         }
       });
       stream.on('end', () => {
diff --git a/packages/grpc-js/src/stream-decoder.ts b/packages/grpc-js/src/stream-decoder.ts
new file mode 100644
index 000000000..3a8e91aec
--- /dev/null
+++ b/packages/grpc-js/src/stream-decoder.ts
@@ -0,0 +1,98 @@
+/*
+ * Copyright 2019 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+enum ReadState {
+  NO_DATA,
+  READING_SIZE,
+  READING_MESSAGE
+}
+
+
+export class StreamDecoder {
+  private readState: ReadState = ReadState.NO_DATA;
+  private readCompressFlag: Buffer = Buffer.alloc(1);
+  private readPartialSize: Buffer = Buffer.alloc(4);
+  private readSizeRemaining = 4;
+  private readMessageSize = 0;
+  private readPartialMessage: Buffer[] = [];
+  private readMessageRemaining = 0;
+
+
+  write(data: Buffer): Buffer|null {
+    let readHead = 0;
+    let toRead: number;
+
+    while (readHead < data.length) {
+      switch (this.readState) {
+        case ReadState.NO_DATA:
+          this.readCompressFlag = data.slice(readHead, readHead + 1);
+          readHead += 1;
+          this.readState = ReadState.READING_SIZE;
+          this.readPartialSize.fill(0);
+          this.readSizeRemaining = 4;
+          this.readMessageSize = 0;
+          this.readMessageRemaining = 0;
+          this.readPartialMessage = [];
+          break;
+        case ReadState.READING_SIZE:
+          toRead = Math.min(data.length - readHead, this.readSizeRemaining);
+          data.copy(
+              this.readPartialSize, 4 - this.readSizeRemaining, readHead,
+              readHead + toRead);
+          this.readSizeRemaining -= toRead;
+          readHead += toRead;
+          // readSizeRemaining >=0 here
+          if (this.readSizeRemaining === 0) {
+            this.readMessageSize = this.readPartialSize.readUInt32BE(0);
+            this.readMessageRemaining = this.readMessageSize;
+            if (this.readMessageRemaining > 0) {
+              this.readState = ReadState.READING_MESSAGE;
+            } else {
+              const message = Buffer.concat(
+                  [this.readCompressFlag, this.readPartialSize], 5);
+
+              this.readState = ReadState.NO_DATA;
+              return message;
+            }
+          }
+          break;
+        case ReadState.READING_MESSAGE:
+          toRead = Math.min(data.length - readHead, this.readMessageRemaining);
+          this.readPartialMessage.push(data.slice(readHead, readHead + toRead));
+          this.readMessageRemaining -= toRead;
+          readHead += toRead;
+          // readMessageRemaining >=0 here
+          if (this.readMessageRemaining === 0) {
+            // At this point, we have read a full message
+            const framedMessageBuffers = [
+              this.readCompressFlag, this.readPartialSize
+            ].concat(this.readPartialMessage);
+            const framedMessage =
+                Buffer.concat(framedMessageBuffers, this.readMessageSize + 5);
+
+            this.readState = ReadState.NO_DATA;
+            return framedMessage;
+          }
+          break;
+        default:
+          throw new Error('Unexpected read state');
+      }
+    }
+
+    return null;
+  }
+}