diff --git a/package-lock.json b/package-lock.json
index d4bfbe5..7d3ccfc 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -22,6 +22,7 @@
         "eslint-config-prettier": "8.8.0",
         "eslint-plugin-prettier": "4.2.1",
         "husky": "^8.0.3",
+        "lambda-runtime": "file:./src/",
         "mocha": "10.2.0",
         "mock-http-server": "^1.4.5",
         "nyc": "^15.1.0",
@@ -3222,6 +3223,10 @@
         "node": ">=6"
       }
     },
+    "node_modules/lambda-runtime": {
+      "resolved": "src",
+      "link": true
+    },
     "node_modules/levn": {
       "version": "0.4.1",
       "resolved": "https://registry.npmjs.org/levn/-/levn-0.4.1.tgz",
@@ -5275,6 +5280,9 @@
       "funding": {
         "url": "https://github.com/sponsors/sindresorhus"
       }
+    },
+    "src": {
+      "dev": true
     }
   }
 }
diff --git a/package.json b/package.json
index 8a7374b..cfb334d 100644
--- a/package.json
+++ b/package.json
@@ -59,6 +59,7 @@
     "node-gyp": "9.4.0"
   },
   "devDependencies": {
+    "lambda-runtime": "file:./src/",
     "esbuild": "^0.18.3",
     "eslint": "8.42.0",
     "eslint-config-prettier": "8.8.0",
diff --git a/src/RAPIDClient.js b/src/RAPIDClient.js
index 84ce5f3..cf02787 100644
--- a/src/RAPIDClient.js
+++ b/src/RAPIDClient.js
@@ -44,7 +44,7 @@ module.exports = class RAPIDClient {
    */
   postInvocationResponse(response, id, callback) {
     let bodyString = _trySerializeResponse(response);
-    this.nativeClient.done(id, bodyString);
+    this.nativeClient.done(encodeURIComponent(id), bodyString);
     callback();
   }
 
@@ -65,7 +65,10 @@ module.exports = class RAPIDClient {
         hostname: this.hostname,
         method: 'POST',
         port: this.port,
-        path: '/2018-06-01/runtime/invocation/' + id + '/response',
+        path:
+          '/2018-06-01/runtime/invocation/' +
+          encodeURIComponent(id) +
+          '/response',
         highWaterMark: options?.highWaterMark,
       },
     });
@@ -108,7 +111,7 @@ module.exports = class RAPIDClient {
     let response = Errors.toRapidResponse(error);
     let bodyString = _trySerializeResponse(response);
     let xrayString = XRayError.formatted(error);
-    this.nativeClient.error(id, bodyString, xrayString);
+    this.nativeClient.error(encodeURIComponent(id), bodyString, xrayString);
     callback();
   }
 
diff --git a/test/unit/ErrorsTest.js b/test/unit/ErrorsTest.js
index 9c0f9a5..8f88ae6 100644
--- a/test/unit/ErrorsTest.js
+++ b/test/unit/ErrorsTest.js
@@ -5,7 +5,7 @@
 'use strict';
 
 require('should');
-let Errors = require('../../src/Errors');
+let Errors = require('lambda-runtime/Errors');
 
 describe('Formatted Error Logging', () => {
   it('should fall back to a minimal error format when an exception occurs', () => {
diff --git a/test/unit/FakeTelemetryTarget.js b/test/unit/FakeTelemetryTarget.js
index e158dbe..21b38fc 100644
--- a/test/unit/FakeTelemetryTarget.js
+++ b/test/unit/FakeTelemetryTarget.js
@@ -112,6 +112,7 @@ module.exports = class FakeTelemetryTarget {
     if (lineLength === 0) {
       return '';
     }
+
     let lineBytes = Buffer.alloc(lineLength);
     let actualLineSize = fs.readSync(
       this.readTarget,
diff --git a/test/unit/InvokeContextTest.js b/test/unit/InvokeContextTest.js
index 58b35a2..c351b5d 100644
--- a/test/unit/InvokeContextTest.js
+++ b/test/unit/InvokeContextTest.js
@@ -7,7 +7,7 @@
 require('should');
 const sleep = require('util').promisify(setTimeout);
 
-let InvokeContext = require('../../src/InvokeContext');
+let InvokeContext = require('lambda-runtime/InvokeContext');
 
 describe('Getting remaining invoke time', () => {
   it('should reduce by at least elapsed time', async () => {
diff --git a/test/unit/LogPatchTest.js b/test/unit/LogPatchTest.js
index 08c8eca..7a8d2f6 100644
--- a/test/unit/LogPatchTest.js
+++ b/test/unit/LogPatchTest.js
@@ -7,8 +7,8 @@
 const util = require('util');
 
 let should = require('should');
-let LogPatch = require('../../src/LogPatch');
-let Errors = require('../../src/Errors');
+let LogPatch = require('lambda-runtime/LogPatch');
+let Errors = require('lambda-runtime/Errors');
 let assert = require('assert');
 
 let {
diff --git a/test/unit/RAPIDClientTest.js b/test/unit/RAPIDClientTest.js
new file mode 100644
index 0000000..828bd6d
--- /dev/null
+++ b/test/unit/RAPIDClientTest.js
@@ -0,0 +1,117 @@
+/**
+ * Copyright 2024 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+ */
+
+'use strict';
+
+require('should');
+
+let RAPIDClient = require('lambda-runtime/RAPIDClient.js');
+let runtimeErrors = require('lambda-runtime/Errors.js');
+
+/**
+ * Stub request object.
+ * Provides no-op definitions of the request functions used by the rapid client.
+ */
+const noOpRequest = Object.freeze({
+  /* no op, return itself to allow continuations/chaining */
+  on: () => noOpRequest,
+  /* no op, return itself to allow continuations/chaining */
+  end: () => noOpRequest,
+});
+
+class StubHttp {
+  constructor() {
+    this.lastUsedOptions = {};
+    this.Agent = class FakeAgent {};
+  }
+
+  request(options, _callback) {
+    this.lastUsedOptions = options;
+    return noOpRequest;
+  }
+}
+
+class NoOpNativeHttp {
+  constructor() {
+    this.lastRequestId = '';
+    this.lastErrorRequestId = '';
+  }
+
+  done(requestId) {
+    this.lastRequestId = requestId;
+  }
+
+  error(requestId) {
+    this.lastErrorRequestId = requestId;
+  }
+}
+
+class EvilError extends Error {
+  get name() {
+    throw 'gotcha';
+  }
+}
+
+const EXPECTED_ERROR_HEADER = 'Lambda-Runtime-Function-Error-Type';
+
+describe('building error requests with the RAPIDClient', () => {
+  let stubHttp = new StubHttp();
+  let client = new RAPIDClient('notUsed:1337', stubHttp, new NoOpNativeHttp());
+
+  let errors = [
+    [new Error('generic failure'), 'Error'],
+    [new runtimeErrors.ImportModuleError(), 'Runtime.ImportModuleError'],
+    [new runtimeErrors.HandlerNotFound(), 'Runtime.HandlerNotFound'],
+    [new runtimeErrors.MalformedHandlerName(), 'Runtime.MalformedHandlerName'],
+    [new runtimeErrors.UserCodeSyntaxError(), 'Runtime.UserCodeSyntaxError'],
+    [{ data: 'some random object' }, 'object'],
+    [new EvilError(), 'handled'],
+  ];
+
+  describe('the error header in postInitError', () => {
+    errors.forEach(([error, name]) => {
+      it(`should be ${name} for ${error.constructor.name}`, () => {
+        client.postInitError(error);
+        stubHttp.lastUsedOptions.should.have
+          .property('headers')
+          .have.property(EXPECTED_ERROR_HEADER, name);
+      });
+    });
+  });
+});
+
+describe('invalid request id works', () => {
+  const nativeClient = new NoOpNativeHttp();
+  const client = new RAPIDClient('notUsed:1337', undefined, nativeClient);
+
+  [
+    // Encoding expected:
+    ['#', '%23'],
+    ['%', '%25'],
+    ['/', '%2F'],
+    ['?', '%3F'],
+    ['\x7F', '%7F'],
+    ["<script>alert('1')</script>", "%3Cscript%3Ealert('1')%3C%2Fscript%3E"],
+    ['⚡', '%E2%9A%A1'],
+
+    // No encoding:
+    ['.', '.'],
+    ['..', '..'],
+    ['a', 'a'],
+    [
+      '59b22c65-fa81-47fb-a6dc-23028a63566f',
+      '59b22c65-fa81-47fb-a6dc-23028a63566f',
+    ],
+  ].forEach(([requestId, expected]) => {
+    it(`postInvocationResponse should encode requestId: '${requestId}'`, () => {
+      client.postInvocationResponse({}, requestId, () => {});
+      nativeClient.lastRequestId.should.be.equal(expected);
+    });
+
+    it(`postInvocationError should encode requestId: '${requestId}'`, () => {
+      client.postInvocationError(new Error(), requestId, () => {});
+      nativeClient.lastErrorRequestId.should.be.equal(expected);
+    });
+  });
+});
diff --git a/test/unit/ResponseStreamTest.js b/test/unit/ResponseStreamTest.js
index dbfe940..b5d46c2 100644
--- a/test/unit/ResponseStreamTest.js
+++ b/test/unit/ResponseStreamTest.js
@@ -9,10 +9,10 @@ const ServerMock = require('mock-http-server');
 const {
   createResponseStream,
   tryCallFail,
-} = require('../../src/ResponseStream.js');
-const { HttpResponseStream } = require('../../src/HttpResponseStream.js');
-const { InvalidStreamingOperation } = require('../../src/Errors.js');
-const { verbose, vverbose, vvverbose } = require('../../src/VerboseLog').logger(
+} = require('lambda-runtime/ResponseStream.js');
+const { HttpResponseStream } = require('lambda-runtime/HttpResponseStream.js');
+const { InvalidStreamingOperation } = require('lambda-runtime/Errors.js');
+const { verbose, vverbose, vvverbose } = require('lambda-runtime/VerboseLog').logger(
   'TEST',
 );
 const Throttle = require('throttle');
diff --git a/test/unit/StreamingContextTest.js b/test/unit/StreamingContextTest.js
index b9e67a0..833ac8f 100644
--- a/test/unit/StreamingContextTest.js
+++ b/test/unit/StreamingContextTest.js
@@ -5,9 +5,9 @@
 'use strict';
 
 require('should');
-const StreamingContext = require('../../src/StreamingContext.js');
+const StreamingContext = require('lambda-runtime/StreamingContext.js');
 const { PassThrough } = require('stream');
-const BeforeExitListener = require('../../src/BeforeExitListener.js');
+const BeforeExitListener = require('lambda-runtime/BeforeExitListener.js');
 
 class MockRapidClient {
   constructor() {
diff --git a/test/unit/UserFunctionTest.js b/test/unit/UserFunctionTest.js
index cf53b09..6ffe4c0 100644
--- a/test/unit/UserFunctionTest.js
+++ b/test/unit/UserFunctionTest.js
@@ -10,8 +10,8 @@ const {
   HandlerNotFound,
   ImportModuleError,
   MalformedHandlerName,
-} = require('../../src/Errors.js');
-const UserFunction = require('../../src/UserFunction.js');
+} = require('lambda-runtime/Errors.js');
+const UserFunction = require('lambda-runtime/UserFunction.js');
 
 const TEST_ROOT = path.join(__dirname, '../');
 const HANDLERS_ROOT = path.join(TEST_ROOT, 'handlers');