From 4d1de4bb6f4f3dff4272f8c3df5fa0cd76ba58a8 Mon Sep 17 00:00:00 2001
From: Patrick McLaughlin <patrickmclaughlin@bitgo.com>
Date: Tue, 28 Jan 2025 16:52:36 -0500
Subject: [PATCH] fix: deduplicate header parameters

---
 packages/openapi-generator/src/route.ts       | 39 ++++++------
 .../test/openapi/union.test.ts                | 61 +++++++++++++++++++
 2 files changed, 83 insertions(+), 17 deletions(-)

diff --git a/packages/openapi-generator/src/route.ts b/packages/openapi-generator/src/route.ts
index 082d671c..fa7c84bb 100644
--- a/packages/openapi-generator/src/route.ts
+++ b/packages/openapi-generator/src/route.ts
@@ -157,25 +157,30 @@ function parseRequestUnion(
     });
   }
   if (headerSchema.schemas.length > 0) {
-    // For headers in unions, take properties from first schema that has headers
-    // Also not perfect but we cannot use the `explode: true` trick for headers
-    const firstHeaderSchema = schema.schemas.find(
-      (s) => s.type === 'object' && s.properties['headers']?.type === 'object',
-    );
-    if (
-      firstHeaderSchema?.type === 'object' &&
-      firstHeaderSchema.properties['headers']?.type === 'object'
-    ) {
-      const headers = firstHeaderSchema.properties['headers'];
-      for (const [name, prop] of Object.entries(headers.properties)) {
-        parameters.push({
-          type: 'header',
-          name,
-          schema: prop,
-          required: headers.required.includes(name),
-        });
+    // For headers in unions, deduplicate and merge properties from all schemas
+    const headerParams = new Map<string, Parameter>();
+
+    for (const subSchema of schema.schemas) {
+      if (
+        subSchema.type === 'object' &&
+        subSchema.properties['headers']?.type === 'object'
+      ) {
+        const headers = subSchema.properties['headers'];
+        for (const [name, prop] of Object.entries(headers.properties)) {
+          // Only add if not already present
+          if (!headerParams.has(name)) {
+            headerParams.set(name, {
+              type: 'header',
+              name,
+              schema: prop,
+              required: headers.required.includes(name),
+            });
+          }
+        }
       }
     }
+
+    parameters.push(...headerParams.values());
   }
 
   const firstSubSchema = schema.schemas[0];
diff --git a/packages/openapi-generator/test/openapi/union.test.ts b/packages/openapi-generator/test/openapi/union.test.ts
index 443f1b5d..ab03df25 100644
--- a/packages/openapi-generator/test/openapi/union.test.ts
+++ b/packages/openapi-generator/test/openapi/union.test.ts
@@ -375,6 +375,67 @@ testCase("route with unknown unions", ROUTE_WITH_UNKNOWN_UNIONS, {
   },
 });
 
+const ROUTE_WITH_DUPLICATE_HEADERS = `
+import * as t from 'io-ts';
+import * as h from '@api-ts/io-ts-http';
+
+export const route = h.httpRoute({
+  path: '/foo',
+  method: 'GET',
+  request: t.union([
+    h.httpRequest({
+      headers: {
+        'x-foo': t.string,
+        'x-common': t.string,
+      },
+    }),
+    h.httpRequest({
+      headers: {
+        'x-bar': t.number,
+        'x-common': t.string,
+      },
+    }),
+  ]),
+  response: {
+    200: t.string,
+  },
+});
+`;
+
+testCase("route with duplicate headers in request union", ROUTE_WITH_DUPLICATE_HEADERS, {
+  info: {
+    title: 'Test',
+    version: '1.0.0'
+  },
+  openapi: '3.0.3',
+  paths: {
+    '/foo': {
+      get: {
+        parameters: [
+          { in: 'header', name: 'x-foo', required: true, schema: { type: 'string' } },
+          { in: 'header', name: 'x-common', required: true, schema: { type: 'string' } },
+          { in: 'header', name: 'x-bar', required: true, schema: { type: 'number' } },
+        ],
+        responses: {
+          '200': {
+            description: 'OK',
+            content: {
+              'application/json': {
+                schema: {
+                  type: 'string'
+                }
+              }
+            }
+          }
+        }
+      }
+    }
+  },
+  components: {
+    schemas: {}
+  }
+});
+
 const ROUTE_WITH_REQUEST_UNION = `
 import * as t from 'io-ts';
 import * as h from '@api-ts/io-ts-http';