fix: multipart/mixed and multipart/form-data interpolation and generic request behaviour (#8087)

* fix: multipart spec additions and interpolation fixes

* test(cli): add interpolation multipart  tests

* Update packages/bruno-tests/collection/multipart/multipart-mixed-form-data-parse.bru

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

* chore: remove assert as curl also gives the same result

* chore: codestyle

---------

Co-authored-by: coderabbitai[bot] <136622811+coderabbitai[bot]@users.noreply.github.com>

packages/bruno-cli/src/runner/interpolate-vars.js

@@ -102,7 +102,9 @@ const interpolateVars = (request, envVariables = {}, runtimeVariables = {}, proc
         }));
       }
     } else if (contentType.startsWith('multipart/')) {
-      if (Array.isArray(request?.data) && !isFormData(request.data)) {
+      if (request?.data && typeof request.data === 'string') {
+        request.data = _interpolate(request.data);
+      } else if (Array.isArray(request?.data) && !isFormData(request.data)) {
         try {
           request.data = request?.data?.map((d) => ({
             ...d,

packages/bruno-cli/src/runner/run-single-request.js

@@ -487,7 +487,7 @@ const runSingleRequest = async function (
 
     const contentType = contentTypeHeader ? request.headers[contentTypeHeader] : '';
     if (typeof contentType === 'string' && contentType.startsWith('multipart/')) {
-      if (!isFormData(request?.data)) {
+      if (typeof request.data !== 'string' && !isFormData(request?.data)) {
         request._originalMultipartData = request.data;
         request.collectionPath = collectionPath;
         let form = createFormData(request.data, collectionPath);

packages/bruno-cli/tests/runner/interpolate-vars.spec.js

@@ -18,6 +18,58 @@ describe('interpolate-vars: interpolateVars', () => {
     const result = interpolateVars(request, { shouldNotApply: 'value' }, null, null);
     expect(result.data).toBe(streamPayload);
   });
+
+  it('preserves raw string body when Content-Type is multipart/mixed', () => {
+    const rawMultipartBody = [
+      '--TestBoundary123',
+      'Content-Type: application/json',
+      '',
+      '{"test": true}',
+      '--TestBoundary123--',
+      ''
+    ].join('\r\n');
+
+    const request = {
+      method: 'POST',
+      mode: 'text',
+      url: 'https://httpbin.dev/post',
+      headers: { 'content-type': 'multipart/mixed; boundary=TestBoundary123' },
+      data: rawMultipartBody
+    };
+
+    const result = interpolateVars(request, {}, null, null);
+    expect(result.data).toBe(rawMultipartBody);
+  });
+
+  it('interpolates variables in raw multipart/mixed string body', () => {
+    const boundary = 'CustomBoundary123';
+    const rawMultipartBody = [
+      `--${boundary}`,
+      'Content-Type: text/plain',
+      '',
+      'Token: {{token}}',
+      `--${boundary}`,
+      'Content-Type: application/json',
+      '',
+      '{"id": "{{id}}", "msg": "{{msg}}"}',
+      `--${boundary}--`,
+      ''
+    ].join('\r\n');
+
+    const request = {
+      method: 'POST',
+      mode: 'text',
+      url: 'https://api.example/send',
+      headers: { 'content-type': `multipart/mixed; boundary=${boundary}` },
+      data: rawMultipartBody
+    };
+
+    const result = interpolateVars(request, { token: 'abc123', id: 42, msg: 'hello' }, null, null);
+    expect(result.data).toContain('Token: abc123');
+    expect(result.data).toContain('{"id": "42", "msg": "hello"}');
+    expect(result.data).toContain(`--${boundary}`);
+    expect(result.data).toContain(`--${boundary}--`);
+  });
 });
 
 describe('interpolate-vars: api key header name sidecar', () => {