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Allow FormData to be passed as input to AI bindings #5590

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18 changes: 14 additions & 4 deletions src/cloudflare/internal/ai-api.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -42,7 +42,7 @@ export type AiOptions = {
};

export type AiInputReadableStream = {
body: ReadableStream;
body: ReadableStream | FormData;
contentType: string;
};

Expand Down Expand Up @@ -87,7 +87,6 @@ export class AiInternalError extends Error {
}
}

// TODO: merge this function with the one with images-api.ts
function isReadableStream(obj: unknown): obj is ReadableStream {
return !!(
obj &&
Expand All @@ -97,6 +96,17 @@ function isReadableStream(obj: unknown): obj is ReadableStream {
);
}

function isFormData(obj: unknown): obj is FormData {
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@JoaquinGimenez1 JoaquinGimenez1 Nov 26, 2025

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Why not use something like this?

function isFormData(obj: unknown): obj is FormData {
  return obj instanceof FormData;
}

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@thatsKevinJain thatsKevinJain Nov 26, 2025 •
edited
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"instanceof" depends on how the object was constructed and can fail to work sometimes.

Referring to the SO article here:
https://stackoverflow.com/a/47204039

Screenshot 2025-11-26 at 9 28 31 AM

The approach used in PR above looks verbose, but it is trying to check if some specific functions of FormData object are present as well.

This is similar to how we check for readable streams:
https://github.com/cloudflare/workerd/pull/5590/files#diff-2fe1e717c62f1145cade283ccc2dabf84edd49d4517103ddc75171c17e5e710fR90

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@JoaquinGimenez1 JoaquinGimenez1 Nov 26, 2025

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If we are saying that we accept FormData then the users should build the object as a FormData and not a random object with append and entries methods. This means that the following object will pass the validation

const fakeFormData = {
  append(key: string, value: string) {
    console.log(`Appending ${key}: ${value}`);
  },
  entries() {
    return [['key1', 'value1']];
  }
};

On a side note: I also don't agree how we check for readable streams either

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@thatsKevinJain thatsKevinJain Nov 26, 2025

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@danlapid Do you have ideas on what can be right approach here?

return !!(
obj &&
typeof obj === 'object' &&
'append' in obj &&
typeof obj.append === 'function' &&
'entries' in obj &&
typeof obj.entries === 'function'
);
}

/**
* Find keys in inputs that have a ReadableStream
* */
Expand All @@ -111,9 +121,9 @@ function findReadableStreamKeys(
value &&
typeof value === 'object' &&
'body' in value &&
isReadableStream(value.body);
(isReadableStream(value.body) || isFormData(value.body));

if (hasReadableStreamBody || isReadableStream(value)) {
if (hasReadableStreamBody || isReadableStream(value) || isFormData(value)) {
readableStreamKeys.push(key);
}
}
Expand Down
19 changes: 19 additions & 0 deletions src/cloudflare/internal/test/ai/ai-api-test.js
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Expand Up @@ -214,6 +214,25 @@ export const tests = {
);
}

{
// Test form data input
const form = new FormData();
form.append('prompt', 'cat');
const resp = await env.ai.run('formDataInputs', {
audio: {
body: form,
contentType: 'multipart/form-data',
},
});

assert.deepStrictEqual(resp, {
inputs: {},
options: { userInputs: '{}', version: '3' },
requestUrl:
'https://workers-binding.ai/run?version=3&userInputs=%7B%7D',
});
}

{
// Test gateway option
const resp = await env.ai.run(
Expand Down
13 changes: 13 additions & 0 deletions src/cloudflare/internal/test/ai/ai-mock.js
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Original file line number Diff line number Diff line change
Expand Up @@ -97,6 +97,19 @@ export default {
);
}

if (modelName === 'formDataInputs') {
return Response.json(
{
inputs: {},
options: { ...data.options },
requestUrl: request.url,
},
{
headers: respHeaders,
}
);
}

if (modelName === 'inputErrorModel') {
return Response.json(
{
Expand Down
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