Respect image model JSON capability

js/polliLib/src/image.js

@@ -1,5 +1,15 @@
 import { getDefaultClient } from './client.js';
 
+function modelSupportsJson(info) {
+  if (!info || typeof info !== 'object') return false;
+  if (info.json === true) return true;
+  const fields = [info.output, info.outputs, info.formats, info.format];
+  for (const f of fields) {
+    if (Array.isArray(f) && f.some(v => String(v).toLowerCase() === 'json')) return true;
+  }
+  return false;
+}
+
 const bool = v => (v == null ? undefined : (v ? 'true' : 'false'));
 const sleep = ms => new Promise(res => setTimeout(res, ms));
 
@@ -19,17 +29,29 @@ export async function image(prompt, {
   if (enhance != null) params.enhance = bool(enhance);
   if (safe != null) params.safe = bool(safe);
   if (referrer) params.referrer = referrer;
-  if (json) params.json = 'true';
 
-  const headers = json ? { Accept: 'application/json' } : {};
+  let expectJson = false;
+  const headers = {};
+  if (json && model) {
+    try {
+      const models = await imageModels(client);
+      if (modelSupportsJson(models?.[model])) {
+        params.json = 'true';
+        headers.Accept = 'application/json';
+        expectJson = true;
+      }
+    } catch {
+      // ignore capability errors and fall back to blob response
+    }
+  }
 
   const r = await client.get(url, { params, headers });
   if (!r.ok) throw new Error(`image error ${r.status}`);
 
   const ct = r.headers.get('content-type') ?? '';
   if (ct.includes('application/json')) {
     const data = await r.json();
-    if (json) return data;
+    if (expectJson) return data;
     if (data?.url) {
       const ir = await client.get(data.url);
       if (ir.ok) return await ir.blob();

js/polliLib/src/models.js

@@ -2,11 +2,26 @@ import { getDefaultClient } from './client.js';
 import { imageModels } from './image.js';
 import { textModels } from './text.js';
 
+// Return true if a model description indicates JSON support
+export function imageModelSupportsJson(info) {
+  if (!info || typeof info !== 'object') return false;
+  if (info.json === true) return true;
+  const fields = [info.output, info.outputs, info.formats, info.format];
+  for (const f of fields) {
+    if (Array.isArray(f) && f.some(v => String(v).toLowerCase() === 'json')) return true;
+  }
+  return false;
+}
+
 export async function modelCapabilities(client = getDefaultClient()) {
-  const [image, text] = await Promise.all([
+  const [img, text] = await Promise.all([
     imageModels(client).catch(() => ({})),
     textModels(client).catch(() => ({})),
   ]);
+  const image = {};
+  for (const [name, info] of Object.entries(img ?? {})) {
+    image[name] = { ...(info || {}), json: imageModelSupportsJson(info) };
+  }
   return { image, text, audio: text?.['openai-audio'] ?? {} };
 }
 

tests/pollilib-image-json-capability.mjs

@@ -0,0 +1,42 @@
+import assert from 'assert/strict';
+import { image } from '../js/polliLib/src/image.js';
+import { modelCapabilities } from '../js/polliLib/src/models.js';
+
+const client = {
+  imageBase: 'https://example.com',
+  async get(url, { params, headers } = {}) {
+    if (url.endsWith('/models')) {
+      return {
+        ok: true,
+        headers: { get: () => 'application/json' },
+        async json() { return { foo: { json: true }, bar: {} }; }
+      };
+    }
+    if (params.model === 'foo') {
+      assert.equal(params.json, 'true');
+      assert.equal(headers.Accept, 'application/json');
+      return {
+        ok: true,
+        headers: { get: () => 'application/json' },
+        async json() { return { model: params.model }; }
+      };
+    }
+    assert.equal(params.json, undefined);
+    assert.equal(headers?.Accept, undefined);
+    return {
+      ok: true,
+      headers: { get: () => 'image/png' },
+      async blob() { return { blob: true }; }
+    };
+  }
+};
+
+const caps = await modelCapabilities(client);
+assert.equal(caps.image.foo.json, true);
+assert.equal(caps.image.bar.json, false);
+
+const data = await image('test', { model: 'foo', json: true }, client);
+assert.equal(data.model, 'foo');
+
+const blob = await image('test', { model: 'bar', json: true }, client);
+assert.deepEqual(blob, { blob: true });

tests/pollilib-image-json.mjs

@@ -4,6 +4,14 @@ import { image } from '../js/polliLib/src/image.js';
 const client = {
   imageBase: 'https://example.com',
   async get(url, { params, headers } = {}) {
+    if (url.endsWith('/models')) {
+      return {
+        ok: true,
+        headers: { get: () => 'application/json' },
+        async json() { return { foo: { json: true } }; }
+      };
+    }
+    assert.equal(params.json, 'true');
     assert.equal(headers.Accept, 'application/json');
     return {
       ok: true,