fix: implicit accept header can be overridden by format query

packages/verified-fetch/src/utils/select-output-type.ts

@@ -55,6 +55,7 @@ const CID_TYPE_MAP: Record<number, string[]> = {
     'application/octet-stream',
     'application/vnd.ipld.raw',
     'application/vnd.ipfs.ipns-record',
+    'application/vnd.ipld.dag-json',
     'application/vnd.ipld.car',
     'application/x-tar'
   ]
@@ -145,7 +146,7 @@ function parseQFactor (str?: string): number {
   return factor
 }
 
-const FORMAT_TO_MIME_TYPE: Record<RequestFormatShorthand, string> = {
+export const FORMAT_TO_MIME_TYPE: Record<RequestFormatShorthand, string> = {
   raw: 'application/vnd.ipld.raw',
   car: 'application/vnd.ipld.car',
   'dag-json': 'application/vnd.ipld.dag-json',

packages/verified-fetch/src/verified-fetch.ts

@@ -25,7 +25,7 @@ import { tarStream } from './utils/get-tar-stream.js'
 import { parseResource } from './utils/parse-resource.js'
 import { setCacheControlHeader } from './utils/response-headers.js'
 import { badRequestResponse, movedPermanentlyResponse, notAcceptableResponse, notSupportedResponse, okResponse, badRangeResponse, okRangeResponse, badGatewayResponse } from './utils/responses.js'
-import { selectOutputType, queryFormatToAcceptHeader } from './utils/select-output-type.js'
+import { selectOutputType, queryFormatToAcceptHeader, FORMAT_TO_MIME_TYPE } from './utils/select-output-type.js'
 import { walkPath } from './utils/walk-path.js'
 import type { CIDDetail, ContentTypeParser, Resource, VerifiedFetchInit as VerifiedFetchOptions } from './index.js'
 import type { RequestFormatShorthand } from './types.js'
@@ -512,7 +512,16 @@ export class VerifiedFetch {
       this.log('incoming query format "%s", mapped to %s', query.format, queryFormatMapping)
     }
 
-    const acceptHeader = incomingAcceptHeader ?? queryFormatMapping
+    let acceptHeader: string | undefined
+    // if the incomingAcceptHeader is autogenerated by the requesting client (browser/curl/fetch/etc) then we may need to override it if query.format is specified
+    if (queryFormatMapping != null && (incomingAcceptHeader == null || !Object.values(FORMAT_TO_MIME_TYPE).includes(incomingAcceptHeader))) {
+      this.log('accept header not recognized, but query format provided, setting accept header to %s', queryFormatMapping)
+      acceptHeader = queryFormatMapping
+    } else {
+      acceptHeader = incomingAcceptHeader ?? queryFormatMapping
+    }
+    this.log('determined accept header "%s"', acceptHeader)
+
     const accept = selectOutputType(cid, acceptHeader)
     this.log('output type %s', accept)
 

packages/verified-fetch/test/verified-fetch.spec.ts

@@ -710,4 +710,62 @@ describe('@helia/verifed-fetch', () => {
       expect(output).to.deep.equal(obj)
     })
   })
+
+  describe('?format', () => {
+    let helia: Helia
+    let verifiedFetch: VerifiedFetch
+    let contentTypeParser: Sinon.SinonStub
+
+    beforeEach(async () => {
+      contentTypeParser = Sinon.stub()
+      helia = await createHelia()
+      verifiedFetch = new VerifiedFetch({
+        helia
+      }, {
+        contentTypeParser
+      })
+    })
+
+    afterEach(async () => {
+      await stop(helia, verifiedFetch)
+    })
+
+    it('cbor?format=dag-json should be able to override curl/browser default accept header when query parameter is provided', async () => {
+      const obj = {
+        hello: 'world'
+      }
+      const c = dagCbor(helia)
+      const cid = await c.add(obj)
+
+      const resp = await verifiedFetch.fetch(`http://example.com/ipfs/${cid}?format=dag-json`, {
+        headers: {
+          // see https://github.com/ipfs/helia-verified-fetch/issues/35
+          // accept: '*/*'
+        }
+      })
+      expect(resp.headers.get('content-type')).to.equal('application/vnd.ipld.dag-json')
+      const data = ipldDagJson.decode(await resp.arrayBuffer())
+      expect(data).to.deep.equal(obj)
+    })
+
+    it('raw?format=dag-json should be able to override curl/browser default accept header when query parameter is provided', async () => {
+      const finalRootFileContent = uint8ArrayFromString(JSON.stringify({
+        hello: 'world'
+      }))
+      const cid = CID.createV1(raw.code, await sha256.digest(finalRootFileContent))
+      await helia.blockstore.put(cid, finalRootFileContent)
+
+      const resp = await verifiedFetch.fetch(`http://example.com/ipfs/${cid}?format=dag-json`, {
+        headers: {
+          // see https://github.com/ipfs/helia-verified-fetch/issues/35
+          accept: '*/*'
+        }
+      })
+      expect(resp).to.be.ok()
+      expect(resp.status).to.equal(200)
+      expect(resp.statusText).to.equal('OK')
+      const data = await resp.arrayBuffer()
+      expect(new Uint8Array(data)).to.equalBytes(finalRootFileContent)
+    })
+  })
 })