feat: support downloading car files from @helia/verified-fetch

Adds support for the `application/vnd.ipld.car` accept header to
allow downloading CAR files of DAGs.

packages/verified-fetch/package.json

@@ -155,6 +155,7 @@
     "cborg": "^4.0.9",
     "hashlru": "^2.3.0",
     "ipfs-unixfs-exporter": "^13.5.0",
+    "it-to-browser-readablestream": "^2.0.6",
     "multiformats": "^13.1.0",
     "progress-events": "^1.0.0"
   },

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

@@ -1,9 +1,12 @@
+import { car } from '@helia/car'
 import { ipns as heliaIpns, type IPNS } from '@helia/ipns'
 import { dnsJsonOverHttps } from '@helia/ipns/dns-resolvers'
 import { unixfs as heliaUnixFs, type UnixFS as HeliaUnixFs, type UnixFSStats } from '@helia/unixfs'
+import { CarWriter } from '@ipld/car'
 import * as ipldDagCbor from '@ipld/dag-cbor'
 import * as ipldDagJson from '@ipld/dag-json'
 import { code as dagPbCode } from '@ipld/dag-pb'
+import toBrowserReadableStream from 'it-to-browser-readablestream'
 import { code as jsonCode } from 'multiformats/codecs/json'
 import { code as rawCode } from 'multiformats/codecs/raw'
 import { identity } from 'multiformats/hashes/identity'
@@ -157,7 +160,27 @@ export class VerifiedFetch {
    * of the `DAG` referenced by the `CID`.
    */
   private async handleCar ({ cid, path, options }: FetchHandlerFunctionArg): Promise<Response> {
-    return notSupportedResponse('vnd.ipld.car support is not implemented')
+    const c = car(this.helia)
+    const { writer, out } = CarWriter.create(cid)
+
+    const stream = toBrowserReadableStream<Uint8Array>(async function * () {
+      yield * out
+    }())
+
+    // write the DAG behind `cid` into the writer
+    c.export(cid, writer, options)
+      .catch(err => {
+        this.log.error('could not write car', err)
+        stream.cancel(err)
+          .catch(err => {
+            this.log.error('could not cancel stream after car export error', err)
+          })
+      })
+
+    const response = okResponse(stream)
+    response.headers.set('content-type', 'application/vnd.ipld.car; version=1')
+
+    return response
   }
 
   /**

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

@@ -1,4 +1,3 @@
-import { car } from '@helia/car'
 import { dagCbor } from '@helia/dag-cbor'
 import { dagJson } from '@helia/dag-json'
 import { ipns } from '@helia/ipns'
@@ -10,7 +9,6 @@ import { expect } from 'aegir/chai'
 import { marshal } from 'ipns'
 import { VerifiedFetch } from '../src/verified-fetch.js'
 import { createHelia } from './fixtures/create-offline-helia.js'
-import { memoryCarWriter } from './fixtures/memory-car.js'
 import type { Helia } from '@helia/interface'
 
 describe('accept header', () => {
@@ -248,27 +246,4 @@ describe('accept header', () => {
 
     expect(buf).to.equalBytes(marshal(record))
   })
-
-  it.skip('should support fetching a CAR file', async () => {
-    const obj = {
-      hello: 'world'
-    }
-    const c = dagCbor(helia)
-    const cid = await c.add(obj)
-
-    const ca = car(helia)
-    const writer = memoryCarWriter(cid)
-    await ca.export(cid, writer)
-
-    const resp = await verifiedFetch.fetch(cid, {
-      headers: {
-        accept: 'application/vnd.ipld.car'
-      }
-    })
-    expect(resp.status).to.equal(200)
-    expect(resp.headers.get('content-type')).to.equal('application/vnd.ipld.car; version=1')
-    const buf = await resp.arrayBuffer()
-
-    expect(buf).to.equalBytes(await writer.bytes())
-  })
 })

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

@@ -0,0 +1,69 @@
+import { car } from '@helia/car'
+import { dagCbor } from '@helia/dag-cbor'
+import { stop } from '@libp2p/interface'
+import { expect } from 'aegir/chai'
+import { VerifiedFetch } from '../src/verified-fetch.js'
+import { createHelia } from './fixtures/create-offline-helia.js'
+import { memoryCarWriter } from './fixtures/memory-car.js'
+import type { Helia } from '@helia/interface'
+
+describe('car files', () => {
+  let helia: Helia
+  let verifiedFetch: VerifiedFetch
+
+  beforeEach(async () => {
+    helia = await createHelia()
+    verifiedFetch = new VerifiedFetch({
+      helia
+    })
+  })
+
+  afterEach(async () => {
+    await stop(helia, verifiedFetch)
+  })
+
+  it('should support fetching a CAR file', async () => {
+    const obj = {
+      hello: 'world'
+    }
+    const c = dagCbor(helia)
+    const cid = await c.add(obj)
+
+    const ca = car(helia)
+    const writer = memoryCarWriter(cid)
+    await ca.export(cid, writer)
+
+    const resp = await verifiedFetch.fetch(cid, {
+      headers: {
+        accept: 'application/vnd.ipld.car'
+      }
+    })
+    expect(resp.status).to.equal(200)
+    expect(resp.headers.get('content-type')).to.equal('application/vnd.ipld.car; version=1')
+    expect(resp.headers.get('content-disposition')).to.equal(`attachment; filename="${cid.toString()}.car"`)
+    const buf = new Uint8Array(await resp.arrayBuffer())
+
+    expect(buf).to.equalBytes(await writer.bytes())
+  })
+
+  it('should support specify a filename for a CAR file', async () => {
+    const obj = {
+      hello: 'world'
+    }
+    const c = dagCbor(helia)
+    const cid = await c.add(obj)
+
+    const ca = car(helia)
+    const writer = memoryCarWriter(cid)
+    await ca.export(cid, writer)
+
+    const resp = await verifiedFetch.fetch(`ipfs://${cid}?filename=foo.bar`, {
+      headers: {
+        accept: 'application/vnd.ipld.car'
+      }
+    })
+    expect(resp.status).to.equal(200)
+    expect(resp.headers.get('content-type')).to.equal('application/vnd.ipld.car; version=1')
+    expect(resp.headers.get('content-disposition')).to.equal('attachment; filename="foo.bar"')
+  })
+})