fix: fix content-type by doing a fall-back using extensions

The JS IPFS gateway was only responding with the correct content-type for some mime-types, see https://github.com/sindresorhus/file-type#supported-file-types.
This commit now fall-backs to detecting based on the extension as well.

Note that SVGs aren't supported by the `file-type` module.

src/http/gateway/resources/gateway.js

@@ -12,6 +12,21 @@ const Stream = require('readable-stream')
 const { resolver } = require('ipfs-http-response')
 const PathUtils = require('../utils/path')
 
+function detectContentType (ref, chunk) {
+  let fileSignature
+
+  // try to guess the filetype based on the first bytes
+  // note that `file-type` doesn't support svgs, thereore we assume it's a svg if ref looks like it
+  if (!ref.endsWith('.svg')) {
+    fileSignature = fileType(chunk)
+  }
+
+  // if we were unable to, fallback to the `ref` which might contain the extension
+  const mimeType = mime.lookup(fileSignature ? fileSignature.ext : ref)
+
+  return mime.contentType(mimeType)
+}
+
 module.exports = {
   checkCID: (request, reply) => {
     if (!request.params.cid) {
@@ -97,7 +112,7 @@ module.exports = {
         }
 
         //  response.continue()
-        let filetypeChecked = false
+        let contentTypeDetected = false
         let stream2 = new Stream.PassThrough({ highWaterMark: 1 })
         stream2.on('error', (err) => {
           log.error('stream2 err: ', err)
@@ -108,29 +123,20 @@ module.exports = {
         pull(
           toPull.source(stream),
           pull.through((chunk) => {
-            // Check file type.  do this once.
-            if (chunk.length > 0 && !filetypeChecked) {
-              log('got first chunk')
-              let fileSignature = fileType(chunk)
-              log('file type: ', fileSignature)
-
-              filetypeChecked = true
-              const mimeType = mime.lookup(fileSignature
-                ? fileSignature.ext
-                : null)
+            // Guess content-type (only once)
+            if (chunk.length > 0 && !contentTypeDetected) {
+              let contentType = detectContentType(ref, chunk)
+              contentTypeDetected = true
 
               log('ref ', ref)
-              log('mime-type ', mimeType)
-
-              if (mimeType) {
-                log('writing mimeType')
+              log('mime-type ', contentType)
 
-                response
-                  .header('Content-Type', mime.contentType(mimeType))
-                  .send()
-              } else {
-                response.send()
+              if (contentType) {
+                log('writing content-type header')
+                response.header('Content-Type', contentType)
               }
+
+              response.send()
             }
 
             stream2.write(chunk)

test/gateway/index.js

@@ -19,7 +19,9 @@ const directoryContent = {
   'nested-folder/hello.txt': loadFixture('test/gateway/test-folder/nested-folder/hello.txt'),
   'nested-folder/ipfs.txt': loadFixture('test/gateway/test-folder/nested-folder/ipfs.txt'),
   'nested-folder/nested.html': loadFixture('test/gateway/test-folder/nested-folder/nested.html'),
-  'cat-folder/cat.jpg': loadFixture('test/gateway/test-folder/cat-folder/cat.jpg')
+  'cat-folder/cat.jpg': loadFixture('test/gateway/test-folder/cat-folder/cat.jpg'),
+  'unsniffable-folder/hexagons-xml.svg': loadFixture('test/gateway/test-folder/unsniffable-folder/hexagons-xml.svg'),
+  'unsniffable-folder/hexagons.svg': loadFixture('test/gateway/test-folder/unsniffable-folder/hexagons.svg')
 }
 
 describe('HTTP Gateway', function () {
@@ -113,6 +115,22 @@ describe('HTTP Gateway', function () {
           expect(file.hash).to.equal(expectedMultihash)
           cb()
         })
+      },
+      (cb) => {
+        const expectedMultihash = 'QmVZoGxDvKM9KExc8gaL4uTbhdNtWhzQR7ndrY7J1gWs3F'
+
+        let dir = [
+          content('unsniffable-folder/hexagons-xml.svg'),
+          content('unsniffable-folder/hexagons.svg')
+        ]
+
+        http.api.node.files.add(dir, (err, res) => {
+          expect(err).to.not.exist()
+          const file = res[res.length - 2]
+          expect(file.path).to.equal('test-folder/unsniffable-folder')
+          expect(file.hash).to.equal(expectedMultihash)
+          cb()
+        })
       }
     ], done)
   })
@@ -166,7 +184,7 @@ describe('HTTP Gateway', function () {
     })
   })
 
-  it('load a non text file', (done) => {
+  it('load a jpg file', (done) => {
     let kitty = 'QmW2WQi7j6c7UgJTarActp7tDNikE4B2qXtFCfLPdsgaTQ/cat.jpg'
 
     gateway.inject({
@@ -184,6 +202,34 @@ describe('HTTP Gateway', function () {
     })
   })
 
+  it('load a svg file (unsniffable)', (done) => {
+    let hexagons = 'QmVZoGxDvKM9KExc8gaL4uTbhdNtWhzQR7ndrY7J1gWs3F/hexagons.svg'
+
+    gateway.inject({
+      method: 'GET',
+      url: '/ipfs/' + hexagons
+    }, (res) => {
+      expect(res.statusCode).to.equal(200)
+      expect(res.headers['content-type']).to.equal('image/svg+xml')
+
+      done()
+    })
+  })
+
+  it('load a svg file with xml leading declaration (unsniffable)', (done) => {
+    let hexagons = 'QmVZoGxDvKM9KExc8gaL4uTbhdNtWhzQR7ndrY7J1gWs3F/hexagons-xml.svg'
+
+    gateway.inject({
+      method: 'GET',
+      url: '/ipfs/' + hexagons
+    }, (res) => {
+      expect(res.statusCode).to.equal(200)
+      expect(res.headers['content-type']).to.equal('image/svg+xml')
+
+      done()
+    })
+  })
+
   it('load a directory', (done) => {
     let dir = 'QmW2WQi7j6c7UgJTarActp7tDNikE4B2qXtFCfLPdsgaTQ/'