Make getWithCurl compatible with older curl

Summary:
We were using `--write-out %{header_json}` but this feature requires curl 7.83.0. Some of our CI environments have an older version of curl so we need a different approach.

Author: motiz88

scripts/releases/__tests__/__snapshots__/upload-release-assets-for-dotslash-test.js.snap

@@ -138,7 +138,7 @@ Array [
 ]
 `;
 
-exports[`uploadReleaseAssetsForDotSlashFile fails loudly if the upstream asset is unreachable 1`] = `"curl --silent --location --output <CURL_TEMP_DIR>/data <serverUrl>/error --write-out %{header_json} --fail exited with non-zero code: 22"`;
+exports[`uploadReleaseAssetsForDotSlashFile fails loudly if the upstream asset is unreachable 1`] = `"curl --silent --location --output <CURL_TEMP_DIR>/data <serverUrl>/error --write-out %{content_type} --fail exited with non-zero code: 22"`;
 
 exports[`uploadReleaseAssetsForDotSlashFile fails loudly if the upstream asset is unreachable: console.log calls 1`] = `
 Array [

scripts/releases/upload-release-assets-for-dotslash.js

@@ -328,12 +328,12 @@ async function fetchAndValidateUpstreamAsset(
   console.log(`[${name}] Downloading from ${url}...`);
   // NOTE: Using curl because we have seen issues with fetch() on GHA
   // and the Meta CDN. ¯\_(ツ)_/¯
-  const {data, headers} = await getWithCurl(url);
+  const {data, contentType} = await getWithCurl(url);
   console.log(`[${name}] Validating download...`);
   await validateDotSlashArtifactData(data, artifactInfo);
   return {
     data,
-    contentType: headers['content-type']?.[0] ?? 'application/octet-stream',
+    contentType: contentType ?? 'application/octet-stream',
   };
 }
 

scripts/releases/utils/__tests__/curl-utils-test.js

@@ -50,9 +50,7 @@ describe('getWithCurl', () => {
   test('success', async () => {
     await expect(getWithCurl(serverUrl)).resolves.toEqual({
       data: Buffer.from('Hello World\n'),
-      headers: expect.objectContaining({
-        'content-type': ['text/plain'],
-      }),
+      contentType: 'text/plain',
     });
   });
 

scripts/releases/utils/curl-utils.js

@@ -18,7 +18,7 @@ const path = require('path');
 /*::
 type CurlResult = {
   data: Buffer,
-  headers: {[string]: Array<string>},
+  contentType?: string,
 };
 */
 
@@ -37,14 +37,17 @@ async function getWithCurl(url /*: string */) /*: Promise<CurlResult> */ {
         tempFile,
         url,
         '--write-out',
-        '%{header_json}',
+        '%{content_type}',
         '--fail',
       ],
       {encoding: 'utf8', stdio: ['ignore', 'pipe', 'pipe']},
     );
     const data = await fs.readFile(tempFile);
-    const headers = JSON.parse(curlStdout);
-    return {data, headers};
+    const contentType = curlStdout.trim();
+    if (contentType === '') {
+      return {data};
+    }
+    return {data, contentType};
   } finally {
     await fs.rm(tempDir, {recursive: true, force: true});
   }