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fix: Use locale-invariant toLowerCase for header normalization #1930

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fix: Use locale-invariant toLowerCase for header normalization #1930

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2 changes: 1 addition & 1 deletion src/internal/headers.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -74,7 +74,7 @@ export const buildHeaders = (newHeaders: HeadersLike[]): NullableHeaders => {
for (const headers of newHeaders) {
const seenHeaders = new Set<string>();
for (const [name, value] of iterateHeaders(headers)) {
const lowerName = name.toLowerCase();
const lowerName = name.toLocaleLowerCase('en-US');
if (!seenHeaders.has(lowerName)) {
targetHeaders.delete(name);
seenHeaders.add(lowerName);
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19 changes: 19 additions & 0 deletions tests/buildHeaders.test.ts
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Expand Up @@ -79,6 +79,25 @@ describe('buildHeaders', () => {
],
[[undefined], `NullableHeaders { }`],
[[null], `NullableHeaders { }`],
[
[
{
'OpenAI-Organization': 'org-123',
},
],
`NullableHeaders { 'OpenAI-Organization': 'org-123' }`,

@chatgpt-codex-connector chatgpt-codex-connector Bot Jun 8, 2026

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P2 Badge Expect normalized header names in the new test

This expected value does not match what buildHeaders returns for object inputs: it ultimately stores the entry in a WHATWG Headers, and Headers.append('OpenAI-Organization', ...) normalizes the name to openai-organization on iteration. As written, this new case fails on the standard Node Headers implementation even though the product code lowercases the header name correctly.

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@anishesg anishesg Jun 8, 2026

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ah good point, the test should expect the lowercased version since that's what Headers actually returns when you iterate

@anishesg anishesg Jun 8, 2026

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ah good point, the test should expect the lowercased version since that's what Headers actually returns when you iterate

],
[
[
{
'OpenAI-Organization': 'org-123',
},
{
'openai-organization': 'org-456',
},
],
`NullableHeaders { 'openai-organization': 'org-456' }`,
],
];
for (const [input, expected] of cases) {
test(expected, () => {
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