feat(vim.net): custom request() headers #38837

Problem
Cannot specify headers in vim.net.request() call.

Solution
Support opts.headers in vim.net.request opts.

test/functional/lua/net_spec.lua

@@ -11,6 +11,15 @@ local function assert_404_error(err)
   )
 end
 
+local function assert_wrong_headers(expected_err, header)
+  local err = t.pcall_err(exec_lua, [[
+    return vim.net.request('https://example.com', {
+      headers = ]] .. header .. [[,
+    }, function() end)
+  ]])
+  t.matches(expected_err, err)
+end
+
 describe('vim.net.request', function()
   before_each(function()
     n:clear()
@@ -163,4 +172,55 @@ describe('vim.net.request', function()
     t.eq(false, rv.modified)
     t.eq(true, rv.zipfile)
   end)
+
+  it('accepts custom headers', function()
+    t.skip(skip_integ, 'NVIM_TEST_INTEG not set: skipping network integration test')
+
+    local headers = exec_lua([[
+      local done = false
+      local result
+
+      vim.net.request("https://httpbingo.org/headers", {
+        headers = {
+          Authorization = "Bearer test-token",
+          ['X-Custom-Header'] = "custom-value",
+          ['Empty'] = '',
+        },
+      }, function(err, res)
+        if err then
+          result = { error = err }
+        else
+          result = vim.json.decode(res.body).headers
+        end
+        done = true
+      end)
+
+      vim.wait(2000, function() return done end)
+      return result
+    ]])
+
+    assert.is_table(headers)
+    -- httpbingo.org/request returns each header as a list in the returned value
+    t.eq(headers.Authorization[1], 'Bearer test-token', 'Expected Authorization header')
+    t.eq(headers['X-Custom-Header'][1], 'custom-value', 'Expected X-Custom-Header')
+    t.eq(headers['Empty'][1], '', 'Expected Empty header')
+  end)
+
+  it('validation', function()
+    assert_wrong_headers('opts.headers: expected table, got number', '123')
+    assert_wrong_headers('headers keys and values must be strings', "{ [123] = 'value' }")
+    assert_wrong_headers('headers keys and values must be strings', '{ Header = 123 }')
+    assert_wrong_headers(
+      'header keys must not start with @ or end with : and ;',
+      "{ ['Header:'] = 'value' }"
+    )
+    assert_wrong_headers(
+      'header keys must not start with @ or end with : and ;',
+      "{ ['Header;'] = 'value' }"
+    )
+    assert_wrong_headers(
+      'header keys must not start with @ or end with : and ;',
+      "{ ['@filename'] = '' }"
+    )
+  end)
 end)