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import { ESCAPE_REGEX } from '../htmlescape'
export function getScriptNonceFromHeader(
cspHeaderValue: string
): string | undefined {
const directives = cspHeaderValue
// Directives are split by ';'.
.split(';')
.map((directive) => directive.trim())
// First try to find the directive for the 'script-src', otherwise try to
// fallback to the 'default-src'.
const directive =
directives.find((dir) => dir.startsWith('script-src')) ||
directives.find((dir) => dir.startsWith('default-src'))
// If no directive could be found, then we're done.
if (!directive) {
return
}
// Extract the nonce from the directive
const nonce = directive
.split(' ')
// Remove the 'strict-src'/'default-src' string, this can't be the nonce.
.slice(1)
.map((source) => source.trim())
// Find the first source with the 'nonce-' prefix.
.find(
(source) =>
source.startsWith("'nonce-") &&
source.length > 8 &&
source.endsWith("'")
)
// Grab the nonce by trimming the 'nonce-' prefix.
?.slice(7, -1)
// If we could't find the nonce, then we're done.
if (!nonce) {
return
}
// Don't accept the nonce value if it contains HTML escape characters.
// Technically, the spec requires a base64'd value, but this is just an
// extra layer.
if (ESCAPE_REGEX.test(nonce)) {
throw new Error(
'Nonce value from Content-Security-Policy contained HTML escape characters.\nLearn more: https://nextjs.org/docs/messages/nonce-contained-invalid-characters'
)
}
return nonce
}
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