react-code-dataset
/
next.js
/packages
/next
/src
/shared
/lib
/segment-cache
/output-export-prefetch-encoding.ts
| // In output: export mode, the build id is added to the start of the HTML | |
| // document, directly after the doctype declaration. During a prefetch, the | |
| // client performs a range request to get the build id, so it can check whether | |
| // the target page belongs to the same build. | |
| // | |
| // The first 64 bytes of the document are requested. The exact number isn't | |
| // too important; it must be larger than the build id + doctype + closing and | |
| // ending comment markers, but it doesn't need to match the end of the | |
| // comment exactly. | |
| // | |
| // Build ids are 21 bytes long in the default implementation, though this | |
| // can be overridden in the Next.js config. For the purposes of this check, | |
| // it's OK to only match the start of the id, so we'll truncate it if exceeds | |
| // a certain length. | |
| const DOCTYPE_PREFIX = '<!DOCTYPE html>' // 15 bytes | |
| const MAX_BUILD_ID_LENGTH = 24 | |
| // Request the first 64 bytes. The Range header is inclusive of the end value. | |
| export const DOC_PREFETCH_RANGE_HEADER_VALUE = 'bytes=0-63' | |
| function escapeBuildId(buildId: string) { | |
| // If the build id is longer than the given limit, it's OK for our purposes | |
| // to only match the beginning. | |
| const truncated = buildId.slice(0, MAX_BUILD_ID_LENGTH) | |
| // Replace hyphens with underscores so it doesn't break the HTML comment. | |
| // (Unlikely, but if this did happen it would break the whole document.) | |
| return truncated.replace(/-/g, '_') | |
| } | |
| export function insertBuildIdComment(originalHtml: string, buildId: string) { | |
| if ( | |
| // Skip if the build id contains a closing comment marker. | |
| buildId.includes('-->') || | |
| // React always inserts a doctype at the start of the document. Skip if it | |
| // isn't present. Shouldn't happen; suggests an issue elsewhere. | |
| !originalHtml.startsWith(DOCTYPE_PREFIX) | |
| ) { | |
| // Return the original HTML unchanged. This means the document will not | |
| // be prefetched. | |
| // TODO: The build id comment is currently only used during prefetches, but | |
| // if we eventually use this mechanism for regular navigations, we may need | |
| // to error during build if we fail to insert it for some reason. | |
| return originalHtml | |
| } | |
| // The comment must be inserted after the doctype. | |
| return originalHtml.replace( | |
| DOCTYPE_PREFIX, | |
| DOCTYPE_PREFIX + '<!--' + escapeBuildId(buildId) + '-->' | |
| ) | |
| } | |
| export function doesExportedHtmlMatchBuildId( | |
| partialHtmlDocument: string, | |
| buildId: string | |
| ) { | |
| // Check whether the document starts with the expected buildId. | |
| return partialHtmlDocument.startsWith( | |
| DOCTYPE_PREFIX + '<!--' + escapeBuildId(buildId) + '-->' | |
| ) | |
| } | |