# How to build the simple streams index

```
Usage:
  simplestream-maintainer build <path> [flags]

Flags:
      --build-webpage           Build index.html
  -d, --image-dir strings       Image directory (relative to path argument) (default [images])
      --stream-version string   Stream version (default "v1")
      --workers int             Maximum number of concurrent operations (default "<max_cpu>/2")
```

The build command is used to update the product catalog and generate a corresponding simple streams
index file. This is achieved by first reading the existing product catalog, and then traversing
through the actual directory tree of the stream to detect the differences.

Each new product version is analyzed to ensure it is complete, which means the version contains all
the required files (metadata and rootfs) and is not hidden. For complete versions, the file hashes
are calculated and, if necessary, delta files are generated.

The final product catalog is generated in `streams/<stream_version>/<stream>.json` and the index
file in `streams/<stream_version>/index.json`.

## Checksum verification

If a specific version contains a `SHA256SUMS` file, checksums are parsed from it, and compared
against the calculated file hashes. If there is a mismatch, the version is not included in the final
product catalog.

This allows verification of images that are built on the remote location and pushed to the
simple streams server.

## Webpage

The build command allows to optionally generate a static webpage (`index.html`) in the stream's root
directory. The resulting webpage contains a table of all products that are extracted from the final
product catalog.