ASF Sentinel-1 Metadata Download tool
copied from cf-staging / asfsmdSmall Python tool (asfsmd) that allows to download XML files containing
Sentinel-1 products metadata from the ASF archive.
Sentinel-1 products are stored in the ASF arcive as ZIP files that are quite large because they contain both the products annotations and the binary image data.
The asfsmd tool is able to retrieve only the relatively samll annotation
files (in XML format) without downloading the entire ZIP archive.
asfsmd exploits Python packages like fsspec or httpio for reading HTTP
resources as random-access file-like objects. In order to do it the remote
server must support the Range header.
This approach allows to open the ZIP archive remotely, inspects contents, and download only the pieces of data that are actually necessary to the user.
Performnces of this approach are quite poor but, in the specific case of Sentinel-1 products, the entire process results to be faster than downloading the entire ZIP archive and extracting only annotation files.
