Optional fetch-and-cache layer for GNSS products (SP3, RINEX clock, broadcast navigation, IONEX).

Orbis.GnssData downloads, decompresses, checksums, and records provenance for the precise- and broadcast-product files that Orbis.SP3, Orbis.BroadcastEphemeris, and Orbis.PointPositioning consume — and then hands back a local file path (or a loaded handle). It is deliberately one-directional: the numerical layers never call into this module, so a solve never depends on network availability. You fetch once, then point the solver at the cached file.

Quick start

product = Orbis.GnssData.mgex_sp3(:cod, ~D[2020-06-24])

# Download (or reuse cache) and get a decompressed file path:
{:ok, path} = Orbis.GnssData.fetch(product)

# Or fetch and load in one step:
{:ok, sp3} = Orbis.GnssData.sp3(product)
{:ok, state} = Orbis.SP3.position(sp3, "G01", ~N[2020-06-24 00:00:00])

Catalog

Products are identified by analysis center, content type, date, and sampling.

Supported centers and what each publishes:

• :gfz — GFZ operational rapid SP3/CLK over HTTPS (isdc-data.gfz.de)
• :cod, :grg, :wum — CODE / CNES-CLS / Wuhan MGEX precise SP3/CLK over anonymous FTP (ESA GSSC mirror, gssc.esa.int); :cod also serves IONEX
• :igs — the IGS merged broadcast navigation file (:nav) and the combined global ionosphere map (:ionex), over FTP

Content types: :sp3, :clk, :nav, :ionex. Precise products and IONEX follow the IGS long-name convention AAAVPPPTTT_YYYYDDDHHMM_LEN_SMP_CNT.EXT; broadcast navigation uses the no-sampling RINEX long-name BRDC00IGS_R_YYYYDDDHHMM_01D_MN.rnx. See Orbis.GnssData.Catalog.

The fetch pipeline

fetch/2 is cache-first:

1. Resolve the canonical filename and cache path (pure, from the catalog).
2. If the file is already cached, verify it: against the caller's :sha256 when given, otherwise against the decompressed SHA-256 recorded in the file's provenance sidecar (every downloaded file has one). A verified hit returns with no network. A corrupt hit (checksum mismatch) or an unverifiable one (no sidecar — e.g. a hand-placed file) is, online, discarded and re-downloaded; offline, a corrupt hit is terminal and an unverifiable one is returned as the best available.
3. Otherwise (and only when not offline:) download the .gz over HTTPS (Req) or FTP (:ftp) to memory, decompress with a gzip-bomb cap, verify any known checksum, and atomically commit the decompressed file into the cache (temp file + rename) together with its required .provenance.json sidecar (the commit fails if the sidecar cannot be written, so a cached file always carries its integrity hash).

Offline mode

Pass offline: true (or set config :orbis, gnss_data_offline: true) to forbid all network access: a verified cache hit is returned, a corrupt hit yields {:error, {:checksum_mismatch, _, _}}, and a miss returns {:error, {:offline_miss, name}}. This is how the test suite — and any user without connectivity — runs deterministically.

Network tests

Live-archive fetching is exercised by tests tagged :network, which are excluded by default (including in CI, which has no network); the rest of the suite is fully offline and deterministic. Run the live gate manually with mix test --include network.

Options

• :offline — when true, never touch the network (default from app config, else false)
• :cache_dir — cache root (default :filename.basedir(:user_cache, "orbis/gnss"), overridable via config :orbis, gnss_data_cache_dir:)
• :sha256 — expected SHA-256 (hex) of the decompressed file; verified on both cache hits and fresh downloads
• :max_decompressed_bytes — gzip-bomb cap (default 500 MiB)
• :timeout_ms — per-attempt network timeout (default 30_000)
• :retries — attempts for transient network errors (default 3)
• :backoff_ms — base backoff between retries, doubled each attempt (default 500)
• :max_compressed_bytes — cap on the compressed payload buffered into memory while downloading (default 64 MiB)

Typed errors

Every failure is a tagged tuple so callers can branch on it:

• {:error, {:offline_miss, name}} — offline: true and not cached
• {:error, {:checksum_mismatch, expected, got}} — digest verification failed
• {:error, {:unsupported_product, detail}} — unknown center/content/sample, or a host outside the catalog
• {:error, :req_not_available} — HTTPS needed but Req is not loaded
• {:error, {:http_status, code}} — non-2xx HTTP response
• {:error, {:redirect_not_allowed, code}} — a 3xx redirect was refused (redirects are not followed, to keep the SSRF allow-list intact)
• {:error, {:file_not_found, url}} — 404 / missing on the archive
• {:error, {:network, detail}} — connection/timeout/DNS failure
• {:error, {:ftp_error, reason}} — FTP-level failure
• {:error, {:download_size_exceeded, max, got}} — compressed payload cap hit
• {:error, {:decompress_failed, reason}} — corrupt gzip
• {:error, {:decompress_size_exceeded, max, got}} — gzip-bomb cap hit
• {:error, {:cache_dir_not_writable, reason}} — cannot create/write cache
• {:error, {:provenance_write_failed, reason}} — the product downloaded but its required provenance sidecar could not be written (the product is rolled back so nothing unverifiable is left in the cache)
• {:error, {:unsafe_cache_name, name}} — filename failed path-safety checks
• {:error, {:temp_file_error, reason}} — temp write/rename failure