52 lines
1.5 KiB
Go
52 lines
1.5 KiB
Go
package radar
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import (
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"context"
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"fmt"
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"io"
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"net/http"
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"strings"
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"time"
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)
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// nwsRadarBase is the NWS public product distribution server.
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// No credentials required; sn.last always holds the most recent scan.
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const nwsRadarBase = "https://tgftp.nws.noaa.gov/SL.us008001/DF.of/DC.radar"
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// Fetcher downloads NEXRAD Level 3 products from the NWS public server.
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type Fetcher struct {
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client *http.Client
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}
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func NewFetcher(_ context.Context) (*Fetcher, error) {
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return &Fetcher{client: &http.Client{Timeout: 30 * time.Second}}, nil
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}
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// FetchLatest downloads the latest Level 3 base reflectivity (0.5°) for site.
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func (f *Fetcher) FetchLatest(ctx context.Context, site string) ([]byte, error) {
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return f.fetchDS(ctx, site, "p94r0")
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}
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// FetchVelocity downloads the latest Level 3 base velocity (0.5°) for site.
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func (f *Fetcher) FetchVelocity(ctx context.Context, site string) ([]byte, error) {
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return f.fetchDS(ctx, site, "p99r0")
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}
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func (f *Fetcher) fetchDS(ctx context.Context, site, ds string) ([]byte, error) {
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url := fmt.Sprintf("%s/DS.%s/SI.%s/sn.last", nwsRadarBase, ds, strings.ToLower(site))
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req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
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if err != nil {
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return nil, err
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}
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resp, err := f.client.Do(req)
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if err != nil {
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return nil, fmt.Errorf("NWS fetch: %w", err)
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}
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defer resp.Body.Close()
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if resp.StatusCode != http.StatusOK {
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return nil, fmt.Errorf("NWS returned %s for %s", resp.Status, url)
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}
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return io.ReadAll(resp.Body)
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}
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