wehub-resource-sync
56 lines
1.5 KiB
Go
56 lines
1.5 KiB
Go
package builtin
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import (
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"bytes"
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"fmt"
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"io"
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"strings"
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"testing"
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)
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type countingReader struct {
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r io.Reader
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n int
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}
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func (c *countingReader) Read(p []byte) (int, error) {
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n, err := c.r.Read(p)
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c.n += n
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return n, err
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}
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// TestScanWindowedReadDoesNotConsumeWholeFile guards the regression where scan()
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// drained the entire file (a second `for scanner.Scan()` loop) just to count the
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// remaining lines for the pagination trailer. A small windowed read of a large
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// file must read only a small prefix, not all of it.
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func TestScanWindowedReadDoesNotConsumeWholeFile(t *testing.T) {
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var buf bytes.Buffer
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for i := 1; i <= 100_000; i++ {
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fmt.Fprintf(&buf, "line %d\n", i)
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}
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total := buf.Len()
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if total < 500*1024 {
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t.Fatalf("test fixture too small (%d bytes) to be meaningful", total)
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}
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cr := &countingReader{r: bytes.NewReader(buf.Bytes())}
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out, err := readFile{}.scan(cr, 0, 3)
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if err != nil {
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t.Fatalf("scan: %v", err)
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}
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if !strings.Contains(out, "1→line 1") || !strings.Contains(out, "3→line 3") {
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t.Fatalf("window content wrong:\n%s", out)
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}
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if strings.Contains(out, "line 4") {
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t.Fatalf("window leaked line 4:\n%s", out)
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}
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if !strings.Contains(out, "more lines below") {
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t.Fatalf("pagination trailer missing:\n%s", out)
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}
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if cr.n > 100*1024 {
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t.Fatalf("read %d of %d bytes for a 3-line window; should read only a small prefix", cr.n, total)
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}
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t.Logf("read %d of %d bytes (%.1f%%) for a 3-line window", cr.n, total, 100*float64(cr.n)/float64(total))
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}
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