33 lines
2.0 KiB
Markdown
33 lines
2.0 KiB
Markdown
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# Network Error Logging (NEL)
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Network Error Logging (NEL) provides out-of-band reporting of network errors
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via the Reporting API (see `//net/reporting`). Site operators can specify a
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NEL policy that defines the Reporting endpoint(s) on which they wish to receive
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reports about client-side errors encountered while connecting to the site. The
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draft spec can be found [here](https://w3c.github.io/network-error-logging/).
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This directory contains the core implementation of NEL.
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## Implementation overview
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Most of the action takes place in
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[`NetworkErrorLoggingService`](https://source.chromium.org/chromium/chromium/src/+/main:net/network_error_logging/network_error_logging_service.h;l=42;drc=a9e9d6cbb3e5920f9207118cf9501ff0745bb536),
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which handles receiving/processing `NEL:` response headers and
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generating/queueing reports about network requests. The
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`NetworkErrorLoggingService` is owned by the `URLRequestContext`.
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Information about network requests comes directly from
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[`HttpNetworkTransaction`](https://source.chromium.org/chromium/chromium/src/+/main:net/http/http_network_transaction.cc;l=1364;drc=a9e9d6cbb3e5920f9207118cf9501ff0745bb536),
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which informs `NetworkErrorLoggingService` of the details of the request such
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as the remote IP address and outcome (a `net::Error` code).
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The `NetworkErrorLoggingService` finds a NEL policy applicable to the request
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(previously set by a `NEL` header), and if one exists, potentially queues a
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NEL report to be uploaded out-of-band to the policy's specified Reporting
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endpoint via the
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[`ReportingService`](https://source.chromium.org/chromium/chromium/src/+/main:net/reporting/reporting_service.h;l=56;drc=c3305c04ac6800d488bfc8b2f3249fd13186984a).
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Received NEL policies are persisted to disk by a `PersistentNelStore`, whose
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main implementation is the
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[`SqlitePersistentReportingAndNelStore`](https://source.chromium.org/chromium/chromium/src/+/main:net/extras/sqlite/sqlite_persistent_reporting_and_nel_store.h;l=30;drc=456596a0b27623349d38e49d0e9812b24d47d5d8).
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